Organbuilders and research: Another point of view

The following is a response to the article “Organbuilders and research: Another point of view,” by John M. Nolte (The Diapason, July 2010, pp. 20–21), which was itself in response to the article “Organbuilders and research: Two points of view,” by Francesco Ruffatti and Judit Angster (The Diapason, January 2010, pp. 24–27).

I found the article in the July issue (pages 20–21) written by my colleague John M. Nolte very interesting and informative. We are probably of the same age: I too have been involved in organbuilding for well over 40 years. Having said that, I should also say that I do not really believe that longevity in organbuilding practice is what counts the most: one can repeat the same mistakes for decades, and at the same time a bright young organbuilder can find innovative ways quickly. Experience plays a role, but it is the personal attitude that makes the real difference. In any case, we both seem to be curious enough to try to get to the bottom of organbuilding issues. For this reason, I have chosen to be involved in research, and have been lucky enough to find the connection, during the last ten years, with the very respected and reputable Fraunhofer Institut für Bauphysik in Stuttgart.
Having practiced both open-toe and closed-toe voicing for quite some time, going through a variety of organbuilding “trends,” and having come in the end to some empirical conclusions, I was always curious to find out why I was considering one method better than the other for certain applications. Specifically, I have no problem in stating that under “average conditions”—let us say at around 3 inches of wind—I obtain better results with open-toe voicing on principals and flutes, and better results with closed-toe voicing on strings. If I have to raise the pressure further, to increase the sound energy at its source (sometimes you have to, especially in poor acoustics), I find it easier to control principals and flutes if I voice them with open toes. “Better results” are always subjective, of course, and personal taste plays an important role, as I stated in my original article.
Dr. Angster, Dr. Miklos, and other scientists—all top names in organ acoustics—have explained to me not only the Bernoulli formula, which in the end is not so complicated, but a number of other theories and esoteric formulas. I tend to be “practical,” like many organbuilders, and will not deny having been taken by surprise in seeing how variable the scenario can be in toe wind pressure values, after boring holes and applying pressure sensors to the sides of the pipe feet.
In a perfect world, one could put each stop on its own wind pressure in order to compensate for open or closed toe, in order to obtain, as Mr. Nolte suggests, equal wind pressure at the languid, which is not an easy thing to actually measure, unless you bore holes at the toes as we did during the research. In the real world, when you are voicing a chest of pipes in a Swell division containing principals, flutes, strings and reeds, then you have fewer choices. This is where a practical comparison of the two methods, given equal windchest pressure, becomes meaningful. While I respect Mr. Nolte’s idea, the choice that we made in establishing a research procedure was different, as Dr. Judit Angster explains well in her section of this article. I will never say that “my way is the only way,” and I would ask for the benefit of the doubt from others as well.
The issue of the so-called “wind noise” is, in my opinion, the key to, not a side aspect of, the whole matter. I have been told that what causes turbulence—and noise as one of the results—is a sudden restriction in the air flow. In other words, if we restrict the maximum flow from the diameter of the windchest hole, by closing the pipe toe, turbulent conditions are created. The “open toe” is so open that it looks exaggerated: this is not done to make sure that enough wind gets into the pipe, but rather to avoid as much as possible a restriction in the flow. The shape of the pipe tip may have some influence in the noise, but the real issue does not change. Actually, by looking at photo 2 of Mr. Nolte’s article, it seems to me that the hole with the countersink, which he refers to as “quiet toe-hole,” seems to direct the flow inwards, towards the center of the flow, thus potentially creating the opposite of what a “diffuser” would do. A diffuser is a device that is aimed at reducing turbulence from flow restrictions. On this matter, we have some interesting results from previous research on wind supply.
If noise is created, at equal windchest pressure conditions, Mr. Nolte agrees with me that by reducing the wind flow at the lower lip, which is the only way to control volume in an open-toe flue pipe, the wind noise is reduced as well. I take this as a strong indication of the validity of the open-toe system for the “classical stops,” where it is not as desirable to nick the languids. For the strings, the matter is different, and the need to reduce the pressure in the toe is linked to the need for keeping the mouth cutup to reasonable levels in spite of the smaller relative diameter of the pipes, to preserve clarity. Nicking is, for these pipes, a normal condition (except in rare occasions—for example, the “Violetta” by Callido).
Voicing is very personal, and tastes are different. I am sure that Mr. Nolte does a fine job with voicing, given his experience, regardless of the method. As to wooden pipes, I am happy to hear that he has done research on this aspect as well. We are doing the same, possibly with some different objectives: not only to find better transitions, but also, for example, to speed up the speech on very large 16′ open wood pipes. I will read Mr. Nolte’s reprint when it becomes available, as well as the description of his all-wood practice organ. I sincerely wish him the best of luck in his efforts. After all, we are all in the same boat, and all for the same reason: we all love the work that we do.
—Francesco Ruffatti

In my contribution to the article, I tried to release information about our current research project on organ pipe voicing and scaling. Within this context, I mentioned our investigation on open and controlled toe voicing, as one example of the ongoing research. Unfortunately, the goal of this experiment was not formulated clearly; therefore I have to accept Mr. Nolte’s ironic criticism as justified.
Certainly, the group of scientists and I, who have been working together for several years on organ pipe research, know very well that “the velocity of air at the flue is determined by the pressure in the foot of the pipe just below the languid” and that “in every case, the voicing pressure is lower than the windchest pressure.” But we also know that not only “the velocity at the flue” “matters for pipe speech,” as Mr. Nolte states. A more important factor for the speech is the velocity at the upper lip, and that velocity depends also on other parameters. The air jet emerging from the flue must obey the physical law of momentum conservation; therefore its maximal velocity V at a distance y from the flue can be given as V(y)≈UB(d/y)1/2, where UB is the Bernoulli-velocity and d is the width of the flue. The air jet is directed usually slightly outside; therefore it hits the upper lip at a velocity that is lower than its maximal velocity. The direction of the jet depends on the relative position of the languid and lower lip. The task of the voicer is to find the optimal adjustment of the mouth area to ensure the required loudness and speech of the pipe. From the standpoint of science, the voicer adjusts only two physical quantities: the air volume through the flue and the velocity at the upper lip. In the case of a constant windchest pressure, the air volume is adjusted for closed-toe pipes both at the toe and at the flue; in the case of open-toe pipes, it is adjusted only by means of regulating the flue width. The velocity at the upper lip depends on several parameters: the Bernoulli-velocity (which depends on the foot pressure), the width of the flue, the cutup, the positions of lower lip, languid, and upper lip, etc. The essence of the art of voicing is to find the optimal adjustment of these parameters only by listening to the sound.
The velocity profile of the air jet depends also on other parameters like the profile and angle of the languid, nicking, etc. In order to get more information about the properties of the air jet, the free outflow from the flue of metal organ pipes and edge tone generation at the upper lip was the subject of a three-year Ph.D. project at the Fraunhofer IBP, which will be completed this year.
If two identical pipes are placed on the same windchest, one with open toe and the other with closed toe, it is possible to get the same velocities at the upper lips by reducing the flue width of the pipe with open toe. This opportunity has led us to the idea of voicing the two pipes on the same windchest pressure, to the same volume of sound. Thus the goal of the investigation was to voice the pipe with open toe and the pipe with closed toe to the same loudness and then compare their steady spectra and attack transients. Preliminary results of this investigation were presented in our article.
For us scientists, it was astonishing to witness how similar the achieved sound was from both types of pipes. Steady spectra and attack transients, measured by our special method, were very similar. The only easily measurable difference was the lower wind noise level on the pipe voiced with open toe at 70 mm water column pressure.
In a closed-toe pipe, the foot pressure may be significantly lower than the pressure in the groove. This pressure difference accelerates the flow through the smaller cross-section of the foot hole. The cross-section of the foot will then suddenly become much wider and the flow velocity will decelerate. This acceleration/deceleration process can generate noise and pressure fluctuations. With open toe, neither pressure difference nor sudden velocity changes occur. As the measurement results in Figure 5 of our original article show, the wind noise level in the pipe sound is lower in the case of voicing with an open pipe foot.
The common research with voicers has proven that good speech and steady sound can be achieved by both voicing methods. The voicer should decide which method he prefers; this is a question of taste and experience, not of science.
—Judit Angster

Since 1968, Francesco Ruffatti has been a partner, along with his brother Piero, of Fratelli Ruffatti—Ruffatti Brothers Family of Artisans—of Padova, Italy. The firm is involved in the restoration of historic organs and the construction of new pipe organs, and has worked for decades in Italy and many other countries, including the United States, Canada, South Korea, Japan, Australia, Mexico, and Sweden. Francesco Ruffatti holds the position of tonal designer with the company. He supervises the design of construction parameters of the pipe stops and their voicing. He is involved directly in the study, cataloguing, and restoration of voicing, and researching the temperament of the pipework of ancient organs undergoing restoration. He has co-authored several publications and has written articles in this area of expertise for both Italian and American journals, including “Gaetano Callido, Organbuilder in Venice,” The Diapason, December 1998, and “The Historical Italian Organ—Tradition and Development,” The Diapason, June 2001. He has also participated as a speaker at numerous conferences. A two-term past president of the Association of Italian Organbuilders, Francesco Ruffatti is currently teaching restoration practices and the theory and practice of flue and reed voicing at the school for organbuilders of the Lombardy region in Crema, Italy. Fratelli Ruffatti is a member of both the Association of Italian Organbuilders and the International Society of Organbuilders. Judit Angster comes from the famous Hungarian organbuilder family Angster. She holds a Diploma and PhD in physics. Since 1986, she has been engaged primarily in pipe organ research. Since 1992, she has been working for the Fraunhofer Institute (IBP) in Stuttgart, Germany, as head of the “Research Group of Musical Acoustics,” where, among other things, important European research projects were carried out in close cooperation with organ building companies. From 1994 until 2003, she taught classes in acoustics for master craftsman courses (the highest level of education and training) for organ building at the Federal College of Organ Building in Ludwigsburg, and intensive advanced training courses for pipe organ and church acoustics at the Fraunhofer Institute (regular workshops for further education of organ experts). She also lectures in acoustics at the University of Stuttgart and at the University of Music and Fine Arts in Stuttgart. Dr. Angster is President of the Technical Committee of Musical Acoustics of the German Society of Acoustics (DEGA) and a member of the Executive Board Council of the German Society of Acoustics (DEGA). She is the author of 115 publications in scientific/technical journals, conference proceedings, etc., ten patents, one book, 113 invited papers for conferences, congresses and at different institutes and societies.

The organbuilder’s viewpoint
Investing in research is foreign to most organbuilders. The pipe organ is a traditional instrument, for which it is natural to think that everything has already been invented. Research is therefore perceived by most as something that has no value, since no advancements can be made. The possible exception to this involves the console systems and controls, where conservative attitudes in many cases have been overwhelmed by the very practical need of many organists to have tools on hand that can facilitate their performances. But what about sound, and the very principles that control the ancient art of voicing? In such areas, one will find that every single pipe voicer thinks that his way is the way it should be done, and procedures cannot be improved upon from his normal practices.
Voicing is largely a matter of taste, and subjective preferences are the only governing factors. Very often, an organbuilder is chosen because of the sound that his instruments produce, meaning essentially the stylistic approach to sound that he takes. Why would he then be interested in research in this field? Why change something that already works?
My entire career has been guided by two principles: anything can be improved upon, and an organbuilder never ceases to learn. The combination of these two beliefs has determined my personal desire to take part in scientific research programs. For almost a decade, Fratelli Ruffatti has participated in joint European projects aimed at finding ways to improve the art of organbuilding. Such projects have determined the need to conduct a great deal of fundamental research, which has been carried out over the years by a number of notable institutions, among which are the Fraunhofer Institut für Bauphysik (IBP) in Stuttgart, Germany, the University of Edinburgh, the University of Prague, the University of Budapest, and the Steinbeis Transfer Center of Applied Acoustics in Stuttgart. The Fraunhofer IBP in particular has been the constant guide and the main force behind fundamental and applied research.
The programs have been encouraged and co-sponsored by the European Commission in Brussels. A small group of organbuilders,1 coming from different European countries, participates in the research investment and actively cooperates with the scientists. Astonishing results have been obtained over the years, ranging from more efficient and silent wind systems, to efficient ways to evaluate room acoustics and to better adapt pipe organs to different acoustical environments. Recently, a revolutionary wind system has been invented, a monumental advancement over the traditional winding methods, which allows the organbuilder to simply avoid the use of reservoirs, schwimmers or related equipment, while at the same time obtaining unprecedented stability and efficiency in the wind supply of pipe organs.
The research currently under way deals with sound. The aim of this two-year process is to find better ways to reduce or eliminate problems that exist both in the field of “scaling,” or pipe dimensioning, and in “voicing,” meaning the process by which the pipes are given their proper sound character. At first sight, one may think that a project of this nature is aimed at “standardizing” organ sound by promoting uniform procedures for all. This is not at all the case. The idea is to provide scientific, undisputable knowledge, which can be used by each organbuilder to better reach his individual tonal ideals. Examples are the application of scientific principles to calculate an efficient shape for large wooden pipes that will make them prompt in their attack despite their size, while ensuring the production of the needed fundamental. Other interesting examples under research are finding practical ways to make the transition between stopped and open pipes, or the transition between wooden and metal pipes within one single rank, as tonally undetectable as possible.
In such a research program, the subject of voicing techniques could not be avoided. Once again, the objective was not that of teaching new ways to voicers with decades of experience, but to find out scientific evidence in a field that has never been properly analyzed with scientific methods, with the purpose of supplying new knowledge that the voicers will then use at their discretion and according to their personal taste.
One of the steps that has been analyzed concerns the investigation of the differences between the practices of open-toe and closed-toe voicing. Open-toe voicing is a technique by which flue pipes are voiced with their toe hole completely open, thus achieving continuity between the size of the toeboard hole and that of the pipe foot. With this technique, the pipe toe opening is not used to control the volume of sound that the pipe produces. On the other hand, with the technique called “closed-toe voicing” the volume control in the pipe sound is achieved by means of adjusting the diameter of the pipe toe opening.
It is the opinion of many that the difference between the two techniques merely represents a choice in the method for controlling the sound volume of pipes and that there are few and marginal effects on the quality of sound. If the volume can be well equalized by closing the pipe toes, why choose to avoid such practice? Even the first, partial results of the investigation are proving that such an assumption is an oversimplification. The two methods produce different tonal results, which can be detected and measured.
An experimental session was called in April 2009 at the Fraunhofer Institute in Stuttgart. The participants spent two solid days investigating a number of metal pipes specially built for the experiment. The research took place in a very sophisticated structure: a huge anechoic room of almost 2,000 cubic meters in volume. The test “floor,” a steel grille placed at mid-height (20 feet from floor level), housed the several people involved in the experiments, plus all of the needed equipment: sophisticated pressure sensors (along with a less sophisticated old-fashioned wind gauge), computers, sound pressure detectors, state-of-the-art microphones, etc.
The group of researchers included Dr. Judit Angster, head of the Research Group of Musical Acoustics and Photoacoustics of the Fraunhofer IBP; Prof. Andras Miklos, director of the Steinbeis Transfer Center of Applied Acoustics and a world-famous researcher in the field; Johannes Kirschmann, voicer and restorer of the firm Mühleisen of Leonberg, Germany; Francesco Ruffatti, tonal director and head voicer of Fratelli Ruffatti of Padova, Italy; and Thomas Trommer and Maria Cabanes Sempere, scientists at the Fraunhofer IBP.
During this intensive session, two sets of pipes, one of Principal scale and one of Open Flute scale, were analyzed. Each set was made of four identical pipes, two of them voiced with the open-toe and two with a controlled-toe opening. To reduce the risk of subjectivity, each voicer worked on and prepared one open- and one closed-toe pipe. The same procedure was repeated at three different wind pressures, ranging from 70 mm water column, just slightly less than 3 inches, to about 170 mm, or slightly less than 7 inches. Pipes were voiced with no nicking at the languids, but further investigations were carried out also with nicked languids in different configurations. All pipes in each set and for each trial were voiced to equal, instrumentally measured sound volume.
The wind pressure was measured not only inside the windchest but also inside the pipe toes of both the open- and closed-toe pipes.2 The sound of each pipe was also recorded simultaneously but separately at both radiating points, i.e., at the mouth and at the top of the resonator. In addition, the “mouth tone”3 was also recorded from each pipe at each step.
A huge quantity of data was collected, which is currently being analyzed. During the test session, however, several interesting phenomena could already be observed. To everyone’s surprise, it was noted that the wind pressure inside the pipe foot in open-toe pipes showed an average pressure drop of 10% or less from the original pressure inside the windchest, while in the closed-toe pipes, even though these were still fairly open, the pressure drop was about 40 to 50%. A further immediate difference was detected in open- versus closed-toe pipes: under equal conditions, the “wind noise,” a natural component of the pipe sound that the voicer normally tends to reduce or eliminate, was by far more noticeable in closed toe pipes. This is not at all an irrelevant difference: in practical terms, it means that pipes voiced with closed or partially opened toes will require a heavier presence of “nicks” at the languids in order to control the wind noise, and this in turn will determine significant modifications to the structure of their sound.
The final results will be presented, with scientific data and measurements, to the project participants in the near future. These are occasions where the various organbuilders share experiences and learn from the scientists, an invaluable help to modern organbuilding.
—Francesco Ruffatti

The scientist’s viewpoint
Organ building is a traditional craft, which entails a valuable body of knowledge passed from generation to generation and which therefore should be preserved. Nevertheless, innovative design methods and technologies can be applied in the daily practice of this craft in order to optimize the design and production of organs, without endangering the valuable traditions inherent to their fabrication. The organbuilding firms that are taking part in the European research projects recognize that the quality and the effectiveness of their work can be considerably enhanced by adopting scientific and technological innovations into their craft.
In the current pipe project, before starting applied research, it was necessary to carry out fundamental research to reach a better understanding of the physics of flue pipes in organs. Furthermore, some special tools had to be developed, including special software for the analysis of pipe attack and stationary sound. The measurements were carried out in the anechoic room of the Fraunhofer IBP, where an acoustic-free field could be achieved. Here the pipe sound can be detected without any acoustical influence from the surrounding space.
The pipes were positioned on a functioning model windchest. All the other parts of the wind system, like reservoir and blower, were set outside of the room so that the sound detection would not be disturbed by any noises (Figure 1). The sound of individual pipes was detected by changing parameters one at the time, in order to evaluate the physical effect of single voicing steps. The evaluation of the experimental results is currently being carried out with the help of the above-mentioned special software.
The selected flue pipes that are the object of the research are being analyzed from the standpoint of the physical features of their steady sound spectrum and of the analyzed onset of the sound. A stationary spectrum of a flue pipe can be seen in Figure 2. This spectrum shows the most important properties of the sound of flue pipes, some of which are listed as follows:
1. A series of harmonic partials. As is well known from the elements of the Fourier theory in mathematics, any periodic signal has a lined spectrum with several harmonic partials and mostly a complicated spectral envelope.
2. A second series of smaller and wider peaks, which are not harmonically related, but slightly stretched in frequency—these peaks are at the frequencies where the sound will be amplified by the pipe body (acoustically called pipe resonator).
3. A frequency-dependent base line—this is the characteristic noise spectrum of the air flowing out of the flue.
An example of attack transient of an organ pipe of the Diapason family can be seen in Figure 3. Three phases can be subjectively distinguished in the attack of flue pipes.1 These parts cannot be entirely separated in time because they overlap quite broadly. Therefore, it is better to refer to them as three components, which start almost simultaneously, but develop at different rates. These three components can be characterized as follows:
• Forerunner. This is the sound heard first. It is very difficult to describe. It may have a pitch, but sometimes no pitch can be assigned to it. Several different terms are used for this component, such as chiff, ping, hiss, cough, etc.
• Appearance of a pitch. The second component in the attack usually has a pitch close to the pitch of a higher harmonic partial. This component is very important for certain stops. For example, for several diapason stops the second or the third harmonic can be heard preceding the fundamental.
• Onset of the fundamental. The third parameter of the attack is the rise time of the fundamental. For stops of the flute family, this rise time is very short, whereas it is very slow for stops of the string family. As the fundamental grows, certain components of the attack simultaneously become weaker.
The presence of the first two components is not compulsory in the attack. Moreover, the voicer can seriously influence the attack by producing, according to his taste, a faster or slower speed, a more or less pronounced forerunner, brighter or more fundamental sound, etc. It is worth mentioning that sometimes one or more partials are quite strong at the beginning of the attack, but become weaker in a later phase of the development of sound. The measurements show that the perception of the attack can be assigned to measurable properties.
The three parts of the attack can be clearly detected in Figure 3. The forerunner appears in every partial, implying its broadband nature (chiff). Then the partials start to grow; the fastest component is the sixth one. After a while, the second will be the strongest; it dominates the attack in the 35–40 milliseconds domain. The fundamental slowly overtakes the second, which becomes slightly weaker as the fundamental rises.
It can be assumed that the presented characteristics of the attack in flue pipes are related to the basic physical properties of the pipes. These relations will be investigated also in the case of voicing with open and closed toe. In Figure 4 another three-dimensional representation of an analyzed onset (attack transient) of a flue pipe is shown. In this case also the time function of the noise between the partials can be observed.
One of the many tasks of the project is the investigation of the advantages and disadvantages of the voicing methods with an open-toe and with a controlled-toe opening. In doing so, an aspect that has been analyzed from a scientific viewpoint deals with the radiated sound power (“volume of sound”) as a physical parameter.
The values of the pressure and flow are indifferent from a physical point of view, since the same sound power can be achieved by
• large foot pressure and small flue area (voicing by open toe)
or by
• small foot pressure and large flue area (voicing by closed toe).
The sound power depends on the air volume, which is proportional to the flue area and to the square root of the wind pressure in the toe. The pressure in the foot is constant in the case of an open toe; consequently there is only one parameter, the flue area, which can be varied by the voicer. By closed-toe voicing, the wind pressure in the foot can be changed, e.g., in this case two parameters can be set: the wind pressure and the flue area.
There is one more difference that must be mentioned. In a closed-toe pipe, a cross-sectional jump in the flow occurs at the foot hole through which flow noises can be generated. As the measurement results show in Figure 5, the noise level in the pipe sound is lower in the case of voicing with an open pipe foot.
The above are only a few and partial examples of the thorough investigation that is being carried out to evaluate the different aspects and characteristics of the open-toe and closed-toe voicing methods. Their influence on the attack transients will also be investigated.
A great advancement in the research process has come from technology that allows one to see the air flow pattern at the pipe mouth. A plexiglass “window” was created in the pipe, and air mixed with smoke was utilized to activate the pipe. By means of sophisticated equipment, involving a laser light source and a high-speed camera, it has been possible to film the movement of the air flow (see illustrations). The process is the work of scientists Hubert Ausserlechner, Fraunhofer Institute for Building Physics (IBP), Stuttgart, and Margit Liehmann, Fraunhofer Institute for Chemical Technology (ICT), Pfinztal.
In addition to the subject above, the research program has already produced excellent results in examining wooden pipes, open and stopped, of different shapes, with the aim of scientifically calculating the best shape from the standpoint of the efficiency of their air column. In addition, specific research will be aimed at finding efficient solutions for the tonal transitions between stopped and open pipes, or between pipes of different shapes and materials within the same rank. This is not an easy task, but a very exciting one, which can bring immediate and tangible results to the day-by-day work of the organbuilders involved in the research.
—Judit Angster

Common reference projects for cooperation for both authors—European CRAFT (Co-operative Research Action For Technology) projects within the framework of Brite-Euram III program:
1. “Development and Modernization of the Wind Supply Systems of Pipe Organs“ (BRST-CT98-5247)
2. “Advanced Computer Designed Open Wind Systems for Pipe Organs” (G1ST-CT2001-50139)
3. “Development of an innovative organ pipe design method” (G1ST-CT-2002-50267)
4. “Innovative Design Method for Matching the Pipe Organ to the Acoustics of the Room” (COOP-CT-2005-017712)
5. “Innovative Methods and Tools for the Sound Design of Organ Pipes” (FP7-SME-2007-1, Research for SMEs – 222104) (current project)

Jim Toevs has a doctorate in nuclear astrophysics. While a professor at Hope College, he taught and consulted in acoustics. A musician, for 20 years he was the principal trumpet in the Los Alamos (NM) Symphony Orchestra and has sung in and directed church choirs.

Introduction1
With the installation and voicing of the wonderful new Fisk Opus 133 tracker organ in the First Presbyterian Church of Santa Fe, New Mexico, a number of interesting effects and impacts of Santa Fe’s thin air became apparent. This article will note the major observations and describe the physical acoustics related to organ pipe function at high altitude.
Santa Fe is located at the foot of the southern Sangre de Cristo mountains at an altitude of about 7,000 feet above sea level. In fact, the altitude at the church is 2,127 meters or 6,978 feet. At this altitude, both the atmospheric pressure and density of air are reduced to about 77% of their values at sea level. This difference in pressure corresponds to about 92 inches of water. Considering that most organs operate with a wind pressure of 2 to 4 inches (water column), this difference is quite significant. It is not surprising that organ operation is impacted by this difference; perhaps what is surprising is that the impact is not greater. The fine people of C. B. Fisk dealt with these differences with little difficulty.
Parameters in which high altitude might impact pipe organ performance include:
• Pipe intonation—essentially no effect;
• Windchest blower requirements—observed significant effect;
• Tone production: pre-voicing and voicing—observed significant effect;
• Sensitivity to windchest pressure—observed significant effect;
• Sanctuary acoustics—small but real effect.

Pipe intonation
The impact of altitude on the basic intonation of the organ pipes themselves is minimal. The frequency at which a pipe sounds (fundamental) is based on the length of the pipe and the speed of sound. The length, of course, does not depend on altitude, and fortunately neither does the speed of sound because the ratio of the pressure to density remains the same so long as the temperature is fixed. Basic intonation is therefore not affected by altitude.

Windchest blower requirements
The relationship between blower output (cubic feet per minute, or CFM) and desired windchest pressure (usually measured in equivalent inches of water column supported above the ambient pressure) is given by Bernoulli’s equation. This is perhaps the most fundamental law of fluid flow and basically is just a statement of the conservation of energy. Because density also decreases with altitude, a higher blower capacity will be required in high altitude installations than at sea level in order to obtain the same windchest pressure used at sea level. Using a higher output blower has become standard practice for high altitude installations.

Tone production: pre-voicing and voicing
As Mitchell and Broome have pointed out,2 windchest pressure must compensate for altitude differences when pre-voicing will be performed in a shop that is at a different altitude than the location at which the organ will be installed and receive final voicing. In both flue and reed pipes, the velocity has a direct impact on tuning and sound quality, and it is clearly desirable to produce the same pipe velocities during both pre-voicing and voicing. Once again from Bernoulli’s equation, since the density of air is greater at sea level than at high altitude, a higher windchest pressure must be used at sea level to produce the same velocities in the shop as in the installation. The desired shop windchest pressure is found by multiplying the desired windchest pressure at altitude by the inverse ratio of the atmospheric pressures at the two locations. This is the formula described by Mitchell and Broome.
Pressures of 3 inches and 4 inches were required for Opus 133, and the inverse pressure ratio between Santa Fe and sea level is 1/0.77 = 1.3. Therefore, pre-voicing in the Fisk Gloucester shop used pressures of 3.9 inches and 5.2 inches (water column).

Sensitivity to windchest pressure
During the final stages of voicing in Santa Fe, Fisk Opus 133 was performing very well, but suddenly developed significant intonation and sound quality problems when the HVAC (heat, ventilation, and air conditioning) system for the sanctuary switched between its two modes of operation. The change resulted in an increase of windchest pressure from 3 inches to 3¼ inches (water column). At sea level a change of ¼ inch could be accommodated without greatly impacting organ tuning and voicing, but in Santa Fe such was not the case. This sensitivity was not anticipated, but can be understood through an examination of tone production in organ pipes. In both flue and reed pipes steady energy is supplied through air streams produced by the windchest pressure, and a complex mechanism converts this energy into oscillating energy (sound).

Flue Pipes
In both a tin whistle and in flue pipes, production of oscillation, that is, tone, is through “edge tone generation.” The edge tone frequency depends strongly on air velocity through the windway, and must resonate with one of the natural modes (frequencies) of the pipe; the fundamental mode is always chosen. However, a small change in frequency of the edge tone can pull the edge-tone-pipe system away from the desired intonation. A small change in windchest pressure at altitude will result in a larger change in velocity (and therefore in pitch) than at sea level, due to the reduced density of air at altitude.

Reed pipes
In a reed pipe, air is supplied to the boot from the windchest at a pressure greater than the pressure in the resonator. This causes air to flow under the reed (tongue) into the resonator. Oscillation and therefore tone generation occur when very specific relationships are met among the variables and the stiffness of the reed. Both the stiffness and the oscillating length of the reed are set by the tuning wire.
The effect of a small change in windchest pressure on the frequency of a reed pipe is also greater than it is at sea level. Furthermore, the operating point of the reed, that is, the zero point of its oscillation, moves closer to the shallot as windchest pressure is increased. This may sharpen the onset of each cycle of the oscillation, increasing high frequency content, and, if close enough to the shallot, cause the flow under the reed to become turbulent. Both effects can alter the sound quality of the reed pipe.
To summarize this discussion, for both reed and flue pipes the sensitivity to small changes in windchest pressure is greater at altitude than at sea level, as the Fisk personnel discovered. The solution to this problem for Opus 133 was to gain a better understanding of the Santa Fe FPC sanctuary HVAC system and take appropriate steps to minimize the windchest pressure difference between the two operating modes. Figure 1 is a schematic of the system. The two modes of operation are as follows:
• Recycle mode: Air flows from the blower room to the sanctuary and is returned through the bellows room to the blower room. Valve R is open and Valve FA is closed down to 15%.
• Outside air mode: Outside air is brought in to the blower room and distributed to the sanctuary, and exits through the roof when the sanctuary pressure rises above that of the outside. The recycle valve is closed and the fresh air valve is 70% open.
Cost and environment are the two reasons for two modes of HVAC operation. During winter when outside air is well below the desired ambient temperature in the sanctuary, the air exchange is limited to the 15% required by code for healthy fresh air in the sanctuary (corresponding to the 15% setting of the fresh air valve). A larger percentage of fresh air would require more preheating, increasing gas costs. During summer when outside air is warmer than that desired for the sanctuary, a larger fresh air fraction would increase electric costs for cooling. On the other hand, during spring and fall, when some cooling is needed and outside air is marginally cooler than the desired sanctuary temperature, an increased recycle fraction saves cooling costs. Of course, environmental concerns track with increased gas and electric costs.
Organ pressure is supplied by the small blower in the bellows room and regulated by the bellows. It was found with a simple manometer (U-shaped tube with water) that the organ pressure during the recycle mode was 3 inches of water (that is, water in the manometer rose 3 inches), and in the outside air mode, the organ pressure was 3¼ inches (water column). The ¼-inch change significantly impacted tuning and sound quality. The reason for the ¼-inch change was that the recycle mode involved a great amount of air flow in the return ducts through the bellows room to the blower room, creating a pressure drop of ¼ inch in the return ducts. In this mode, then, the bellows regulating system had to supply 3¼ inches of pressure in order to yield the desired 3 inches of windchest pressure.
When the recycle valve closed to change to the fresh air mode of operation, the only flow in the return duct from the sanctuary to the bellows room was the much smaller flow used by the organ itself. Therefore, there was no loss in that section of duct, and the bellows room was essentially at the same pressure as the sanctuary. With the bellows regulation system still set at 3¼ inches, the windchest pressure became 3¼ inches.
During this time, the main HVAC blower was operating at 100% capacity (60 Hz) even though the blower system included a variable speed control. The following experiment was performed: the variable speed control was set to reduce the blower speed to 2/3 of full capacity (40 Hz), and the pressure differential between the sanctuary and the blower room was measured for both modes of operation—recycle with 15% air exchange and fresh air with 70% air exchange. The only change from the original HVAC settings is that the blower now operates at a lower speed. It was found that the pressure differential at 15% air exchange was 1⁄8 inch, and at 70% air exchange (recycle valve closed) was 1⁄16 inch. As expected, with the organ operating with the bellows regulating system set at 3¼ inches, the organ pressure was 33⁄8 inches at 15% air exchange (recycle mode) and 35⁄16 inches at 70% air exchange.
The bellows regulating system is now set at 31⁄16 inches, yielding an organ-to-sanctuary pressure of 3 or 31⁄16 inches in the two modes of operation—a difference of 1⁄16 inch, small enough that tuning is now not adversely affected. In addition, HVAC noise has been greatly reduced, and the air circulation in the sanctuary, while quite adequate, is less drafty for those sitting in the ends of pews near the walls, where the supply air vents are located.

Sanctuary acoustics
FPC Santa Fe underwent major renovation before Fisk Opus 133 was installed. This included considerable acoustic work in the sanctuary to prepare it for this fine instrument; much of the focus was on steps to increase the reverberation time. The chancel has diamond plaster side walls, which diverge slightly to help sound radiate into the sanctuary. The sanctuary has hardwood floors with minimal carpeting, hard plaster walls, and hardwood pews with reasonably reflective pew cushions. The ceiling was rebuilt with heavy plywood above latillas, and fine sand one foot deep was poured onto the plywood to help contain low frequencies from the organ. Although the reverberation time has not been measured, it is estimated to be about 1.5–2.2 seconds.
In addition to sound energy absorption each time a sound wave encounters a surface, sound energy can be lost through absorption in air. Absorption in air is a rather complex phenomenon involving molecular dynamics, and it varies with air density and relative humidity in a manner that is counterintuitive: thin, dry air attenuates sound more than thick, wet air. Furthermore, the attenuation varies with frequency. Table 1 provides values for attenuation at different frequencies for sea level and the Santa Fe altitude and for 10% and 50% relative humidity. Notice that absorption is greater at low humidity, high altitude, and higher frequency. At high altitude air is thinner and can hold less moisture; relative humidity of 12%–15% is not unusual on summer days in Santa Fe. To mitigate against the drying effects on organ components, a humidifying system is used to maintain relative humidity at around 40%; this also helps to reduce air absorption at higher frequencies.
In Table 1, the sound absorption is given in decibels per kilometer, which is just a little farther than sound travels during a reverberation time of 2.2 seconds. Figure 2 provides a plot of these attenuation data at sea level and in Santa Fe at 50% relative humidity.
Clearly, the attenuation is greater at high altitude and high frequency. However, to understand whether or not this will impact the sound of the organ in the sanctuary, the attenuation must be compared with reverberation decay, the decay in sound energy due to reflection off surfaces. This comparison showed that at 4 kHz, the air attenuation at sea level would be barely noticeable if at all, and would be completely negligible at lower frequencies. In Santa Fe a very astute listener might notice the lack of high frequency components after initial transients on a very dry day, but otherwise the sanctuary acoustics should be little affected by the high altitude.

Conclusion
The differences in organ acoustics and operation between sea level locations and Santa Fe are real and observable, but not severe. Judicious choices of windchest pressure for pre-voicing and voicing and better understanding of the HVAC system both have contributed to a very successful installation: Fisk Opus 133 is now performing regularly and brilliantly. It is hoped that these observations will serve others who choose to install a fine organ at similar altitudes.

Berghaus Pipe Organ Builders, Bellwood, Illinois
St. Jerome Catholic Parish, Oconomowoc, Wisconsin
Berghaus Pipe Organ Builders has built a new pipe organ for the people of St. Jerome Catholic Parish in Oconomowoc, Wisconsin. Opus 226 contains 53 ranks, 42 stops, and 3,019 pipes. The project was made possible by the generosity of the people of St. Jerome Catholic Parish, as well as other benefactors and contributors from the community.
Plans to relocate St. Jerome Parish began in the fall of 1997 as it became clear that the parish was expanding beyond the physical limitations of their historic downtown church. By August 1998, the parish had purchased 37 acres of land and begun planning for a parish-wide campaign. The school was constructed first, and was dedicated on September 11, 2004. A second parish-wide campaign began in January 2005, resulting in the dedication of the church on November 15, 2008. The new 1,000-seat nave nearly tripled the previous sanctuary’s capacity of 350, and provided the parish with a bright, modern worship space with a more favorable acoustical signature.
From the onset of the project, it was clear the existing 1918 Kimball organ would need to be incorporated into the new instrument to minimize new pipe costs. The two-manual, 15-rank organ, located in the center of the rear balcony, was entirely installed in a case against the rear wall. Despite additions in the early 1980s, the organ was of typical early twentieth-century liturgical design. The stoplist incorporated six stops at 8′ pitch, two stops at 4′, and a 16′ Bourdon in the Pedal. Added ranks included a 22⁄3′ Quinte, 2′ Octave, and Mixture IV in the Great. Original voicing and pressures were retained on the Kimball pipes at the time when the organ was augmented, which did little to bridge the gap between the old and new pipes. Thankfully, the new pipes were under-voiced, which would give Berghaus ample latitude in tonal finishing. Additionally, the bottom octave of the 4′ Flute d’Amour was abandoned, and the pipes were shifted down to create a 2′ Flute in the Swell.
In the new church, the organ was planned to occupy both ends of the nave. Great, Swell, and Pedal divisions would be entirely new, and located in the rear gallery. The Antiphonal division would be installed in one chamber, above and to the left side of the chancel. We chose not to divide the resources of the Kimball, but rather use them to create the new Antiphonal division. Furthermore, the Antiphonal chamber would be situated at the same height as the gallery organ to promote tuning stability.
Special consideration was taken in planning pipe scales for the gallery instrument, with the intent that the Antiphonal organ would not be a dark distraction to the new organ. Our present tonal philosophy reflects an eclectic approach, which is conducive to blending early twentieth-century voicing styles. We took our cues from the best elements of late nineteenth-century English organs, tempered somewhat by elements of romantic French and early romantic German organbuilding. All flue scales in the gallery are variable, changing throughout the compass for acoustic and practical reasons. The result is an instrument that, while separated by distance, successfully works as a whole tonal concept, which in turn is able to effectively provide the combinations necessary for liturgical music and beyond. Differing foundation and flute resources are available for cantorial accompaniment, projecting close to the lectern. The Antiphonal also contains the softest string sounds for tonal effects in anthems and voluntaries. When the full resources of the Antiphonal are coupled to the gallery organ, the Antiphonal “carries” the sound of the gallery organ forward down the nave, while at the same time seamlessly blending with the gallery without detracting from its timbre.

Great
The Great division consists of 15 stops, 16 ranks, and is divided between one large slider chest and one electro-pneumatic chest. The division is located directly above the Swell enclosure, and is based on the 8′ Principal, which is located primarily in the façade and constructed of 75% tin, with spotted metal in the treble. The 8′ Principal is scaled near Normalmensur plus two, which on 80mm wind pressure fills the nave with a warm yet gentle tone. It is voiced full in the bass, and has clarity in the treble to reinforce the melody line. The Principal chorus is complete through a four-rank mixture, and includes mutations that are meant to reinforce the plenum. Flues are primarily in spotted metal with the intent to add warmth to the overall tone, yet allow for brightness in finishing.
Additional 8′ stops (Flute Harmonique, Bourdon, Gemshorn, and Gemshorn Celeste t.c.) complete the standard fonds d’orgue, as well as add the unique flexibility of a third, unenclosed celeste. Tonal considerations were made to allow the scaling of this hybrid pair to be generous, yet with a low cut-up to provide clarity of tone. The 8′ Trumpet is designed with German shallots to provide a blending quality, which is meant to enhance the plenum. By contrast, the horizontal Trompette en Chamade, which is mounted on the front of the case, is scaled and voiced to blend with full organ registration, and can be used as a solo stop for processionals and fanfares. Both reeds are voiced on 100mm pressure.

Swell
The Swell division consists of 17 stops, 15 ranks, and is also divided between one large slider and one electro-pneumatic chest. The division is based on the 8′ Diapason of spotted metal, which provides foundation to a complete principal chorus through the Plein Jeu. The scale of the Swell Diapason is three steps smaller and completely different in tone than the Great Principal. The Swell contains a wide variety of stops, ranging from French-style strings to a liquid 8′ Rohrflöte, which is unified at 16′ and made of wood. Mutations are broadly scaled to provide for a rich Cornet decomposée. We elected to use English construction for the 8′ Trompette in the Swell in order to provide a contrast in tone to the Great Trumpet.

Antiphonal
Restoration of the Kimball pipework involved restoration of each pipe in one form or another. While minor repair and remedial voicing work was necessary, the general pipe-making was excellent. Few pipes had been physically altered in previous rebuild efforts, which allowed for maximum flexibility in finishing. We replaced the leather on the stoppers of all wood pipes, and in the spirit of the original Kimball, we provided twelve bass pipes to the Flute d’ Amour, and returned it to 4′ pitch. We also replaced the low twelve pipes of the Open Diapason, which replaced the badly damaged pipes of the original façade. All spotted metal pipes were dunked in a restorative solution, and fitted with new stainless steel sleeves. Finally, an 8′ Vox Humana was provided by Dr. Lee Erickson, friend to the project.
The 8′ Open Diapason of this division provides the organist with yet another Diapason tone. Made from a high-lead alloy, these pipes provide the tone one would expect from a Diapason of this vintage. The pipes are cut dead-length and scrolled. Undoubtedly they would have been originally over-length and slotted. Deep nicks in the languid and lower lip allow for open-toe voicing, which allows this stop to truly enhance the gallery instrument.

Pedal
Consisting of 19 stops, 8 ranks, the Pedal provides a solid foundation to this full instrument. Through calculated borrowing and tonal finishing, this division provides an ample variety of timbres and volumes. The 16′ Principal in the Pedal division (façade) is made from a combination of zinc and 70% tin pipes, and is finished with a silver-tone patina. The Pedal is further supported by an impressive unit 32′ Kontra Posaune, which is voiced full in order to provide an equal blend of harmonics and fundamental. We used tin-faced German shallots throughout the compass of this reed, which provides unique overtones required to enhance the pedal plenum, particularly when considering this stop will be used in part in cantus firmus.

Chests and wind system
Flue pipes of the Great, Swell and Antiphonal sit on Berghaus slider and pallet chests. Reeds and offset chests are electro-pneumatic action. The entire organ is supported by an interior steel structure, which provides stability while allowing unimpeded access to interior parts of the mechanism. Wind to the pipes is supplied by two blowers—one blower for the gallery organ, and one for the Antiphonal. Our wind system provides absolutely steady wind through a balance of schwimmers and reservoirs. Wooden wind conductors help eradicate turbulence and are effective in eliminating noise. Slider chest wind pressures are 80 and 75mm, while reeds and Pedal are on 100mm.
The gallery organ case and organ console are constructed of maple, and are designed to incorporate architectural elements found throughout the worship space. Keyboards are in bone and rosewood, with African Kewazinga Bubinga stop jambs and coupler rail.
The construction of the organ at St. Jerome Parish was achieved through the dedication and teamwork of the entire Berghaus organization, which extends its sincerest gratitude to the people of St. Jerome Parish for enabling us to contribute to the life of their parish:

President: Brian Berghaus
Director of sales and marketing: David McCleary
Tonal design: Jonathan Oblander, tonal designer; Kelly Monette, head tonal finisher
Reed specialist: Steven Hoover
Structural and visual design: Steven Protzman
Shop foreman: Jeff Hubbard
Office manager: Jean O’Brien
Service coordinator: Joseph Poland
Construction/assembly/installation: Stan Bujak, Chris Czopek, Steve Drexler, Jeff Hubbard, Trevor Kahlbaugh, Kurt Linstead, Kelly Monette, David Mueller, Jonathan Oblander, Joseph Poland, Daniel Roberts, Tim Roney, Paul Serresseque, Ron Skibbe, Jordan Smoots, Paul Szymkowski, Mark Ber, Randy Watkins.

In addition, Berghaus Pipe Organ Builders gratefully acknowledges the invaluable assistance of Scott R. Riedel & Associates, Ltd. in the project, as well as the expertise and leadership of Fr. John Yockey, pastor, and Tom Koester, past organist of St. Jerome Parish.
­—Kelly Monette & Jonathan Oblander
Berghaus Pipe Organ Builders

John Bishop is executive director of the Organ Clearing House.

Wind
I’m a nut for a good wind. We live by the ocean, and I never tire of the feeling of the wind coming off the water bringing fresh air and all the good tidal smells into the house. I love to open the sliding doors that face the water and a door at the other end of the house to create a wind tunnel. (It’s not always popular with other family members.)
Years ago I was active in a small inland sailing club on the shore of a lake in the center of a suburban town. The lake was less than two miles north-to-south, and less than one mile east-to-west, so you couldn’t go for very long without coming about (turning to take the wind on the other side of the boat).
Since ours was a single-class racing club, the size of the lake didn’t matter. Depending on the speed and direction of the wind, the race committee set a course using inflatable markers (yellow tetrahedrons) with anchors. The classic Olympic sailing course uses three marks labeled A, B, and C set in an equilateral triangle. A is directly upwind from the starting line, C is directly downwind, and B is to the left, so boats go clockwise around the upwind mark. The basic course is A-B-C-Finish, but you can add an extra lap or two, and we often modified it to read A-B-C-A-C-Finish. These patterns would expose all the sailors to all points of sail as they went around the course.
One drizzly afternoon I headed the race committee. The wind was northerly, so I set the upwind mark close to the northern shore. A few minutes after the start, I noticed that the entire fleet was heading in the wrong direction. These were pretty good sailors, and it would be unusual for the whole group to get the course wrong. They were following what looked like a yellow tetrahedron that was a little east of upwind—a fellow in a yellow slicker and a yellow kayak who was heading away from the mark! I flew the recall-signal flag and started the race again, but not until we had all had a good laugh.

Know your wind
To sail a small boat is to be intimate with the wind. You have telltale streamers on the sails so you can tell exactly where the “lift” is and you watch the surface of the water for the ruffles that indicate the presence of wind. When there’s an updraft on the shore, air rushes in off the water to fill the void—so hawks, ospreys, and eagles soaring can tell you something about the wind on the water. In fact, this is the cause of a “sea breeze.” When the sun heats up the land in the afternoon, air rises off the land and the cool air rushes in off the water to take its place. Where we live, you can have a quiet picnic in the boat around twelve-thirty and put your things away in time for the sea breeze to come in around two in the afternoon.
If you sail often in the same place, you get used to how the wind comes around a certain point, swirls in a cove, or rushes directly from the sea toward the land depending on the time of day. There was an old salt at that inland club who had figured out how to predict the local wind by observing which direction airplanes were traveling to and from Boston’s Logan Airport twenty miles away. During a race you’d notice him heading off alone to some corner of the lake only to pick up the strongest wind of the afternoon and shoot across to a mark ahead of the rest of the fleet. I never did figure out how that worked, but he sure won a lot of races.

§

The steadiness, reliability, and predictability of wind is a huge part of playing and building pipe organs. We compare “wobbly” with “rock-steady” wind, debating their relative musical merits. One camp hates it when the organ’s wind wiggles at all (ironically, those are often the same people who love lots of tremolos!), the other claims that if the wind is free to move a little with the flow of the music, there’s an extra dimension of life. I think both sides are right. I love good organs with either basic wind characteristic, but because they are so different it seems awkward to try to make real comparisons. The instrument with gentle wind that makes the music of Sweelinck sing does not do well with the air-burning symphonies of Vierne or Widor.
As a student at Oberlin in the 1970s, I spent a lot of time with the marvelous three-manual Flentrop organ in the school’s Warner Concert Hall. The organ was brand new at the time (dedicated on St. Cecelia’s Day of my freshman year) and is still an excellent study of all the characteristics that defined the Classic Revival of organbuilding. It has a large and complete Rückpositiv division (Rugwerk in Dutch) and a classic-style case with towers. There are independent sixteen-foot principals on manual and pedal, and the whole thing was originally winded from a single wedge-shaped bellows behind the organ. End a piece with a large registration and make the mistake of releasing the pedal note first, and the wind slaps you in the back, giving a great hiccup to the grand conclusion.
As students, we worked hard to learn to control the organ’s wind, marking in our scores those treacherous spots where the wind would try to derail you. There were no hawks there to warn about the updrafts. A little attention to the lift of your fingers or a gentle approach to the pedal keys would make all the difference, and I remember well and am often reminded that such a sensitive wind system can be very rewarding musically.

Totally turbulent
It’s interesting to note that while the older European-style organs are more likely to have unstable wind supplies, organs like that were originally hand-pumped and had more natural wind that anything we are used to today. The greatest single source of turbulence in pipe organ wind is the electric blower. Because the wind is hurried on its way by a circular fan, the air is necessarily spinning when it leaves the blower. If the organbuilder fails to pay attention to this, the organ’s sound may be altered by little tornados blowing into the feet of the pipes.
I learned this lesson for keeps while renovating a twelve-stop tracker organ in rural Maine ten years ago. Before I first saw the organ, the organist said that the sound of the Great was fuzzy and strange, but the Swell was fine. Sure enough, she was exactly right, and I was surprised by the stark contrast between the two keyboards. Every pipe of the Great wobbled like the call of a wild turkey.
This was the ubiquitous nineteenth-century American organ, with an attached keydesk and a large double-rise parallel reservoir taking up the entire floor plan. There were wedge-shaped feeder bellows under the main body of the reservoir and a well at each end to provide space for the attachment of the square wooden wind trunks. In the 1920s an electric blower was installed in the basement some thirty feet below the organ, and a metal windline was built to bring the air to the organ through a crude hole cut in the walnut case (Oof!). The easiest place to cut into the organ’s wind system was the outside face of the Great windtrunk—piece of cake. But the effect was that the Great was winded directly from the violently turbulent blower output, while the wind had to pass through the calming reservoir before it found its way to the Swell. Every wiggle and burble of the wind could be heard in the sound of the pipes. Relocating that blower windline sure made a difference to the sound.
That lesson was enhanced as I restored a wonderful organ by E. & G. G. Hook in Lexington, Massachusetts. Part of that project was to restore the feeder bellows and hand-pumping mechanism so the instrument could be blown by hand or by an electric blower. Of course, it’s seldom pumped by hand, but there is an easily discernible difference in the sound of the organ when you do.
The introduction of electric blowers to pipe organs must have been a great thrill for the organists of the day. Marcel Dupré wrote in his memoir about the installation of the first electric blower for the Cavaillé-Coll organ at St. Sulpice in Paris, where Charles-Marie Widor was organist between 1870 and 1933. I have no idea just when the first blower was installed, but it was certainly during Widor’s tenure, and it must have been a great liberation. I suppose that for the first forty years of his tenure, Widor had to arrange for pumpers. That organ has a hundred stops (real stops!), and pumping it through one of Widor’s great organ symphonies must have consumed the calories of dozens of buttery croissants.
Since electric blowers became part of the trade, organbuilders have worked hard to learn how to create stable air supplies. A static reservoir in a remote blower room is the first defense against turbulence. We sometimes attach a baffle-box to the output of a blower—a wooden box with interior partitions, channels, and insulation to interrupt the rotary action of the air and quiet the noise of the large-volume flow.
Another source of turbulence in organ wind is sharp turns in windlines. The eddy caused by an abrupt ninety-degree angle in a windline can be avoided by a more gradual turn or by the geometry of how one piece of duct is connected to another.
Air pressure drops over distance. Run a ten-inch (diameter) windline above the chancel ceiling from Great to Swell chambers and you’ll find that four inches of pressure going in one end becomes three-and-a-half inches at the other. Drop the diameter of the windline a couple times along its length (first to nine, then to eight inches for example) and the pressure doesn’t drop. As pressurized air and pressurized water behave in similar ways, you can see this principle demonstrated in many large public rooms in the layout of a fire-suppressing sprinkler system. The water pipes might be four inches in diameter at the beginning of a long run and step down several times, so the last sprinkler head has only a three-quarter inch pipe. It’s a direct inversion of the sliding doors in our house. When four big doors are open facing the wind and one small one is open at the other side of the house, all that ocean air gets funneled into racing down the corridor past the kitchen and out the back door. If you don’t prop the door open, it slams with a mighty bang.
We measure air pressure in “inches of water.” The basic gauge (called a manometer) is a U-shaped tube filled halfway with water. Water under the effect of gravity is the perfect leveling medium—when the U-shaped tube is half filled with water, the water level is exactly the same on both sides of the tube. Blow into one end, and the water on that side of tube goes down while the other side goes up. Measure the difference of the two water levels and you have “inches of water”—we use the symbol WP.
Many of the ratio-based measurements we use are two-dimensional. When we refer to miles-per-hour for example, all we need is a statement of distance and one of time. To measure pipe organ air we consider three dimensions. The output of an organ blower is measured in cubic-feet-per-minute at a given pressure—so we are relating volume to time to pressure. Let’s take a given volume of air. There’s a suitcase on the floor near my desk that’s about 24″ x 18″ x 12″. I make it to be three cubic feet. We can push that amount of air through a one-inch pipe at high pressure or through an eight-inch pipe at low pressure. The smaller the pipe and the higher the pressure, the faster the air travels. It doesn’t take much of an imagination or understanding of physics to realize that those two circumstances would produce air that behaves in two different ways.
A mentor gave me a beautiful way to understand the wind in a pipe organ—simply, that air is the fuel we burn to make organ sound. Put more air through an organ pipe, you get more sound. To get more air through an organ pipe, you can make the mouth (and therefore the windway) wider. A pipe mouth that’s two-ninths the circumference can’t pass as much air as one that’s two-sevenths. You can also increase the size of the toe hole and raise the pressure.
I’m not doing actual calculations here, but I bet it takes the same number of air molecules to run an entire ten-stop Hook & Hastings organ (ca. 3″ WP) for five minutes as it takes to play one note of the State Trumpet at the Cathedral of St. John the Divine in New York (ca. 50″ WP) for thirty seconds. Imagine trying to hand-pump that sucker. It was mentioned in passing that when that world-famous stop was being worked on in the organbuilder’s shop during the recent renovation of that magnificent organ, the neighboring motorcycle shop complained about the noise!
I’ve written a number of times in recent months about the project we’re working on in New York. Because it’s an organ with large pipe scales and relatively high wind pressures, we’re spending a lot of time thinking about proper sizes of windlines to feed various windchests. I use the term windsick to describe an organ or a portion of an organ that doesn’t get enough wind, as in, “to heal the windsick soul . . .”
This organ has a monster of a 16′ open wood Diapason that plays at both 16′ and 8′ pitches. The toe holes of the biggest pipes are four inches in diameter (about the size of a coffee can). If the rank is being played at two pitches and the organist plays two notes (say for big effect, lowest CCC and GGG), we have four of those huge toe holes gushing wind. If we might have as many as four of those big holes blowing at once, what size windline do we need going into that windchest? To allow for twice the flow of air do we need twice the diameter windline? Here’s pi in your eye. To double the airflow, we need twice the area of the circle, not the diameter. The area of a four-inch circle (πr2) is about 50.25 square inches. The area of a five-and-a-half inch circle is about 95 inches. The larger the circle, the bigger the difference. The area of a nine-inch circle is 254.5 square inches. Two nine-inch windlines equals 509 square inches. One twelve-inch circle is 452 square inches, almost twice the area of the nine-incher.
That Diapason plays on 5″ WP—a hurricane for each note.
You can use any liquid to make a manometer. We can buy neat rigs made of glass tubes joined at top and bottom by round fittings. A longer rubber tube is attached to a wooden pipe foot (such as from a Gedeckt). You take an organ pipe out of its hole, stick the foot of the gauge in the same hole, play the note, and measure the pressure. You can also buy a manometer with a round dial, which eliminates the possibility of spilling water into a windchest—heaven help us. Measuring to the nearest eighth-inch, or even to the nearest millimeter, is accurate enough for pipe organ wind pressure. But using a denser liquid allows for more accurate measurement.
A barometer is similar in function to a manometer, except that it measures atmospheres instead of air pressure. Because the difference between high- and low-pressure areas is so slight, mercury (the only metal and the only element that’s in liquid form in temperate conditions) is commonly used in barometers. The unit of measure is inches-of-mercury (inHg); 29.92 inHg is equal to one atmosphere. Right now, right here, the barometer reading is 29.76 inHg. According to my dictionary, the record high and low barometric readings range from 25.69 inHg to 32.31 inHg. I guess today we’re pretty close to normal.
Measuring and reading barometric pressure takes us back to my eagles and hawks. An updraft creates a low-pressure region, which is filled by air rushing in from areas of higher pressure. That’s how wind is made. Wind doesn’t blow, it’s just lots of air running from one place to another.
On July 4, 2002, Peter Richard Conte played Marcel Dupré’s Passion Symphony on the Grand Court Organ of Philadelphia’s Wanamaker (now Macy’s) Store as a special feature of that year’s convention of the American Guild of Organists. It was an evening performance, and the store’s display cases were moved aside to allow for concert seating. This was early in the great rebirth of that singular instrument, and organists and organbuilders were thrilled by its majesty. Dupré conceived this monumental work of music as an improvisation on the Wanamaker Organ in 1921. (You can purchase the live recording of Conte’s performance from Gothic Records at <http://www.gothic-catalog.com/The_Wanamaker_Legacy_Peter_Richard_Conte_…;.)
The last minutes of that piece comprise a barrage of vast chords, chords that only a monster pipe organ can possibly accomplish. When I hear an organ doing that, I picture thousands of valves of all sizes flying open and closed and the almost unimaginable torrent of air going through the instrument. I remember thinking (and later writing) that as Conte played the conclusion of the symphony, barometers all across New Jersey were falling. Must have been some eagles soaring above the store. 

by Neil Carson Criddle

Some topics in organ building, such as history, receive much
attention.  Other topics, such as turbulence in the organ wind, receive little. A major ingredient needed for turbulence ishigh speed motion with the most obvious culprit being the electric blower. Turbulence did not exist much in the days of hand-pumped bellows. It was not until electricity came along that it got a significant boost, along with wind pressure. Even so, an organ that plays with turbulence is far superior to one that sits silently due to lack of pumpers. The use of electricity has expanded since the first introduction of blowers. This has given rise to the possibility of turbulence being generated in other areas as well.

The desired air flow is nonturbulent, or laminar flow. This
happens when all the air moves smoothly in the desired direction. This is
depicted in Figure 1, which shows a wind trunk with all the air moving smoothly
in a straight path.

Turbulent flow is different. Not only does air move down the
trunk, but it also spins in large circles. The combination of these two
movements results in the air spinning in great spirals. Figure 2 is a drawing
of air spiraling down the wind trunk. Figure 3 shows the same wind trunk as
viewed from the end with the arrow depicting the circular motion.

A simple way to reduce turbulence is through the use of a
fluid collimator. (Fluid refers to any substance that flows, be it liquid or
gas.) It does this by breaking the large circular air flow into many smaller
circular flows which tend to cancel each other, thus resulting in a significant
reduction of turbulence. An easy way of making such a device is gluing pieces
of PVC pipe together and inserting it into the wind trunk. Figure 4 is an end
view of the same wind trunk showing this type of collimator and its effect on
turbulence. The large circular flows of Figure 3 cannot exist while inside the
collimator because that would require air passing through the tube walls from
one tube to another. What comes out of the collimator is many small circular
flows the same size as the tube. These smaller and numerous air flows tend to
mix and cancel each other. While there is no set rule for proportions, a pipe
length ten times greater than the diameter is reasonable. (If, for example, the
pipe diameter were 20 millimeters, the length would be 200 millimeters.)

While the collimator is very effective at reducing
turbulence, it does have a potential drawback. It is an obstacle to air flow
and thus can cause a pressure drop. The larger the pipe diameter, the less will
be the obstruction, but it will also be less effective at reducing turbulence.
Fortunately, while blowers can produce turbulence, they can also produce an
abundance of pressure. The negative side effect of obstruction is easily
overcome by simply using a higher pressure blower, if needed.

The pressure dropping effect of the collimator dictates that
it be placed upwind from the pressure sensing device, be it a pressure
regulator plate or reservoir top. It should be in the stream of unregulated
air. If placed between the regulated reservoir and the organ, there would be a
pressure drop in the organ wind. Worst of all, the pressure drop would vary
with the volume of air used. The air should also flow evenly through the entire
collimator. Beware of placing it directly in front of the blower outlet where
the air will be forced through only a small section of the collimator. If space
is a problem, it can be incorporated into the curtain valve assembly. It would
be mounted in the curtain valve plate such that the pipe ends are flush with
the plate surface. The curtain would roll up and down on the pipe ends which
support the curtain against blower pressure. However, because the air flows
only through that part exposed by the curtain, the full collimator is not taken
advantage of.

Another way to reduce turbulence is through nature. If given
time, turbulence will naturally dissipate. This can be accomplished through the
use of plenums. Plenums are simply large chambers. The reservoir is a good
example. Turbulent air enters the reservoir, mixes with other air, and has time
to dissipate. The larger the plenum, the greater this effect.

While turbulence may be produced by electric blowers, it may
also be produced by other electric devices. Electric chest action (where each
pipe has its own magnet-powered valve) has a reputation for sometimes having speech
defects during the attack. One explanation proposed for this is that the valve
opens too fast, causing the air pressure to rise too quickly. An expansion
chamber, it has been explained, between the valve and pipe, will cushion this
abrupt change in air pressure resulting in it changing more slowly, and thus
correct the problem. The problem and its correction can also be explained in
terms of turbulence. The magnet may be moving the pallet so quickly that a
region of turbulent air is created immediately above the pallet. If the pipe's
small toe hole is also immediately above the pallet, there is only turbulent
air available to enter the pipe. Instead of entering the toe hole smoothly like
stagnant air, the swirling currents of turbulent air enter the toe hole in fits
and jerks. Figure 5 shows this relationship of close proximity.

The first step in addressing this problem is to generate
less turbulence by using a slower-moving valve. This means using no more
powerful magnet than necessary. The greater the magnet's power, the faster the
pallet moves and the greater the turbulence.

The pallet can also be slowed by increasing the mass of the
armature. If weights are added to the armature, it is more massive and thus
more sluggish when it moves. Just as an automobile is more sluggish when
weighted down, so is the valve armature more sluggish when it is weighted down.
Spring tension at the other end of the armature must be adjusted so it remains
balanced. Even if there is no speech defect, the slower opening pallet eases
the pipe into speech and makes a noticeable difference in the attack. This
gentler attack is very important.

There are ways of dealing with electric chest action
turbulence after it has been created. One way is to use open toe voicing. (See
Figure 6) The larger the toe hole, the more easily turbulent air can get
through. Once through, it dissipates in the pipe foot due to the foot acting as
a plenum.

A final way to reduce electric chest action turbulence is
through the use of a plenum between the valve and pipe. The plenum provides a
space for valve turbulence to dissipate naturally just as the organ reservoir
provides a space for blower turbulence to dissipate naturally. Figure 7
provides an illustration of this.

A simple example of these corrective measures can be seen in
the cross sectional view of Figure 8. Here a plenum of large size has been
added between the valve and toeboard. In addition, weights have been attached
to the end of the armature. This increases the mass of the armature making it
more sluggish and thus slower to open. The magnet has been selected to be no
stronger than needed.

It is interesting that the oldest of organ designs, slider
chests with mechanical action, incorporates these principles. Human fingers are
very slow compared to magnets and thus insure a slow opening of the pallet. The
chest channel acts as a plenum to dissipate turbulence. Also, the modern
electric pull-down magnets in slider chests are examples of the magnets'
armatures being slowed down by the addition of mass to them. Instead of weights
glued to the armature, the large pallet acts as the mass needed to slow the
magnet.

Electric chest action has received a bad reputation. The
problem may not lie with the action but with how it is used. Electric action
provides an easy way to build a chest. Some people are attracted to it because
they do not want to put much work into building a chest. This same attitude
will carry over into other aspects of organ building such as not wanting to put
much work into voicing, planning, or any of the other innumerable areas.
Incorporating improvements such as plenums and weighting of the armature
tremendously increases the work load. Gone is the attraction of being easy.
However, in organ building it seems the one characteristic common to good
results is a lot of work. A good organ builder will come up with a good organ
regardless of what action he is given to use. The secret of success is in the
builder, not the action.

The principles of turbulence can be seen throughout the organ
from the old (slider chest with mechanical action) to the new (electric chest
action); from the microscopic (individual pipe valves) to the macroscopic
(organ blower and reservoir). The principles are everywhere, but that should
not be surprising. After all, it is all about wind.

Neil C. Criddle received his B.S. in electrical engineering
from the University of Illinois (Urbana) and the M.S. in electrical engineering
from Purdue University. While majoring in engineering he minored in music,
studying piano in college and then privately for several years, and is now
studying trumpet. He maintains an interest in the technical aspects of musical
instruments, especially the harpsichord. Criddle has built an organ in his
home, and has had articles published in the journal of the International
Society of Organbuilders (ISO).