Organbuilders and research: A clarification

John M. Nolte has been in organ building for more than 40 years. In 1986 he founded his own company, which has grown to a staff of five, including his sons Benjamin and Jeremy. The firm has an international reputation for quality wood pipes. They have supplied voiced and unvoiced pipes to many of the best American organbuilders, and recently completed a commission for all of the wood pipes in the new Nicholson organ at Llandaff Cathedral. Nolte has been active in the American Institute of Organbuilders for the past ten years, and has shared technical information with that organization with a Journal of American Organbuilding article, convention lecture, and mid-year seminar on various aspects of wood pipe scaling, production, and voicing. The firm is currently focusing on a highly refined mechanical action.

The January 2010 issue of The Diapason featured an article by Judit Angster and Francesco Ruffatti on organbuilders and research.1 This kind of work is very necessary and useful, and it can generate profitable discussion that leads to a better and broader understanding of the pipe organ. The research reported in January is far from complete, but it is a very good discussion starter. Several things in the article struck a chord with me, and I will elaborate on two of them. In this article I will discuss the open-toe versus closed-toe question on the basis of a little technical background that goes back to Daniel Bernoulli, an 18th-century Swiss scientist. This will be followed by a reprint of my article, “Scaling Pipes in Wood,” originally published in the Journal of American Organbuilding in March 2001.
The question of open-toe versus closed-toe requires an understanding of what organ wind pressure is with respect to voicing. There is a big difference between windchest pressure and voicing pressure. Windchest pressure is the pressure present at the toe of the pipe when the valve is opened. Voicing pressure is the pressure at the languid. In every case, voicing pressure is lower than windchest pressure. When we say an organ is on 5 inches wind pressure, measured in the chest, all we know about voicing pressure is that it is less than 5 inches—it could be 2 inches or less. What happens in the foot of the pipe is the key.
In the research article, one measurement that was taken was the wind pressure in the foot of the pipe. The author states, “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%.”2 I was surprised that a group of voicers and physicists was surprised. This is exactly what one should expect. Let’s look at what happens in the foot of the pipe. See Figure 1.
When the organist plays the note, air enters the foot of the pipe through the toe, and it exits the foot of the pipe through the flue. If the pipe is well made, and the toe is seated properly in the chest, all of the air that enters the toe leaves through the flue. When the chest pressure is higher, the air coming out of the pipe hole travels faster. When the pressure is lower, the air travels slower. The size of the hole does not affect the speed of the air—it just controls the volume of air that comes out of the chest. If the flue is completely closed so the air has nowhere to go, when the valve is open the pressure in the foot will rise until it is equal to the pressure in the chest. If we open the flue, air will escape from the foot, and the toe hole will replace it as fast as it can. In every case the pressure in the foot will be lower than the pressure in the chest. Because the volume of air leaving the pipe at the flue is the same as the volume of air entering at the toe, we can use variations of Bernoulli’s equation to predict what the difference in chest pressure and foot pressure will be. The rule is that the pressure drops at the toe and the flue vary inversely with the squares of their areas. Here is the formula:

(Atoe)2 = ΔPflue
(Aflue)2 ΔPtoe

where A is the area of the toe or flue, and ΔP is the pressure drop at the toe or flue.
Let’s illustrate this with a chart. If the original chest pressure is 100mm, then the area of the toe compared to the area of the flue will give these results for the pressure in the foot:

Atoe Aflue Foot Pressure
1 2 20mm
1 1 50mm
2 1 80mm
9.95 1 99mm

Notice that when the area of the toe opening and the area of the flue are the same, half of the chest pressure is lost in the toe, and half is lost when the air exits the flue to the atmosphere. When the toe opening is smaller than the flue, the pressure in the foot is even less than half of chest pressure. We have seen examples of pipes voiced on 10″ wind pressure that were actually speaking on 2″ wind pressure. For flue pipes, wind pressures of 8–10″ are found at the languid of fairground organs designed to be played outdoors and heard up to a quarter mile away. Rarely do indoor pipes receive pressures over 4″ at the languid. When the toe is larger than the flue, more than half of the chest pressure is present in the foot of the pipe. When the ratio is about 10:1, the toe is fully open and 99% of chest pressure is present in the toe.
For many years the American Institute of Organbuilders has recommended that in good flue voicing we aim for a toe that is twice the area of the flue. Notice from the chart that this yields 80% of chest pressure in the toe. This allows the voicer a little latitude to make the pipe louder or quieter by regulating the toe more or less open.
Why the emphasis on the pressure in the foot? Air passes through the flue to the upper lip where an oscillation develops that creates the standing wave in the body of the pipe. What matters for pipe speech is the velocity of the air at the flue, and that velocity is determined by the pressure in the foot of the pipe just below the languid. The blower pressure, the pressure in the chest, and the pressure at the bottom of the ocean are all irrelevant.
With this technical information in mind, I really must question the experiments that were supposed to determine whether or not there is a difference between closed-toe and open-toe voicing. The experiments referred to in the article state that windchest pressure was constant, and that pressure in the foot was twice as much for the open-toe compared to the closed-toe. Then both pipes were voiced to match loudness. This proves nothing about the difference between open-toe and closed-toe voicing.
If I voice a pipe with an open toe on 70mm wind pressure, and then voice a pipe with an open toe on 35mm wind pressure, and I make the two pipes equally loud, will there be a difference in tonality? Of course there will be. The pipe voiced on the higher pressure will drive the upper harmonics more in relation to the fundamental, and the tone will be brighter. That is exactly what the chart in Figure 5 in the article illustrates. The only difference is that the researchers achieved a pressure in the foot of about 35mm by closing the toe, instead of opening the toe and setting windchest pressure at 35mm.
If I want to compare open-toe voicing to closed-toe voicing, the pressure in the foot must be the same, not the pressure in the windchest. If we use the toe-to-flue ratio of 2:1, that means that to achieve the same tonality between the two voicing methods, the chest pressure for the closed toe must be 25% higher. If I voice an open-toe pipe on 80mm windchest pressure, I must voice the comparable closed-toe pipe on 100mm windchest pressure. The cut-up, the size of the flue, and the treatment of the languid should be the same.
When organs started to use tubular pneumatic and electro-pneumatic actions, these early actions required windchest pressures of 4″ to 6″ to operate properly. When these new chests were used to rebuild older organs that were voiced on lower pressures with open or nearly open toes, the old pipes had to be revoiced to the higher windchest pressures. Frequently, all the voicers did with the old pipes was to close the toes until the pressure in the foot was lowered to where it had been originally. This method is fast, and if the pipes were going back into the same room, the original voicing and regulation was already correct.
In the last few years we happened upon a large supply of treble pipes that were well made and voiced with open toes on low pressure, around 65mm (21⁄2″). We have used them to replace inferior trebles in a number of sets of pipes on several different, but higher, pressures. Closing the toes was all that was necessary, unless the pipes needed to be made significantly louder.
To do a meaningful comparison between open-toe voicing and closed-toe voicing, several identical pipes should be voiced to match as perfectly as possible with open toes. Then raise the windchest pressure for one of them and see if closing the toes will bring back the match. It will.
The researchers also noted another difference:

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 wind noise, and this in turn will determine significant modifications to the structure of their sound.3

There are several distinct ways wind noise can be generated in a pipe with closed toes, and the treatment must address the problem. Nicking is seldom the only solution, and rarely is it the best solution for eliminating wind noise.
At the toe, if chest pressure is quite high, the velocity of the air through the toe can create turbulence and, consequently, noise. Turbulence is exacerbated when friction in the toe opening slows down the air at the boundary of the hole, while the air towards the middle of the hole is unimpeded. The solution is to carefully countersink the toe hole so that the smallest part of the hole comes to a point in the cross-section. See the photos for examples of a noisy and a quiet toe. The closed toe pictured in the research article has not been properly treated to keep it as quiet as possible.
At the flue, noise is generated when the flue is overly large. This happens for different reasons. When the chest pressure or foot pressure is too low, the flue must be opened more to get enough volume of air to produce a loud enough sound. This can happen with either open or closed toes. When the pressure in the foot is too high, opening the flue will lower the foot pressure, but it also creates a wider air stream than necessary to create the musical note, so some of the air generates noise, not tone. Large flues are also sometimes used to compensate for upper lips that are too thick. Once again, excessive amounts of air traveling through the flue create unwanted and unnecessary noise. A thinner lip and smaller flue will eliminate the problem.
When the area of the toe is relatively small compared to the flue, the velocity of the air entering the toe is substantially higher than the velocity of the air exiting the flue. As the air in the foot slows down, the degree to which it has to slow down will create turbulent conditions in the foot of the pipe, which generate noise both in the foot and at the flue. Some voicers use steel wool or other devices in the foot itself to overcome this.
Nicking can be used to control wind noise in all of these circumstances, and if the tonal quality resulting from the nicking is what one wants, so be it. If, instead, we want a tone more like what is achieved without nicking in open-toe voicing, attention to detail can achieve this quite easily.
The 2:1 relationship of toe area to flue area, along with the correct windchest pressure, will overcome these problems. A ratio of 1:1 can be used with good results if the voicer is very attentive to detail. When the toe becomes smaller than the flue, trouble is not far behind. The use of partially closed toes to regulate pipe speech can provide results equal in virtually every respect to what can be achieved with open toes. In order to accomplish this, it is necessary for the windchest pressure to be higher than it would be for open-toe voicing so that the pressure in the pipe foot is ideal. Raising the chest pressure too high can cause wind noise problems, but these can be controlled by keeping the windchest pressures from being excessive. So much for my contribution to this part of the discussion.
The researchers also mentioned investigations into transitions between stopped and open pipes, or between wood and metal pipes within the same rank. My research on wood pipes will be presented in the reprint of my March 2001 article, “Scaling Pipes in Wood.” The research for this article was based on years of making reproductions of wood pipes for antique orchestrions, and a study of historic wood pipe scaling, notably the Compenius organ of 1610. On the practical side, this led to a commission for an all-wood practice organ, which also had strict action requirements. This organ will be featured in a future article.

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.

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. 

Fratelli Ruffatti, Padua, Italy
Wesley Chapel, Elkton, Maryland

From the builder
Fratelli Ruffatti is mostly known in the United States for building large four- and five-manual instruments with electric action. Two five-manual organs have been completed in the past 15 months, and two four-manual organs are currently being manufactured in the Ruffatti workshop. Few people, however, know that the majority of instruments that the firm produces outside of the United States are of mechanical action.
In tune with the trends and ideas that were coming from across the Alps at the beginning of the 1960s, Ruffatti was among the first in Italy to restore the tradition of building pipe organs with suspended mechanical action. One of the most famous of these instruments is in northern Italy, installed in 1970 in the parish church of the small medieval city of Noale. It is not a huge instrument, numbering 27 stops and 35 ranks of pipes over two manuals, but it became quickly famous from the beginning as the concert instrument for the first Italian competition of young organists. It is still today the centerpiece of a quite famous concert series, involving big names among international organists.
Ruffatti is here presenting to the American organ community an instrument that is quite small, but of large significance. Everyone knows that ancient Italian organs were, for the most part, of small size—one manual, with a limited number of stops—but quite musical and versatile. Since our predecessors could not depend upon a large number of voices to produce variety, they refined their voicing techniques to the point that every sound could be combined with every other to produce the most versatility even within a very limited number of stops. This is the tradition that Italian organbuilders come from and that constitutes the inspiration for Fratelli Ruffatti even today, whether it may be applied to very large or, even more importantly, to small instruments.
The organ manufactured for Wesley Chapel of Elk Neck is a good example of how a very small instrument can be pleasing and effective in spite of its very limited size. With only one manual and a total of six stops, including the Pedal, it is difficult to imagine any kind of versatility at all. However, a few special ingredients grant this instrument a real flexibility: the divided stops, the composition of the Mixture and, above all, the voicing techniques.
Splitting the stops in bass and treble is an old practice in ancient organs, as we all know, and it allows the organist to create two different tonal “platforms” within the same manual. In this case, both the Principal and the Spitzflöte are divided between C and C# in the middle of the keyboard, thus increasing the number of possible combinations. The Mixture, whose composition is shown below, has been designed in such a way that no “double pitches” occur when combined with the 2′ Fifteenth. The Fifteenth and Mixture are conceived as an effective three-rank Mixture when pulled together, but at the same time the Mixture can also be independently used in a “mezzo ripieno” combination without the Fifteenth, creating a very interesting tonal color.
Although English names have been chosen for the stops, as a sign of respect for the users, a number of tonal features are present that link this instrument in many different ways to the classical Italian tradition.
The Principal pipes, both internal and in the façade, are without “ears,” as in the classical Principale. The low octave of the stop is made of stopped mahogany pipes, housed against the ceiling inside the case. They are connected to the windchest through a complicated series of metal windways. A stopped wooden low octave for the Principale is a common feature of the Positivo Italian organs of the 17th and 18th centuries, and effective ways have been refined over the centuries—through proper scaling and voicing—to make the bridge between wood and metal remarkably smooth.
The Octave is of slightly smaller scale, or relative diameter, than the Principal, as found in many historical organs of northern Italy, as are the Fifteenth and the subsequent Mixture ranks.
The 4′ Spitzflöte is an almost identical replica of the Flauto in Ottava, a stop of rare singing quality used by Gaetano Callido1 in his instruments.
With the primary purpose of providing a good foundation, especially considering the rather dry acoustical environment of Wesley Chapel, an independent, real 16′ Bourdon has been provided for the Pedal, with pipes made of African mahogany, which are located behind the organ case.
The voicing technique is probably the element of highest significance. At the lowest wind pressure allowed by the acoustical conditions of the room (65 mm at the water column, or slightly over 21⁄2 inches), all pipes have been voiced with completely open toe and a minimum number of barely visible nicks at the languids. The result is a very pleasing, singing tone without excessive chiff or unnecessary non-harmonic overtones. This constitutes the foundation for a successful blending of the stops as well as for the creation of successful, pleasing solo voices. The pitch is 440 Hz at 20° Celsius and the temperament is equal.
Architecturally, the organ case has been designed to fit in the historical surroundings of Wesley Chapel. Although inspired both mechanically and aesthetically by the ancient Positivo organs, it must not be defined as a copy: its design is definitely a new, original creation. It features a façade composed of 22 pipes divided in two symmetrical sections. Each is topped by a hand-carved panel designed to add beauty to the ensemble while at the same time allowing for maximum sound egress. Two hand-carved wooden elements at the sides provide the necessary continuity between the top and the lower part of the case.
The casework is made completely from solid African mahogany. The keyboard features bone naturals with carved key fronts, and natural ebony sharps with bone inlays. The key cheeks are inlaid with thin strips of bone. The draw knobs are of ebony, with maple insets. The concave and parallel pedalboard (BDO measurements) is made of oak, with the sharps topped by ebony.
The mechanical action is suspended. The rollerboards are made from solid aluminum rollers with wooden arms.
The task of designing and manufacturing an instrument within such a small space has not been an easy one. In spite of this, every part is easily accessible for maintenance and ordinary tuning. The layout of pipes over the slider windchest in particular has been carefully designed to allow favorable conditions for the radiation of sound from all pipes.
—Francesco Ruffatti

Notes
1. Gaetano Callido was the most famous Venetian organbuilder of the 18th century. A pupil of Pietro Nacchini, he built over 430 organs in his lifetime, many of which are still preserved.
2. The basic principle of the open toe voicing technique is that of leaving the pipe toe completely open and regulating the sound volume by reducing the opening at the flue, or lower lip of the mouth. By operating this way several advantages are achieved, among which are a less turbulent air supply through the pipe foot and a more focused wind column at the mouth. These features are effective in reducing the “mouth noise” or “air noise” and, consequently, in reducing the need for languid nicking, a practice that can alter the natural timbre and that tends to reduce the development of upper partials in the sound spectrum.

From the organist
Several years back Glenn Arrants inquired: if he purchased an organ, would I play it?—and fortunately I said yes. He then informed me this would be no ordinary organ, but a pipe organ to be built in Italy. Through the months ahead, Glenn kept me informed of the progress.
The anticipation increased over the two and a half-year wait for the organ to be built. Finally we received word it would be delivered to the chapel on July 3, 2007. I was so excited about the opportunity to see this process firsthand, that I took off from work to be there to take photos and witness the arrival.
Spread throughout the chapel were all of the pieces that would be assembled into a pipe organ—in two weeks! I thought I understood the complexity of the pipe organ until I witnessed this firsthand. Imagine my excitement to hear that I would be playing the organ the first time that Sunday morning, although the pedals were not completed—the sound filling the sanctuary that morning was just a sweet taste of what was to come the following week when the instrument was complete.
There was concern that a pipe organ would overpower the small sanctuary and the congregation, but this is not the case. The sanctuary is filled with wonderful music, and the congregation’s voices are supported beautifully. Even with full organ, there is no vibration anywhere in the 177-year old chapel.
To be the first organist of the Wesley Chapel Fratelli Ruffatti pipe organ is indeed an honor, and a once in a lifetime opportunity. One cannot help but think of the dedicated craftsmen who built the organ, all the attention to detail, and the beautiful voices of the pipes. It gives me great joy to be able to sit down and play this organ, so much so that what seem like minutes in time are actually hours of enjoyment—this fine instrument will serve the congregation and community of Elk Neck for generations to come.
—Alice Moore

From the dedication recitalist
It was a great pleasure to prepare a program for the dedication of the new Ruffatti organ for Wesley Chapel of Elk Neck. It turned out to be much less of challenge to prepare for a “small organ” than one might have suspected. The organ is well capable of playing standard literature, Bach and Telemann, and there is, in fact, wonderful variety to be had in various combinations of the voices. Most surprising was the excellent way the organ could be adapted to the modern works of Michael Burkhardt and Donald Johns in hymn-based partitas. Equally important, the gentle and very artistic voicing of this instrument allows it to lead congregational song with all the color and emotion one could ask for in an instrument of larger design. The divided stops are an ideal way to get “more organ” than the package seems to contain. Bravo Fratelli Ruffatti and congratulations to Wesley Chapel of Elk Neck.
–Donald McFarland

A brief history of Wesley Chapel of Elk Neck, Elkton, Maryland
Elkton, Maryland, a city of some 13,000 people, sits on Chesapeake Bay near the Delaware border. It dates from the 1700s and was a strategic crossroads during the Revolutionary War. Washington and Lafayette passed through it frequently, and it is very near the spot where the British landed for their march on Philadelphia. The Wesley Methodist Society formed its congregation there in 1797 and, in 1830, the parcel of land was bought “for and in consideration of the sum five dollars current money of Maryland,” and the Reverend William Ryder laid the cornerstone of a new building in which to hold the society’s services. Handhewn beams formed the 25′ x 30′ single-room chapel on a fieldstone foundation. The little building has several features that make it a particularly important structure architecturally, including a perfect half-circle arched ceiling, and varying-width clapboards that hide its vertical plank construction. Wesley Chapel seats about 50, and is one of the oldest rural chapels still in use in the area.
Glenn Arrants remembers how his mother served as church organist for almost 50 years. She played on an early 20th-century Möller organ, which took up considerable space in the tiny building. In the mid-1990s, the chapel went through a complete restoration and the Möller, which was then beyond repair, was replaced with a restored Estey reed organ. Church members missed the sound of a pipe organ, however, and, in 2005, set in motion plans to acquire an instrument specially built for the chapel. Because of the design work, the quality of construction, and the reputation of the company, Wesley Chapel chose Fratelli Ruffatti, distinguished pipe organ builders of Padua, Italy, to build its new instrument.

MANUAL—unenclosed, 56 notes (C–G)
8′ Principal Bass 25 pipes mahogany + 95% façade + 70% interior
8′ Principal Treble 31 pipes 95% façade + 70% interior
4′ Octave 56 pipes 70%
4′ Spitzflöte Bass 17 pipes 30% 1–8 common bass with Octave
4′ Spitzflöte Treble 31 pipes 30%
2′ Fifteenth 56 pipes 70%
II Mixture 11⁄3′–1′ 112 pipes 70%

PEDAL—unenclosed, 27 notes (C–D)
16′ Bourdon 27 pipes mahogany

7 ranks, 355 pipes
% = percentage of tin in tin-lead alloy

Composition of the Mixture II by itself
1–36 11⁄3′ 1′
37–48 22⁄3′ 11⁄3′
49–56 4′ 22⁄3′

Composition of the Mixture II together with the Fifteenth 2′
1–36 2′ 11⁄3′ 1’
37–48 22⁄3′ 2′ 11⁄3′
49–56 4′ 22⁄3′ 2′

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).