Cases and Chambers

Cases | Chambers | Swell Shades

Introduction

Some parts of an organ are usually visible in the room in which the instrument is installed, while others are almost never seen. The most distinctive visual feature of an organ is the pipes themselves, and they may be displayed in different ways, or they may be enclosed in one fashion or another. In general a division of pipes may be

• placed in a case.
• placed in a chamber.
• exposed, with neither case nor chamber around the pipes themselves.

Cases

An organ case is a free-standing structure that is essentially a wooden box open to the front. A chest is positioned at the bottom of a case, and the pipes above it are free to speak through the opening in the front. A separate case may be provided for each division of an instrument, or several divisions may be placed in one case. The diagram to the right shows the essential parts of a case that contains one division. The pipes of one rank are represented graphically by red rectangles, and the interior surfaces of the case are shown in blue.
Pipes are usually placed in a case with the taller pipes in front with progressively smaller pipes behind the front or façade pipes. Two exceptions are common:

• In divisions which are built into the front part of a case, as in a Brustpositiv division, taller pipes are to the rear.
• Reed pipes are usually placed where they can be most easily reached for tuning. This may mean they are behind flue pipes, when tuning access is through a panel that opens to the rear, or that they are in front of flues when tuning access is from the front.

Cases serve two primary functions:

• They provide a resonating chamber in which the sounds produced by different ranks of pipes are blended with one another.
• They provide a means for projection of the sound of the pipes forward into the room through the opening in the front of the case. The sides, back and top of the case must be made of a reflective material in order that they can serve this function.

Historically, cases have been treated as almost sculptural objects, and their design can be a distinguishing feature of several types of organ built in different centuries. The organ in the photograph to the right has a case modeled on a sixteenth century Dutch organ. It is fitted with folding panels which can be used to close the front of the case.⁷¹

Chambers

In the later years of the nineteenth century, builders began placing organs in chambers, often a separate room open to the space in which the instrument was meant to be heard. This practice continues, although the movement since 1950 has been to avoid chambers when possible so that the sound is not trapped by architectural elements that define the chamber itself.

Chambers can be covered with grills that completely hide the pipes behind them. The photograph to the left does not show any pipes. The chest and pipes are behind the arched grill, which forms the wall behind the choir loft. ⁷²

In other installations, a façade that is modeled on the front of a case can allow some pipes to be seen, even though most of them are located behind a wall in a chamber. ⁷³

Swell Shades

A pipe sounds at only one dynamic level when it is played. If more wind is supplied the pipe in order to increase its dynamic level, the both its pitch and its timbre are affected. In order to provide some method of changing the dynamic level of pipes, a case or a chamber may be fitted with a set of louvered shades that form a fourth wall, the opening through which sound emerges to the listener. Exposed pipes, or those that are in cases or chambers that do not have these devices, sound at only one dynamic level. The photograph to the right shows an installation in which the pipes of the Great, Positiv and Pedal divisions are exposed. ⁶⁸

The fourth division of the organ above is a Swell division, located in a chamber behind the exposed pipes. As in all such divisions, the front of the chamber - - the side that is open to the room in which the organ is to be heard - - is fitted with swell shades or swell shutters, which allow the organist to open or close the opening from the console. In this example, the shutters themselves are covered with a grill, so that they cannot be seen; in other installations, they are visible, and their movement can be seen by the listener.

Swell shutters may be placed in either a horizontal or a vertical position. Regardless of their direction, they work in essentially the same way. The diagram to the left represents the view from above of a small enclosure, outlined in blue, that contains twelve pipes, represented by the black circles. The red shapes represent the swell shutters. When they are closed, they form a fourth wall, but when they are open, the fourth wall is open to allow the sound of the pipes to exit the enclosure.
The action that controls the movement of swell shutters can be one of several types:

• A mechanical connection can be made between the shutters and the swell pedal, sometimes called the "swell shoe." In this case, a system of rods and traces operates the shutters in a manner that is similar to the trackers, stickers and rollers of mechanical key action.
• The shutters can be operated by electro-pneumatic motors, which move the shutters in a way that is similar to the action found in electro-pneumatic chests, using wind pressure controlled by a n electromagnet. In this case, an electrical switch, or a series of switches, is controlled by the swell pedal.
• The shutters can be controlled directly by an electric motor. In this case also, the swell pedal operates a switch.

Although many installations do not allow the swell shades to be seen, some organs use the shades as an effective part of their facades. The photograph to the left shows a set of swell shutters in a home installation, where the shutters themselves form one wall of a room. ¹⁰³ The way shades are seen as they open is demonstrated in the three photographs below. They show a small instrument with an enclosed division immediately above the keydesk. ¹⁰⁴

1. In the first photograph, the swell shutters are closed.
2. In the second, the shutters are partially open.
3. In the third photograph the shutters are fully open as seen from the angle at which the photograph was taken.

A short film of a set of shades in motion is available.

• The file is in AVI format (Cinepak Codec) and is about 2.5 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.
• A chord is sustained at the beginning of the film, with the shades in the closed position. The shades are first opened, then closed, while the chord is being sustained.
• With some browsers, it will be necessary to use the "back" button to return to this page after viewing the film.

© 1998 James H. Cook