Organ Wind Turbulence

John Bishop

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. 

John M. Nolte

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.

 

Francesco Ruffatti and Judit Angster

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

Abstract 

Whether mechanical organ actions allow organists to control the way in which they move the key and thus influence the transients has been discussed for many decades, and this is often given as their main advantage. However, some physical characteristics of mechanical actions, notably pluck, make it difficult for the player to control the key movement and thus vary the transient. This project looks primarily at how organists use rhythm and timing to play expressively, but also provides some evidence about whether transient variation is significant. Rhythmic variation can be through the use of deliberate “figures”, or the player may be unaware that they are making such variations. These variations in style lead to clear groupings of the pressure rise profile under the pipe and thus limit the amount of transient control possible. This is supported by informal listening tests. It also considers other factors that might lead to transient variation that are outside the player’s direct control.

Introduction 

This paper presents results from a project funded by the UK Arts and Humanities Research Council at the University of Edinburgh and is based on papers presented at ISMA 2010 (International Symposium on Musical Acoustics) in Australia¹ and Acoustics 2012 in Nantes.²  The organ has been described as a “dangerously inexpressive” musical instrument.³ The project set out to investigate the extent to which organists use rhythm and timing to achieve expression on mechanical action pipe organs rather than varying the transient by the way in which they move the key, although it inevitably also considered the latter. Transient control is widely considered a basic factor of organ playing but this is not universal, and a number of prominent organists and builders, such as Robert Noehren,⁴ disagree. However, there is little published research about this or whether other mechanisms may be important for expressive organ playing. 

This project originally started because  of the construction of a number of large organs in the UK that have dual mechanical and electric actions. The curators of these organs reported that the mechanical consoles were hardly ever used, suggesting that any advantage was not overwhelming. It also implied that there may be significant unnecessary expenditure and also the possibility that either or both of the actions were compromised. 

The PhD work that preceded this project concluded that players did not vary the way in which they moved the key to the extent that they thought they did.⁵

Background 

The bar (groove) and slider windchest has existed more or less unchanged for some 600 years even down to the materials generally used. 

The one characteristic that defines the nature of the touch of a mechanical pipe organ action is pluck (being analogous with the feel of the plectrum plucking the string of a harpsichord. It is also called “top resistance”). Pluck is caused by the pressure difference across the closed pallet (H) in Figure 1, which is a modification of an illustration by Audsley of a cross section of a bar and slider windchest.⁶ The bar is the channel on which all the pipes for one note are planted. The sliders (S) are movable strips, traditionally of wood, that determine which ranks of pipes receive air from the groove, by lining up holes in the slider with corresponding holes on the top of the groove. They move perpendicularly to the plane of the diagram. With the pallet closed, the pallet box (ABDH) contains pressurized air whereas the groove contains air at atmospheric pressure. The net force of the pressurized air on the bottom of the pallet has to be overcome in order for the pallet to start opening. As soon as the pallet starts opening as the tracker (attached to N) moves downwards, the pressures on either side of the pallet start to equalize and the additional force reduces very quickly (Figure 3). The feeling has been likened to pushing a finger through a thin layer of ice. 

When a note is not sounding, the pallet is kept closed by the force exerted by the pallet spring (G) and the air pressure  against its lower surface. As a force is applied to the key, the various action components bend (key levers, backfalls), twist (rollers), stretch (trackers) and compress (cloth bushes), etc., until sufficient energy is stored to overcome the force keeping the pallet shut. Figure 2 shows a 200g key weight on a key of the model organ in Edinburgh just before the pluck point, with the pallet still closed. The key is depressed by about 40% of its total travel. Any further movement will result in the pallet immediately opening by a similar amount before the key has moved significantly further—the pallet “catches up” with the rest of the action. 

The need to keep the playing force and repetition rate within acceptable limits means that the action can never be made completely rigid, and it will always act like a spring to some extent. The basic characteristics of the movement of a key through to the sounding of the pipe are illustrated graphically in Figure 3. 

The low frequency variation in the pressure at the beginning of the note is due to the delay of the pressure regulator, described more fully later, and the high-frequency component throughout is due to the pipe feeding back into the groove. The most important features of Figure 3 are: 

• The key moves a significant distance before the pallet starts to open and catches up with the rest of the action ~ 40% 

• The key slows down due to the increasing resistance as the action flexes (rollers twisting, washers compressing, levers bending, etc.) 

• As the resistance due to pluck is overcome, the key increases in speed of movement, as it is not possible to reduce the force being applied by the finger in the time available 

• The air pressure in the groove starts to rise at the same time as the pallet starts to open 

• The force applied to the key increases until just after the pluck point, when it reduces, although not suddenly. This is probably due to the airflow through the pallet opening applying a closing force to the pallet 

• The force increases suddenly as the key hits the key bed 

• The air pressure reaches a peak early  in the pallet movement (after about 45% pallet travel) 

• The pallet starts to open at about 40% of key travel and the pressure in the groove reaches a maximum at about 57% key travel. This is the only part of the key movement that could affect the transient, but during this movement the  pallet is out of control of the key because  it is still catching up with it 

• There is a delay before the pipe starts to speak 

• The key is on the key bed and the pallet is fully open before the pipe has reached stable speech 

• There is a delay before the pallet starts to close when the key is released (probably due to friction) 

• Later in the release movement the pallet starts to close in advance of the key movement (due to air pressure) 

• The pallet is firmly seated before the key has returned to its rest position (in this case the key has 23% travel to go) 

• The sound envelope does not start to diminish until the point at which the pallet closes 

• During the key release, the force is gradually reduced but the key does not start returning until the force due to the  pallet spring is greater than the force applied by the finger 

• There is slight increase in force as the pallet “snaps” shut due to the flow of air through the opening. This helps to reduce leaks around the closed pallet, but would also make it very difficult to control the pallet in the final stage
of travel. 

The time of travel of the pallet from starting to open to fully open is typically  around 30ms (0.03 seconds). Reaction times in sporting events are generally around a best of 100ms.⁷ This implies that the player is unlikely to be able to respond to pluck and reduce the force being applied by the finger. 

These effects were noted in every organ measured, to a greater or lesser extent, depending on the size and rigidity of the action and the magnitude of pluck, and even on a light, suspended action the effect is significant. 

Initial work

Some tests were carried out with the University of Edinburgh organist, Dr. John Kitchen, playing the 1978 Ahrend organ in the Reid Concert Hall. This has a very “light” suspended action (50g key force, 50g pluck, Hauptwerk, middle C Principal). In the first exercise he played an improvised theme and was then asked to repeat it, varying nothing but the speed of key movement. The measurements of the key movements are shown in Figure 4, in which the curves are superimposed on the main part of the key movement rather than the pluck point.⁸ Kitchen felt that he had moved the key “five times faster” the second time (black curve) and changed nothing else. In fact, the time from the key starting to move to hitting the key bed in the fast note was about half the length of the slow note, with all of the difference at the beginning. Figure 4 does not show that the overall tempo was also faster with the fast key movement, but it can clearly be seen that the fast attack has resulted in a significantly shorter note. Even on this relatively rigid action, the effect of pluck is apparent at the beginning of the key movement at about 0.8mm key travel. 

In the next exercise Kitchen tried to accent a note by “hitting it harder.” Figure 5 shows that again with the non-accented movement the effect of the flexibility of the action is apparent, but the majority of the movement is very similar in both cases. 

In the two previous examples, the main part of the key movement has been superimposed. Since the relative timing of the pluck point varies, a further test was designed to indicate the point at which the player perceived the note to start. He was asked to play in the two manners from Figure 4 one octave apart simultaneously. Figure 6 shows the two notes to the same time reference and indicates that the player perceived the start of the note to be the point at which the key started to move. This introduces a timing difference between the two notes of approximately 30ms as the pipes will not start to speak until after the pluck point at a displacement of approximately 10% of travel. The “slow” note will sound after the “fast” note and is also slightly longer by about 10ms. The differences between the shapes of the beginnings of the key movements are discussed later. It is interesting that the notes do not end simultaneously. 

A further exercise was carried out at the Canongate Kirk in Edinburgh (Frobenius 1998, IIP20). A simple visual examination (confirmed by informal listening tests) shows that distinctly different key movements are not reflected in the sound profiles. Figure 7 represents a “fast” attack and Figure 8 represents a “slow” attack as perceived by the player. As observed throughout, the “slow” attack also resulted in a longer note. 

Rhetorical figures 

A frequent comment by organists was that even if it were possible to vary the way that they moved the key at the start of a piece of music, it was not possible to maintain these variations throughout a piece. Dr. Joel Speerstra is studying rhetorical figures at the University of Göteborg, based on his research into clavichord technique. These are physical gestures that can be maintained throughout a performance and are based on rhetorical figures in German baroque music described by Dietrich Bartel.⁹ 

Examples of Speerstra’s figures are listed below with his descriptions,¹⁰ along with graphs of some of these showing the key movements, pallet movements, pressure rise in the groove, and sound recordings. The measurements taken showed that phrasings closely followed the descriptions given, and some examples are shown below. 

Transitus (Figure 9) 

“You are standing a certain amount of the weight of your arm on a stiffened finger with a relaxed elbow, and moving from the first finger to the second without completely engaging the muscles of your arm that would lift it off the keyboard. This technique makes it easy to control heavy actions, and you would expect this kind of paired fingering to have fast attacks for both notes and a longer first and third note a shorter second and fourth note and, hopefully, as slow a release as possible after the second and fourth note.” 

The releases of the second and fourth notes are not significantly different from the others. 

Suspiratio (Figure 10) 

“It is a figure that starts with a rest followed by three notes, so the first note is now an upbeat, and I would expect that there is a faster release after the first note, and the second and third would form a pair much like the first and second in the transitus example.” 

Portato (Figure 11) 

“Portato [uses] separated notes but with slower attacks and releases.” 

To these can be added more familiar styles such as legato and staccato, although these may benefit from being more clearly defined. Whenever players were asked to play fast attacks, they also played shorter notes. 

Measurements were made of Speerstra playing in these styles on the North German organ in the Örgryte Church in Göteborg (built in the style of Arp Schnitger by the Göteborg Organ Art Centre [GOArt] as a research instrument). The key movement (middle C, D, E, F), pallet movement (C, D) and pressure in the groove of middle C (measured by removing the Principal 8′ pipe) were measured, as well as sound recordings being made. All magnitudes are to an arbitrary scale. 

Figure 12 shows all of the key movements and pressure profiles for the rhetorical figures described above. Despite the low number of data points, it can be seen that there are two groups of key movements and two very close groups of pressure rise profiles. The graph has been produced to show the two groups superimposed within the group but separated between the groups. If the player perceives the note starting at the point at which the key starts moving, there will also be time differences between the start of the notes as in Figure 6 above. There is an initial pressure drop in the “faster” group. Full listening tests have not been carried out, but initial tests across a wide range of musical levels did not indicate consistent differences in flue pipe transient between styles, although highly trained ears will detect subtle changes that others may not be able to. Reed pipes were not included in this study, although clear control of the final transient of some of the solo reeds was apparent when played in isolation. 

This organ is unbushed and there is a considerable range of noise response from the action—from almost silent to distinctly audible in the church, depending on the performer’s technique. This noise can mask the attack transient of the pipe, particularly close to the console. This issue was also encountered later in Rochester, and Speerstra considers that playing in a way that causes excessive noise is both undesirable and avoidable. John Kitchen also stated that he played in a style that minimizes the action noise on the Ahrend organ in Edinburgh. This avoidance of excessive action noise may limit variations in key and thus pallet movements. Excessive noise on key release may also mask the release transient. 

An example from each group is shown in the following graphs. Figure 13 illustrates an example from Group 1 and shows a relatively gradual start of the key movement, the first in the sequence. The accent is on the second note of the sequence.

Figure 14 shows a comparable note from Group 2. The key initially accelerates quickly and shows a distinctly different form of movement from Figure 13. The accent is on this note. 

The initial movement of the key is fundamentally different, and tests on the model at Edinburgh indicate that in the case of the portato playing style, the finger was in contact with the key at the start of the movement, whereas in the transitus example, the finger started its movement from above the key and thus was moving with significant speed when it contacted the key, causing a much greater acceleration of the key. 

Measurements were also made on the copy of the Casparini organ of 1776 from Vilnius, Lithuania, built by GOArt in Christ Church, Rochester, New York, for the Eastman School of Music (ESM). A number of doctoral organ students played in styles of their choice that they considered resulted in variations of expression, including different transients. They used their own descriptions of these styles; some of these were long and descriptive and cannot be incorporated onto the graphs. The pressure was measured directly under the pipe foot using a device made by the ESM organ technician Rob Kerner, and is not directly comparable with the previous example. The groupings of pressure rise profile have again been superimposed to highlight the similarities, and the time scale does not represent a constant start point of the note. All recordings are of the same theme used in the previous exercise.

Figure 15 shows the measurements from the first student, CP. There appear to be three distinct groups. The initial gradient of the first group shows some variation, but again, initial listening tests did not consistently identify differences even between the two extremes. The other two groups are more closely matched. It is not clear why there is a pressure reversal in group 2. Note again the initial pressure drop in group 3 and the extreme pressure variation. It is not yet clear what differentiates group 3 from the others. There were significant variations in the overall tempo, length of individual notes, relative lengths of adjacent notes, and overlap of notes.

The student’s description of each of the styles is shown in the following tables:

Table 1. Descriptions of playing styles in Group One, Figure 15. Student CP

259	Classical Mendelssohn
260	Romantic pp
262	Romantic pp
265	Baroque, two beats per measure
269	Bach 1st inversion suspiratio
270	Legato

Table 2. Descriptions of playing styles in Group Two, Figure 15. Student CP

256	One accent per measure
257	One accent per measure
258	Classical Mendelssohn
267	Baroque, one beat per measure
268	Baroque, two beats per measure
271	Harmonized

Table 3. Descriptions of playing styles in Group Three, Figure 15. Student CP

263	Virtuosic light ff
264	Virtuosic light ff

Two styles, 265 and 268—Baroque two beats per measure, and 258 and 259—Classical Mendelssohn, fall into both groups one and two, implying a fundamental difference between the two finger movements.

The key movements of the two extreme styles, Romantic pp and Virtuosic light ff, are shown on page 26. Figure 16 shows Romantic pp (262).

Figure 17 shows “Virtuosic Light ff” (263) to the same scale. It is unnecessary to state that the overall tempo is different.

Figure 18 shows the measurements of the first note in each sequence from student LG. Here there are two groups for the Principal 8′ alone, corresponding with groups one and two of CP’s playing. The measurements from the plenum are not readily distinguishable from the Principal alone. 

The descriptions of the styles are:

Table 4. Descriptions of playing styles in Group One, Figure 18. Student LG

274	Normal
277	Weight on 2nd
278	Weight on 2nd
283	Plenum equal accents
284	Plenum accent on 1st of pair
285	Plenum accent on 1st of pair
286	As 285 but faster tempo

Three of these are played on the plenum and not a single stop as with the others.

Table 5. Descriptions of playing styles in Group Two, Figure 18. Student LG

273	Normal
275	Paired notes with more weight on 1st
276	As 275
280	Weight on 2nd, 3rd and 4th finger
281	As 280
287	Fast, stronger on 1st

All of the pallet movements are shown in Figure 19. There is little difference in the initial movement, even though there were much wider variations in the key movements (Figures 20–22). There is very little difference in the key releases, but with two exceptions. In the case of examples 277 and 278, “Weight on 2nd” (marked with X on graph 17), there was a distinct elongation of the pre-pluck part of the key movement and the key, and thus the pallet did not reach full travel. As the pallet stopped at exactly the same point in each case (the key stopped at very slightly different points), it seems probable that there was high friction at this point. The attacks of these two key movements produced a shallower gradient at the start of the pressure rise, although informal listening tests did not indicate that this variation was sufficient to produce an audible difference with the single stop used in this test. The key and pallet movements for one of these are shown in Figure 20. The two “Normal” playings are split between the two groups, which again suggests a very distinct difference between them.

The curves are in sequence of time of closing and are from left to right, using the numbers in Tables 4 and 5, 278, 277, 287, 280, 274, 273, 286, 276, 281, 284, 285, 283. The consistency in speed of closure is worthy of note. The two curves at P are for the plenum and not a single pipe. It is possible that two non-accented notes marked with X would have closed similarly to the others had the pallet not stopped part way. There is a wide variation in the length of the notes and the overlap with following notes.

Two of the plenum notes in Figure 19 are marked with P at the point at which they cross. One of them shows a slower release of the pallet, whereas the other is similar to the rest of the movements. The key and pallet movements of the slower release are shown in Figure 21. This clearly shows that the pallet shuts before the key is fully released as shown in Figure 3. The key movement slows down when the pallet is no longer being pulled shut by the airflow round it.

Figure 22 is an example of a typical key and pallet movement, no. 275 “Paired notes with more weight on 1st.” Note that in all of Figures 20–22 the pallet does not start closing until after the key has started moving, indicating a degree of friction in the action.

Comparing Figure 20 with Figure 22, the weak note in Figure 20 has resulted in an extended pre-pluck movement of the key compared with the strong note in Figure 22. This is not reflected in the pallet movements to the same extent and, as discussed above, may result in timing differences in the sounding of the pipe if the player perceives the note as starting when the key starts to move.

All of the six student subjects demonstrated significant groupings of pressure along the lines of the examples shown above.

Key release 

Throughout this project, players have stated that even if there may be reasons why the attack may be difficult to control, it is possible to control the release accurately. There seems little evidence that this is actually the case.

While it is possible to control the initial movement of the key during the release stage because there are no similar effects to pluck, this does not necessarily allow for control of the ending transient. In the same way that the pressure in the pipe foot reaches its peak very early in the pallet opening it starts to reduce very late in the pallet closure. The corollary of pluck is felt as the airflow around the nearly closed pallet starts to “suck” it shut. Due to the flexibility in the action, the pallet closes before the key has returned to its rest position. Also, because the key force reduces due to this effect it is very difficult for the player to control the last part of the key release.

Some key releases were recorded at Göteborg. A fast release is shown in Figure 23 and a slow release in Figure 24. The blue line is the key movement and the pink line the sound recording.

By editing the steady part of the slow movement out to make the notes the same length just leaving the transients, informal listening teats confirmed that there is no difference in the sound of the transients. The difference between the notes is that the slow release results in a longer note.

Pressure changes in the wind system

In most organs the pressure regulator is remote from the windchest. Any variation in the air supply, such as when a note is sounded, will not be immediately compensated for. There will therefore be an overall pressure reduction when a note is started and a pressure increase when it is released. This was investigated by Arvidsson and Bergsten at GOArt in 2009.¹¹ This has been extended at Edinburgh to consider how these pressure waves in the wind system might affect pipe speech. Figure 25 shows a single note being played, and it can clearly be seen that the pressure in the pallet box reduces as the pallet opens, oscillates for a few cycles, and then steadies. This is reflected in the pressure measured under the pipe foot and also in the sound envelope of the pipe speech. When the pallet closes there is a corresponding increase in pressure. The variations shown here are around 35% of the steady pressure. These measurements were made on the model organ in Edinburgh and, while the effect will occur in any organ, the magnitude of these effects may be greater than normally encountered. A schwimmer system will reduce these effects.

Figure 26 shows the effect of playing a note before the note being measured. The pipe of the first note, E, was removed so that its sound did not interfere with that of the pipe being investigated. It can be seen that the effect of the release of the first note and of the attack of the second, F, have resulted in an even greater variation in the pressure throughout the wind system, and this is reflected in the outline of the sound recording. Listening tests have not been carried out, but this may lead to an audible difference in the transient of the second pipe.

Many notes being played together will produce large and random pressure variations in the wind system. These effects are also apparent with electric actions.¹²

It should also be noted that since pluck is directly related to the pressure in the pallet box, it will vary in proportion to it. It is thus possible that a momentary change in the magnitude of pluck could influence the time at which a key is depressed—especially if the player is already applying some force to the key.

Length of transient

In Figures 27 and 28, played on the ca. 1770 Italian organ in the Museum of Art, Rochester, New York, the pipe is slow to speak and starts at the octave and then breaks back to the fundamental. 

If a short note is played, as when the player is asked to make a “fast” attack, most of the pipe speech will be at the octave and that is what the listener perceives as the pitch of the note.  If a longer note is played, most of the pipe speech will be at the fundamental, and that is what the listener will hear. If the player is expecting a variation in transient, he may associate the different perceived sounds with what he believes are different key movements. In Figure 27, there is also evidence of initial mechanical noise. Note again that the nature of the attack has been reflected in the length of the note.

Conclusion

There is clear evidence that rhythm and timing are critical aspects of organ playing. In some cases they are the result of deliberate and systematic efforts by the player, as in the use of rhetorical figures, and in others the players may be unaware that they are making variations. Analysis of the various performances of the same sequence of notes showed wide variations in overall tempo, relative lengths of notes, and degree of overlap of notes, all of which will affect how it sounds to the listener. These and some other effects like variations of pressure in the wind system are independent of the type of action.

There is some evidence that transient control is difficult to achieve by the inherent design of the mechanical bar and slider windchest. Variations in key and thus, to some extent, pallet movement cause the pressure rise in the pipe foot to fall into distinct groups, the reason for which is still under investigation but would appear to be due to whether the finger starts in contact with the key or is already moving from above the key when it starts the note. Whether these differences result in audible changes is not clear and is likely to vary from organ to organ, and it is necessary to carry out properly controlled listening tests. Action noise may be a factor in informal listening tests. The player cannot react to pluck and any variations in key movement are predetermined.

Many of the characteristics of the bar and slider windchest work against transient control and this may have been one of its advantages—the aiding of clean consistent attacks due to the rapid opening of the pallet when pluck is overcome, but there is clear empirical evidence that players like mechanical actions. The immediate reason for this may be that it provides good tactile feedback. The organist can apply a certain force to the key in the certain knowledge that the note will not sound, but the force reduces to a comfortable level when the key has been depressed. It may also help reduce the risk of accidentally sounding a note if an adjacent key is brushed. 

It is unlikely that the original builders of the first windchests applied theoretical fluid dynamics to the design, and other reasons for its endurance may include:

• Ease of construction

• Reliability

• Ease of repair

• Snap closing of the pallet to give a good seal.

Every organ is different and this project has been limited by the instruments available. While this work may suggest that direct transient control is difficult, this may not be the case on instruments with different characteristics. There are, however, other mechanisms in play that may explain different perceptions of the sound.

This project is continuing and, with the cooperation of our colleagues around the world, it is expected that a clearer understanding of these important issues will emerge. 

Acknowledgements

My thanks to the Arts and Humanities Research Council, Professor Murray Campbell and Dr. John Kitchen at Edinburgh, the staff and students of GOArt and the Eastman School of Music, Joel Speerstra for his very helpful review of this article, Dr. Judit Angster and Professor Andras Miklos, Laurence Libin, John Bailey of Bishop and Sons in Ipswich, David Wylde of Henry Willis and Sons in Liverpool, and many others.

Notes

1. Alan Woolley, Mechanical Pipe Organ Actions and why Expression is Achieved with Rhythmic Variation Rather than Transient Control (Proceedings of ISMA, Sydney and Katoomba, 2010), paper number 2.

2. Alan Woolley, How Mechanical Pipe Organ Actions Work Against Transient Control (Proceedings of Acoustics 2012, SFA, Nantes, 2012), paper number 410, pp. 1969–1974.

3. Stephen Bicknell, “Raising the Tone,” Choir and Organ (March/April 1997), pp. 14–15.

4. Robert Noehren, An Organist’s Reader (Michigan: Harmonie Park Press, 1999), p. 161.

5. Alan Woolley, The Physical Characteristics of Mechanical Pipe Organ Actions and how they Affect Musical Performance (PhD Thesis, University of Edinburgh 2006).

6. George Ashdown Audsley, The Art of Organ Building (Mineola: Dover, 1965 republication of 1905 edition, Dodd, Mead & Co.), p. 215.

7. International Amateur Athletic Association, Rulebook, Chapter 5, Rule 161.2.

8. Alan Woolley, “Can the Organist Control Pallet Movement in a Mechanical Action?” (Journal of American Organbuilding, December 2006), pp. 4–8. 

9. Dietrich Bartel, Musica Poetica: Musical-Rhetorical Figures In German Baroque Music (University of Nebraska Press, 1997), pp. 57–89.

10. Discussion with author.

11. Mats Arvidsson and Carl Johan Bergsten, Wind system measurements in the Craighead Saunders organ (GOArt 2009), unpublished.

12. Alan Woolley, Transient variation in mechanical and electric action pipe organs (Proceedings of Meetings on Acoustics, Acoustical Society of America, Montreal June 2013, Volume 19), Paper no 4aMU3.

 

James W. Toevs

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.

 

The Isle of Man

From Peter Jones, the Offshore Organbuilder

This article is coming to you from the Isle of Man, an island some 30 miles long by about 14 miles wide, and sitting midway between Ireland and England. Its longest river--the Sulby--stretches for a full 10 miles or more, and Snaefell--the highest mountain--reaches a height of over 2,000 feet. Anyone with a world atlas and a magnifying glass to hand will have no trouble in locating the "Island," as those who live here often term it, off the west coast of England, facing Liverpool.

 

 

The Isle of Man may be little known in the wider world (or even on the "adjacent island" of England--we don't say "mainland," of course!) but like most places it does have its peculiar features which mark it out for those with special interests. It is an off-shore finance center, for example, with relatively low rates of tax. It is known for its motorcycle races (the "TT Races") which take place on the public roads--one of the largest (and arguably most dangerous) circuits of its kind in the world. For those who like unspoiled countryside to look at or walk over, and a quiet and relatively unhurried way of life, the Isle of Man is the place to be. It is an island of Fairies, one of the largest water-wheels you are ever likely to see, Celtic stone crosses and much more. Most important to me, and I hope of interest to readers, its small area is home to a surprising variety of some 50 or so pipe organs, and I am more than happy to have been the resident organ builder here for over 20 years.

For those of us with a fascination for the King of Instruments, there is much to be said about life here--too much for one article such as this--and rather than describe the organs as a whole in greater or lesser detail, I thought it might be better to describe some of the incidents which make the life of "the organ man" anything but tedious.

Looking back over the work undertaken in the recent past, I see one job which will be of interest to the great majority of organ players, from the professional recitalist to the home enthusiast who plays only for his own enjoyment. I refer to an ambition which attracts so many organists, and which eludes all but a few--the luxury of a real pipe organ in one's own home.

How many have investigated this possibility, only to find that the cost (and sometimes the space) involved ensures that the pipe dream remains just that? True, there is the electronic substitute--smaller and cheaper, with a great variety of Golden Tones of one kind or another--and then again the organ in church is usually available to the serious player--albeit not so attractive in the winter, nor so convenient for that odd 30 minutes practice at the end of the day. But for those badly infected by the organ bug, the unfortunates with an acute case of "organitis," there can never be any hope of a cure until they can see for themselves those gleaming ranks of metal and wooden pipes and the console with its several keyboards, waiting in the music room for their sole use!

So it was with The Reverend Alec Smith. His love of the organ had actually led him to start an apprenticeship in organ building as a young man, but he quickly saw the light, heard the call, and became an ordained priest in the Church of England. At that time, he assembled a worthy (if somewhat ungainly) collection of pipes, old keyboards, bits of mechanism, etc., into a Frankenstein creation which crouched in the corner of one of the large rooms of the vicarage in his country parish in England. This creation was a credit to its owner, but more than a little ponderous for anything other than a large house (preferably not your own) with plenty of spare rooms. When, in the fullness of time, Alec became an army chaplain, and he and his wife Jean were inevitably posted abroad, the organ was dispersed, almost all of it never to be seen again.

On retirement from the army, Alec settled in the Isle of Man and became Organ Advisor to the Diocese. It was now that the organ-building bug, which had lain dormant for so many years, was re-awakened, and the idea of a house organ was again proposed. There were, of course, several problems. The usual ones--centered around lack of space and finances--were, quite rightly, pointed out by Jean, and in any case there was a seemingly adequate 2-manual electronic, with its equally large speaker cabinet, already taking up far too much room in their small cottage in the Manx countryside. Jean correctly pointed out that it was more room they needed, not a pipe organ!

In a attempt to save some space, and acting on the advice of the local music shop, new and much smaller speakers were fitted to the electronic by an "expert" from Douglas, the Island's capital. After a day spent fitting the new speakers into the ceiling (with the novel use of a screwdriver to create some suitable holes in the plaster), the expert switched on, at which point there was an impressive bang followed by an ominous burning smell. It seemed, on later examination, that the amplifiers (intended to power two large speaker banks in a church setting) had seen the modern speakers as a virtual short circuit in electrical terms, with the inevitable result. The expert withdrew, promising to "work something out." I believe he left the Island, and, in any case, was never seen again. The electronic was no longer adequate. It was dead.

At this point, a further discussion took place on the subject of a new pipe organ, and Jean was persuaded, but only agreed on one seemingly-impossible condition: aside from the console, the new organ must not project into the room any further than the line of the first ceiling beam (some 14≤ from the end wall). Since there was no possibility of siting anything behind the walls (three of them being external, and the fourth taken up with the fireplace) the situation appeared hopeless, and it was at this point that Alec called me in.

Impossible situations regarding space are a challenge to the organ builder. More than one has succumbed to the temptation to push too-large an organ into too-small a space, with disastrous results, and I have seen the consequences of several of these unhappy situations. In one such case, an instrument was built in which the Great and Choir (mounted one above the other and in front of the Pedal pipework) "speak" into a solid masonry wall some 3 feet thick. Tuning/maintenance of such an organ is difficult if not impossible, and a warning to any organ designer. Alec's requirement was for the cheapest possible instrument, with a fair selection of stops over two manuals and pedals, all within a depth of 14≤. It had to fit into one small room of a cottage which has only three rooms on the ground floor (the other two being the kitchen and porch) and it must not be a monster from the tuning/maintenance standpoint.

There was space for only two or three sets of pipes, but Alec stated from the outset that, "I want more than three wheels on my car," so we were obviously looking to something other than mechanical action with two or three stops. This need to make the most of the available pipework suggested an "extension organ" of some sort. This, and the restrictions of the site, dictated electric action, and financial considerations suggested the simple mechanism as shown in the sketch. The question of electric versus mechanical action is one of those subjects likely to provoke strong opinions both for and against. In my view, each system has its merits and I am happy to work with either, but when a client requests more stops than the room or budget will allow, the obvious way forward is for a stoplist extended from a small number of ranks, and this means an electric mechanism. The design shown, if correctly made, is reliable, very quick (giving good repetition) and quiet. Incorrectly handled, it is none of these things, and has thereby acquired a poor reputation in some circles. With sufficient funds, and more space, an electro-pneumatic action would have been more sophisticated, but with enough care taken in its design and construction, direct electric action (as shown) is almost as good.

Some readers may be unfamiliar with the idea of an "extension" organ. This is an instrument in which a set, or "rank," of pipes is available to be played at more than one pitch. For example, a set of flute pipes could be played at 8' pitch (via a console stop labeled, say, Stopt Diapason 8') and the same set could also be available at 4' pitch (via a console stop labeled Flute 4') or at 16'  pitch (in which case the console stop might be labeled Bourdon 16') and so on. Clearly, the idea has its uses and abuses, as in the case of the 2-manual and pedal organ in which every console stop was actually taken from a single rank of Dulciana pipes!

The final stoplist is one which I have used successfully on various occasions. It is based on three ranks representing the three main tone-colors of the organ:  Diapason, Flute and String. Each of the three ranks consists of 73 pipes, and are listed below as:

Rank A/ Open Diapason, running from C13,

Rank B/ Stopt Diapason, running from C1, and

Rank C/ Salicional, running from C13.

In addition there are 12 stopped Quint pipes (shown below as "Q") running from G8 (at 8' pitch) for the pedal 16' stop (see later).

(Reed tone was not included, as it is difficult to have conventional reeds sufficiently quiet for such a small setting. In any case, there was no space available.)

Note that the Open Diapason is of small scale, and this made it much more suitable, for our purpose, than the more usual scaling of such a stop. When selecting second-hand pipes for a home extension organ, a Principal would be the first choice  to provide the Open Diapason--Principal--Fifteenth "stops," as they appear on the console, and I have even known a Gamba to make a very acceptable open metal extension rank, once it had been re-scaled and re-voiced. Ideally, where finances are not a limiting factor, new pipes should be made for all ranks, so that their scaling can be suited to the room and stoplist.

If an "extension" scheme is to work, musically, it is important to avoid the temptation of too many stops from too few pipes. I know of one organ with the stops simply repeated on each keyboard, and though this gives maximum flexibility, it is very confusing from the player's point of view, and the instrument as a whole is strangely bland and characterless. The three sets of pipes for Alec's organ were made available at different pitches, under the guise of different stop names, to make registration more straightforward from the player's point of view. In this way, some 15 speaking stops are available to the organist, instead of three which would result from the use of mechanical action.

The specification shown has only one stop (the Stopt Diapason) actually repeated on each manual. This is because it is so frequently used, and blends with the other two ranks at 8' pitch.  None of the other manual stops are repeats, and they have been arranged so as to discourage the use of the same rank at only one octave apart. (E.g.,  the Open Diapason 8' is intended to be used with the Salicet 4', or the Flute 4', not the Principal 4', as you might expect.) Using the stops of an extension organ in this way reduces or (more usually) eliminates the well-known "missing note" problem, which occurs when one strand of the music runs across another, and both need a pipe from the same rank, albeit from different extended "stops." If, for instance, the Stopt Diapason 8' and Flute 4' are drawn on the same manual and key C25 is held down, the pipes heard, as counted from the flute rank, will be C25 and C37. Now add manual key C13, which will sound pipes C13 and C25 (which is already playing from key C25). In this example a pipe at the pitch of C25 should appear twice, but actually appears only once. The missing note will be most obvious if either of the two manual keys is held down while the other is repeated.

One of the most important criticisms to be levelled at an extension scheme is this problem of missing notes, which can lead to a lack of clarity. For all practical purposes, this drawback can be completely overcome by a combination of the organ builder (in preparing a modest stoplist) and the player (in thoughtful use of the instrument, so that the smallest number of stops is drawn at any one time, preferably from different ranks, or at least from ranks separated by more than one octave). In actual practice, this kind of stop selection becomes automatic to the organist who realizes the limitations of the instrument.

Another important factor in the success of this type of organ is the regulation of volume and tone quality of the pipes within a stop, and also the regulation of the stops in relation to each other. Each stop is regulated with a very gradual crescendo from bass to treble. This requires subtle handling, but when correctly carried out results in a clear ensemble in which the treble parts can be heard above the tenor and bass.

The ranks themselves are regulated with much less distinction in power than would usually be the case, so that equivalent pipes of the Stopt Diapason are similar in volume to those of the Open Diapason, and the Salicional, while quieter, is not far behind. This results in much less contrast in power among the 8' stops and this is a compromise, of course, though you still have variety of tone. The blend between ranks played at different pitches is much better than if they are regulated in a conventional manner, with the Open Diapason much louder than the Stopt Diapason and Salicional distinctly quieter. In an instrument such as this, contrast in power is created more by contrasting combinations of stops than between the ranks themselves. Regulating the ranks as if they were separate stops (a mistake often found in both church and house extension organs) results in the Open Diapason and Principal obliterating everything else, while the Fifteenth screams. 

I have used the specification shown several times, including my own house organ, and find it to behave very much as a 'straight' instrument would. I seldom use the couplers, though there are occasions when they become necessary. While it requires thoughtful registration to get the best from an extension organ, a scheme such as this, with a small number of stops, arranged so as to discourage the use of the same rank in two stops separated by only one octave, is very successful.

To cut down costs, Alec agreed to the use of his old electronic as a console, and also to the use of any other second-hand parts which could be obtained. He was also interested and able to lend a hand in the actual construction, when his earlier experiences in organ building were a great asset. The need to keep within 14≤ maximum depth was easily dealt with, by taking up the entire width of the room, side-to-side.

Knowing the number and range of the ranks and the space available, the first step, in a job such as this, is to measure the pipework, in order to see how best to arrange the pipes, and, indeed, if they will fit in at all!

Metal pipes need to be measured in height and in diameter, wooden ones in height only (including any stoppers). In practice, nearly all metal pipes run to a standard scaling (i.e., the rate at which the diameters reduce from note C1 through to the top pipe). Wooden pipes vary considerably, both in scaling (the internal width and depth) and in the thickness of the wood used, which in turn decides the external width and depth. There is also the question of the foot, which, in second-hand wooden pipes (and some new ones) can be bored well off-center. For these reasons it is best to make a paper template of the bottom of each wooden pipe, as described later.

I already had a small scale (i.e., relatively small diameter) Open Diapason rank, and a Salicional, both running form C13 (so the longest pipe in both sets was about 4' speaking length) and Alec located, from a friendly organ builder on the mainland, the Stopped Diapason pipes (running from C1) and a bundle of miscellaneous stoppered wooden pipes for the pedal Quint.

The necessary measurements were taken and noted down in the form of a table. I find it convenient to have a sheet of paper with the 12 notes C through to B in a column down the left-hand edge, followed by vertical columns headed "1--12" then "13--24" then "25--36" and so on, up to "73--84," placed from left to right across the page. This forms a table which will cover an 84-note rank, the biggest usually needed. (Note C85 is only necessary in the case of a rank which runs from 8' pitch to 2' pitch, where the organ has a manual key compass of 61 notes. This C85 pipe needs an additional square to itself.) Every square represents a pipe, and in each one can be written the length and diameter (if metal), together with other details such as size of a rackboard hole, and toe hole etc., which are also measured at this time.

Notice that only the Stopped Diapason rank has its bottom octave (in organ building terms, a "Stopped Bass") the largest pipe of which is, like the other two ranks, something over four feet long. The Salicional and Open Diapason share this bottom octave, as does the 16' pedal stop (the "Harmonic Bass") which produces an acceptable 16' substitute, in the first 12 notes of the pedalboard, by playing the Stopped Bass pipes with the appropriate Quint pipe (from a separate and therefore very soft, 12-note rank of wooden pipes). The resultant note (actually a low hum) which is created from a combination of any stop of 8' pitch and its quint is at 16' pitch. Admittedly, this is much softer than the two pipes actually sounding. The pedals from C13 up play the Stopped Bass again, and then the rest of the Stopt Diapason, thereby sounding at true 16' pitch. These compromises are necessary to reduce the size of the organ, and, if carefully carried out, are soon accepted by the player and listener, especially in a small room.

While there is no substitue for the soft, heavy, warm tone of a full-length Bourdon bass, I have asked many players (including several professionals) their opinion on this "resultant" 16' pedal stop. So far, no one has realized what he was playing until it was pointed out. They all accepted it as a pedal 16'  stop, like any other. The least convincing notes in the bottom octave are, predictably, the smallest three or four. If there is room for full-length pipes down to, say, F#7, so much the better.

It is worth noting that a quinted 16'  effect which uses the pipes of the Stopt Diapason rank only is almost always a failure, because the quint will be too loud. If you have no room for the extra Quint pipes, it is better to use the 8' octave of the Stopt Bass on its own (from pedal keys C1 to B12) before completing the pedal compass by repeating the Stopt Bass followed by the rest of the Stopt Diapason. Another possibility worth considering is a 16' bottom octave in free reeds.

Full-size card or paper templates are needed to represent the metal pipes, as seen from above. It is not normally necessary to make these for every pipe, as different stops usually reduce in diameter, note for note, to a more or less standard pattern. If this pattern is known, the set of templates need cover only the range of diameters from the fattest metal pipe in the organ (in this case C13 of the Open Diapason) down to the minimum spacing dictated by the pipe-valve mechanism. (As direct electric action was being used and the smallest magnets were 3/4≤ wide, with pipes placed directly above the valves, minimum pipe spacing = 3/4≤ + 1/8≤ clearance [= 7/8≤] no matter how small the pipes.)

Like most organ builders, I have a set of these circular templates for general use, so templates for the metal pipes were already at hand, but the wooden pipes had to have paper templates individually made to show their exact shape and the center of the pipe feet. Such a template is made by taking an over-sized piece of paper, drawing on it a circle which equals the diameter of the pipe foot, cutting this out, and sliding the paper up under the pipe and creasing around the four sides. Once the paper is removed and trimmed to size, the original circle can be taped back into place, resulting in an accurate template.

Alec's wooden Stopt Diapason (reputedly by the well-known Victorian organ builder, William Hill) was over 100 years old, and may have been in more than one organ during its lifetime. Its mouths were rather high, which made the tone breathy, and some of the pipes had been mitred, or were cut too short, possibly where they had been in a crowded swell box. But it was basically sound and we went on the basis that it could be made acceptable by repairs, lowering the mouths and re-voicing. The Salicional and Open Diapason ranks were also Victorian, from a local Methodist church. Again, they were not perfectly scaled or voiced for a house  organ, but were basically well-made and capable of re-voicing. All the pipes were measured, and with the tables of measurements and templates to hand, and a given space into which to fit the pipes and action, the process of "setting out" could begin.

An instrument with direct electric action enables the builder to arrange pipework in almost any pattern, within the limits of the room and the physical space taken up by the pipes themselves (or, in the case of the tiny treble notes, the size of their magnets and valves). My preferred system of setting out is slightly unusual, in that I like to place the taller pipes behind the smaller pipes, regardless of their rank. Most other builders would plant pipes in rows, each row being made up from pipes of the same rank.

Secondly, and in common with many of my colleagues, I prefer to plant pipes in "sides," i.e., pipe C1 on the extreme left of the organ, and C#2 on the right, working down to the treble pipes in the middle. In this way, all the pipes of the "C side" (C, D, E, F#, G#, A#) will be on the left, and those of the "C# side" (C#, D#, F, G, A, B) will be on the right.

These two underlying principles result in a pipe set-out which is visually attractive, compact, and which offers the greatest accessibility for tuning and maintenance. Admittedly, it does lead to some complications in the cabling patterns between the console and the magnets, but this is not an insurmountable problem. (In fact, the many cables for this organ were made up, wire by wire, by my school-boy workshop assistant, with no errors at all.)

Alec and I set out our templates on strips of white paper, as wide as Jean would permit, (the 14≤ maximum) and as long as the space available (i.e., the width of the room: 157≤ or just over 13 feet). After a day or two of pushing the templates around, and, bearing in mind the many details such as how the pipes could be best faced away from each other, the space to be allowed for rack pillars, cable registers, assembly screws and many other essentials beyond the scope of this account, we decided upon the ideal arrangement, with the pipes set out on three chests. The chests were placed one above the console, for the treble pipes, and one on each side at a lower level, for the bass pipes. The central chest was just under 13≤ from front to back, and the two other chests were only 9≤ wide. The whole organ would stand in the maximum ceiling height of 91≤ (barely over 71/2 feet). The actual planting pattern was so tight that every possible space has been used, given the limited width and length available. Even so, no pipes are crowded, and all of them have been accommodated. The fronts of the three chests were made from oak-veneered ply salvaged from the old speaker cabinet and console back of the electronic. Consequently, they matched the finish of the console exactly.

Admittedly, there was no room for any casework or building frame, and we had yet to solve the problem of space for the blower, wind pressure regulator, wind trunks, low voltage current supply and one or two other essentials, but these are minor obstacles to the true organ fanatic!

The actual construction of the instrument started with the chests--comprising the pipe ranks, toe boards, or top boards (on which the pipes stand) "wells"  (the sides and ends) and bottom boards. Details of each chest varied with the numbers of rows of pipes, but the sketches showing the basic mechanism will give a good idea of a typical chest in cross-section.

Strips of mdf (a sheet material available in 3/4≤ thickness) were cut for the top boards for each of the three chests, and the pipes centers were punched directly onto them, using the paper setouts, taped down, as a template. Based on these centers, the magnets, valves, pipe racks and the many other details of the mechanism can be marked out and fitted. Unfortunately, a detailed description of this procedure is beyond the scope of a general article such as this. While the basis of the mechanism is shown clearly in the sketch, there are a great many practical details which must be finalized in design and observed in manufacture, if this deceptively simple idea (drilling a hole, screwing a magnet and valve under it, and planting a pipe on top of it) is to be carried through to create a reliable musical instrument. Such a mass of information has not, to my knowledge, ever been written down, as it is essentially based on practical experience over the years. If any readers are interested in further practical details, it may be possible to describe some of the problems involved, and how they are overcome, in a future article, but only a practicing organbuilder can have all the necessary skills and knowledge to cope with every situation, and this makes it impossible to give a general "recipe" for building an organ.

The wind supply is provided by a small electric blower of course, but this one is unusual, in that it was passed on to Alec by an organ-building friend from the days of his original house organ. Indeed, it turned out to be the very same blower, which had returned to him, after an absence of 30 or more years! It proved to be an excellent machine, and very quiet when housed in a new silencing cabinet.

It was necessary to regulate the wind pressure to a value suitable for the pipes and their setting, and, of course, we had no space for traditional bellows. In a case such as this, I used my own design of wind pressure regulator (basically a hinged plate of 1/2≤ sheet material, "floating" over a rubbercloth diaphragm, and supporting some suitably-tensioned springs). Movement of the plate controls a valve which allows wind from the blower through to the chests. As the pipework makes a demand on the supply, the valve opens just far enough to maintain pressure to within 1/8≤ or less at peak demand. This is an acceptable degree of control, and only a very critical ear will notice the slight fall-off in power. Every builder has his favorite design for such a regulator (sometimes called a 'schwimmer' or, in my case, a 'compensator') and they all bear a strong family resemblance. Not all are equally effective, however, and some are prone, under adverse conditions, to fluttering (creating an effect like a very rapid Tremulant). Again, only experience of such devices can provide a way out of trouble, though there are some basic rules in compensator design.

The steady, regulated wind from the compensator is fed to the chest by a rather broad, but shallow, wind-trunk (made in mdf, like the blower box and compensator). This is fixed to the back wall, out of sight, behind the console.

With all the basic elements designed, there still remained the question of the 14≤ limit on width. Obviously, the blower box and compensator were too wide to keep within the limit, so it was decided to camouflage them, together with the circuit boards, transformer/rectifier unit, and other large components.

In the final design, the three chests were screwed to plates of 3/4≤ ply, previously fixed, in a true vertical position, to the rather uneven stone wall. The console was placed centrally, with the two outer chests (holding the bass pipes) low down on each side. The third chest (containing all the treble pipes) was fixed centrally on the wall, just behind and above the console's music desk. Two bookcases were made to fill completely the gap between the sides of the console and the side walls of the house. They were set rather further forward than would be usual, with a broad top which ran back to the wall behind, effectively disappearing under the side chests.

On the left of the console, the bookcase is a real one, with its top extending over the circuit boards and transformer/rectifier unit hidden behind. To the right of the console the seemingly identical bookcase is, in fact, a dummy. Its shelves and books are only about 11/4≤ deep. (One of the more bizarre scenes in the workshop was that of pushing large quantities of scrap books through the circular saw, leaving their spines and an inch or so of paper and cover. These truncated volumes look convincing when glued, side-by-side, onto the foreshortened bookcase back.) The space under the dummy bookcase top contains the blower box and compensator. The bookcases, blower box, compensator, etc., all sit on 3/4≤ ply panels which have been leveled onto the floor.

Once Alec had installed his real books and ornaments, the organ (while visually dominating such a small room, as it must) blended into its domestic setting beautifully, with a spectacular visual touch being provided by a trumpet-blowing angel, carved in oak, which had been salvaged from a local church altarpiece,

What of the finished product? Naturally, the instrument is a compromise--but then this is true of all but the largest organs. It is a pity, for instance, that there was no room for a swell box, or another rank, but it is a wise builder or player who knows when he has gone as far as space and finances will allow. The wooden Stopt Diapason rank had its top lips lowered, and was re-voiced to produce a charming, rather quaint sound, with none of the original's unattractive, breathy tone. The Open Diapason had to be softened to just short of dullness, and now adds considerable fullness and warmth. The Salicional has made an excellent quiet voice, and is also very useful in its other pitches, where it adds brightness without shrillness. This is most important in a small room, and it is worth noting that, the larger the room (up to cathedral proportions) the brighter and more cutting the treble pipework can, and must, be. But the opposite is true for a small space, where top notes can easily become uncomfortably piercing--hence the lack of Mixtures on small house organs with no swell boxes. Many visiting organists, both professional and amateur, have played Alec's instrument since its completion, and all have been pleasantly surprised by its resources and the fact it is possible to produce satisfying performances of both classical and romantic works, albeit with some ingenuity on the part of the player.

True, it would have been possible to install a "large" electronic with three or four manuals, a wide range of stops and artificial reverberation, and I can see the attraction of such an idea, especially for the player whose interest lies in large-scale, romantic works. But, I cannot imagine anything less convincing than the sound of pedal and manual reeds, with Diapasons and mixtures, echoing with a five-second reverberation, across a room some 16 feet long and 8 feet high. The sound of a small organ in a small room, with no reverberation at all, is an authentic one and has a special charm. Whether it be two or three ranks of pipes offered with mechanical action as two or three stops, or whether, as in this case, the ranks are extended to several "stops," the small domestic instrument has a sound and fascination all its own, and is capable of giving much pleasure, both visually and musically, over many years.

 

Peter Jones will be pleased to receive comments, either on this article, or relating to readers' own experiences, at: The Bungalow, Kennaa, St. John's, Isle of Man, 1M4 3LW, Via United Kingdom

 

Manual I

                  8'            Open Diapason A

                  8'            Stopt Diapason B

                  4'            Salicet C

                  4'            Flute B

                  22/3'    Twelfth C

                  2'            Fifteenth A

                                    Man II/Man I

Manual II

                  8'            Stopt Diapason B

                  8'            Salicional C

                  2'            Salicetina C

                  11/3'    Nineteenth C

Pedal

                  16'         Harmonic Bass B & Q

                  8'            Bass Flute B

                  4'            Fifteenth A

                  2'            Salamine C

                                    Man I/Ped

                                    Man II/Ped

Summary

                  A              Open Diapason 73 pipes

                  B              Stopt Diapason 73 pipes

                  C              Salicional 73 pipes

                  D              Quint 12 pipes