The 1755 John Snetzler Organ, Clare College, Cambridge, restored by William Drake, Ltd., Joost de Boer, Director

Michael McNeil

Michael McNeil has designed, constructed, voiced, and researched pipe organs since 1973. Stimulating work as a research engineer in magnetic recording paid the bills. He is working on his Opus 5, which explores how an understanding of the human sensitivity to the changes in sound can be used to increase emotional impact. Opus 5 includes double expression, a controllable wind dynamic, chorus phase shifting, and meantone. Stay tuned.

Editor’s note: The Diapason offers here a feature at our digital edition—two sound clips. Any subscriber can access this by logging into our website, click on Magazine, then this issue, View Digital Edition, scroll to this page, and click on each <soundclip> in the text.

Part 1 of this series appeared in the December 2022 issue, pages 12–17.

Deductive logic is tautological; there is no way to get a new truth out of it, and it manipulates false statements as readily as true ones. If you fail to remember this, it can trip you—with perfect logic. . . . Inductive logic is much more difficult—but can produce new truths.²¹

A range of voicing styles

In Part 1 we discovered the features of Silbermann’s pipe construction and voicing that make his sound unique. What could we learn by comparing Silbermann’s voicing to other styles? A great deal, as it turns out, and to do this we will take a much deeper dive into the voicing parameters shown in Part 1.

Toe diameters

Toe diameters control power by limiting the flow of wind and reducing the pressure in the pipe foot. We often hear the term “open toe” voicing, but what does this really mean? And how could we compare the very different regulation of toes in Germanic and French voicing? Tables of raw pipe toe diameters do not convey the intent of the organbuilder or allow us to make meaningful comparisons. 

In 1972 Dirk Flentrop advised me that a starting point for estimating the diameter of a pipe toe is the square root of its resonator diameter, and that is assuredly not the widest possible toe.²² Building on this idea I devised what I call a toe constant “c” to compare the flow of wind through pipe toes. Flentrop’s advice, the square root of a pipe’s diameter, defines a toe constant “c” of exactly 1. Interestingly, the toe constant for Andreas Silbermann’s pipe shown in Figure 2 in Part 1 is 0.97, virtually identical to Flentrop’s guidance.

Toe constants can be larger or smaller to suit the acoustics and the power balances within a chorus, and they can vary for different levels of wind pressure. For example, if we want more power at the same pressure, we will use larger toe constants and larger toes, and vice versa for less power. If we want the same power at a higher pressure, we will use smaller toe constants.

The toe constant also needs to take into account the larger or smaller flows of wind needed by different mouth widths. Mouth widths are specified as a fraction of the pipe circumference. A 2⁄7-width mouth is wider than a 1⁄4-width mouth on the same pipe, and it will need a larger toe to feed more wind to the wider flueway of that mouth. I added a term to Flentrop’s advice (he typically used 1⁄4 mouth widths) to adjust the wind required to feed wider or narrower mouths. For example, Silbermann’s toe constants in Figure 8 (page 17) have values of 1 at 2′ pitch, but those values reflect toes that are larger in diameter than the square root of their pipe diameters—those toe diameters are adjusted proportionally larger to provide the extra wind needed by the flueways of Silbermann’s wider 2⁄7 mouths. Note 23 shows the very simple equation for calculating the toe diameter from the pipe diameter, mouth width fraction, and toe constant. 

The toe constant now allows us to visually compare the relative flow of wind among voicing styles and wind pressures for pipes of any scale or mouth width. While the term “open toe” is vague, the toe constant is quantifiable.

Silbermann adjusted the toes of the Freiberg Dom chorus in Figure 8 for more wind flow in the bass and treble. None of the toe constants are below Flentrop’s guidance of 1. The highest trebles at 1⁄8′ pitch have reduced wind flow, and we will soon see a very interesting explanation for this. 

Note the regularity of Silbermann’s toe constants. All pipes of the same pitch have the same toe constants and wind flow regardless of where they appear in the stops or the compass. The mixtures appear to have slightly larger toes, perhaps as a compensation for their slightly narrower scale, indicating that Silbermann wanted the same power from the mixtures but with the brighter timbre of their narrower scale. 

Such regularity is extremely rare, and it suggests that Silbermann calculated his toe diameters prior to voicing. These data also suggest the idea that he approached organ design from an inductive viewpoint, using data to infer the design rules with which he achieved his sound. Some might criticize this regularity, but we might also learn something from it. Let’s see how other builders controlled their pipe toes.

Figure 14 (page 14) shows the toe constants for a vast range of voicing styles, most of which represent 4′ Octave stops in the main manual division. All of these styles have toe constants entirely above a value of 1 except for two cases: the classical French voicing of the Isnards and the high treble of D. A. Flentrop’s example. 

The data in the pink line are from D. A. Flentrop’s 1977 organ at California State University, Chico, voiced on a low pressure of 66 mm. This organ was built at a time when all classical voicing was considered “open toe,” but readers may be surprised to see that Flentrop’s voicing does not remotely use the most open toes in Figure 14. He deviated from his guidance (the square root of the pipe diameter) as needed, extending above 1 in the bass and mid-range, and dropping below 1 in the highest treble. The acoustically dry concert hall in which the Flentrop resides is also the smallest of the acoustics in Figure 14. His wind pressure is the lowest in Figure 14, and this might suggest the use of the most open toes, but Flentrop was willing to restrain these toes for a more restrained treble power.

The data in the orange line are from Silbermann’s organ at Großhartmannsdorf on 90 mm pressure, and the data in light blue are from his organ at Reinhardtsgrimma on 70 mm pressure. Note that Silbermann uses much more open toes on lower pressure. The Großhartmannsdorf data is virtually identical to the toe constants at the Freiberg Dom in Figure 8, evidence that these toes may have been calculated to accommodate the similar wind pressures of these organs. 

The data in the dark blue line are from the 1774 Isnard organ at Saint Maximin on 83 mm pressure. Here we have mid-range toe constants that dip well below a value of 1, and with this visual graphic we can now see what is meant by “closed toes” in this French voicing example.

The individual data points in the pink boxes are from the 16′ Hauptwerk Principal in Arp Schnitger’s 1688–1692 organ at the Jacobikirche in Hamburg on 80 mm pressure, one of the largest acoustics in the Figure 14 examples.²⁴ These are widely open toes, and they also compensate for the wind pressure drop that occurs in the conductors between the windchest and the pipe feet of these offset façade pipes. Principal pipes that sit on the windchest of the Schnitger organ have toe constants closer to those of Silbermann at Reinhardtsgrimma in the light blue line. All of the other pipes in Figure 14 from 4′ to ¼′ pitch sit directly on the windchest without pressure losses.

The data in the yellow line are from the 1863 organ by E. & G. G. Hook at the former Immaculate Conception Catholic Church in Boston. This Romantic organ is voiced on 76 mm pressure, and it may surprise readers to see that it has the most “open toe” voicing in Figure 14 for pipes sitting directly on the windchest. 

The toe constants in Figure 14 show us that all of these organbuilders adjusted the toe to regulate wind flow and power. The toe constant gives us the means to make meaningful comparisons.

Flueway depths

Flueway depths control power. Flueway data are essential for understanding organ sound, but they are exceedingly rare. Figure 15 shows how flueway depths are measured. Figure 16 shows flueway depths for the same pipes shown in Figure 14. Figure 9 shows the very deep flueways of the Freiberg Dom Silbermann.

The Flentrop data in the pink line in Figure 16 explore the lower limits of flueway depths with excellent musical effect on 66 mm pressure. Figure 17 shows the bright, harmonically rich, “instrumental” voicing of a Flentrop pipe from about 1980. In addition to the two obvious deeper nicks and the extremely light nicks in the middle of the counterbevel, note the unusual bold nicks placed at the far right and left sides of the flueway, the absence of ears, and the moderate cutup. Flentrop’s harmonically rich voicing contrasts with the much less bright vocale style of voicing.

The data in the yellow line from the Romantic Hook organ explore the upper limits of musicality. These pipes are voiced on 76 mm pressure with many bold nicks. The Flentrop and the Hook data give us some idea of the range of historic flueway depths.

The Silbermann flueways in the orange and light blue lines represent the range of Silbermann’s flueway depths for the range of pressures represented by these data. Note that at 90 mm of pressure at Großhartmannsdorf, Silbermann’s flueways are virtually identical to the flueways of the Freiberg Dom chorus in Figure 9, more evidence suggesting calculation of flueways for a specific wind pressure. The treble flueways are as deep as those found in the Hooks’ Romantic voicing.

It is interesting that Silbermann adjusted his flueways shallower at lower pressure and deeper at higher pressure, an unexpected relationship. Open flueways without bolder nicking have a breathy component to their sound, and Silbermann may have adjusted his flueways shallower in smaller, more intimate acoustics to minimize that effect. The high frequencies that characterize breathiness are absorbed by the atmosphere, and distance reduces their audibility in larger acoustics.

The restorers of the Isnard organ interestingly noted that the very generous flueways in the dark blue line were more “closed up” relative to typical French voicing. As we will later see, the Isnards appear to have adjusted their flueways and toes to achieve remarkable balances. 

The individual data points in the Figure 16 pink boxes are from Schnitger’s 16′ Principal on 80 mm pressure. These Schnitger flueways correlate extremely well to the deepest flueways used by Gottfried Silbermann. All of the illustrated Schnitger data were taken by Hans Henny Jahnn in 1925.

For those interested in Schnitger’s work, Figure 18 shows a subset of Jahnn’s original data (he took data on every pipe in this stop). The data in the pink font in Figure 18 are represented in Figure 16 by the pink boxes. 

The single pink triangular data point well below the Flentrop data at 1′ pitch is the razor-thin flueway of the neo-Baroque pipe illustrated in Figure 3 of Part 1; it is voiced on 65 mm pressure with a very low cutup. The data clearly show that this flueway does not remotely resemble any historic voicing style in Figure 16, and the reason for that brings us to cutups.

Cutups

Cutups (also known as “mouth height”) are often described as some fraction of the mouth width. While using a mouth width fraction with dividers to scribe preliminary cutup heights on upper lips has some practical value during voicing, it has been shown that the tonal effect of cutup has absolutely nothing to do with the width of the mouth.²⁵

Cutups are adjusted to control timbre, and cutups will be higher for the same timbre at a higher level of power. We will get continuously less bright timbres as cutups are increased at any specific power. Cutups that are too low will cut the vortex in the flueway at too high a frequency for the resonator to quickly respond, and the fundamental will form more slowly.

Some neo-Baroque efforts to recapture historic voicing invoked a recipe where cutups were required to be ¼ of the mouth width and toes were vaguely required to be “open.” This recipe is a perfect example of an untested opinion based on deductive logic (which the author, too, naively embraced in his Opus 1).

Pipes voiced with deep flueways, wide-open toes, and low cutups will either screech with powerful harmonics or overblow to the octave on higher pressures. Closing the flueway takes away the strident screech, but it also strangles the power of the fundamental. Using the neo-Baroque recipe of wide-open toes and ¼-cutups, the voicer was forced to close the flueway to extremely small values. Without reducing the wind pressure, this was the only option left to the voicer. A typical compromise in this style of voicing allowed for some stridency in the timbre to preserve some modest power in the fundamental, and in this condition the pipe was often too close to overblowing. The result was the slow, gulping speech and thin fundamental so often heard in early Orgelbewegung movement voicing. 

The solution to this problem is by now quite obvious to the reader—adjust the toe and/or the flueway (according to your preferences) until the desired fundamental power is achieved, and then raise the cutup to get the desired timbre and prompt speech. If Silbermann had used ¼-cutups at the Freiberg Dom, the values of his Normal Scale mouth heights in Figure 10 would look identical to the values of his Normal Scale mouth widths in Figure 5. Unsurprisingly, Silbermann’s high cutups bear no relationship at all to his mouth widths. 

Figure 19 shows cutups for the same pipes shown in Figure 16. The data in the pink line are from the Flentrop organ voiced on 66 mm pressure. Cutups trend higher on higher wind pressures, depending, of course, on the regulation of toes and flueways. The Flentrop data represent the lowest wind pressure in this graph with a harmonically rich, restrained power in the smallest acoustic among these examples. The lower cutups of the Flentrop voicing are no surprise.

The data in the orange line are from Silbermann’s organ at Großhartmannsdorf on 90 mm pressure, and the data in light blue are from the Reinhardtsgrimma organ on 70 mm pressure. This is the same data we saw in Part 1 where Silbermann used higher cutups at higher wind pressures to maintain similar timbres. Again, it is no surprise that these cutups are higher than Flentrop’s lower pressure voicing. In Figure 19 the wind pressures appear just to the right of the data lines, and in the treble they progress smoothly from lower cutups on lower pressure to higher cutups on higher pressure.

The data in the dark blue line are from the Isnard organ on 83 mm pressure. The Isnard cutups follow the same wind pressure trend as the Silbermann data and lie mostly between them. We might expect the 83 mm pressure Isnard cutups to lie closer to Silbermann’s 90 mm cutups. Figure 14 tells you why they do not (hint: look at the Isnard toe constants and the implied pressure drop in the pipe feet).

The individual data points in the pink boxes are from the Schnitger example on 80 mm pressure. The treble cutups from 4′ pitch reflect significant power in this 16′ stop, as would be expected from its copiously winded toes and flueways in Figures 14 and 16. 

The data in the yellow line are from the Romantic Hook organ voiced on 76 mm pressure. The highest treble data lie just above Silbermann’s 70 mm pressure data as expected. But the bass and mid-range cutups are much higher than expected, and this reflects the higher bass power of a Romantic organ, a power fed by the largest toes in Figure 14 and the deepest flueways in Figure 16. The Hook does not have the highest wind pressure in Figure 19, but it is a good example of getting more power out of larger toes and deeper flueways (and bold nicking). 

Higher cutup with more wind gives us power, and a good example is the Pedal 32′ Bourdon at Saint Ignatius Catholic Church in San Francisco, California. This large room seats about 1,800 people, and as a 64′ resultant this Bourdon is able to cause visible vibrations in the pews at its 8 Hz pitch. It has a scale of 535 mm on the diagonal, a mouth width of 349 mm, a 4.0 mm flueway, a 100 mm toe, and it is winded on 203 mm (8 inches) pressure. The power of this pipe is reflected in its cutup of +20 HT (203 mm average, arched). This cutup is literally way off the top of the graph in Figure 19. You do not hear such a sound; you feel it. On his next visit to the Atlantic City organ, John Bishop might regale us with the cutup of the Pedal 32′ Contra Diapason on 20 inches of pressure!

Toe and flueway ratios 

Areas are more important in many ways than diameters and depths, and the ratio of the toe area to the flueway area strongly affects speech articulation (also known as “chiff”). Figure 20 shows these ratios for the same pipes in Figure 19. Figure 11 shows the ratios for Silbermann’s Freiberg Dom organ. 

Ratios larger than 1 mean that we are trending toward more “open toe” voicing, where a pipe’s toe area is larger than its flueway area. A ratio less than 1 means that we are trending toward more “closed toe” voicing, where the toe is smaller and will flow less wind than the flueway. Examples of pipes with ratios far below 1 with very closed toes feeding especially deep flueways are common in theatre organs on exceptionally high wind pressures.

Articulation provides percussive clarity to rhythm, but lower ratios will reduce articulation. Wind pressure builds more slowly in the foot with smaller toes, and a slower buildup of pressure will make articulation more gentle and less percussive. Ratios above 1 tend to accentuate more articulate speech, and this is why we hear more articulation with “open toe” voicing. Classical French voicing, with its closed toes, deeply open flueways, and lower ratios will have much less articulation than North German voicing and less response to the touch of the key. 

All of the pipes below 1′ in pitch in the entire Grand Orgue principal chorus of the Isnard organ at Saint Maximin originally had ratios so close to 1 as to suggest that it was a purposeful goal.26 It is an exception in classical French voicing with its more moderate flueway depths, and it exhibits gentle articulation. In this soundclip we hear the exquisite articulation of the Isnard Positif 8′ Montre in Louis Marchand’s Tibi omnes angeli. <soundclip 4>
From the middle of the compass to the high treble, the toe constants of this stop range from 0.6 to 1.2, and the toe/flueway ratios range from 0.7 to 1.8.27

In Figure 20 we see that Silbermann’s organ at Großhartmannsdorf has ratios that never drop below 1, and they closely parallel the French voicing of the Isnards. The ratios of the Freiberg Dom organ in Figure 11 on a similar wind pressure are virtually identical, and we might gain some insight from this data to explain why the toe constants in Figure 8 drop at 1⁄8′ pitch. The ratios in Figure 11 continue to rise right up to 1⁄8′ in pitch, and this means that the flueways in Figure 9 have increasingly more wind from the toes as the pitch rises. The toe constants at 1⁄8′ pitch in Figure 8 obviously drop in their relative flow of wind, but those toes are still feeding increasingly more wind to much smaller flueway areas (i.e., the flueway areas are dropping at a faster rate than the toe areas). This is very strong evidence that Silbermann was calculating toe and flueway areas. 

Silbermann’s lower pressure organs have much higher ratios, i.e., they are much more “open toe,” and the more unmolested examples tend to exhibit more articulate speech. This is why the Orgelbewegung, which prized clear articulation, emphasized “open toe” voicing on lower wind pressures. The movement got it partly right, that more open toes will emphasize articulation, but the factor that matters more is the ratio, not the diameter of the toe. D. A. Flentrop’s voicing does not have the most open toes in Figure 14, but with the most closed flueways in Figure 16, the Flentrop ratios are generally the highest in Figure 20, and the articulation of this Flentrop is very clear.

Arp Schnitger did not use heavy nicking. His ratios in Figure 20 are high in both bass and treble, and his more unmolested pipes have clear articulation.

Fine nicking will reduce articulation, but bold nicking will eliminate it in all conditions. (Nicks likely stabilize the formation and position of the vortex on the languid edge.) About 90% of the pipes in the Isnard organ have no visible nicks on their languids. Much of the very fine nicking occurs on the separate mutations, giving them a smoother legato as a solo voice.²⁸ French Romantic voicing evolved from the deep flueways of Classical French voicing, and it employed bold nicking to achieve a smooth Romantic legato. Nicking also has the same effect as raising the cutup, and the sound is less bright after adding nicks, i.e., nicking permits lower cutups for the same timbre. The Hook ratios in Figure 20 are high, but the bold nicking of the Romantic Hook voicing completely suppresses its speech articulation.

While on the subject of Romantic voicing we should note that this style often employs a tuning device, known as a Reuter tuning slot, which greatly reduces articulation. The tuned length is achieved by cutting a slot into the pipe that does not extend to the top of the pipe. If you want clear articulation, pipes need to be cut dead length or fitted with tuning slides that extend to the top of the pipe. Anything that makes the tuned length of the pipe indeterminate will reduce articulation. Classical French façade pipes with extreme overlengths and multiple cutouts at their backs to achieve the correct pitch have little articulation, and this is consistent with their closed toe voicing style. Articulate Germanic voicing trends toward dead-length tuning, which is also typical of Silbermann’s work. 

Ears 

There are more details that affect voicing in more subtle ways that are not within the scope of this article, but we should address one of them: ears. Romantic and neo-Baroque voicing make consistent use of ears because they significantly increase the power of the fundamental by about 1.5 dB. This is not trivial, and it represents a scaling increase of three halftones. But ears also come at a price with a strong increase in the power of a few discrete higher harmonics, and the resulting blend is worse. The blend of pipes with high cutups and few harmonics will be less impacted by ears. The spectral data on the change in power and timbre caused by ears is shown in the author’s book.²⁹

Classically inspired voicing

We can readily grasp the Silbermann brothers’ use of deep flueways from their exposure to French voicing. But the deep flueways of Arp Schnitger’s work shown in Figure 18 are unexpected. Schnitger may indeed have significantly reduced his flueways for a more restrained power in smaller acoustics, much as we see in the data for D. A. Flentrop’s organ, but this is speculation without data on unmolested pipes. The Steinkirchen organ is reportedly the least tonally modified of Schnitger’s organs, but Rudolf von Beckerath’s documentation of that organ lamentably omits the crucial toe diameters and flueway depths.³⁰

Perhaps of more interest, Schnitger’s Germanic voicing is not considered vocale by some American organ builders who practice that style; it is considered an instrumental style with brighter harmonic richness more like that of D. A. Flentrop. The vocale voicing I have observed trends to more open toes, more closed flueways in modern work (and very deeply open flueways in some ancient examples), varying degrees of languid counterbevels, and very high cutups in both older and modern work. Vocale cutups tread in that range of timbres between a principal and a brighter flute.31 Subjective impressions suggest that vocale voicing cuts the vortex above the height where it spins at the frequency of the tuned resonator, i.e., above the point where Coltman’s impedances match and Ising’s fundamental forms most quickly at I = 2. This is a very rough model for vocale voicing, but voicing data are virtually non-existent for pre-Schnitger vocale archetypes or their modern American practitioners. A recent YouTube video featuring George Taylor and John Boody contains an excellent discussion of vocale cutups: https://www.youtube.com/watch?v=_NT65GJNBrU.

American classically inspired voicing has evolved. In their description of their lovely Opus 24 in The Diapason, Richards, Fowkes & Co. stated that “voicing our pipes a little slower relaxes the speech and helps them blend better.”³² “Slower voicing” does not mean that a pipe’s speech is slow to form, it means quite the opposite. With slower voicing the speech is slower to overblow to the octave when blown on higher pressure, and in that condition Ising has shown that the fundamental forms more quickly. To obtain this condition we raise the cutups and/or the languids. (Harmonic flutes will more easily overblow to their octave with languids set very low.) Gottfried Silbermann built very fast speech and “slower voicing” into his pipes with his extended upper lip, extremely high languids, and generous cutups. The blend of a Silbermann chorus is exceptional.

Bruce Shull has worked with John Brombaugh, Taylor & Boody, and Paul Fritts & Co. He has recently written a very informative article on the tonal qualities of sand-cast pipe metal. When voicing pipes made with this metal,

. . . [they] behave the best when they are rather open at their wind[flue]ways. . . . A counter bevel on the front edge of the languids is quite frequently found in antique pipework; today this can be achieved simply by abrading the front edge of the languid with a simple brass file with cross hatching scribed into one surface. The inside edge of the lower lip should remain smooth and must have a burr-free inside edge. . . . It may be that voicing styles that utilize nicking of the languid front edge will produce tonal results that are not very different between sand-cast and stone-cast pipe metal. . . . The organs [voiced with these pipes] have a solid and full sound with a very sweet character at the same time. There is a hint of breath in the sound due to the open windways and abraded languid fronts but the speech is immediate and yet gentle, and the blend is superb. The speech is such that the voicers find themselves doing less “fussing” with the pipes, and, in fact, the pipes have taken much less time to finish on site.³³

Although Silbermann’s resonators had thin and very stiff walls of about 90% hammered tin, he would no doubt agree with these voicing comments.

The power of inductive logic

The sound of a pipe organ can spark strong emotions, and the subject of voicing can spark fierce emotional debate. Voicing is indeed complex. We could spend a lifetime exploring its wonderful variety, but with some effort it is comprehensible.

This brings us full circle to the leading quote in this article: “Inductive logic is much more difficult­—but can produce new truths.” Inductive logic requires data, and the collection of data and its analysis requires effort. Some may find the effort required by inductive logic inconvenient if they accept the idea that all opinions have equal value, an extraordinary belief that curiously took root in American public education in the 1970s. But we have known since the time of Francis Bacon’s formalization of the scientific method that Nature yields only to data and cares nothing about our opinions. The inductive models in this article represent a significant effort to understand the data, and as new data emerges these models will no doubt be refined or replaced by others with better models. This is the power of inductive logic.

Silbermann’s inductive brilliance

The organs built at Freiberg in 1714 and much later at Großhartmannsdorf in 1741 are voiced on similar wind pressures. The regularity and similarity of the toes and flueways in these two organs establish that Silbermann devised successful models of voicing at the beginning of his career. Many organbuilders experiment with these complex variables to improve their sound over the course of their careers. Data previously published in The Diapason suggest that Silbermann’s regularity is probably unique among organbuilders. Figure 21, for example, shows that the Hooks treated toe constants as a completely free variable.³⁴ The regularity of Silbermann’s work may imply a limited tonal palette, but his youthful brilliance in finding a set of scaling and voicing models that would work in a wide range of acoustics and wind pressures is simply astounding. 

Silbermann’s data reveal an intellect that embraced inductive models. These models are not recipes from received wisdom. They are unique to Silbermann, and they exhibit the traits of inductive logic based on experimental data. Consider for a moment that Silbermann, the son of a carpenter, was not likely given a formal education in mathematics and science; this was the province of the wealthy and political elite during the time of Silbermann’s youth. Greß’s data and their implied theoretical models of voicing clearly represent an intellectual tour de force. Silbermann’s sound is indeed controversial, but Silbermann’s insights can teach us a great deal about the theoretical foundations of tonal design and voicing.

Organ literature often waxes nostalgic about the “secrets” of the old masters. The secret to their success was just the hard work of analyzing the problems they faced. Whether we are looking at the balanced ratios of the Isnards, the carefully calculated toes and flueways of Silbermann, or the Romantic sounds of Cavaillé-Coll, we see the work of analytical minds in the pursuit of artistic beauty. It may come as a surprise to know that Cavaillé-Coll and John Brombaugh were both trained as engineers. There is no gulf between art and science; they are mutually bound.

Silbermann’s unique sound

Gottfried Silbermann’s sound does not follow classical North German or French models. A typical North German chorus has a restrained power from its more closed flueways, a chorus fire supplied by its mixtures, and a strong fundamental supplied by the very wide, leathered shallots of its chorus reeds. A Classical French chorus has a restrained power from its more closed toes and a chorus fire supplied by its reeds. Silbermann combines powerful French reed fire with a powerful flue chorus derived from deep flueways, more open toes, and the widest possible mouths. Gottfried Silbermann’s sound is not a synthesis of classical French and North German organs, it is unique, and its blend and clarity make the sound of Bach come alive. Follow this YouTube link to the carefully restored Silbermann at Lebusa: https://www.youtube.com/watch?v=oOoSkB2UVMw.³⁵ The temperament is a form of meantone devised by F.-H. Greß.³⁶

Meantone

Gottfried Silbermann’s voicing and blend work very well in meantone. With the exception of “big city” organs such as the Frauenkirche organ in Dresden, Silbermann maintained the use of a very mild 1⁄6-comma meantone even when confronted with strong opposition from Johann Sebastian Bach. There is no dispute that equal temperament is essential to a vast range of wonderful literature, but we have also come to understand that meantone has a tonal beauty and gravity sorely lacking in equal temperament. This was a concept well understood by Bédos, who abhorred equal temperament.³⁷ Meantone was perhaps a part of Silbermann’s French legacy. 

Very few of Silbermann’s organs have survived in any form of meantone, but the lovely organ in the Freiberg Dom had organists who mostly succeeded in protecting it from the good intentions of its restorers. Here is a soundclip of the end of Bach’s Passacaglia and Fugue in C Minor, BWV 582, written in Bach’s early years, and played on the Freiberg Dom organ in 1980 in an approximation of its original meantone. The Picardy shift to C major at the end of the fugue resolves in a radiant third. This is Gottfried Silbermann’s sound. <soundclip 5>

Uncredited images reside in the collection of the author. Fr. Thomas Carroll, S.J., graciously suggested clarifications in the prose of this article.

Notes

21. Robert A. Heinlein, The Notebooks of Lazarus Long (New York: G. P. Putnam’s Sons, 1973). 

22. In 1972 I asked Dirk Flentrop for permission to measure his pipework and organs, which he graciously gave, adding that imitation was the finest form of flattery. Flentrop went on to predict that I would use my observations of his work to find my own sound (“Your ears will be different than mine”). He was a generous teacher, and secure in his knowledge. The Flentrop data shown in Figures 14, 16, 19, and 20 were taken in 1978 with the kind permission of David Rothe. The Hook data were taken in 2000 with the kind permission of Fr. Thomas Carroll, S.J. The Isnard data can be found in the original source in Note 26 and fully graphed in the source in Note 23.

23. Michael McNeil, The Sound of Pipe Organs, CC&A, 2014, Amazon.com. The toe constant equation: diameter of the toe = √ (toe constant*4*mouth width fraction*pipe diameter).

24. Heimo Reinitzer, Die Arp Schnitger-Orgel der Hauptkirche St. Jacobi in Hamburg, 1995. This is one of only three publications known to the author to include complete data for understanding the sound of an organ, i.e., its pipework, windchests, wind system, temperament, action, and layout. The other examples can be found in the author’s “The 1755 John Snetzler Organ, Clare College, Cambridge, restored by William Drake, Ltd., Joost de Boer, Director,” The Diapason, September 2019, pages 17–21, and “The 1864 William A. Johnson Opus 161, Piru Community United Methodist Church, Piru, California,” The Diapason, August 2018, pages 16–20, September 2018, pages 20–25, October 2018, pages 26–28, and November 2018, pages 20–24. I use Jahnn’s data for the Hauptwerk 16′ Principal on page 117 for Schnitger’s voicing; located in the façade, these pipes may have been the least accessible to changes in voicing. The restorer, Jürgen Ahrend, states on page 252 that the cutup, flueway, and toe hole data in this book were taken after his voicing (“. . . nach meiner Intonation”). Ahrend had to deal with previous interventions, and the current sound reflects his voicing. The toe data of the 16′ Principal taken after the restoration show extremely wide variations and some excessively open toes; Jahnn brilliantly solved this problem in 1925 by measuring the smallest diameters in the wind conduction between the windchests and the offset pipe feet—these are the values shown in Figure 14.

25. The Sound of Pipe Organs, pages 64–80. 

26. Pierre Chéron and Yves Cabourdin, L’Orgue de Jean-Esprit et Joseph Isnard dans la Basilique de la Madeleine à Saint-Maximin, ARCAM, Nice, 1991. The Isnard Grand Orgue toe/flueway area ratios on page 166 are almost exactly 1 up to 1′ in pitch for the entire principal chorus including both mixtures. The 8′ Montre deviates because it was revoiced in 1885. See page 59 on “closed up flueways” and page 175 on languids, which have about 50-to-58-degree bevels and about 75-degree counterbevels that slope inwards (counterbevels are more commonly vertical). Per my on-site observations on June 24, 1995, the upper lips are aligned with the lower lips, and the languids are lower than Silbermann’s, where the top of the Isnard counterbevel is level with the top edge of the lower lip.

27. McNeil. The Sound of Pipe Organs, pages 177–182.

28. Pierre Chéron and Yves Cabourdin, L’Orgue de Jean-Esprit et Joseph Isnard dans la Basilique de la Madeleine à Saint-Maximin, pages 132–133.

29. McNeil, The Sound of Pipe Organs, page 94.

30. Richards, Fowkes, & Co. See richardsfowkes.com/5_technical/beckerath for the Schnitger data taken by Beckerath. 

31. Vocale voicing has affinities to smooth Romantic English voicing with its very high cutups. None of the English Romantic chorus stops are harmonically rich, but they are intense with deep flueways; brightness is built by adding the smoothly voiced sounds of higher pitched stops. Instrumental voicing features harmonic richness in the individual stops, and those harmonics, when carefully voiced, can create a chorus of rich harmonics; this is the sound of a D. A. Flentrop. This distinction is also applicable to a reed chorus. The broad, leathered shallots of English and German reeds add smooth fundamental power. The rich harmonics of Clicqout, Callinet, and Cavaillé-Coll chorus reeds create a scintillating chorus depth. Much voicing resides in the broad range between these styles.

32. Opus 24, “Cover Feature,” The Diapason, May 2021, pages 26–28.

33. Bruce Shull, “Casting Pipe Metal on Sand,” Vox Humana, April 25, 2021.

34. See the toes, flueways, and ratios for E. & G. G. Hook, J.-E. & J. Isnard, W. A. Johnson, and J. Snetzler in “1863 E. & G. G. Hook Opus 322, Church of the Immaculate Conception, Boston, Massachusetts,” Part 2, The Diapason, August 2017, pages 18–21, “The 1864 William A. Johnson Opus 161, Piru Community United Methodist Church, Piru, California,” Part 4, The Diapason, November 2018, pages 20–24, and “The 1755 John Snetzler Organ, Clare College, Cambridge, restored by William Drake, Ltd., Joost de Boer, Director,” The Diapason, September 2019, pages 17–21. With the sole exception of Gottfried Silbermann, these are free variables for all other builders known to the author.

35. J. S. Bach, Komm, Heiliger Geist, Herre Gott, BWV 651, Christopher Lichtenstein, organist.

36. Frank-Harald Greß, Die Orgeln Gottfried Silbermanns (Dresden: Sandstein Verlag, 2007), pages 72–73.

37. Michael McNeil, “The elusive and sonorous meantone of Dom Bédos,” The Diapason, September 2020, pages 14–17.

Soundclips

4. [00:33] Louis Marchand, Tibi omnes angeli, Jean-Esprit Isnard, Couvent Royal de Saint-Maximin, 1774, Bernard Coudurier, BNL 112851 A, © SCAM/BNL 1995.

5. [00:55] Johann Sebastian Bach, Passacaglia and Fugue in C Minor, BWV 582, Gottfried Silbermann, Freiberg Dom, 1714, Karl Richter, Archiv 2533 441, © Siegfried Schmalzriedt, 1980.

Michael McNeil

Michael McNeil has designed, constructed, and researched pipe organs since 1973. He was also a research engineer in the disk drive industry with twenty-seven patents. He has authored four hardbound books, among them The Sound of Pipe Organs, several e-publications, and many journal articles.

Very few organs survive the depredations of time. Some are the victims of wars and fires, but most are the victims of the good intentions and interventions driven by changing tastes in sound. Those few that have survived such calamities usually have something special about them in their sound or their visual impact. The 1750 Joseph Gabler organ at Weingarten, Germany, is special on both counts—its dramatic chorus makes music come alive, and the architecture of its casework and façade is a stunning tour de force.

The Gabler organ has been criticized since almost the time it was built for its lack of power, having almost a chamber instrument quality. But the Gabler organ has a dramatic flair and musicality that sets it apart from most pipe organs, perhaps teaching us some valuable lessons in tonal design.

Human sensory perception takes notice only of changes. The old joke about cooking a live frog has more than a grain of truth to it. Place a frog in hot water, and it jumps out; raise the temperature of the water slowly, and the frog will take no notice and become dinner. It is the same with sounds. If a sound does not change, we do not notice it or we lose interest. Gabler was a master of the control of change in sound, and this is the heart of the drama in his organ. By way of example, Johann Sebastian Bach’s early composition, the Toccata in E major, BWV 566, requires an organ with a dramatic sound to pull it off, not just a loud organ. Peter Stadtmüller’s 1975 recording of BWV 566 on the Gabler organ takes us to new emotional dimensions <soundclip1>.¹ The Gabler organ’s lessons go to the heart of musicality.

In 1986 Friedrich Jakob and the organbuilding firm of Kuhn published a wonderful book on the Gabler organ at Weingarten. Die Grosse Orgel der Basilika zu Weingarten is available from Orgelbau Kuhn AG, Männedorf, Switzerland.² We are very fortunate that Jakob and Orgelbau Kuhn took the time to write this book and publish it. In an effort to better understand the sound of this instrument, I translated some of its passages with Google Translate, edited the translation as an organbuilder would understand it, and then graphically analyzed the data from the appendix of this book. This is but a very small part of what this book has to offer, and those seriously interested in this organ should purchase this wonderful book.

The current basic specifications of the organ after the restoration by Kuhn are:

Manuals: compass C to c′′′, 49 notes; pitch a′ = 419 Hz at 15 degrees Celsius; wind pressure = 70 mm water column.

Pedal: compass C to d′, 27 notes (originally C to g); pitch a′ = 419 Hz at 15 degrees Celsius; wind pressure = 70 mm water column.

Orgelbau Kuhn restored the Gabler organ between 1981 and 1983. The work was carried out partly in Männedorf, partly in Weingarten, and was summarized as follows:  

A. Static remedial measures:

• Renovation of the gallery floor, partial replacement of supporting beams. 

• Improvement of the Kronpositiv position. 

• Improved support for the bracing of the Positive chest.

B. Removal of added features:

• Demolition of the additional works built in 1954.

• Rebuilding of the Barker machine and restoration of the continuous direct mechanics.

• Rebuilding of the electric trackers for the Kronpositiv, reconnection to the Oberwerk by means of the original conductor blocks.

• Rebuilding of the numerous bellows as well as the newer wind ducts and blower system.

• A reconstructed wind system with six wedge bellows.

C. Normal cleaning and restoration work.

• Make the whole organ wind-tight again.

• Treatment against wood pests. 

• Reworking of all mechanical parts, in particular the axle points. 

• Repair and reconstruction work on the pipework. 

• Tuning in an unequal temperament.³  

Pipework repair

Orgelbau Kuhn performed the normal repairs on pipes that would be expected from centuries of tuning damage. Split pipe seams and loose languids were resoldered, deformed pipe bodies were rounded, and new sections were added to the tops of damaged pipes. 

The effect of the wind system on sound dynamics

The dynamic response of the Gabler wind system is one of most important aspects of its dramatic sound. While measurement data of the wind system is lacking, Orgelbau Kuhn carefully described what they found and what they changed:

The Gabler wind supply in the north tower had already been replaced for the first time in the work of 1861/62. In place of the six original wedge bellows, there were ten box bellows of a new design. Probably in 1912 during the installation of an electric blower the wind system was again modernized by the construction of a large, so-called double-rise bellows.

In the course of the restoration, six wedge bellows were again set up, however, according to practical requirements, with motor operation. The old beams of the bellows chamber did not allow any definite conclusions as to the former position of these six bellows, so free assumptions had to be made.

The original wind duct system, in so far as this had not been done earlier, was practically completely expanded in 1954 and replaced by a new version with cardboard pipes. On the basis of a large number of traces (cut-outs on the casework, color traces on the walls, cut-outs on the beams and on the grids, as well as on the original windchest connections), the course as well as the dimensioning of the Gabler wind duct system could be known.

In three places, where it was obviously not possible to expand, some of the original ducts were preserved. On the one hand, these are the supply ducts to the two Rückpositives under the floor, on the other by a section of the connecting channel above the façade middle flat. This remainder was of particular importance. This is a double channel (57 x 17.5 cm outer dimensions) with a middle wall. The upper part of the duct is marked with “Manual” and the lower part with “Pedal” with a weakly readable red pencil. This was the proof of the actual execution of the wind separation for manual and pedal, which was already required in the contract.⁴

Data on the size of the bellows, ducts, and pallet boxes would allow a calculation of the capacitance (volume) and the inductance (mass, or weight on the bellows) of the wind system. From this data the resonant frequency could be calculated, giving insight into the slow, dramatic risetime of this wind system on full demand. What we do know from the elegant layout drawings of the Gabler organ by Orgelbau Kuhn is that the wind ducts were very long, and the cardboard ducting from 1954 (heard in the 1975 recording by Peter Stadtmüller) was apparently larger in cross section. (“In three places, where it was obviously not possible to expand, some of the original ducts were preserved.”⁴) This means that the internal volume of the wind ducts was larger in 1975, and the sheer length of the ducting indicates a very large internal volume for the entire wind system.

In the 1975 recording we hear a very long, slow surge in the sound of the full pleno driven by a very low resonant frequency in the wind system, and this is a large part of the dramatic sound of the instrument. Such a slow wind system obviously forces a slower tempo, and that is how Stadtmüller interpreted the Toccata in E Major in the glorious acoustics of the basilica. From this we see an essential component of dramatic change: a slow buildup of power when the full organ is played and the wind system is forced to work hard <soundclip2>.¹ The current sound of the organ post-restoration still retains a very dramatic sound, but it is slightly faster, and may be the consequence of the smaller ducting cross sections with less capacitance.¹⁵ When asked about the pipe organ, Igor Stravinsky is reported to have said, “The monster doesn’t breathe.” Although it may have been unintended, Gabler’s gift to us is that he makes the organ breathe.

To put this into perspective, the author took careful measurements in 1996 of the J.-E. & J. Isnard wind system on their organ at St. Maximin, France, and calculated its resonant frequency to be 1.2 cycles per second, a value that correlated very well with actual measurements of the slow, grand surge of this wind system.⁵ Although it is not as long a surge as what we hear in the Gabler organ, the J.-E. & J. Isnard organ at St. Maximin also features a dramatic buildup in power on full organ, the result of high capacitance and high mass in the wind system.

Famous organs with dramatic chorus effects, e.g., the Isnard at St. Maximin, tend to exhibit a purposeful starving of the wind supply where the total area of the toes that can be played in a full plenum are roughly equal to or even greater than the cross section of the wind duct that feeds them. Gabler’s reduction of ranks in the Kronpositiv to alleviate wind starvation, as noted by Orgelbau Kuhn, does indeed suggest that Gabler restricted the cross sections in his ducting. To more fully understand the wind flow of this organ we need measurements of the ducting, pallet openings, channels, and pipe toe diameters for each division.

The effect of the mixture designs on sound dynamics

Pipes are very effective sources of change in sound when they are out of tune (think of the richness of a celeste). We also hear complex dynamic changes in the sound when the speech transients of many pipes combine to form a complex onset of speech in the attack of a chord. The most obvious sources of tonal change are Gabler’s immense mixtures that contain as many as twelve ranks in a single stop. His Sequialters are also constructed of many ranks, and they are scaled exactly like the mixtures. The combination of the Hauptwerk Mixtur, Cymbalum, and Sesquialter contains a vast number of pipes that, as Jakob nicely phrased it, have the effect of a “string choir.”

Multiple ranks at the same pitch do not produce significantly more power (the power increase of doubling the pipes at a single pitch is the square root of 2, or 1.4 times the power). The significant effect is in the depth of the chorus, which is heard as subtle celesting (mistuning) in sustained chords, and which is also heard in the attack of a chord where many pipes speaking together have subtle differences in the speed of their speech and their harmonic content. To some degree these effects are mitigated by the “pulling” effect; pipes of the same pitch placed closely together on the same channel will tend to “pull” each other into tune. But the Gabler chorus has not only many duplicated pitches in a single mixture, it has three such mixtures on the Hauptwerk with limitless possibilities for subtle mistuning effects. The upper pitch ceiling in Gabler’s mixtures is a 1⁄8′ pipe. The preponderance of mixture tone resides in the region from 1⁄2′ to 1⁄8′ pitch, precisely the frequencies to which human ears are most sensitive.

Understanding the sound of the Gabler organ

The appendix of the book contains wonderful data on pipe diameters, mouth widths, and mouth heights (cutups). No data exists on the diameters of the toe openings or the depths of the pipe flueways. This data would allow us to understand the very high cutups of the pipework in this organ. Furthermore, the ratio of the areas of toes to flueways plays a large role in the speech of these pipes. We can only hope that this data will someday be made available. The very useful reed pipe scales in the appendix would benefit from additional data on shallot opening widths, tongue lengths from the tuning wire, tongue widths, and tongue thicknesses, all of which would help us to better understand the sound, especially the very effective Pedal 16′ Bombarde.

Orgelbau Kuhn addressed the low power of the Gabler organ in their description of its scaling and voicing.

The sound of the Gabler organ was already felt as comparatively weak, often as too weak. From the construction period, there were no complaints, because the deadlines and costs were too much in the foreground. Even so, the sound development must have been perceived as partially deficient. This is borne out by the various supplementary technical measures taken by Gabler to increase the sound: the lifting of the roofs by means of cable mechanics, the opening of the side walls of the Oberwerk and the Pedal. All these changes, however, did not benefit much. The reason lay deeper . . . .

The weak sound of the Gabler organ . . . finally led to the construction of auxiliary works, along with stylistic considerations as a result of the altered sound tastes of the time. This resulted in 1912 in the construction of the Seraphonwerk with seven high-pressure registers (150 mm water column) as well as the supplementation of the Kronpositiv by a Cymbal.

What is the source of the relatively weak sound, or rather the relatively low decibel performance of this organ? According to our findings, there are essentially four. The scales of the pipework by Gabler, the sometimes precarious wind conditions, the inhibited sound egress due to Gabler’s compact design, and finally the throttling by the narrowing of the toeholes of the pipes. The number of nicks is irrelevant in this context.

Orgelbau Kuhn pointed to the casework as a source for the low power of the organ.

A[nother] reason for the relative weakness of the sound is to be found in the comparatively small openings for egress of the sound . . . . The big façade pipes are very closely spaced. Apart from the triangle openings around the pipe feet only very narrow slots between the pipes are available for the egress of sound.

Interestingly, images of the façade show that Gabler added carved ornaments between the feet of the façade pipes, further blocking the egress of sound.

Massive, unperforated pipe shades also reduce the egress of sound. While the three problems of scaling, wind supply, and compact construction were already present, the fourth problem only arose as the organ aged: the narrowing of the toe holes due to the very steep angles of the toeboard bore chamfers on which they sat. Last but not least, it was also due to late maintenance. This secondary damage was discovered and corrected in the course of the restoration, while the other characteristics of the Gabler style, of course, remain untouched.⁶

Scaling

The scaling of the Gabler organ is unusually narrow for such a large acoustical space. And unlike the French who scaled their foundations wide but kept the upperwork stop scales narrow, Gabler uses a constant scale, which is narrow in both the foundations and upperwork. Why would Gabler do this? The answer may lie in the layout of his unusual principal chorus, which with its enormous mixtures looks more like an ancient Blockwerk than a typical chorus of his time. Here is Orgelbau Kuhn’s description of the problem:

We can only confirm: Gabler had difficulty with the scales. It is not only in the strings, but in general, that the composition of the scaling is quite narrow. Obviously, he looked at the size of the scales as an absolute one, whereas in reality they were dependent on space. For the giant room of the Weingartner Basilica, respectable distance considerations were appropriate. As a result of these under-nourishing scales, the principal is already near the strings, while the strings are already struggling against the frontier, where a clean, precise, and reliable approach to the fundamental tone is scarcely possible.

That is why Gabler also had to make extensive use of voicing aids, not only of nicking, but also of other voicing aids such as front and box beards. By making use of these aids, at least, all the pipes were able to speak in the fundamental, but a development of the power of the organ was not possible.

Gabler sought to compensate for this scaling deficit through numerous double-ranked and multiple-ranked voices. In the mixture voices, Gabler goes much further. In the Hauptwerk, for example, he built the Mixtur 2′ with ten ranks, the Cimbel 1′ with twelve ranks, and the Sesquialter with nine ranks. Through these chorus effects, Gabler sought to achieve sound power, a power that was not due to the too narrow scales. As we have seen in the Kronpostiv, but also in the Mixturbass, he had wanted to go further in this direction of multiple ranks, but he was, to a certain extent, overtaken by the second evil: he came to the limits of the wind supply. The long wind trunks made an inadequate supply, so that in the course of the work he was forced to cut back on the number of ranks (in the Kronpositiv, for example, a reduction from 18 to 2 ranks).

This struggle for sound and wind is clearly visible to the expert on the evidence in the construction. This desperate wrestling resulted in a great success. But it is clearly a struggle and not a virtuosic play with the principles of organbuilding. The result is a result of the struggle and not artistic design.⁶

The wonderful scaling data in this book was entered into a spreadsheet that normalized the measurements into Normal Scales for pipe diameters, mouth widths, and mouth heights (or “cutups” to a voicer). This graphical presentation allows a much easier interpretation of the data. A set of graphs of the Hauptwerk (Figures 7, 8, and 9) and Pedal (Figures 10, 11, and 12), with commentary, are presented at the end of this article.

The graphs of the pipe diameters (Figure 7) corroborate Orgelbau Kuhn’s assertion that much of the low power was due to narrow scaling. Mouth widths are usually a better indication of relative balances of power, but Gabler used mouth widths that were generally very close to the normalized mouth width scale (one fourth of the pipe circumference), and as such, the normalized mouth width scales (Figure 8) are very similar to the normalized pipe diameters.

The normalized mouth height (or cutup) scales (Figure 9) are remarkable. Gabler’s mouth heights are generally fairly low in the bass increasing to extremely high values in the trebles, so high in fact, that 1⁄8′ pipes are cut up roughly 40% of their mouth widths. The relatively high mouths would suggest pipes with very open toes and flueways, although this data is unfortunately not tabulated. 

Gabler knew how to use very wide scales, but he only used them in his flutes (see the graph of the Hauptwerk, Figure 7). Is Gabler showing us what a Gothic chorus would look like? The chorus effects of these multiple-ranked mixtures are astounding, unique, and very musical. Chorus dynamics, not power, may have been his objective. The subtle imperfections of tuning in these ranks produce subtle celesting on a grand scale. Subtle differences in voicing will produce a rich chorus effect resulting from random differences in the speech onset of the pipes in these mixtures. Gabler may have aimed at the grand sound of a Gothic Blockwerk, not loud, but rich in texture and chorus effects.

Few unmolested pipes remain from the Gothic period, much less complete organs, but one example stands out: the 1475 organ by da Prato in the Basilica of San Petronio, in Bologna, Italy. As recent research shows, this organ is largely original and serves as an elegant example of a Gothic chorus.⁷ The author graphed and combined the data for both the Gabler and da Prato organs. In Figure 1 we see data for normalized pipe diameters, and in Figure 2 we see normalized mouth widths. The data for the da Prato chorus extends to 24′ low F; the 32′ value is a straight-line extrapolation of the 16′ and 24′ da Prato data.8 The Gabler chorus includes the Hauptwerk and Pedal pipes, which extend to 32′.

Scaling data are intrinsically noisy; variations from the intended scale are produced both by the pipemaker and by the person who measures a pipe. Variations of +/- a halftone are normal. The data are remarkable because both sets of data converge on the same intended diameter and mouth scale. We do not know if Gabler imitated the da Prato scales or any other Gothic design, but the similarity of the Gabler and da Prato scales is unquestionable. The dotted black line represents the approximate intended scale, the red lines represent the actual Gabler pipes, and the blue lines represent the actual da Prato pipes.

Gothic pipework (Figure 3) from an organ by an unknown builder in Ostönnen, Germany, exhibits an unusual design characteristic also seen on the façade pipes of the Gabler organ (Figure 4). Figure 3 shows an extension of the upper lip at the sides of the mouth (red arrow), making the mouth width slightly narrower than the width of the flueway.⁹ We do not know if Gabler was taking his cue from a Gothic model, but the comparison is interesting.

Voicing

The minimum data set to understand the voicing of an organ includes the mouth height (“cutup”), toe diameters, flueway depths, treatment of the languids (bevel angles and types of nicking), and presence or absence of ears and other such devices. Like the da Prato organ of 1475, the Gabler organ exhibits no ears on the façade pipes and presumably none on the internal pipes of the principal chorus. Orgelbau Kuhn provides data on cutups, but not on toe diameters or flueway depths. Voicers adjust toe diameters and flueway depths to affect the flow of wind for more or less power. Voicers raise cutups to make the pipe tone smoother with less harmonic bite. More wind, from either the toe or flueway, will increase power and make the tone brighter with more harmonic bite. A more powerful and brighter timbre can be made smoother again with higher cutup. Hence, it is important that we know all three variables—cutups, toe diameters, and flueway depths—if we are to understand the voicing. We have only mouth height data. 

A common precept of neo-Baroque voicing was the rule that the mouth height should be 1⁄4 of the width of the mouth. There is, of course, no basis for this in historic work, nor is there any theoretical basis, and it produces a rather strident timbre in most pipework. The normalized mouth heights of the Gabler organ, seen in Figure 5, are remarkable. Only in the bass do they approach a value which produces a height 1⁄4 of the mouth width (this occurs when the normalized mouth height scale in halftones is the same as the normalized mouth width scale in halftones). But as the pitch ascends for the Gabler pipes, so do their normalized mouth heights, until at the highest 1⁄8′ pitches the mouths are very high, about 40% of their mouth widths. Also of note is that the treble mouth heights of the principal chorus are almost as large as the mouth heights of the very wide flutes in the Hauptwerk. The same trend is seen in Figure 6 of the da Prato mouth heights, but the typical da Prato values are lower, a reflection of that organ’s lower wind pressure. The highest mouths in the da Prato graph are also those of its flutes. Gabler’s treatment of mouth height looks very much like the Gothic work of da Prato, adjusted for higher wind pressure.

Reiner Janke sent the author photos of pipe mouths from the 1743 choir organ at Weingarten, also built by Gabler. These photos show very generous flueway depths and deep, fine nicking. Although we do not have toe diameters to confirm this, it may be reasonable to assume that Gabler’s high mouth heights in the treble reflect a desire for a more ascending treble.

Orgelbau Kuhn limited their analysis of the voicing to the presence of nicking and the method of tuning:

While ‘tuning’ means the mere regulation of the pitch, the ‘voicing’ includes the processing of all partial aspects of a musical tone, including the loudness, the tone color, the tone accent, or the transient response. This eminently artistic work is generally performed only when a new organ is being built, or when a major rebuilding is carried out.

A restoration, especially if it also includes changes or regressions in the wind supply system (bellows and wind duct system), also causes a new voicing of the pipework. It is necessary to think philosophically about the original Gabler voicing, and it would be wrong to assert that it had remained intact, for the intervening interventions were too great. Of course, we did studies on other Gabler organs, but also on instruments of other South German masters such as Holzhay and Höss, but there were no exact models for the voicing in the Weingarten types, one simply had to work with the existing pipe material. The technical procedure can be easily rewritten. First, the pipes were normalized and repaired where necessary (open solder seams and loose languids soldered). The languids were then carefully placed in the correct position for an optimal response to the pipe in the fundamental. In the rest, as little as possible was changed.

Gabler has made extensive use of nicking. This can be seen in the non-speaking but voiced façade pipes c′–d′ of the Kronpositiv, which are completely unchanged. In addition to the original nicking of Gabler, the main body of the pipes also contains nicking of other handwork. It turned out to be impossible to assign only the newer nicking, but to leave the Gabler nicking unmarked. So it was decided not to work the languids; the insertion of new languids was not considered at all . . . .

The labial bass pipes are provided with cleanly inscribed tuning slots proportioned to the pipe diameter up to the 2′ position. Attempts have shown that stops without these tuning slots could not be tuned over the entire range of octaves. These tuning slots are therefore to be regarded as original. In contrast to later practices, however, these tuning slots are only scribed and not fully enrolled.

Tuning 

The absolute pitch is A = 419 Hz at 15 degrees Celsius. The original temperament was very similar to Gottfried Silbermann’s meantone. It was characterized by eight not pure, but good, major thirds, eleven tempered fifths, and one large Wolf fifth on D-sharp to G-sharp. It had an equal temperament fifth at C, extending to -12 cents at G-sharp and extending to +5 cents at D-sharp.

The current milder tuning deviates from the original meantone and has an equal temperament fifth at C, extending to -9 cents at G-sharp and extending to +1 cent at D-sharp.10 It is not known if the Musical Heritage Society recording of 1975 reflects Gabler’s original tuning or something closer to the present tuning.1 Like Gottfried Silbermann, Gabler uses high cutups in his voicing for a less strident timbre, and this works well with meantone temperaments, mitigating the harshness of the more dissonant intervals.

Reflections

Friedrich Jakob reflected on the sound of the Gabler organ:

How is the sound of the Gabler organ to be characterized? We are confronted with the general problem of describing sound with words. With features such as warm, round, pointed, sonorous, bright, and so on, no exact statements are possible. Still, be tempted.

The Gabler organ is certainly not a forceful organ. Power and brilliance are missing in comparison to the normal large organ. The sound is somewhat reserved, veiled, poetic, and pastel colored. The tremendous multiple ranks of the mixtures give the effect of a string orchestra. Minimal deviations of the individual voices do not result in any false tone, but a larger range of the right one. It was very important to leave the organ intimate in character with the chamber music and not to have a wrong symphonic influence. But since everything is wind-tight again, and every pipe is speaking the fundamental, the organ sounds a little more powerful than before.¹¹

The claim has been made that Gabler did not understand the principles of scaling as they relate to larger rooms, and Jakob describes very convincing evidence that Gabler struggled with the power. But the inflection point of Gabler’s constant scale at 1⁄2′ demonstrates that Gabler had a good grasp on the effect of distance on the sound absorption of higher frequencies. Tones extending from the deep bass up to the pitch of a 1⁄2′ pipe will carry very effectively over long distances, but pitches above that point will lose energy in their interaction with the atmosphere, so much so that the sound of a 1⁄8′ pipe will lose 5 dB in power at 500 feet.¹² One halftone of scaling is equivalent to 0.5 dB of power, so this means that 10 halftones of wider scaling must be used at 1⁄8′ to compensate for the atmospheric losses at 500 feet. Gabler widened his mixture pipes by 8 halftones from 1⁄2′ pitch to 1⁄8′ pitch. The length of the Basilica of Saint Martin and Saint Oswald at Weingarten is 102 meters, or 335 feet. Gabler has compensated very well for the distance losses. The absolute values of these scales are indeed much narrower than what we would typically find in rooms of this size, but the mathematics show that Gabler was cognizant of the effects of large distances. But Jakob also convincingly demonstrates that Gabler was not satisfied with the power, went to some trouble to correct it, and ultimately failed in the effort.

Figures 7 and 8 show the diameter and mouth width scales of the Hauptwerk. Note how much wider Gabler scales his flutes relative to the principal chorus. These flutes are quite powerful and provide an extremely effective contrast to the mixture plenum. A wonderful example of this contrast can be heard in Ton Koopman’s interpretation of the Bach Concerto in A Minor after Vivaldi, “Allegro,” BWV 593 <soundclip3>.¹⁵ Here Koopman demonstrates that Gabler’s flutes can cut through the principal chorus. While typical interpretations of this concerto use contrasting principal choruses, Koopman’s performance gives a clarity and beauty to this concerto that can only be heard with Gabler’s tonal balances. Gabler’s organ, if it is not powerful, is extremely musical, and we can learn much from his example, all of it applicable to organs with more power.

To summarize, some of Gabler’s musicality derives from the intense chorus effects of the mixtures with their many ranks, the many duplicated pitches, and the subtle depth created by the mistuning of those multiple ranks. Multiple ranks do not significantly increase power, but they do increase the sense of chorus.

Another aspect of the musicality of the organ resides in its very slow wind response, which takes the form of a dramatic surge to full power when the organ is playing a full pleno. Another effect that produces a slower wind is a high resistance in the wind system, and Jakob mentions this in his description of the Kronpositiv ducting, which was so restrictive that Gabler was forced to remove a large number of ranks on that chest. Many classical organs feature wind trunks that were purposely designed with smaller cross sections to barely flow the required wind, or even starved the wind to a degree.¹³  

Finally, Gabler employed very large scales in the deep bass of the Pedal. Along with the robust Bombarde 16′, the Pedal produces a tactile effect underpinning the modest power of the manual pleno. The overall effect of the Gabler organ is intensely dramatic without being at all overbearing. To reduce this to a basic philosophy, Gabler was a master of designing for a sense of change in the sound, both aural and tactile. The acoustician R. Murray Schafer observed that “. . . a sound initiated before our birth, continued unabated and unchanging throughout our lifetime and extended beyond our death, would be perceived by us as—silence.”¹⁴ His point was that for a sound to have drama, to grab our attention, it must change: change in pitch with the subtle mis-tunings of his multiple-ranked mixtures, and change in power with the slow rise in the pressure of the wind. The organ at Weingarten is the singular achievement of a master, and even if by today’s standards the overall power seems modest, we can use Gabler’s lessons to great advantage.

 

Excellent recordings exist of the restored Gabler organ.¹⁵ See also Youtube for a cut from this CD: Präludium & Fuga C Moll, BWV 549: www.youtube.com/watch?v=hWWtpS-yvKI.

 

The following normalized graphical data for the Hauptwerk and Pedal were constructed from Jakob’s data. Email the author for a copy of the original Excel file with the data and normalizations, which also includes the Oberwerk: [email protected]. Readers interested in the theory behind these normalizations may refer to The Sound of Pipe Organs.¹²

Hauptwerk data (see Figures 7–9)

Jakob’s claim that narrow scaling is responsible for much of the low power of this organ is amply supported by the normalized pipe diameter data. Gabler is using a “constant scale,” where all pipes speaking the same pitch are the same scale, regardless in which stop they appear or in which part of the keyboard compass they appear. This constant scale averages -7 halftones from 16′ to 1⁄2′ pitches, then increases rather linearly to +1 halftone at 1⁄8′ pitch. The normalized mouth widths seen in the next graph follow a similar trend because Gabler scaled his mouth widths very close to 1⁄4 of the pipe’s circumference, the basis of the normal mouth width scale.

Gabler’s normalized mouth heights are remarkable in their deviation from the pipe diameter and mouth width Normal Scales, and they tell us something about Gabler’s intentions in power balance from the bass to treble. High mouths are a tool of the voicer to achieve a smoother, less bright tone, or alternatively, a more powerful tone when the pipe is winded with larger toes or larger flueways. Gabler uses the mouth height as an independent variable, perhaps to achieve an ascending treble power in the plenum. Data on the toe diameters and flueway depths would give us a deeper understanding.

The diameter and mouth scales of the Hauptwerk 8′ and 2′ flutes are very wide. The Gabler flutes are very smooth and liquid in tone and have very high mouths when plotted on the Normal Scale, but those mouth cutups would appear low when looking at the actual pipes because the diameter and mouth scales are very wide. Gabler knew how to use very wide scales, but he only applied such scales to the flutes, perhaps suggesting that his narrow principal chorus scales were an intended result, even in this large acoustic.

Pedal data (see Figures 10–12)

In Gabler’s Pedal we also see a constant scale, but it has a different shape, averaging about +3 halftones at 32′ pitch, descending linearly to about -7 halftones at 2′ pitch, and thereafter remaining roughly flat at that scale up to 1⁄2′ pitch. These wide scales in the deep bass are the source of the tactile effect in Gabler’s sound. Human hearing becomes dramatically less efficient in the bass; at about 20 Hz we hear and feel a sound at about the same level. Below that frequency we tend to only feel the sound. The frequency of a 32′ pipe is 16 Hz and is much more felt than heard. Note the very wide scales of the 16′ Octavbass. It is powerful enough to achieve a strong tactile effect; also note its very high cutups, which imply full wind at the toes and flueways. 

Like the Hauptwerk, the Pedal mouth widths are similar in normalized scaling to the pipe diameters and tell a similar story. Also like the Hauptwerk, the Pedal mouth heights dramatically ascend with higher pitch. 

The Pedal Bombarde is full length with rectangular wooden resonators. The effective scale of a wooden resonator is its diagonal measurement, i.e., the width of its standing wave, and this reed measures a very generous 240 mm at low C. Combined with the tactile character of the deep bass flue pipes, the Bombarde is a very strong component of the drama achieved by the Gabler chorus.

Notes:

1. Peter Stadtmüller, Toccata in E major, BWV 566, J. S. Bach, Musical Heritage Society MHS 3195, Gabler organ, Basilica of Saint Martin and Saint Oswald at Weingarten.

2. Friedrich Jakob, Die Grosse Orgel der Basilika zu Weingarten, Geschichte und Restaurierung der Gabler-Orgel, Verlag Orgelbau Kuhn, Männedorf, Switzerland, 1986, 146 pages. The book and shipping totaled 73.00 Swiss Francs. At this time Kuhn is only able to receive funds wired to their account, which makes the book rather expensive to those of us who live across the Atlantic Ocean. Email Orgelbau Kuhn AG: [email protected]. Website: www.orgelbau.ch.

3. Ibid., pp. 40–43.

4. Ibid., pp. 55–56.

5. My statement of the “. . .motions of the bellows plates. . . to be ≈ 1.25 Hz” for the Isnard wind system in The Sound of Pipe Organs, page 108, has errors that I missed as a result of the closeness of the calculated resonance in Hz and the measured period of the response in seconds. My measurement of the bellows response at 1.25 seconds represented three motions of the bellows, down-up-down, which is 1.5 times the period of the wind surge. Therefore, the correct period, one cycle of two motions, down-up, is 1.25 / 1.5 = 0.83 seconds. Inverting that (1 / 0.83 seconds) gives us 1.20 Hz, or cycles per second, which perfectly correlates to the correctly calculated resonant frequency of the system.

6. Die Grosse Orgel der Basilika zu Weingarten, pp. 72–79.

7. Oscar Mischiati and Luigi Ferdinando Tagliavini, Gli Organi della Basilica di San Petronio in Bologna, Pàtron Editore, Bologna, 2013, 577 pp.

8. Michael McNeil, A Comparative Analysis of the Scaling and Voicing of Gothic and Baroque Organs from Bologna and St. Maximin, e-publication, PDF, Mead, Colorado, 2016. Email the author for free copy:
[email protected].

9. See Youtube video of the organ at Ostönnen: www.youtube.com/watch?v=YxmsZ5ksaVY. Also see the Youtube panoramic video of the Gabler organ in which you can zoom in to see the same treatment of the façade pipe mouths: www.panorama-rundblick.de/gabler-orgel-weingarten. Click on the red arrow to move to the front of the console to see the 32′ façade.

10. Die Grosse Orgel der Basilika zu Weingarten, p. 78.

11. Ibid., p. 79.

12. The Sound of Pipe Organs, pp. 13–14.

13. Ibid., pp. 119–127. See the example of the wind flow calculations for the Isnard organ at St. Maximin.

14. R. Murray Schafer, The Tuning of the World, Alfred A. Knopf, New York, 1977, p. 262.

15. Ton Koopman, J. S. Bach Orgelwerke II, Gabler-Orgel, Basilika Weingarten, Novalis CD, 150 020-2, 1988.

 

Photo: The 1750 Joseph Gabler organ, Basilica of Saint Martin and Saint Oswald, Weingarten, Germany (photo credit: Thomas Keller; see the source in Note 9)

Michael McNeil

Michael McNeil has designed, constructed, voiced, and researched pipe organs since 1973. Stimulating work as a research engineer in magnetic recording paid the bills. He is working on his Opus 5, which explores how an understanding of the human sensitivity to the changes in sound can be used to increase emotional impact. Opus 5 includes double expression, a controllable wind dynamic, chorus phase shifting, and meantone tuning. Stay tuned.

Editor’s note: The Diapason offers here a feature at our digital edition—three sound clips. Any subscriber can access this by logging into our website (thediapason.com), click on Magazine, then this issue, View Digital Edition, scroll to this page, and click on each <soundclip> in the text.

Part 2 of this article is found here.

Deductive logic is tautological; there is no way to get a new truth out if it, and it manipulates false statements as readily as true ones. If you fail to remember this, it can trip you—with perfect logic. . . . Inductive logic is much more difficult—but can produce new truths.¹

 

The late Peter Williams, pipe organ scholar extraordinaire, occasionally remarked to John Brombaugh that he most favored the sound of Gottfried Silbermann. Brombaugh thought this was perhaps a contrarian view, a position Williams often took in their conversations.² Silbermann’s sound is indeed both deeply admired and controversial.

The sound of an organ is the sum of its scaling, voicing, temperament, windchest design, action, layout, wind system, wind pressure, position in the room, and room acoustics. Among these factors, only the art of voicing is perceived as the elite province of a select and gifted few, shrouded in mystery. But as Reiner Janke has so ably demonstrated, voicing can be understood by anyone willing to commit the effort.³

Pipe organ literature abounds with subjective opinions of organ sound and the received wisdom of voicing recipes. These often contain a kernel of truth, but they can sometimes lead us down perilous paths. We will use data and inductive logic to give us insight into Silbermann’s voicing. And in Part 2 of this article we will use those insights to gain a wider perspective on voicing in general by comparing Silbermann’s voicing with a wide range of other styles. In the process we will see what makes Gottfried Silbermann’s sound so interesting.

Fundamentals of scaling and voicing

A quick overview of the features of organ pipes, scaling, and voicing may help readers unfamiliar with these terms. Figure 1 shows the basic features of an organ pipe and the terms used in this article.

Scaling and wind pressure determine the maximum power of a pipe. Scaling includes the diameter of a pipe’s resonator and the width of its mouth. Wider resonators and wider mouths will produce more power, as will higher wind pressure. Scaling also affects the vowel sound, or timbre, of a pipe, ranging from the “ah” of wider scales to the “ee” of narrower scales. The “ah” consists of the fundamental that increases in power in wider resonators. Narrower resonators will emphasize the power of higher harmonics with a brighter timbre.

In Figure 1 we see that the flueway of a pipe is the slit formed by the lower lip and the languid, the horizontal plate soldered on top of the pipe’s foot. The wind from the chest enters through the toe hole into the pipe’s foot and exits through the flueway slit. The languid’s edge turns the sheet of wind formed by the flueway into a spinning vortex. The upper lip cuts the vortex, creating pulsations of pressure that will drive the resonator to sound if the conditions are right.

The vortex spins fastest at the languid edge and spins slower as it expands towards the upper lip. If the height, or “cutup,” of the mouth’s upper lip cuts the vortex where it pulsates at the same frequency that the resonator is tuned, the pipe will speak very quickly.⁴ Lower cutups create higher frequency pulsations where the vortex spins faster. The resonator has more difficulty with faster pulsations, and the speech is both slower to form and brighter with more powerful harmonics. Keep lowering the cutup, and at some point the resonator cannot “resonate” with the vortex at the fundamental, and an open pipe will overblow to the octave, its second harmonic. More pressure or more wind from a larger toe will make the vortex spin faster with more energy, and the cutup will have to rise.

Voicing begins by adjusting the flueway depth and/or the diameter of the toe to control the power (this is also known as “regulation”). More wind from larger toes and deeper flueways produces more power.

A voicer will raise the height of the cutup by degrees to adjust the timbre, making the sound continuously less bright and more like a flute as cutup is increased. Cutup is by far the most sensitive aspect of voicing—very small changes in cutup will make big changes in timbre. While toe areas, flueway areas, and wind pressure have proportional effects on a pipe’s power, its cutup has an exponential effect on its timbre; Ising showed that it is a cube function!

When we say that an organ is voiced in a Germanic or French style, what does this mean? Received wisdom relates that Germanic voicing leaves the toe wide open and closes the flueway to regulate power, while French voicing emphasizes a deeply open flueway and closes the toe to regulate power. Does this make a difference? Charles Fisk thought it made a great difference, and he wrote with passion about the musicality of deeper flueways in 1975.⁵ Subjective impressions suggest that deeper flueways result in a warmer fundamental with less percussive speech when power is regulated with closed toes. Physics tells us that the pressure in the foot and the velocity of air in the flueway will be lower as the toe area decreases and the flueway area increases, and the vortex will spin more slowly.

The musical range of flueway depths spans the very deep flueways of romantic voicing to the more closed flueways exemplified by the work of organ builders like D. A. Flentrop. The received wisdom of Germanic voicing often assumes the sole use of closed flueways to regulate power, but the reality is more complex. How do we know this?

The minimum required data

Typical organ documentation lists pipe diameters, mouth widths, and cutups, but ignores the crucial voicing data of flueway depths and toe diameters, and this unfortunately tells us little about the sound. For example, without the toe and flueway data we do not know if the cutup data imply a softer and smoother sound with more closed toes and flueways or a powerful, brighter sound with more open toes and flueways. As Ising has shown, cutups and the timbre they control are extremely sensitive to changes in pressure and the flow of wind in toes and flueways.

While voicing data of most organbuilders, including Arp Schnitger, are exceedingly rare, our knowledge of Gottfried Silbermann is made possible by the work of Frank-Harald Greß and his documentation of voicing for several of Silbermann’s organs.^{6, 7, 8} To make matters far worse in our quest to understand historic voicing, many organs have been revoiced, repitched, retuned in new temperaments, and their wind pressures raised or lowered during their restorations, often on multiple occasions. We will have great difficulty discovering the original sound of most older organs. We owe a great debt to F.-H. Greß, who has documented the changes made to each of Silbermann’s surviving organs.

Early influences

Gottfried Silbermann was born in 1683 in Kleinbobritzsch, Saxony, the son of a carpenter. His older brother, Andreas, “left home in great haste to avoid military conscription” and worked for Eugenio Casparini on the Görlitz organ before settling in Strasbourg, Alsace, as an independent organbuilder.⁹ Andreas spent the years 1704–1706 learning French organbuilding from François Thierry in Paris. Andreas was at first rebuffed in Paris, but found a willing mentor in Thierry, who would later build the organ we now see in Notre Dame de Paris. Little is known of Gottfried’s youth, but we know that he joined Andreas in Strasbourg in 1702, earned his title as a master organbuilder, and returned to Saxony with two journeymen and an apprentice. He built his first organ in Frauenstein in 1709 and 1710 and spent the rest of his life building nearly all of his organs in Saxony. Gottfried died late one night in August of 1753 while voicing the organ in the Dresden Hofkirche.¹⁰

Gottfried “was accustomed to throw his cane on the floor when he wanted to judge the acoustics in a church.”¹¹ This shrewd test creates a broad range of frequencies which will decay at different rates, informing Silbermann of the room’s different absorption of sound from bass to treble. This is very similar to what acousticians do today with a blank gunshot. He notoriously refused to build organs in churches whose acoustics were poor, and he would likely be appalled at the acoustics of most American churches.¹²

Scaling

Gottfried Silbermann’s scaling, voicing, and stoplists were extremely consistent. He had three sets of principal chorus scales, wider to narrower, which he used to differentiate the timbre of his different divisions. He also used one of the narrower scales for his mixtures.¹³ More wind pressure was employed to fill larger or less efficient acoustics. Unlike most other organbuilders, he never found the need to experiment with different sounds.

Silbermann’s layouts were well engineered and featured easy access, which probably has much to do with the longevity of his organs. He has been criticized for the regularity of his tonal schemes, but this regularity helps us understand how he achieved that sound by comparing his least modified surviving organs. Silbermann became relatively wealthy as an organbuilder, an impossible achievement for modern organbuilders who design their classically inspired organs as completely unique creations.

We will use graphs presented in Normal Scales to understand Silbermann’s sound. Tables of raw numbers do not convey the underlying intent of the organbuilder, and Normal Scales allow us to make easy visual comparisons. These Normal Scales were published in the author’s article, “1863 E. & G. G. Hook Opus 322: Church of the Immaculate Conception, Boston, Massachusetts, Part 1,” The Diapason, July 2017, page 18. Those who want actual measurements can use those tables to convert the Normal Scale data in this article into raw data.¹⁴

Diameter scales of the 1714 Freiberg Dom Hauptwerk principal chorus are shown in Figure 4. The mid-range scales are narrower, emphasizing less power and more harmonic brightness. In Figure 5 we see the mouth widths. Normal Scale mouth widths are based on mouths which are ¼ of the pipe circumference. Silbermann’s mouths are wider, a very unusual practice. The figure captions describe Silbermann’s scaling in more detail.

Influence of French voicing

The roots of Gottfried Silbermann’s sound lie in French voicing, and an essential feature of classical French voicing is a deeply open flueway. Figure 2 shows an image taken by Reiner Janke of Andreas Silbermann’s voicing. We are looking down into the mouth of a tenor G pipe from the Hauptwerk 4′ Prestant in the 1709 organ at Marmoutier. Note the deep 0.7 mm flueway, the absence of ears, and the alternating deeper and shallower nicks on the languid edge. To put this flueway into perspective, Figure 3 shows an image of a modern, “neo-Baroque” pipe of a similar pitch with a low cutup, a flueway of 0.27 mm depth, and ears. The flueway in Figure 3 is the thin black line.

Divergence from French influence

Gottfried Silbermann designed his organs for exceptional power, even by modern standards. While the sound of Gottfried Silbermann is based on the deep flueways of French voicing, it differs from French voicing in specific ways to get that power.

French flueways tend to be very deep, pushing the maximum limits of musicality, and this might lead us to think that these pipes are very powerful. But classical French voicing uses more closed pipe toes to limit the wind for a more restrained power. We will see in Part 2 that Gottfried’s toes are more open than typical French voicing, and they feed wider mouths.

Mouth widths range from about 2⁄7 to 1⁄7 of the circumference of a pipe. Wider mouths on the same resonator will have more wind flow and proportionally more power. Very small mouths will have a delicate effect. Classical French scaling does not trend toward the maximum limits in mouth widths, but the scaling of Gottfried Silbermann’s principal chorus does exactly that. The combination of very wide mouths, deep flueways, and more open toes is the source of Silbermann’s power. To get a sense of his wind pressures, Andreas Silbermann’s 1709 organ at Marmoutier is voiced on 69 mm, Gottfried’s organ at the Rötha Georgenkirche is voiced on 76 mm, and Gottfried’s Freiberg Dom organ originally had pressures of 97 mm in the manuals and 109 mm in the pedal.¹⁵

Unusual pipe construction

Figure 6 shows the basic features of Gottfried Silbermann’s pipework as recreated by C. B. Fisk, Inc. The bottom image in Figure 6 shows a generous flueway and very fine nicking. The 2⁄7 mouth width is evident here, the maximum practical width. The image at top shows a vertical counterbevel (also called a “counterface”) on the languid and a very high position of the languid; you can see the bottom edge of the languid rising just above the top edge of the lower lip. Such a languid position will move the windsheet outwards, and to compensate for this, Fisk has moved the upper lip outwards by extending the side walls of the pipe. There are no added ears. These are the hallmarks of Gottfried Silbermann’s pipes. The pipe in Figure 2 by Andreas Silbermann shares the deep flueway, counterbevel, and nicking, but it does not have the extended upper lip, high languid, and wider mouth.

The sound

At the 1980 American Institute of Organbuilders convention Charles Fisk demonstrated the voicing of a pipe constructed in the style of Gottfried Silbermann. This pipe produced a sound with very prompt and articulate speech of great power and intensity, which I measured at 90 dB at a distance of one meter.¹⁶ The mouth of this pipe is shown in Figure 7.

In voicing this pipe Fisk first set the toe diameter and the flueway depth. He then raised the cutup by degrees and added nicks by degrees to reduce harmonic brightness, while adjusting the languid height for prompt speech. He set the languid high as a consequence of the outward extension of the side walls and upper lip.¹⁷ To hear the sound of this pipe, listen to a soundclip of Bach’s Duetto I in E Minor, BWV 802, on Silbermann’s nearly original Principal at the Rötha Georgenkirche. <soundclip 1>

Zacharias Hildebrandt apprenticed to Gottfried Silbermann in 1714. He and Silbermann soon became bitter rivals, but upon Silbermann’s death in 1753, Hildebrandt was given the task of finishing Silbermann’s last organ in the Dresden Hofkirche. The sound of Hildebrandt’s 1746 organ at Naumburg is reminiscent of Silbermann’s deep flueways, but I do not have data to confirm this. Like Silbermann, Hildebrandt used different scales of principals to give his divisions a different character. Here is a soundclip of the Naumburg principals, played in contrast to each other in Bach’s Concerto in D Minor after Vivaldi, BWV 596. <soundclip 2>

The voicing

Voicing data for the Freiberg Dom Hauptwerk are shown in Figure 8, Toe Constants, Figure 9, Flueway Depths, Figure 10, Mouth Heights (cutups), and Figure 11, Ratios of Toe Areas to Flueway Areas. See the figure captions for descriptions of these voicing parameters; their derivations can be found in the author’s book.¹⁸ In the simplest terms, toe and flueway areas control power, cutups control timbre, and the ratio of the toe area and flueway area affects speech articulation (also known as “chiff”). The crucial takeaway is that Silbermann’s toes and flueways were extremely regular and not treated as free variables. The free variable for Silbermann was cutup.

The regularity of Silbermann’s voicing is remarkable, and it suggests that he calculated his flueway depths and toe diameters prior to voicing. In Part 2 we will see that this regularity is consistent with other organs voiced on similar wind pressures and built at very different times. The regularity of his tonal designs, scaling, and voicing is evidence that he approached organ design from a set of inductively-derived design rules based on very early experimentation. As we will see in Part 2, the design rules for Silbermann’s toes and flueways were different for lower wind pressures.

Greß’s voicing data encompass several of Silbermann organs in acoustics ranging from smaller and more intimate to spacious and grand.¹⁹ Silbermann used higher wind pressure for more power, and at higher pressure a pipe is also brighter. Higher cutups will restore a pipe’s timbre at a higher power.²⁰ In Figure 12 we see mouth heights (cutups) plotted in Normal Scale halftones against pitch. The data in the orange line show the higher cutups of powerful principal pipes voiced on 90 mm pressure at Großhartmannsdorf; the data in the light blue line show the lower cutups of less powerful principal pipes voiced on 70 mm pressure at Reinhardtsgrimma; the timbres are similar.

Gottfried Silbermann used cutups to differentiate the timbre of his flutes and principals at the same pressure. In Figure 13 we see that Silbermann cut his 8′ Bordon pipes at the Freiberg Dom (data in the blue line) far higher than his principals (Figure 12 data in the orange line). This is why a Silbermann Bordon is extremely smooth and his principal has harmonic bite. It is also why they have similar power and can be played against each other. If the flueways had been closed to make the Bordon less bright, it would have had far less power than the principal. Listen to a soundclip at the Rötha Georgenkirche of Bach’s O Mensch, bewein’ dein Sünde Groß, BWV 622, where the Bordon holds its own against the powerful principal. <soundclip 3>

The striking feature of Silbermann’s voicing is that he used only cutup as a free variable during voicing to achieve his sound. The regularity of his toe diameters and flueway depths is virtually unique, and that regularity strongly implies that they were calculated.

In Part 2 we will take a much deeper dive into these voicing parameters and compare Silbermann’s voicing to the work of other organbuilders. Some of the data may challenge conventional assumptions and yield surprising and very useful insights.

To be continued.

Uncredited images reside in the collection of the author. Fr. Thomas Carroll, S.J., graciously suggested clarifications in the prose of this article.

Notes

1. Robert A. Heinlein, The Notebooks of Lazarus Long (New York: G. P. Putnam’s Sons, 1973).

2. John Brombaugh. Personal communication, used by permission via telecommunication of June 2, 2021.

3. Reiner Janke, Copy and Intonation: The tacit knowledge of Reiner Janke, Universität Göttingen, 2018, Youtube video: youtube.com/watch?v=isEWba9rLRY&feature=youtu.be. Figure 2 image is at 9:47. In this video Janke skillfully demonstrates a recreation of the Andreas Silbermann pipe in Figure 2 and its exact voicing. You will not find a better tutorial on voicing. Here are Janke’s instructions to the pipemaker (translated from German), with my notes in brackets [ ]. Pitch: g° Prestant 4′. Wind pressure: 69 mm. Alloy of resonator: 85% tin. Alloy of foot and languid: 10% tin. Inside diameter: 36.5 mm [-2.5 HT]. Mouth width: 29 mm (¼ of circumference) inscribed straight and only lightly pressed [-2.5 HT]. Mouth height (cutup): 8–8.5 mm, upper lip not beveled [arched 0 to +1.5 HT]. Resonator wall thickness: 0.8 mm. Foot wall thickness: 0.9 mm. Foot length: 200 mm. Resonator length: 426 mm. Languid face: 50° with a small counter bevel, 90° to the languid underside. Toe hole: 6 mm [0.97 toe constant and 1.4 toe/flueway ratio]. Flueway depth: 3⁄4 metal thickness [0.68 mm]. Soft, intense, warm onset. Soft attack without harshness, set slightly fast. (“Weich, intensiv, warmer Strich. Weiche Ansprache ohne Härten, etwas zu schnell eingestellt.”)

4. Michael McNeil, The Sound of Pipe Organs (CC&A, amazon.com, 2014). When the pipe speaks most quickly, John Coltman would say that the impedances match and Hartmut Ising would say that I = 2; for more detailed descriptions see pages 64–67 and 77–80. Coltman dealt only with the fundamental harmonic, but Ising’s equation shows the crucial relationships between pressure, flueway depth, and cutup on timbre. For descriptions of toe diameters see pages 43–47. The toe constant equation: diameter of the toe = √(toe constant * 4 * mouth width fraction * pipe diameter). A full graphical analysis of the Isnard organ at Saint Maximin on pages 159–190 can be compared to the Silbermann data at Freiberg.

5. Charles B. Fisk, “Pipe Flueways,” Music: The AGO and RCCCO Magazine, December 1975, page 45. A reprint of the article can be found on the website of C. B. Fisk, Inc., www.cbfisk.com/writing/pipe-flueways/.

6. Heimo Reinitzer, Die Arp Schnitger-Orgel der Hauptkirche St. Jacobi in Hamburg (1995). This is one of only three publications known to the author to include complete data for understanding the sound of an organ, i.e., its pipework, windchests, wind system, temperament, action, and layout. The other examples can be found in the author’s “The 1755 John Snetzler Organ, Clare College, Cambridge, restored by William Drake, Ltd., Joost de Boer, Director,” The Diapason, September 2019, pages 17–21, and “The 1864 William A. Johnson Opus 161, Piru Community United Methodist Church, Piru, California,” The Diapason, August 2018, pages 16–20, September 2018, pages 20–25, October 2018, pages 26–28, and November 2018, pages 20–24.

7. Frank-Harald Greß, Die Klanggestalt der Orgeln Gottfried Silbermanns (Wiesbaden: Breitkopf & Härtel, 1989). Regrettably, this crucially important book is not easy to find.

8. Frank-Harald Greß, Die Orgeln Gottfried Silbermanns (Dresden: Sandstein Verlag, 2007), pages 36, 52. Greß carefully documents the modern changes to Silbermann’s organs, e.g., wind pressures, temperament, voicing, pitch, etc.

9. Poul-Gerhard Andersen, Organ Building and Design (London: George Allen and Unwin, 1969), page 192.

10. Ibid, pages 193, 200.

11. Ibid, page 26.

12. The architectural standard of -60dB for the measurement of reverberation length has a solid basis in physics, but it creates vast confusion and disappointment. At -60dB reverberation is 1/1000 or 0.1% of its original power, the lowest level of sound perceptible to (young) human ears. We do not even remotely hear such sounds in the context of music and singing. Reverberation that is audible during singing and organ performance will be louder than about -26dB, or 5% of its original level. The -60dB standard is not relevant to human perception in the context of music. Now you know why your architect will guarantee you three seconds of reverberation in your new church, but you are aghast when you first walk into the new room and find the reverberation barely audible. The residual of sound for reverberation length should be specified at no less than -26dB to architects and acousticians, a request that will make them quite aghast, too, but your music will come alive.

13. Greß, Die Klanggestalt der Orgeln Gottfried Silbermanns.

14. An Excel analysis of diameters, mouth widths, mouth heights, toe diameters, and flueway depths of the Freiberg Dom Hauptwerk, Oberwerk, and Pedal can be obtained from the author by emailing [email protected]. Wind pressures on the Freiberg Dom organ have been lowered. The 85 mm pressure noted in Figures 4 and 5 is the current pressure; the original pressure according to Greß was 97 mm.

15. Greß, Die Orgeln Gottfried Silbermanns, page 36.

16. Specifications of Fisk’s pipe: Inside diameter 24.5 mm [-2.5 HT]. Pitch 4′ middle e, about 659 Hz. Very thin and stiff 0.36 mm wall of 90% hammered tin. Mouth width 19.6 mm [-2 HT]. Toe 7.7 mm [2.35 toe constant] with 65 mm pressure. An upper lip extension approximately equal to the wall thickness. Cutup 6.6 mm [+5 HT]. Languid counterbevel 90 degrees with five fine nicks alternating with four extremely fine nicks. Flueway depth 0.8 mm [2.9 toe/flueway area ratio].

17. I attended the featured voicing demonstration by Charles Fisk. Our conversation afterward turned to the dynamics of the wind system, and with a common analytical approach to such problems, we became deeply engaged in this subject. Fisk started looking for a place where we could have a conversation without interruption. He found a janitor’s closet with folding metal chairs and shut the door. He gave me the pipe in Figure 7 and offered me the chance to work for a few months in his shop, and to this day I regret not taking him up on that offer; he died three years later.

18. McNeil, The Sound of Pipe Organs.

19. Greß, Die Klanggestalt der Orgeln Gottfried Silbermanns.

20. McNeil, The Sound of Pipe Organs, pages 64–80.

 

Soundclips

1. [00:18] Johann Sebastian Bach, Duetto I in E Minor, BWV 802 (Clavierübung III), Gottfried Silbermann, St. Georgenkirche 1718, Rötha, Johannes Unger, GEMA VKJK 0111 (2001), © Verlag Klaus-Jürgen Kamprad 2001.

2. [00:27] Johann Sebastian Bach, “Grave,” Concerto in D Minor after Vivaldi, BWV 596, Zacharias Hildebrandt, Wenzelskirche, 1746, Naumburg, Robert Clark, Calcante CAL CD041, © Calcante Recordings, Ltd. 2001.

3. [00:35] Johann Sebastian Bach, O Mensch, bewein’ dein Sünde Groß, BWV 622, Gottfried Silbermann, St. Georgenkirche 1718, Rötha, Johannes Unger, GEMA VKJK 0111 (2001), © Verlag Klaus-Jürgen Kamprad 2001.

Michael McNeil

Michael McNeil has designed, constructed, voiced, and researched pipe organs since 1973. Stimulating work as a research engineer in magnetic recording paid the bills. He is working on his Opus 5, which explores how an understanding of the human sensitivity to the changes in sound can be used to increase emotional impact. Opus 5 includes double expression, a controllable wind dynamic, chorus phase shifting, and meantone. Stay tuned.

Editor’s note: The Diapason offers here a feature at our digital edition—four sound clips. Any subscriber can access this by logging into our website (thediapason.com), click on Magazine, then this issue, View Digital Edition, scroll to this page, and click on each <soundclip> in the text.

Many American organists have traveled to Europe and heard the sounds of older organs that make Bach a revelation. American organ building was for much of its history rooted in the Anglican tradition and the Romantic sounds of organbuilders like Ernest M. Skinner, and neither of those great art forms are an ideal medium for Bach. Tentative steps in the Anglican tradition were made as early as the 1930s to recreate this European sound, but they did not amount to a revelation. The revelation occurred with a British-born virtuoso, E. Power Biggs, who brought a sound to America that would convincingly play Bach in the form of an organ built by D. A. Flentrop. Biggs paid for this organ out of his own pocket and in 1958 found a home for it in the very reverberant acoustics of what was known at the time as the Busch Reisinger Museum.¹ His recordings of this Flentrop energized the budding Organ Reform Movement in the United States and inspired many American organbuilders. Listen to the end of the Fugue in A Minor, BWV 543ii <Soundclip 1>.

Dirk Andries Flentrop (1910–2003) worked in his father’s organbuilding shop and with Theodor Frobenius in Denmark, eventually taking over his father’s business. He was intensely interested in classical organ design, and he gave a lecture at a very young age in 1927 in which he promoted the use of mechanical action and slider windchests.² A conversation with Flentrop in the 1970s turned to his earlier career, and he recalled that he was traveling on a streetcar in Rotterdam when bombs started falling on that city in World War II. Everyone on the streetcar agreed there was no point in getting off, and they continued traveling to their destinations as bombs fell. The date was May 10, 1940, the year he took over his father’s business. I sailed with my parents on the SS Rotterdam in 1964 and still remember the shock of seeing upturned docks as we approached the harbor at Rotterdam and whole city blocks of uncleared rubble decades after the bombing.

Flentrop’s sound

The sound of pipe organs can be described subjectively and objectively. Subjectively, the sound of D. A. Flentrop is bright and “instrumental,” where individual pipes in the principal chorus have rich harmonic content. This is very different from what is today called vocale voicing, which emphasizes less harmonic power. Flentrop’s richly harmonic sound creates a scintillating principal chorus with clarity of pitch.

A key component of this sound, and a strong departure from the Romantic and Anglican traditions, is the expression of “chiff.” E. Power Biggs described chiff as the articulate “ictus” of a sound, adding clarity to rhythm and contrapuntal harmony. Chiff is not just percussive noise. It consists of higher natural harmonics to which the human ear is very sensitive, quickly defining the pitch. Flentrop was a master of this percussive speech, and it was always musical and fast. Chiff can be modulated with a sensitive mechanical action and low wind pressures (i.e., with little or no key pluck). Biggs was adept at this on his Flentrop, easing the pallets open for a smooth treble line while crisply opening the pallets to delineate inner voices with more chiff.

Later expressions of this articulation in what became known as neo-Baroque voicing are often heard as a slow, gulping sound. You never hear slow, gulping speech in a Flentrop organ, and as the data will show, Flentrop’s voicing exhibits no relationship to neo-Baroque voicing recipes.³

There is ample evidence that much of D. A. Flentrop’s sound is based on examination of the work of Arp Schnitger, and Schnitger’s sound is much more instrumental in character than modern vocale voicing. The similarity to Schnitger extends also to the design of the reeds, whose basses are the source of a smooth and powerful fundamental.

Flentrop organs have considerable presence, due in large part to the shallowness of the casework found in all of his organs. Flentrop related that the maximum depth of a case should be no deeper than the reach of an arm from the back doors of the case to its façade pipes. Deep cases and chambers will tend to absorb sound, especially the higher harmonics that create the sense of presence. I find it interesting that unaltered manual divisions of Cavaillé-Coll organs, while using higher pressures with Romantic scaling and voicing, almost never exceeded twelve stops and always used slider chests with mechanical action, reflecting some of the important design features of Flentrop organs.

The generosity of D. A. Flentrop

D. A. Flentrop was secure in his knowledge and very willing to share it. I was the recipient of his generosity on several occasions when he toured the United States with his senior voicer, Sijmen “Siem” Doot, to maintain and tune his organs. Doot, born in 1924, entered Flentrop’s service in 1939 and retired in 1988. Ed Lustig at Flentrop Orgelbouw confirmed that Franz Rietsch, Rob Oudejans, Johannes Steketee, and Doot assembled the Flentrop organ in Saint Mark’s Episcopal Cathedral, Seattle, Washington, in 1965, while Steketee and Doot remained to voice the organ. The voicing data in this article is a testament to their skill. I was introduced to Flentrop by Albert Campbell in 1971. After scouring the literature and finding mostly subjective opinions with very little data, I quickly discovered that Flentrop was genuinely interested in answering the detailed questions of a budding organbuilder. When I asked him if he would grant me permission to take measurements of his organs, he replied, “imitation is the finest form of flattery. Your ears will be different than mine, and you will use your observations to find your own sound.” He was right, but it took quite some time before I began to understand some of those observations, and the data continues to generate insights.

I again met Flentrop in the Campbell home after completion of my Opus 1, and by that time I had learned enough to ask deeper questions. Flentrop had nearly completed the tuning of his organ at the University of California, Santa Barbara, and in a further gesture of generosity, Flentrop said, “If you finish the cone tuning of the Hoofdwerk Mixtuur, we can answer your questions.” I agreed to finish the tuning work on the Flentrop organ, and both he and Mr. Doot spent the whole day answering my questions.

Flentrop slider windchests

D. A. Flentrop organs have exclusively featured mechanical key action and slider windchests since 1949. Stop actions were mechanical, as well, and only in his larger organs do we find electric slider motors and combination actions. Organbuilders who looked to the literature for the design principles of slider chests in the 1970s often found the effort frustrating. Flentrop willingly shared a great deal of his design practice. In Figure 1 we see a drawing made by the author from notes of a conversation with Flentrop regarding channel design. Flentrop recommended that the cross-sectional area of the key channel should have about 20–30% more area than the combined areas of all of the pipe toes it would need to wind. A small vent hole at the end of the channel served two functions—to prevent ciphering and to dampen resonances in the channel that would interfere with reeds. Reeds that are equal in length to the channel that feeds wind to them may get much louder, and those not quite equal to that length may get much weaker and more dull in timbre from channel resonance. I noted that the bottom of the key channels in the Flentrop organ at the University of California, Santa Barbara, were covered in a thick paper that had pin pricks in a few channels in various positions, likely done to reduce channel resonance.

Flentrop stated that pallets did not need to exceed 200 millimeters (about eight inches) in length, but I have found much longer pallets in Hook organs. I did not ask how to trade off key channel widths and heights for a given area, nor the flow areas of the pallets, and these tradeoffs can be complex. Suffice it to say that the flow area of a pallet is the length of its opening times the distance the pallet is pulled open by the key (an open pallet has a triangle of flow at each side, and when combined, these triangles make a rectangle). It is also interesting to note that a pallet will not flow significantly more wind to a channel when its pull is more than half of the channel width (think about the height of those triangles that flow wind relative to the width of the channel). For a given pallet pull and a key channel width that is twice the pull, only a longer pallet will flow more wind to the channel.

The 1863 Hook organ at the former Church of the Immaculate Conception in Boston, Massachusetts, has roughly 460-millimeters-long pallets feeding 406-millimeters-long flue and reed channel openings in the Great bass octave (there are two pallets per note). The Romantic voicing of the Hook organ requires a very large volume of wind to feed its very deep flueways and very widely opened toes, which are much larger than Flentrop’s. At Saint Mark’s, Flentrop likewise used two pallets for the six bass notes of the Hoofdwerk, with pallet opening lengths of 155 millimeters, flue and reed channel widths of 21 millimeters and 17 millimeters, respectively, and a channel height of 79 millimeters. Readers who are interested in comparing the differences in the voicing of Flentrop and Hook organs can find the Hook data in The Diapason.⁴

Flentrop’s patented slider

Slider windchests in ancient organs often suffered from the advent of central heating. Topboard bearers are shimmed with layers of paper for a close fit between the slider, the windchest table on which it rests, and the topboard above it. With central heating and the resulting low humidity, shrinking wood caused these sliders to leak wind and impair the tuning. Many different forms of slider seals were invented in the twentieth century, most of which worked quite well. Flentrop’s system is patented and rather complex, but it is extremely reliable. Flentrop used two sliders, separated by springs with a leather-faced conduit for the wind between the two sliders. Figure 2 (see page 15) shows this slider seal mechanism in relation to the pallets, key channels, and topboards.

An objective approach to Flentrop’s sound

If you want to discover how to achieve a certain sound, it is often educational to closely observe the organs you like and those you do not. The objective differences will teach you what matters. Readers who want some perspective on the following Flentrop data will find a description of the voicing of several historic organs in The Diapason.⁵

The absolute minimum data needed to understand the sound of an organ is:

• pipe diameters (inside);

• mouth widths;

• toe diameters;

• mouth heights (also known as “cutups”)

• flueway depths.

Complete descriptions of these parameters can be found in the article mentioned above.⁶ In a nutshell, larger pipe diameters, wider mouth widths, larger toe diameters, and deeper flueways yield more power. Mouth heights control timbre, and higher mouths reduce harmonic power and brightness. Flutes typically have much higher mouths than more harmonically rich principals.

Wider scales produce an “ah” timbre, and narrower scales will progress towards an “ee” timbre, emphasizing higher harmonics. Flentrop stated that he used a constant scale of pipe diameters and mouth widths for the principal chorus in most environments and acoustics, which meant that he wanted a specific vowel timbre for all of the pipes at the same pitch and a specific power balance across the range of frequencies from bass to treble.

For different acoustics Flentrop used different pressures and voicing, adjusting the toe diameters and cutups. Ascending trebles were achieved in the toe diameters. Figure 3 shows Flentrop’s chorus scaling written in his own hand in 1971 with numerical values he had memorized.

Flentrop reeds were often made by the firm of Giesecke to Flentrop’s specifications. A description of the data needed to understand the sound of a reed can be found in an article in The Diapason.⁷ The author’s measurements of the Saint Mark’s reeds were not taken in sufficient detail to merit showing them. Flentrop reed designs are very similar to Schnitger’s and use tin-lead plates with restricted openings soldered to wide, lightly tapered, and deeply cut shallots for powerful, smooth basses. These typically transition to open, parallel shallots without plates in the tenor.

Taking the data at Saint Mark’s

I have been fortunate that many of those who are a gate to the access to some important organs have granted me permission to measure them. In 1972 that good fortune allowed me to take measurements of Flentrop’s organ at Saint Mark’s Episcopal Cathedral, Seattle, Washington, the organ Flentrop considered his largest by virtue of its 32′ façade pipes. The stoplist of the Saint Mark’s organ is easily found on the internet.⁸

The cathedral measures an estimated 150 feet in length and width, with a flat, wooden ceiling about 90 feet high. The walls are very thick concrete, yielding an acoustical reverberation of about five plainly audible seconds in the soprano range.⁹ The reverberation drops dramatically in the tenor and bass as a consequence of the very large windows, through which the lower frequencies easily pass.

Richard Frickmann, a life-long friend, and I drove over a thousand miles to visit this organ, and upon arrival in the early morning we sat in the pews in the empty cathedral, looking back at the organ. Glenn White, who maintained the organ, noticed our interest in this magnificent Flentrop and struck up a conversation. Learning that we were eager to find scaling data of the pipes, he questioned us for about five minutes and admitted that no one had taken the time to measure the pipework. He took us to the office and gave us the keys to the Flentrop casework, the organ loft, and the cathedral, asking that we return them when we were done. This was a stunning opportunity and one rarely offered. Mr. Frickmann and I took over fifty pages of data, interspersed with trips to the local twenty-four-hour pancake house to refuel with food and coffee. I had brought with me copies of scaling sheets and measuring tools, and Mr. Frickmann wrote down the numbers as I called them out from the walkways behind the windchests. After about twenty-four continuous hours of work, we handed in the keys to the office.

A word of caution on the data is in order. I took this data in 1972, very early in my career. I had experience with Flentrop’s organ at the University of California at Santa Barbara, and I understood basic scaling and data collection. But what I did not yet appreciate at the time was the importance of measuring the depth of the flueway. My general observations of the flueways of the Saint Mark’s organ were that “they tend to be consistent throughout the organ relative to pitch, much wider than current neo-Baroque work, but narrower than the voicing of the early American builders like Johnson and the Hooks.” Later measurements of Flentrop flueways provided a generalized model of the flueways for the Saint Mark’s organ. Please be aware that these are probably in the ballpark, but they are assumptions.

I was very careful in the handling of the pipes and making sure that their mouths faced in their original directions (this affects tuning on larger pipes whose mouths can be close to other pipes and shaded by them, lowering their pitch). The measurements of these pipes will have some inaccuracy from the time constraints. For larger pipes the measurements are likely better than +/- 1 millimeter, and for the very smallest pipes, about +/- 0.2 millimeter. The data is presented in halftone deviations from Normal Scale to make the relationships clear, as tables of numbers do not easily convey their meaning. These Normal Scales were published in the author’s article, “1863 E. & G. G. Hook Opus 322: Church of the Immaculate Conception, Boston, Massachusetts,” Part 1.¹⁰ Those who want actual measurements can use those tables to convert the Normal Scale data into dimensions, or they can email the author for a copy of the Excel spreadsheet with the more accurate raw dimensional data.¹¹

The Hoofdwerk

Larger pipe diameters generate more power, and smaller diameters generate a brighter timbre. Flentrop’s principal chorus scales combine these factors into the sound he wanted. His scaling model in Figure 3 is seen as a dashed blue line in Figure 4. The model generally follows the Saint Mark’s data. As Flentrop noted, the mixtures are narrower. Flutes trend much wider as the pitch ascends.

Sound clips of the Saint Mark’s Flentrop in the digital edition of this article allow one to hear these power and timbre balances. They were derived from 1981 recordings of James Welch, organist, another life-long friend. The recording engineer, Dave Wilson, was known as one of the world’s best, and he recorded Welch on Flentrop organs. I was present in 1981 for the Saint Mark’s recordings, mostly to help with touching up the tuning of the reeds. I also made suggestions for stop registrations that ran counter to the prevailing wisdom of the time, dictating a minimal use of foundations to aid in clarity of pitch. This was not necessary on a Flentrop, whose foundations can be combined to any degree and still maintain clarity of pitch. Amassing foundations, as any Romantic organist knows well, is a source of rich chorus depth, and it is heard to great effect in Charles-Marie Widor’s “Andante cantabile” from Symphonie IV in <Soundclip 2>.

We made many experiments with microphone placement. The proper power balances of the different Flentrop divisions were finally achieved by placing microphones on very tall stands about twenty to thirty feet in front of the Rugwerk, the division that has the most presence for the congregation. Having been accustomed to the practice of using fast tempos in dry acoustics, Welch and I discussed appropriate tempos for the reverberant acoustic of Saint Mark’s. Borrowing headphones from the recording engineer to hear what the sound was like in the room at the microphones, he arrived at the tempo we hear in C. P. E. Bach’s Toccata and Fugue in D Minor, which takes full advantage of Saint Mark’s long reverberation <Soundclip 3>.

Late in the all-night recording session a note went dead in the Rugwerk. The organ had been in service for only sixteen years at this time, and a failure was unexpected. I pulled up the floor panels in the choir loft, which gave access to the Rugwerk trackers, and the culprit was a torn piece of weak leather that connected a long horizontal tracker at a suspension point. None of the other connectors showed the slightest sign of wear. I made a temporary fix, adjusted the action, and we continued recording well into the next morning.

Figure 5 shows the scales of the mouth widths, and these generally imitate the diameter scales. Normal Scale mouth widths are based on 1⁄4 of the circumferences of Normal Scale diameters, and as Flentrop almost exclusively used 1⁄4 mouths, we would expect a similarity to the diameter scales. Some of these mouth widths appear to be a bit wider than 1⁄4 of the circumference, and this may indicate that the pipes were slightly tapered, something I did not measure, and which is not uncommon. Inside diameters were measured at the top of the pipes. If the pipes have a slight taper, the true diameter scales at the bottom will be larger and will more closely match the Flentrop model in Figure 4, as well as the mouth scales in Figure 5.

Figure 6 shows mouth heights, or what is more commonly known as “cutups.” The cutup controls timbre. A higher mouth will reduce the harmonic content, and smooth flutes have higher cutups. These can be clearly seen in the lofty cutups of the 8′ Roerfluit. Normal Scale mouth heights are calculated as 1⁄4 of the Normal Scale Mouth Width, a common recipe in neo-Baroque voicing. In Figure 6 we see that Flentrop did not use this recipe. The Saint Mark’s cutups are much higher, and they have no relationship to the mouth width scales. They are also highly variable as a free voicing parameter. Flentrop raised the cutup until the desired timbre was achieved and the speech was fast. This is why you do not hear slow, gulping speech in a Flentrop organ.

The soaring cutups of the Roerfluit

The soaring cutups of the 8′ Roerfluit illustrate how Flentrop achieved a rich harmonic timbre in his principal chorus and a smoother, warmer timbre in the flutes. While Flentrop is noted for a brighter, “instrumental” timbre, which strongly implies lower cutups, Figure 6 clearly shows that his cutups were much higher than the neo-Baroque recipe. As an example, the cutup of the 8′ Roerfluit tenor C pipe in Figure 6 is +5 halftones, while its mouth width in Figure 5 is -5 halftones, revealing a cutup that is a stunning 10 halftones higher than the neo-Baroque recipe.

Figure 7 (see page 18) shows the relative flow of wind in the pipe toes. Larger pipe toes will flow more wind and yield more power. Received wisdom relates that Flentrop used “open toe” voicing, but Flentrop toes are in most cases quite restricted. Much more open toes can be found in Hook organs. Hook toe diameters also have high variability at a specific pitch, very unlike the more regular wind flow patterns we see with D. A. Flentrop and Gottfried Silbermann.¹³

The values in Figure 7 are toe constants, a number that represents relative flow. Flentrop suggested to me that a reasonable starting point for a toe diameter is the square root of its resonator diameter. The area of that closed toe represents a constant of “1,” and as you can see in Figure 7, Flentrop converged on that number at about 1′ pitch and increased the flow in both deeper and higher pitches. The area of the toe is proportional to the toe constant, i.e., a toe constant of “2” has twice the area of a toe with a constant of “1.” One added feature is that the toe constant compensates for mouths that are wider or narrower than the Normal Scale mouth of 1⁄4 of the circumference. For Flentrop this does not matter, because he used 1⁄4 mouths, but for a builder like Gottfried Silbermann who used 2⁄7 mouths, or Ernest M. Skinner who used 1⁄5 mouths, this compensation is critical, because wider mouths need more wind and narrower mouths need less. The toe constant allows us to compare the relative flow of wind in pipes with different diameters and different mouth widths. A good example in Figure 7 is the 8′ Roerfluit, which has slightly more wind than the 8′ Octaaf. Although it has a much smoother timbre, the 8′ Roerfluit’s slightly more powerful fundamental adds chorus depth to the much brighter 8′ Octaaf.

Toes control power, and in Flentrop organs designed for smaller acoustics I have found toe constants of 0.6 in the lowest mixture pitches, and this is a very restricted toe. A fully open toe has a toe constant of about 4, which we see in the highest pitches of the 2′ Octaaf and III Scherp in Figure 7.

Note the consistency of wind flow in the Flentrop principal chorus pipes at a given pitch, with a minimum flow of wind at about 1′ in pitch and much more flow in the bass and treble. This represents a voicing model for the Saint Mark’s acoustic. Similar patterns of wind flow exist in the 1692 Schnitger organ in the Hamburg Jacobikirche.¹⁴

The wind flow of the 4′ Speelfluit in Figure 7 is very instructive. Its lower cutups, relative to the 8′ Roerfluit, are explained by its more restricted toes. Closing the toe has the tonal effect of raising the cutup for a much warmer timbre at a lower power. The Speelfluit adds color to the more powerful Roerfluit, while restraining the power of the combined flutes as accompanimental stops.

Figure 8 data are estimated flueway depths based on observation of other work by Flentrop. In 1972 I did not have tapered wedges for measuring flueway depths. Wooden wedges are the safest material for documentation, but for a voicer, brass or steel wedges will last longer.¹⁵ The important feature of Flentrop flueways is that they are not used as a primary means of controlling power. Flentrop flueways do vary, but they vary within a restricted range at a given pitch. Neo-Baroque voicing emphasized a cutup recipe set to 1⁄4 of the mouth width with “open toes.” The result was that a voicer was often forced to use very narrow flueways to regulate both power and timbre, and the resulting sound was typically thin in fundamental warmth with a slow, gulping speech on the verge of overblowing. Flentrop used wind pressures and toes to control power, not the flueways, and he adjusted the cutup to achieve the desired timbres with fast speech.

In both modern and ancient work we will find an enormous variation in flueway depths. Although it is very rarely measured, flueway depth is of critical importance in understanding the different sounds of pipe organs. As the flueway deepens, more breathiness is heard in the sound. This is corrected by an increasing amount and boldness of nicking as the flueway depth increases. This is one of the reasons you will find many bold nicks in deep Romantic flueways. Flentrop’s voicing finds the flueway depth that will yield a tolerable breathiness with a minimum degree of nicking, and this is the optimum point for chiff. This is not a deep flueway, but it is much deeper than the razor-thin neo-Baroque flueways that resulted from arbitrarily low cutups. Both Andreas and Gottfried Silbermann used much deeper flueways than Flentrop, and their milder chiff is the result of their bolder nicking. Readers can find the flueway depths for some important historical styles in The Diapason.¹⁶

Figure 9 shows what happens when we divide the area of the pipe toe (the radius of the toe, squared, times π) by the area of the flueway it feeds (the flueway depth times the mouth width). In Figure 9 we see this data as a ratio of those areas. This tells us a great deal about the speech onset of the pipes. If the pipe toe is closed to the point where its area is less than the flueway area, the pressure will drop in both the foot and the flueway.¹⁷ We often see this in organs with higher wind pressures where the toes are strongly reduced to control power. In this situation, however, not only does the pressure drop at the flueway, the buildup of pressure in the foot is slower, and this can lead to slower speech. This form of slower speech is not immediately obvious, but a chorus with ratios above 1.0 will have a prompt attack, while pipes with ratios of 0.5 will have a noticeably slower attack, as is often heard in the smooth solo voice of the classical French cornet.¹⁸ When we look at theatre organs with extremely high wind pressures and deep Romantic flueways, we also find extremely small toes that produce ratios well below 0.5. This is why the attack of theatre organ flue pipes is much slower than what we hear in a Flentrop.

Ultra-low area ratios also explain in part why theatre organ pipes never have chiff. A fast rise in pressure in the foot and flueway is essential to the production of chiff, and we hear this when Biggs crisply opens the pallets on his 1958 Flentrop. Ratios close to 1 or above will be conducive to a fast pressure rise and the production of chiff, and in Figure 9 we can see that no Flentrop pipes have values below 1, and most pipes have values well above 1. This is a feature of Flentrop voicing in all of his organs for which I have data, and it is a significant factor in Flentrop’s fast, articulate voicing. Flentrop flueways are not deep in the Romantic style, and their areas are relatively small, with the result that even Flentrop’s more restricted toes still supply much more wind than the flueways need, and the fast pressure rise produces chiff.

Chiff can be eliminated in any ratio of toe and flueway areas by simply applying many bold nicks, but Flentrop used nicking sparingly, and when it is used, it is typically very fine in nature. Hook voicing also features relatively high area ratios, but the voicers used many bold nicks on every pipe, and no chiff is audible in their voicing. Theatre organs combine ultra-low area ratios with very bold nicking and unsurprisingly never exhibit chiff.

Figure 10 shows the mouth of a Flentrop pipe from about 1980, which is articulate, even with its two bolder nicks. The finest nicking in the center of the languid is more typical of the Saint Mark’s organ. Note that the flueway, while not deeply open in the Romantic style, is much deeper than typical neo- Baroque voicing.

The Pedaal

Figure 11 shows the diameter scales of the Pedaal. The scales of the larger pipes are consistent with the Flentrop model in Figure 3, and the diameters of the larger pipes were measured at the bottom. The Mixtuur is also consistent with the model notes. Like the Hoofdwerk, the flutes trend much wider as the pitch ascends.

The wind pressure of the Hoofdwerk is 80 millimeters, which is interestingly the same pressure found in the restored 1692 Hamburg Jacobikirche Schnitger. All other divisions at Saint Mark’s are winded on a very modest 68 millimeters of pressure, including the Pedaal. Flentrop once commented that wind pressure in a pipe organ is analogous to the tension of strings on a violin, with similar effects in the sound.

When I visited in 1972, the 32′ Prestant featured large ears at the sides of the mouths, and a few years later I observed that large wooden rollers had been added between the ears. This was perhaps an effort to make the 32′ sound more audible, as human hearing is very poor in the deep bass. At about 20 cycles per second we feel sound as much as we hear it, and a 32′ pipe resonates at 16 cycles per second. The addition of the rollers increases audible harmonic power to the sound, just as they add harmonic power to very narrow string pipes. Joseph Gabler found an elegant solution to this problem in his organ of 1750 at Weingarten: drawing the 32′ stop also draws the 16′ stop at the same time, making the sound both felt and more easily heard.

Tin was very expensive when Saint Mark’s Flentrop was constructed, the result of a powerful tin mining cartel. Many Flentrop organs utilized copper for larger façade pipes during this time as an alternative to zinc. The colorful patina on Flentrop copper pipes exhibits reddish earth tones and subtle greens. I asked Flentrop how he achieved this, and he laughed. The process was the result of long experimentation, and it involved strongly heating the pipes and applying the urine of cows to the heated metal. Flentrop smiled when he said that the smell in the shop was not at all pleasant. The lovely pastel colors of those copper pipes enhance the deep reds of the mahogany used in the casework, which Flentrop carefully selected from his supplier in Africa.

The full principal chorus of Flentrop’s magnum opus in its 1981 configuration is electrifying in the Praeludium in E Major by Vincent Lübeck <Soundclip 4>. The organ today features some wonderful additions by the shop of Paul Fritts.¹⁹

Paul Fritts and Company Organ Builders

Additions and changes to pipe organs can result in irreparable harm to the original sound. The additions and changes by the Fritts shop, however, are sympathetic to Flentrop’s original concept. They are exceedingly well executed, and Flentrop’s original voicing was left unchanged.²⁰

In 1991 the console action was replaced with a suspended action. Germanic reeds were added at 16′ and 8′ to the Hoofdwerk, and the horizontal reeds were replaced at their original pitches with designs based on the 1762 work of the Iberian organbuilder Jordi Bosch. The original Flentrop reeds have been carefully packed and stored. The addition of a 32′ Pedaal Bazuin on the back wall to the rear of the Pedaal casework is a welcome one in a room whose large windows consume a great deal of bass sound. These alterations will hopefully diminish future appetites for changes to Flentrop’s historic magnum opus.

The precarious life of historic sounds

D. A. Flentrop’s organs are probably a very good representation of the sound of Arp Schnitger, which has very rarely if ever survived in its original form. Between 1953 and 1955 Flentrop undertook a major restoration of the 1720 Schnitger organ at Saint Michael’s Kerk in Zwolle to return it to its original condition, and Biggs recorded that magnificent sound in the 1960s.²¹ History teaches us that original sounds only survive in the very rarest of circumstances, and these are often found in depressed economies where there is no funding for restorations. Historically important sounds quickly disappear with the good intentions of restorers who change wind pressures, temperaments, pitch, and voicing to suit their own ears.²² This is why early documentation is so important, and it can expose later changes.

This article features a sample of scaling and voicing data from D. A. Flentrop’s magnum opus taken in its original form in 1972.²³ It has hopefully provided readers with a better appreciation of the sound of D. A. Flentrop. Astute readers will also no doubt notice that fifty-one years elapsed before I carefully analyzed this data. I should have done this long ago. Tempus fugit, carpe diem.

Notes and references

All images are found in the collection of the author unless otherwise noted.

1. Barbara Owen, E. Power Biggs: Concert Organist (Bloomington, Indiana: Indiana University Press, 1987), pages 128–133.

2. wikiwand.com/en/Dirk_Andries_Flentrop, accessed July 6, 2023. From their reference: Kerala J. Snyder (Spring 2005), Symposium in Honor of Dirk A. Flentrop, Resonance.

3. Michael McNeil, “The Sound of Gottfried Silbermann,” Part 2, The Diapason, January 2023, pages 13–19.

4. Michael McNeil, “1863 E. & G. G. Hook, Opus 322, Church of the Immaculate Conception, Boston, Massachusetts,” The Diapason, Part 1, July 2017, pages 17–19, and Part 2, August 2017, pages 18–21.

5. McNeil, “The Sound of Gottfried Silbermann,” Part 2.

6. McNeil, “The Sound of Gottfried Silbermann,” Part 2.

7. Michael McNeil, “Designing an Historic Reed,” The Diapason, June 2023, pages 14–20.

8. saintmarks.org/music-arts/organs/the-flentrop-organ/ accessed July 12, 2023.

9. “Plainly audible” reverberation is measured at about -26 dB. The -60 dB architectural standard does not take into account the audibility of reverberation in the context of music, and it is also a source of grave disappointment for musicians and organbuilders. The standard needs to be revised for music.

10. Michael McNeil, “1863 E. & G. G. Hook Opus 322: Church of the Immaculate Conception, Boston, Massachusetts,” Part 1, The Diapason, July 2017, page 18.

11. Email the author for Excel files with the Saint Mark’s Flentrop data and/or the Jacobikirche Schnitger data at no charge at: [email protected]. The Schnitger data is derived and graphed from: Heimo Reinitzer, Die Arp Schnitger-Orgel der Hauptkirche St. Jacobi in Hamburg (Hamburg: Christians Verlag, 1995), with restoration by Jürgen Ahrend and data measurements by Cor Edskes.

12. Ibid.

13. McNeil, “The Sound of Gottfried Silbermann,” Part 2; McNeil, “1863 E. & G. G. Hook, Opus 322, Church of the Immaculate Conception, Boston, Massachusetts,” Part 1.

14. Email the author for Excel files with the Saint Mark’s Flentrop data and/or the Jakobikirche Schnitger data at no charge at: [email protected]

15. Michael McNeil, “The Sound of Gottfried Silbermann,” Part 2, The Diapason, January 2023, see Figure 15 on page 14 for an illustration of a wedge for measuring flueway depth.

16. McNeil, “The Sound of Gottfried Silbermann,” Part 2.

17. Email the author for Excel files with the Saint Mark’s Flentrop data and/or the Jacobikirche Schnitger data at no charge at: [email protected]. The Schnitger data is derived and graphed from: Heimo Reinitzer, Die Arp Schnitger-Orgel der Hauptkirche St. Jacobi in Hamburg, (Hamburg: Christians Verlag, 1995), with restoration by Jürgen Ahrend and data measurements by Cor Edskes.

18. McNeil, “The Sound of Gottfried Silbermann,” Part 2.

19. saintmarks.org/music-arts/organs/the-flentrop-organ/.

20. saintmarks.org/music-arts/organs/the-flentrop-organ/.

21. E. Power Biggs, The Organ in Sight and Sound, Columbia Masterworks, KS 7263, ca. 1969. Many examples of Schnitger organs are included in this landmark recording. D. A. Flentrop wrote a primer on classical organ design for the twenty-eight-page book included with this vinyl recording.

22. Flentrop was right when he remarked that I would use my observations of his work to find my own sound. The temptation to modify organs to the taste of the restorer is very strong, and I have regrettably succumbed to that temptation, too. I carefully documented a Wm. A. Johnson organ and described the changes I made to it in these articles, “The 1864 William A. Johnson Opus 161: Piru Community United Methodist Church, Piru, California,” The Diapason, Part 1, August 2018, pages 16–20; Part 2, September, 2018, pages 20–25; Part 3, October, 2018, pages 26–28; and Part 4, November 2018, pages 20–24.

23. Email the author for Excel files with the Saint Mark’s Flentrop data and/or the Jakobikirche Schnitger data at no charge at: [email protected].

Sound clips

1. [00:34] Johann Sebastian Bach, Prelude and Fugue in A Minor, BWV 543, E. Power Biggs, Bach, the Great Preludes and Fugues, Volume 2, CBS Records, 42648, recorded in 1964 at the Busch Reisinger Museum, Harvard University, Cambridge, Massachusetts.

2. [00:30] Charles-Marie Widor, “Andante cantabile,” from Symphonie IV, opus 13, number 4 (1872), James Welch, Magnum Opus, Volume 2, Wilson Audiophile, WCD-8314, recorded in 1981 at Saint Mark’s Cathedral, Seattle, Washington.

3. [01:01] Carl Philipp Emanuel Bach (often attributed to Johann Sebastian Bach, BWV 565), Toccata and Fugue in D Minor, James Welch, Magnum Opus, Volume 1, Wilson Audiophile, WCD-8111, recorded in 1981 at Saint Mark’s Cathedral, Seattle, Washington. Exhaustive research by Michael Gailit has convincingly shown C. P. E. Bach as the most likely composer of this work. See “Exploring the unknown of BWV 565,” The Diapason, Part 1, June 2021, pages 18–19; Part 2, July 2021, pages 12–14; Part 3, December 2021, pages 16–18; Part 4, August 2022, pages 15–17; Part 5, September 2022, pages 19–21; and Part 6, October 2022, pages 15–17.

4. [00:40] Vincent Lübeck, Praeludium in E Major, James Welch, Magnum Opus, Volume 2, Wilson Audiophile, WCD-8314, recorded in 1981 at Saint Mark’s Cathedral, Seattle, Washington.

—It is strongly recommended to use Sony MDR 7506 headphones for the sound clips. Earbuds will not generate bass sound.

Saint Mark’s Episcopal Cathedral website: saintmarks.org.

Flentrop Orgelbouw website: flentrop.nl.

Michael McNeil

Michael McNeil has designed, constructed, voiced, and researched pipe organs since 1973. He was also a research engineer in magnetic recording with 27 awarded patents. He has authored four books, among them The Sound of Pipe Organs, which explores the scaling and voicing of organ pipes, the effects of wind system dynamics on musicality, and the relationship of temperaments to tonal design.

Editor’s note: The Diapason offers a feature at our digital edition—two sound clips. Any subscriber can access this by logging into our website (thediapason.com), click on Magazine, then this issue, View Digital Edition, scroll to this page, and click on each <soundclip> in the text.

This article was written after the author received reed pipes built to specifications in this article by Aug. Laukhuff GmbH. A victim of the economic retraction during the pandemic of 2020 and 2021, Aug. Laukhuff GmbH closed its doors in June of 2021. Established in 1823, it served the needs of organbuilders worldwide. Its unimaginable loss is catastrophic to the profession, not only in the unique products it provided, but also in the centuries-old expertise of its managers and employees. Making an historic reed with the necessary detail will be a challenge.

The sound of an historic reed chorus may strike us like an emotional thunderclap and leave us with the wish that we might make such reeds today. I had one such experience with the sound of the reed chorus from the 1754 Joseph Riepp organ at Dole. Those reeds were a later addition in 1787 by the French builder François Callinet. You can get a sense of the drama of these reeds from a performance by the late Michel Chapuis <soundclip1>.¹ The great Romantic organbuilder Cavaillé-Coll often preserved Callinet reeds in the organs he rebuilt.

The sheer complexity of reed construction is daunting, but we might begin to understand reeds by trying to recreate one we like. Although one of my dear colleagues rejoiced that I did not tackle the subject of reeds in my recent book on the sound of pipe organs, this article takes a deep dive into the subject. An exact copy would be prohibitively expensive, but we can capture the sound using the resources available to us from modern suppliers. For this example we used the resources of Aug. Laukhuff GmbH, Weikersheim, Germany, as they described their capabilities in great detail on their website. 

There are hurdles to clear before we can reproduce such a reed, and perhaps the greatest of these is sufficient documentation. The detailed data required to really understand a reed is extremely rare, and the greatest practitioner of data collection was Pierre Chéron. We owe him a great debt for the complete measurements of every pipe in the 1774 Isnard organ at St. Maximin.²

The data

Sufficiently complete measurements of the reeds at Dole are unknown to the author, but a wonderful book gives just enough data to get a feel for the scaling of the entire reed chorus of that organ.^{3, 9}
Although we lack sufficient data for the Dole reeds, it is our great fortune that Chéron’s data for the 1st Trompette from the 1790 Callinet organ at Auxonne has been published in exquisite detail by Laurent Plet.4 The complete data from the Callinet reed at Auxonne and the limited data from Dole correlate very well. Chéron took the Auxonne reed data in 1990 prior to the restoration of the organ by Laurent Plet, and you will find a wealth of data and photos on Plet’s website for this organ.⁵ The complete table may be seen in Figure 25.

Chéron’s table has lettered data columns that are made clear by the drawing of a reed pipe in Figure 1 and the detail of a shallot in Figure 2. Chéron’s dimensions are in millimeters except thicknesses of the tongues, which are in hundredths of a millimeter. Here are descriptions of Chéron’s lettered columns:

Description of the Chéron data

Diameters

A is the name of the note (there is no bass C-sharp)

B is the inside top diameter of the resonator

C is the thickness of the resonator at the top

E is the inside bottom diameter of the resonator

F is the thickness of the resonator at the bottom

Lengths

G is the length of the shallot from the block, or “nut” 

H is the height of the block, or “nut”

K is the length of the resonator from the block to the top 

L is the total tuned length of the reed (there are no tuning slots)

Shallots

M is the outside diameter of the shallot

N is the outside depth of the shallot at the block

O is the outside depth of the shallot at the end

P is the inside diameter of the shallot

Q is the wall thickness of the shallot

R is width of the shallot face (the slot opening width is R-2Q)

S is the total shallot length, including the section inserted into the block

Tongues

T is the width of the tongue

U is the thickness of the tongue under the wedge

V is the thickness of the tongue under the tuning wire

W is the thickness of the tongue at the free end

X is the vibrating length of the tongue

Y is the extension of the tongue beyond the end of the shallot

Boots

AA is the diameter of the toe hole in the boot.

This seems like a lot of detail, but as you will see, Chéron recorded exactly what is needed to understand a reed.

Diameters 

Let’s start with the top diameters in the table in Figure 3, which control power. The amplitude of a standing wave in a resonator gets larger with larger resonator diameters, and Callinet’s diameters are very robust. In Figure 3, column 1 we see the raw values of the Callinet diameters. 

We will use an Excel spreadsheet to analyze the Callinet reed, and we will start by graphing the raw diameters. The beauty of the Excel spreadsheet is that a simple click of the mouse on the graph finds the equation of the line that best fits those diameters. That exponential equation is shown in the graph in Figure 4.
We can use that equation in Excel to calculate the smoothed data we see in Figure 3, column 2, which now fills in all of the missing gaps! Note that there are many missing pipes in the original data. The diameters in Figure 3, column 2 are placed into an Excel table, Figure 5, which will be the basis for the new design.

The diameter of the bottom tip of the resonator is usually not less than the inside diameter of the shallot, and it is often larger. Reiner Janke relates that Cavaillé-Coll used a ratio of approximately 8 for top to bottom diameters.⁶ The Callinet data shows ratios changing from 10.9 in the bass to 9.3 in the treble. These bottom diameters are narrower than Cavaillé-Coll would have specified (larger ratios yield smaller bottom resonator diameters), but as we will see, Callinet carefully designed the bottom inside resonator diameters to be about one millimeter wider than the inside diameters of his shallots, making a smooth transition from the bore of the shallot to the bore of the resonator. 

Using these Callinet ratios we let Excel calculate the inside bottom diameters of the resonators. Callinet tapers the thickness of his resonators in the bass, making them thicker at the bottom for added strength. These thicknesses are entered in the Excel file, and we have the specifications for the resonators. We also added a note to make the resonators of 75% polished tin, the highest tin alloy Laukhuff offered. Figure 5 shows the first steps in this table for the low octave. We will show the entire table when it is complete.

Lengths

Resonators will be longer with a lower temperature, lower pitch, higher wind pressure, and the flat-tuned intervals in an unequal temperament. For this exercise we will specify temperature at 20 degrees Celsius, wind pressure at 85 mm (the original Callinet pressure), pitch at A = 440 Hz, and Pietro Aaron’s 1⁄4-comma meantone temperament.¹⁵

Lengths obviously relate to the pitch, but they also strongly influence the timbre. Resonators voiced to the maximum lengths will have a strong “Bourdon” fundamental in the tone, and resonators voiced shorter will have less fundamental and stronger harmonic fire. The goal in the total tuned length is a resonator where the “flip” or “Bourdon” point preserves considerable fundamental in the tone while not sacrificing harmonic fire. The Bourdon point can be modified to some degree with the curve of the tongue and the diameter of the foot hole during voicing. An article by Reiner Janke has an excellent discussion of the Bourdon point.^{6, 10} Those interested in the math of the effect of temperature on pitch can refer to a very useful website (www.sengpielaudio.com/calculator-pitchchange.htm). The calculator on this website indicates that pitch changes a full halftone from 32 to 92 degrees Fahrenheit. 

As we can see, resonator length is very important, and it is doubly so if we are designing resonators with no tuning slots—like most classical, “dead-length” French resonators. Tuning slots are often used to tune reeds to changing temperatures, and while this maintains the timbre of the reed, such tuning slots nearly always end up molested thus that the pipes become extremely uneven in voicing. The lack of tuning slots in French pipes has preserved the intent of their voicers; the reeds are tuned “on the wire.”

Although we have been talking about resonator lengths, the important length in a reed is its total tuned length, and this includes the length of the resonator, the block to which the resonator attaches, and the extension of the shallot below the block. This total length is what really determines the pitch and timbre of the pipe. Chéron gives us the total tuned length in column L of his data. The original pitch of the Callinet organ was A = 415 Hz, and Plet displays a table for these pipes with the estimated total tuned lengths they would have had at their original pitch.⁷ The current lengths of the pipes in the Chéron table reflect a pitch closer to A = 440 Hz, and as this pitch is the goal of our new reed, we will use those lengths with the understanding that there is uncertainty in Callinet’s intended pitch of the Bourdon point. 

We can enter the total lengths of the Callinet pipes into Excel and fit a curve. Figure 6 shows a table with the raw total tuned length data in column 1. Figure 7 graphs that data for the actual Callinet tuned lengths and shows a fitted curve with its exponential equation. The very high R2 value indicates a close fit to the data.¹⁶ With this equation we can fill in the missing gaps with the fitted data in Figure 6, column 2. 

We need to add one more wrinkle to the lengths—temperament. The intended 1⁄4-comma meantone temperament will give us an opportunity to show how to make length corrections (the original Callinet temperament with the missing bass C-sharp probably had major thirds of less purity than the Pietro Aaron meantone). We can approximate that correction by calculating an octave of frequencies for this temperament and finding the differences in the intervals as seen in Figure 8. For this type of meantone, pipes speaking C-sharp, E, F-sharp, G-sharp, and B will need to have resonators with lengths that are approximately 2⁄3 of the whole step in which they reside, not the typical half step of equal temperament. Figure 6, column 4 shows the total tuned meantone lengths of new pipes with adjusted lengths in blue font. The values in Figure 6, column 2 work well for equal temperament. 

We can now enter these total tuned length values into our Excel table in Figure 9. The estimated block height “H” values are placeholders that will be modified by the pipemaker to suit the Laukhuff blocks. The estimated shallot, from block, “G” values are likewise placeholders; the entered values are approximations based on the vibrating lengths of the tongues plus the necessary clearances of the tuning wires to the wedges. Once the values for “H” and “G” are known, the pipemaker will subtract them from the total tuned length “L” to give the estimated resonators “K,” i.e., K = L - (H + G). The values of the estimated resonator lengths in the table reflect that equation.  

It is important to note that the octave ratios of the lengths are 1.94, where the resonators are shorter than a pure doubling of length at the octave as they descend into the bass. This will be addressed in the comments on voicing.

Shallots

Shallots are usually made of brass, and they provide the surface and openings on which the tongues beat to make the sounds we hear. A variety of shallot and opening sizes and shapes gives us a vast range of power and timbres.¹⁷ Callinet shallots are parallel with parallel slot openings. It would be prohibitively expensive to make custom shallots for every pipe, so we will refer to Laukhuff’s selection of shallots to achieve a close approximation of Callinet’s ratios of resonator top diameters to shallot inside diameters. Figure 10 shows a portion of Laukhuff’s shallot selection for their Type II Clicquot shallots with rounded ends, which closely resemble the Callinet shallots in shape (all dimensions are in millimeters).

Callinet’s ratio of “12” for resonators to shallot inside diameters is a crucial part of his sound. Reiner Janke relates that Cavaillé-Coll’s ratio is approximately 11, and this means that Callinet’s shallots are slightly smaller and drive his wide resonators with slightly less energy.⁶ In the first three rows of our Excel table under the heading “Shallots” in Figure 11 we see the Laukhuff shallot number, the shallot inside diameter “P,” and ratio we are trying to achieve. The Excel file calculates the ratio for us. We cannot achieve exact ratios with the shallot sizes available to us, so we select shallots to get as close as we can to a ratio of 12, i.e., a range of about 11.5 to 12.5. We enter the Laukhuff wall thicknesses in the next row, and the table calculates the outside diameter “M” as simply the inside diameter plus two times the wall thickness. 

The slot opening width of the shallot, “CC” in Figure 12, is extremely important; wider slots yield more power and more harmonic fire. While Chéron did not measure this parameter directly, it is implied in his measurement of the face width “R” minus two times the wall thickness “Q,” a calculation that is accurate for shallots that are cut deeply and nearly fully open. The “face” is the surface of the shallot on which the tongue beats. Tables of reed data most often record the height of the cut of the shallot (Chéron’s data “N” and “O”), but this is a very indirect method of getting at the slot width, especially if the wall thickness is unknown. A more direct method is to simply specify that the shallots are cut until they yield the desired slot opening width, and these are the values you see in the next to last row of Figure 11, slot width “CC.” The last row is a calculation of the ratio of the slot width “CC” to the shallot inside diameter “P,” and while the Callinet data is somewhat noisy, it averages about 0.85, a very widely cut shallot. We adjust our slot widths to achieve that ratio. The pipemaker can now cut the shallots of a given Laukhuff number to the same height and slot widths.

Blocks

We specified Laukhuff’s French blocks for this reed. French boots extend well beyond the block, or the “nut” as it is often called, to support the resonator, a design that minimizes the collapse of the resonator above the block, a common problem in reeds. Bass resonators have a narrower taper, and to keep the boot from extending too far, a “ring” is inserted above the block on the resonators of those pipes. This ring is deleted when the resonator taper sufficiently widens. Figure 13 shows the two classical forms. We specified half-round teak wedges and tinned bronze tuning wires bent at the top at right angles for ease in tuning. The Callinet originals at Dole have wires bent in this manner.

Tongues

We specified Laukhuff’s tongues made of rolled, spring elastic brass. Laukhuff gave us the option of voiced or unvoiced reeds, and we specified voiced with French tongue curves. The art of reed voicing encompasses power, the Bourdon point and timbre, and the promptness of the speech. With a dead length resonator, the voicer adjusts the diameter of the toe opening in the boot to control the wind along with the stiffness and curve of the tongue.

Stiffness relates to wind pressure and the amount of curve that can be tolerated. With a large curve a thick tongue may speak slowly or not at all. If too thin, it will speak quickly but the sound will be weak in fundamental. A range of timbres can be coaxed from tongues with different curves. We will start by characterizing the Callinet tongues with their stiffness. The power of this method will be demonstrated, and it appears that to some degree Callinet thought in these terms as well.

The stiffness of a tongue, especially if it is a simple parallel tongue, may be understood with some very simple ideas. Stiffness is inversely proportional to length, meaning that a tongue of half the length will be twice as stiff. You can demonstrate this to yourself by taking a metal ruler, holding it down at the edge of a table, and letting a portion of the ruler extend beyond the edge of the table; pull up the ruler at the free end, let it go, and listen to the sound it makes. Now extend the ruler only half as far off the table and listen to the sound it makes—it will sound an octave higher with twice the stiffness. Tongues obviously come in different lengths, and the longer tongues beat at lower pitches. Tongues also come in different widths, and what is intuitively obvious is also correct—a tongue of half the width will have half the stiffness.

Tongues also come in different thicknesses, but our intuition may fail us here—the stiffness will be the cube of the thickness. For example, if we double the thickness of a tongue, its stiffness will be 23, and that means it will be eight times stiffer (23 = 8). That makes thickness by far the most sensitive parameter.

In Figure 14 we see a portion of Laukhuff’s thicknesses for tongue brass. These dimensions, like Chéron’s, are in hundredths of a millimeter, e.g., brass with a thickness of “25” is 0.25 mm thick.

Figure 15 shows a table compiled from Chéron’s data on tongues. Chéron gives us not only tongue thickness in column 6 and width in column 5, he also gives us the vibrating length of the tongue from the tuning wire to its end in column 4, a parameter that is very rarely seen in reed documentation. With this data we can make a calculation of the stiffness of the tongues. These stiffness values involve relatively complex calculations that are illustrated in Figure 24. You do not need to understand them in detail if the math is daunting, and they are already worked into the Excel spreadsheet available from the author.⁹

The real point of using stiffness values is that we get a method to adapt the tongues to our shallots and to available tongue thicknesses. The value of this may not at first be obvious, but bear with me. We will take it step by step.

We first take the raw values for vibrating lengths in Figure 15, column 4, graph the values, fit an equation, and calculate the smoothed and missing data in column 2. Figure 16 shows the raw data and fitted equation; the fit with an R2 value of 0.99 is quite reasonable. 

The next step is to calculate the stiffness of Callinet’s tongues.¹³ We use the raw data in Figure 15, columns 4, 5, and 6 to calculate the Callinet tongue stiffnesses shown in column 7. We graph those stiffnesses in Figure 17, and fit it to an equation. This data is quite noisy with a low R2 value.¹⁶ The new equation yields the smoothed stiffness data for all of the tongues in Figure 15, column 8.

This has been a long slog through data and calculations, but we are now very close to reaping the rewards. In our Excel table for tongues in Figure 18 we have entered the smoothed Callinet vibrating length data in the row for vibrating length “X” and the smoothed Callinet stiffness data in the row for target Callinet stiffness. With this data we can now design our tongues.

We make trial entries in the rows for “width” and “thickness,” and the Excel spreadsheet calculates the resulting stiffness in the row “stiffness.” The last row, “width of tongue-slot/2,” tells us when the width we have entered is so narrow that the tongue will literally fall into the slot opening of the shallot, i.e., when the value in this row is zero or less. Ideally, we would like to have a generous overhang of the tongue on the slot opening of the shallot, and this would be something like a minimum of 2 mm on each side of the bass shallot openings and at least 1 mm on each side of the treble openings. It does not matter if the tongue is significantly wider than the face of the shallot (the slot opening width plus the two shallot walls), but it cannot be less than the slot opening itself. 

Now look at the table in Figure 18. The first data column is low C followed by C-sharp, etc. We enter the thickness for low C at 0.47 mm, then we adjust the tongue width until the relative stiffness matches the target Callinet stiffness. A few iterations gives us a tongue width of 14.3 mm and produces a 2.5 mm overhang of the tongue (last row, “width of tongue – slot/2”). If we had selected Laukhuff’s 0.50 mm tongue thickness, we would need to significantly narrow the tongue to achieve the target stiffness, and while it would not fall into the slot, it would be dangerously narrow. This is all there is to it. Just keep doing this for all 49 tongues!

Callinet apparently thought of tongue design in similar terms, although his noisy stiffness data indicates that he was not at all rigorous about this.16 In the table in Figure 19 we see the first two rows of Chéron’s data for the low C and low D pipes. The columns for tongue thickness, “V” and “W,” show that the tongue for D is thinner than the tongue for C. But note in the column for tongue width, “T,” that the 13.0 mm tongue for D is wider than the 12.5 mm tongue for C. Remember that thickness is our most sensitive parameter (it is a cube function of stiffness), while width is simply proportional to stiffness. The thinner tongue for D would lack the necessary stiffness if it were narrower than the tongue for C, and Callinet has compensated by treating tongue widths as an independent variable; he does not care if the tongue is wider than the face of the shallot, and the math for stiffness explains why we should not care, either.

To summarize, we have reproduced Callinet’s stiffness of the tongues with this method. We have achieved this while accommodating the shallots and tongue thicknesses that were available to us from Laukhuff. Figure 20 shows the tongue thicknesses we selected to make the tongues wide enough to extend over the shallot faces, and Figure 21 shows the final adjustments we made to the tongue widths to achieve continuous stiffness. With careful voicing we should be able to reproduce Callinet’s sound <soundclip2>.¹⁴

Boot toe hole diameters 

Toe hole diameters may be used to control the pressure in the boot, and there is evidence that Callinet made extensive use of this. In the bass and tenor octaves the toe holes are narrower than the shallot inside diameters (the maximum flow of wind is limited by the shallot diameter and its opening). These toe hole diameters, Figure 22, are much narrower than those found in Chéron’s data for a Trompette of similar scales and wind pressure in the Isnard organ at St. Maximin.⁸ I have entered the fitted data of Callinet’s toe hole diameters in the last data row of Figures 23a and 23b. Like the stiffness data, the toe hole diameters are quite noisy with an R2 value of 0.49, indicating that Callinet used the toe holes as a voicing variable. There is a poor R2 correlation of 0.20 between the tongue stiffnesses and the toe hole diameters, perhaps indicating that Callinet used this variable to accommodate different tongue curves, thicknesses, and widths.

We can now see our completed table in Figures 23a and 23b (the bass and treble are shown separately to make the table more readable). This table specifies our reproduction of the Callinet 1st Trompette at Auxonne, France! The Excel file shown in this article took considerable time to create, and it is available at no charge from the author.⁹ It can be used as a template for other reeds.

Voicing 

Power balances are greatly affected by scaling and voicing, and Callinet’s data are instructive. Total tuned lengths will be approximately a ratio of 2 for each descending octave if bass power is strong relative to the treble, and we find octave ratios averaging 1.99 for the three Trompettes in the Raisonnance and Grand Orgue of the Isnard organ at Saint Maximin. The Callinet octave ratios are significantly smaller at 1.94, indicating shorter tuned lengths with descending octaves and reduced power in the bass. Reduced wind pressure and reduced power will result in shorter resonators at the same Bourdon point, i.e., at the same timbre.¹⁰ This observation is reinforced by the significantly reduced toe hole diameters in the bass and tenor of Callinet’s reeds. The Bourdon point is also affected by the curve of the tongue—a larger curve makes the sound more powerful, the timbre brighter, and moves the Bourdon point to a longer resonator. Larger curves require more pressure and larger toe holes for prompt speech.

We begin to get a feel for Callinet’s power balances: a restrained power in the bass with still brilliant timbre and fundamental warmth—or put another way, a more ascending treble. A smoother, more sonorous treble can be accentuated with a Bourdon point that is closer to the tuned point in the treble, farther in the bass. For example, Reiner Janke relates that Cavaillé-Coll voiced normal-length reeds close to their Bourdon point just before they transitioned to harmonic-length reeds.¹¹

We might also note that Callinet lets his tongues extend by a small and varying amount beyond the end of his shallots, a technique that subtly affects timbre in much the same manner as adding weights to the tongues. See Chéron’s data in column Y, Figure 25. 

Reed voicing is a complex subject with much subjective opinion. The goal in voicing this reed, and especially the curve of its tongues, is the scintillating French voicing of Callinet. I can think of no better source for understanding French reed voicing than the wonderful essay on this subject by Reiner Janke.⁶ I have translated this essay into English, and it is available by contacting him at [email protected]. He has a gift for finding the important variables in scaling and voicing; see the professional documentary in which he shows how to make and voice perfect copies of a Baroque Silbermann pipe and a Romantic Walcker pipe.¹²

Janke provides further guidance in the voicing of tongues.¹¹ Tongue brass is made by rolling sheets to the desired thickness. The process of rolling produces work-hardened surfaces, and the direction of rolling produces a grain with more stiffness in the direction of rolling. Tongues will be less stiff if they are cut from sheets where the grain is parallel to the width of the tongue. Baroque voicers also commonly filed their tongues to different thicknesses, and this removed the work-hardened surfaces, making their tongues less stiff. A thinner tongue will yield a more rounded timbre, and a thicker and stiffer tongue will be brighter in timbre. Narrowing the tongue will make it louder (it will be less stiff and can be curved more). These are all issues to keep in mind during the voicing process, and they probably account for most of the variability we see in the Callinet stiffnesses in Figure 17 and the toe holes in Figure 22. For those who want to experiment with different tongue configurations, you will need an assortment of reed brass of different thicknesses and a guillotine to cut tongues.

Reflections

This analysis of a Callinet Trompette helps us understand Callinet’s intentions. For those wishing to replicate the entire Callinet chorus at Dole, the Excel model described in this article may be useful as a template to help us interpret the more limited data available to us for the Dole organ.^{3, 9} The author ordered and received a Trompette from Laukhuff based on these specifications as part of a new organ to demonstrate the range of wind dynamics, among other things. This new organ will be fully described in a future issue of this journal with sound clips—stay tuned.

There are many ways to design a reed, and the varieties of reeds and their sounds are virtually limitless. This essay on reed design should not be understood as the only way to tackle this complex subject, but taken rather as a contribution to its discussion. When we hear a sound that commands our attention like the Callinet reeds at Dole, this article reminds us that a great deal of time and effort is required before we can understand those sounds. Callinet reeds are worth our time.

Notes & References

1. Michel Chapuis. Michel Chapuis joue la suite gothique à Dole, a Youtube video by Frederic Munoz, January 25, 2018 <soundclip1>. www.youtube.com/watch?v=oxWHMPS6Lp4.

2. Yves Cabourdin and Pierre Chéron. L’Orgue de Jean-Esprit et Joseph Isnard dans la Basilique de la Madeleine à Saint-Maximin. Nice: ARCAM, 1991, 208 pages, ISBN 2-906700-12-6. 

3. Pierre-Marie Gueritéy et al. L’orgue de Dole, Canevas Editeur, Frasne, France, 1995, 127 pages, ISBN 2-88382-058-9.

4. Laurent Plet. Restauration de l’orgue d’Auxonne, accessed January 11, 2019. lplet.org/orgues/auxonne/tuyaux/tgo_tr1c.htm.

5. Laurent Plet. Restauration de l’orgue d’Auxonne, accessed January 11, 2019. lplet.org/orgues/auxonne/auxonne.htm#sommaire.

6. Reiner Janke. See the article Grundzüge Zungenintonation, accessed January 3, 2019. www.orgel-info.de/. An English translation is also available. The Cavaillé-Coll ratios are general approximations and were reported to Janke by Pierre Chéron. 

7. Plet, Laurent. Restauration de l’orgue d’Auxonne, accessed January 11, 2019. lplet.org/orgues/auxonne/tuyaux/tgo_tr1.htm.

8. L’Orgue de Jean-Esprit et Joseph Isnard dans la Basilique de la Madeleine à Saint-Maximin, pages 139, 155, 156.

9. Michael McNeil. Designing an Historic Reed, Excel file, Mead, Colorado, 2019. Email the author for a free copy: [email protected]. This file also contains data on the Callinet reeds at Dole.

10. See also my discussion of the Bourdon or “flip” point in “1863 E. & G. G. Hook Opus 322, Church of the Immaculate Conception, Boston, Massachusetts, Part 3,” The Diapason, September 2017, pages 20–22.

11. Personal communications, January and March 2019.

12. Reiner Janke. Organ Voicing, Experiential Knowledge of Reiner Janke. www.youtube.com/watch?v=isEWba9rLRY&feature=youtu.be. This professionally produced video by the Universität Göttingen, April 26, 2018, is a revelation for those wishing to understand the voicing of flue pipes. The sound track is in English.

13. In Figure 24 we see the stiffness calculations of the tongues with proper physical units of Newtons of force and Newtons/meter of stiffness. While the force is admittedly applied uniformly over the surface of the tongue and not at the end as modeled in the equations, the resulting stiffness increases uniformly with pitch in the expected manner. See the website: www.tribology-abc.com/calculators/t14_9.htm.

14. Michel Chapuis. Beauvarlet à Dole avec Michel Chapuis, a Youtube video by Frederic Munoz, December 5, 2017
<soundclip2>. www.youtube.com/watch?v=T_wPdGUfuD8&feature=youtu.be.

15. This temperament is described in detail in the author’s article, “Exploring the Sound of Keyboard Tunings,” The Diapason, April 2016, pages 20–21.

16. The term “R2” or “R-squared” describes how closely the data fits to the equation on the graph. If all of the data points fall on the line, the R² is equal to “1” and the fit is perfect. If the R2 is zero, the data is just a scatterplot looking much like a shotgun blast with no correlation at all to the line described by the equation. A click of the mouse in Excel will show the R2 for any graphed data fitted to an equation. The noisy fit of R2 = 0.56 for the Callinet tongue stiffnesses in Figure 17 may very likely indicate that Callinet used stiffness as a variable during voicing.

17. Personal communication of March 2019. Janke points out that the shallot functions as a resonator which strongly affects the timbre of the sound. Extremely wide shallots, typical of North German Baroque practice, produce an “oo” vowel with strong harmonics in the range of 200 Hz; less wide shallots will produce an “ah” vowel with strong harmonics in the range of 400 Hz; French Baroque shallots are narrower and produce an “ee” vowel with strong harmonics in the range
of 600 Hz.

Michael McNeil

Michael McNeil has designed, constructed, and researched pipe organs since 1973. He was also a research engineer in the disk drive industry with twenty-seven patents. He has authored four hardbound books, among them The Sound of Pipe Organs, several e-publications, and many journal articles.

C. B. Fisk, Inc., Opus 133

The C. B. Fisk, Inc., shop, located near sea level in Gloucester, Massachusetts, had to carefully consider the delivery of their Opus 133 to an altitude of 2,127 meters (6,978 feet) at First Presbyterian Church, Santa Fe, New Mexico. Would that affect its sound? With 74% of the world’s population living below an altitude of 500 meters (1,640 feet), the effects are unnoticed, and we rarely have to deal with this.¹ Others have addressed this problem, and we can find excellent guidance in an article by James W. Toevs using Fisk’s Opus 133 as an example, where he noted that altitude had no effect on “basic intonation” (here meaning “pitch,” not “voicing”), but had a “significant effect [on] . . . pre-voicing and voicing.”² I am a voicer, I live at 5,000 feet altitude, and I want to understand how altitude affects the sound and the voicing. We can find answers with Hartmut Ising, a man who thought very deeply about voicing.

Toevs explains that at higher altitudes air will be less dense, and at sea level the voicing must be done at a higher pressure than the intended pressure at altitude. The compensation is simple: find the ratio of the air density at the workshop to the air density at altitude, and then multiply it by the desired pressure at altitude to find the correct pressure for voicing in the shop. In the example of Fisk’s Opus 133, the air density at Santa Fe is 77% of that at sea level, and we get a ratio of 1 / 0.77 = 1.3. Fisk’s desired pressure at altitude was 76 mm water column, so at sea level the pressure needed for voicing was 76 mm x 1.3 = 99 mm. As any voicer knows, that is a big change in wind pressure and a lot more power!

Hartmut Ising and Johan Liljencrants

The Fisk example shows us how to compensate for voicing at different altitudes, but if we want to understand how the voicing and sound is affected, it might help to explain the need to adjust wind pressure.

In a 1971 internal publication of the Walcker firm, Hartmut Ising proposed an equation to show how the timbre of a pipe (a primary goal of voicing) is affected by its pitch, the height of its mouth (also known to voicers as “cutup”), the depth of its flueway, and the velocity of air (this last term was transformed by Johan Liljencrants into air density and wind pressure).³ For those not familiar with these terms, Figure 1 illustrates the front, side, and cross-section views of an organ pipe, showing its mouth height H and its flueway depth D. This equation is rarely seen, but it gives profound insight into many aspects of voicing.

I am going to take a great risk here by showing the somewhat intimidating Ising equation (in its form by Liljencrants). This is where readers will normally storm for the exits, but bear with me, I will do all the math for you in Excel, and I will show you what it can teach us:

[Ising equation]

I is the timbre of a pipe—the German word for “voicing” is Intonation. An I value of 1 is the timbre of a smooth flute. A value of 2 is an optimal state for the “shortest duration between the opening of the pipe valve and reaching the steady pipe sound (fundamental plus overtones).”⁴ In this state the timbre of a pipe also has more power in its harmonics, i.e., it is more like a principal and brighter. A value of 3 is the point where the harmonics have become so strident and powerful relative to the fundamental that the pipe overblows to the octave (strings can operate in this region with help from devices like roller beards to prevent overblowing). Most organ pipes are voiced in a range of values from about 0.8 (a very smooth flute with delicate harmonics) to about 2.3 (a principal with very well-developed harmonics and brightness).⁵

F is the frequency of the pitch in Hz.

D is the depth of the flueway in meters.

H is the height of the mouth in meters.

P is the wind pressure in Pascals, or N/m². Organ pressure is measured by the height of a water column, and 1 mm of pressure = 9.80665 Pascals. This is the term we will vary to see how it affects the timbre of the pipe I.

ρ is the density of air in kg/m³, which is 1.2 kg/m³ under standard conditions at sea level. This is the term we will adjust for different altitudes.

The beauty of Ising’s equation is that it lets us “hear” the changes to the timbre of a pipe’s voicing when we change its altitude or its pressure. Let’s see what it can show us.

Air density at different altitudes is a subject with complex compensations that include temperature and humidity. Figure 2 shows online data that yielded air densities ρ in very close agreement with Toev’s example.⁶

We are now ready to create the Excel table shown in Figure 3, and we will begin with a sea level air density ρ of 1.20 in the last column. A full range of pipes from 16′ to 1⁄8′ are shown in column 1, and the frequencies F of the pitches of those pipes are seen in column 3. The flueway depths D in column 4 are typical of the principal chorus voicing of the Isnards at Saint-Maximin, and the mouth heights H in column 5 are all Normal Scale.⁷ In column 6 the pressure P in the foot of the pipes is adjusted to 35 mm (343.2 Pascals). The Ising equation now calculates timbre values I of 2.21, shown by the red arrow in column 2.

The flueway depths D were fine-tuned to get the same I values for all pitches (with minor rounding variations). This is probably in the ballpark for the Isnard sound. The bellows pressure of the Isnard organ is 83 mm, but the toes of the flue pipes are closed and the actual pressure in their feet is far lower.⁸ Figure 3 represents voicing at sea level.

Now we are ready to see what happens if we adjust our altitude to 1,500 meters by changing the air density ρ from a value of 1.20 to 1.00 in the last column in Figure 4. We are not changing the sea level voicing in the flueways, mouth heights, or wind pressure. The change to the timbre I is a revelation.

The timbre I increases to a value of 2.42 for all pitches. This is a much brighter and more powerful sound, and it is not what the voicer intended at sea level! While I do not recommend this as a solution (it would involve a great deal of work), we could raise the mouth heights (cutups) on all of the pipes to restore the timbre of the original sound. For example, in Figure 5 we see the new mouth heights H (in red font) that would restore the timbre of the pipes at 1,500 meters altitude to an I value of 2.21.

The mouth heights and flueways in this table are noted in meters, so the mouth height on the 16′ pipe is 54.5 mm, and so on for the other pitches. You can compare these heights (cutups) to the table in Figure 4—very small changes in mouth height make big changes in the timbre. The point of this example is to show that mouth height can be adjusted to keep a constant timbre at different levels of power.⁹

The much better solution for moving an organ to a higher altitude, just as Toevs suggests, is to lower the wind pressure. For our new example, we find the ratio of the air densities at 1,500 meters altitude and sea level: 1.0 / 1.2 = 0.83. Using this ratio, our new lower wind pressure is 0.83 x 35 mm = 29.1 mm. Figure 6 demonstrates our original sea-level voicing, but the air density ρ is 1.00 for 1,500 meters altitude in the last column, and our new lower wind pressure P of 29.1 mm (285.4 Pascals) is shown by the red arrows at the right). Figure 6 now calculates an I timbre value of 2.21 at 1,500 meters altitude, the exact timbre we had at sea level on the higher pressure with our original voicing!

Higher altitude brightens the timbre

The Ising equation confirms the Fisk method of altitude compensation with wind pressure, and it shows why we have to compensate for it—while we might be gasping for breath at higher altitudes, the sound of a pipe organ gets brighter. If we reduce the wind pressure in the bellows with higher altitude, we can keep the same timbre at any altitude with the same voicing. This is a key insight from Ising, and his equation works in the real world of voicing.⁹

The final piece of the puzzle

We might correctly surmise from the Ising equation that the power of both the fundamental and the harmonics increases with altitude, and the power of the harmonics will increase faster than the fundamental, making the sound brighter. Adjusting our wind pressure lower corrects both the timbre and the power. But there is one more crucial effect at play here: the intensity of sound decreases in rough proportion with the air density.¹⁰ This means that power will drop with altitude.

And this is why Fisk chose a target pressure for their normal power at altitude and raised that pressure at sea level for pre-voicing. They simply voiced the pipes at sea level with normal timbre and more power on higher pressure. Then, when the pressure was reduced at altitude, the normal timbre was maintained and the power dropped to normal as well. Now we know how the sound and voicing of organ pipes are affected by altitude and why the Fisk method works.

What this means for the organ builder

The bottom line here is very important. Once an organ is voiced at a desired power level, timbre, and pressure at a specific altitude, it cannot maintain both its timbre and its power at a different elevation with the same voicing.

Pressure can be adjusted lower if the organ is moved to a higher elevation to keep the timbre the same, but the power will be lower. If the original pressure is maintained, the power will be the same, but the timbre will be much brighter (requiring higher cutups to restore the timbre).

Pressure can be adjusted higher if the organ is moved to a lower elevation to keep the timbre the same, but the power will be higher. If the original pressure is maintained, the power will be the same, but the timbre will be much duller (and cutups are not easily lowered).

A graph for altitude compensation

If you are able to plan ahead for a change in altitude, I have used the Ising equation and the air densities from Figure 2 to do the calculations for you in the graph in Figure 7. This graph will give a constant timbre and power for flue pipes spanning a range of altitudes from sea level to 2,500 meters (8,202 feet). See Figure 7 for instructions on its use and a worked example.

The graph in a nutshell

Voicing at a lower altitude for delivery to a higher altitude: Adjust the pressure higher than normal and voice for higher power with normal timbre; drop to the target pressure at higher altitude. The timbre and power will be normal. Voicing at a higher altitude for delivery to a lower altitude: Adjust the pressure lower than normal and voice for lower power with normal timbre; raise to the target pressure at lower altitude. The timbre and power will be normal.

Notes & References

1. Joel E. Cohen and Christopher Small, “Hypsographic demography: The distribution of human population by altitude,” Proceedings of the National Academy of Sciences of the United States of America, November 24, 1998, 95 (24), pp. 14009–14014.

2. James W. Toevs, “Organ Acoustics at High Altitudes,” The Diapason, October 2009, p. 31.

3. Hartmut Ising, “Erforschung und Planung des Orgelklanges,” Walcker Hausmitteilung, no 42, Juni 1971, pp. 38–57. Johan Liljencrants shows a form of this equation on the website www.fonema.se, accessed on October 18, 2020, which contains not only Liljencrant’s work but also the original Ising article. On this website we see that Liljencrants modified Ising’s original equation to use pressure and air density rather than velocity, making the equation more easily used by the organbuilder. Here is his transformation of Ising’s equation:

4. Personal communication from Dr. Hartmut Ising, October 2020. Previous literature has translated I = 2 as an optimal state for the fundamental, but did not define what was optimal about it. Dr. Ising continued to clarify this: “for I = 2 the transient of the sound is optimal (Einschwingvorgang).”

5. John Nolte, “Scaling Pipes in Wood,” ISO Journal, no. 36, December 2010, pp. 8–19. The original website referenced in this article by Nolte that posted the English translation of Ising’s equation by Liljencrants and his description of the range of values for I has disappeared. The website, www.fonema.se, contains much of this information. See also note 4 above.

6. www.engineeringtoolbox.com/air-altitude-density-volume-d_195.html, accessed August 25, 2020. The baseline at sea level assumes 20 deg C temperature, 40% humidity, and standard pressure.

7. Michael McNeil, The Sound of Pipe Organs, CC&A, 2014, Amazon.com, pp. 68–72. This chapter explains the derivation and use of the Normal Scale for cutups and displays a chart for all pitches from 32′ to 1⁄8′.

8. The scintillating Isnard reeds have far more open toes and their thicker tongues are more effective with the higher bellows pressure. The higher pressure also compensates for pressure losses in the tubing to the many offset pipes, which have much more open toes than the pipes on the windchests. Open toe voicing of flue pipes on even modest wind pressures requires compensation in the flueway depths, just as we find in neo-Baroque voicing. The warmth of French Classical voicing resides in its open flueways.

9. The Sound of Pipe Organs, pp. 77–84. A spectral analysis of a pipe’s sound measures the power of its harmonics and objectively quantifies its timbre. This chapter uses Ising’s equation to show how timbre, pressure, and cutup are related, using examples of spectral data from organ pipes taken with a state-of-the-art (in 1975) spectrum analyzer.

10. www.physics.stackexchange.com/questions/672/what-is-the-relation-of-sound-propagation-to-air-pressure, accessed October 3, 2020. Sound intensity is roughly proportional to the air density.

The equation for sound intensity is   I = ξ2 ω2 c ρ,  and I here represents intensity, not Ising’s I for timbre.

I = intensity

ξ = particle displacement

ω = frequency

c = speed of sound

ρ = density of air