Wind Supply | Wind Regulation | Flexible Wind and Tremulants
Audio and Video Files

Introduction

Wind Supply

Because the mechanics of organ wind supply are usually hidden from view, the way in which organ wind is generated is often overlooked. Historically several different means of creating a wind supply have been used.

• Simple hand-operated bellows, of the "fireplace" variety. These were part of some of the earliest instruments, and their use is documented in several extant sources.
• Larger wedge-shaped bellows operated by levers. These were used from the Middle Ages through the early twentieth century. They are also to be found in modern copies of instruments originally built in the seventeenth through nineteenth centuries.
• Electric blowers. These have become in the twentieth century the normal means of creating a supply of wind for the organ. They are usually rotary fan blowers driven by an electric motor. A typical organ blower is shown below.

In the photograph to the right, ⁵⁴ the electric motor on the right powers the blower in the housing that forms the center and leftmost sections of the photograph. The blower itself is a rotary fan that drives air out of the housing through the black conduit seen at the rear of the photograph.

After the wind leaves the blower, it is directed through conduits made of wood, metal or plastic materials to the windchests, which serve to store the wind and make it available to specific pipes as determined by the organist. However, wind cannot be used directly from an electric blower; its volume and pressure must be regulated in some way.

Wind Regulation: Volume

Control of the amount of wind entering a pipe - - the volume of air - - is not accomplished through mechanical means along the wind line, but at the pipes themselves. The "toehole," the opening in the lower part of the foot of a flue pipe or of the boot of a reed pipe, can be increased or decreased in size to regulate the amount of air that enters each individual pipe. This is usually done as a part of the voicing process.

The toeholes in the photograph to the left demonstrate the different sizes that can be made in the toes of pipes. Larger openings admit more wind, while smaller openings restrict its volume. The pipe on the left has a lead toe attached to the foot. Because lead is a soft metal, the size of the toehole can be changed to regulate the amount of air that is admitted to the pipe mouth. On the other hand, the pipe on the right is entirely open, without a lead toe. In order for this pipe to sound at the correct volume and pitch, the amount of wind used to produce sound would be controlled at the mouth itself. Voicing pipes is this way is usually called "open-toe voicing."

Wind Regulation: Pressure

Once a source of pressurized air has been obtained, there must be a means of controlling it. Without some means of regulating the air pressure so that it remains constant, playing a large number of pipes simultaneously would deplete the air in a windchest, causing a drop in pressure until the blower could replace it. The result would be a drop in pitch, because the pipes would be inadequately winded. In order to prevent this unmusical result, several different means of controlling the wind pressure so that it remains constant have been developed and are in common use.

Reservoirs

In most organs in the United States, wind from the blower is directed first into a reservoir, an enclosed space that not only acts as a storage space for wind from the blower, as its name implies, but also acts to control the pressure of the wind as it leaves. A reservoir may take several different forms, including wedge shapes similar to a bellows. In addition, several different means of controlling the pressure may be used. Regardless of the shape or method found in a reservoir, however, certain characteristics are found in all of them:

• Reservoirs are located along the wind conduit from the blower to the chest.
• Reservoirs serve as a storage place for organ wind.
• Reservoirs regulate the pressure of organ wind as it enters the chest.

The graphic to the right shows how one type of reservoir works. This type of reservoir is usually an airtight wooden box with two conduits attached to it. One leads into the reservoir, bringing wind from the blower, the other allows wind to exit and be directed to the chest. The top of the reservoir is fitted with an accordion fold lid that can move up and down to meet demands of air pressure within the reservoir. As air enters the reservoir (illustrated by the red arrow), the increasing pressure presses the flexible lid upward, filling the space inside the reservoir with pressurized air. When pipes are played, and wind leaves the reservoir on its way to the chest (illustrated by the blue arrow), a weight or springs attached to the lid pull it down, maintaining the wind pressure. More air then enters the blower to raise the lid, and the cycle continues. A reservoir must be large enough to prevent chords that sound many pipes from withdrawing too much of the air from the reservoir. If that happens, the organ is said to be underwinded. The instrument is literally starved for air - - its "breath of life."

The photograph shows a typical reservoir of the type described above. ⁵⁵ The reservoir is fully open, at its maximum capacity for storing wind. At the edges of the lid, the white material is leather, which is glued to the wooden pieces to make a flexible hinge. Although the graphic illustration shows a weight placed on top of the reservoir, the example in the photograph has springs to aid in maintaining a steady pressure inside the reservoir.

In another type of reservoir, the lid does not have the hinged wooden panels. Instead it is a wooden panel that is attached to the frame of the reservoir on all sides by rubber cloth, a flexible, airtight material. The rubber cloth is glued to all sides of both the lid and the frame, so that the lid is free to move up and down with changes in the wind pressure. As in the other type of reservoir, either springs or weights may be used to provide the force that is necessary to counteract the pressure of wind entering the reservoir.

Schwimmers

Another device used either alone or in combination with reservoirs is a Schwimmer. A Schwimmer differs from a reservoir chiefly in location, because a Schwimmer is attached directly to the underside of a windchest rather than being located along the windline from blower to chest. The movement of a Schwimmer is downward instead of up because of this position. Springs instead of weights provide upward pressure to counteract the downward force of the wind pressure. In practice, this construction resembles an inverted version of the second type of reservoir described above.

The photograph to the left shows the underside of a windchest with a Schwimmer built into it. ⁵⁶ The movable panel is identified by the letter "A," and the black material surrounding it is flexible rubber cloth. The letter "B" identifies housings containing the springs which provide counterforce to the wind pressure.

Other Devices

Reservoirs and Schwimmers are the most common devices used to control pressure in organ wind, but they are not the only ones. Two others are also found frequently:

• Universal Wind Chest. The Austin Organ Company uses a patented Universal Air Chest in its organs. The Universal Chest can be made large enough that it acts as both chest and reservoir. In these cases a side wall can be fitted with an expansion panel and springs so that is in effect a Schwimmer-type device that moves into the chest to maintain a steady supply of wind to the pipes.
• Concussion Bellows. A small wedge-shaped bellows is occasionally added externally to a wind chest, connected to it by a small tube which conducts air to the bellows. A concussion bellows is opened by pressure from the wind in the chest, and if a sudden draw of air through the pipes results in decreased pressure, a spring forces air in the bellows to return to the chest. Small concussion bellows are frequently called "winkers," probably in reference to the resemblance of their motion to a moving eyelid.

Flexible Wind and Tremulants

Although the presence of a reliable supply of wind is normal for instruments of the late twentieth- century, there are two instances in which a steady wind supply is actually avoided or discouraged:

• Instruments in which a "flexible" wind supply is present.
• Instruments in which a tremulant is present.

Flexible wind is a characteristic of some instruments of the last quarter of the twentieth century that have been built to incorporate technical design elements of organs from the sixteenth through the nineteenth centuries. While some of these organs are attempts at copying existing earlier instruments, many of them are serious attempts at creating an instrument that artistically incorporates elements that were once common in organ building, but have been replaced through the intervening centuries by other ways of accomplishing the same goals.

When these organs have a flexible supply of wind, there is no reservoir or other device to provide a steady supply of wind - - one without any fluctuation in pressure. This is not to say that these instruments have no control at all, or that their wind supply is unsteady. The gentle falls and rises in pressure are subtle, and in the most successful applications contribute a quality to the sound that is often described as "breath-like" or "breathing."

Although the breath-like quality of the sound is appropriate for music written when such systems were common in organ-building, it is not a property that is found in most instruments today.

A Tremulant - - which might be identified as a Tremblant, Tremolo or a Schwebung on different instruments - - is, on the other hand, a quite common device that intentionally introduces a fluctuation into the wind supply, thus creating a wavering quality in the sound of the pipes. The tremulant is usually included as a non-speaking stop that allows the organist to control its use. When the tremulant is off, the wind supply is steady, but when the stop is on, the wind supply is made to waver through one of several means.

Although there are several ways in which the mechanics of a tremolo operate, most organs in the United States use either a pneumatic system or an electrical motor to move the regulator - - either the reservoir or the schwimmer.

The photograph to the left shows reservoir of the type that is made with a movable panel surrounded by black rubber cloth. ⁹⁷ Above the top panel, a wooden bar is attached by a frame identified with a green A. When a motor (above the green B) is turned on by the Tremulant stop, the bar moves up and down and disturbs the steady pressure normally created by the reservoir. The effect of the tremulant can be heard in the sound of the pipes as a wavering in pitch caused by the differences in wind pressure from moment to moment.

In the case of the Austin Universal Air Chest ^tm, the larger volume of air present in the chest means that providing variations in air pressure at a fast enough rate to hear it is impractical. ⁹⁸ In these chests, an alternative tremulant is made by placing large wooden fan blades above the pipes, as seen in the photograph to the right. ⁹⁹ An electric motor turns the fan, forcing an unsteady current against the upper end of the pipes. This disturbance in the air pressure results in a fluctuating difference between the wind pressure in the chest and that outside it, so the desired wavering sound is produced.

Audio and Video files

• A short passage played on a 4' flute, first without tremulant, then with tremulant.
  • For PC users: file in .WAV format
  • For Mac users: file in .AIF format

• A short film of a reservoir with tremulant is available.
  • The file is in AVI format (Cinepak Codec) and is about 1.7 MB in size.
  • Some browsers will show a set of controls to begin the film. Others will require a click on the image to start the film.
  • The film shows the reservoir pictured above, with electric tremulant. A chord is sustained at the beginning of the film, and then the tremulant is turned on. The effect of the tremulant on the sound will be audible on most PC speakers.
  • With some browsers, it will be necessary to use the "back" button to return to this page after viewing the film.
• A short film of an Austin fan tremulant is available.
  • The file is in AVI format (Cinepak Codec) and is about 1.4 MB in size.
  • Some browsers will show a set of controls to begin the film. Others will require a click on the image to start the film.
  • The film shows a portion of a chamber in which can be seen
    • the tops of some pipes.
    • the fan tremulant with its electric motor at the far end of the fan blade.
    • horizontal swell shades behind the fan blade.
  • A chord is sustained at the beginning of the film, and then the tremulant is turned on.
  • With some browsers, it will be necessary to use the "back" button to return to this page after viewing the film.