The example of the organ in RibeauvillÚ
(the background images) :
the various sound planes
To each keyboard (and to the pedal) of an organs, corresponds a
"sound plane", i.e. a given position, resulting in a characterized
A lot of devices have been designed to enable the organ stops to play more or less loud. Some of these used the variation of the wind pressure, but they never gave complete satisfaction, because a pipe is tuned and voiced for a given pressure, and thus, changing the pressure gives poor sound effects.
The register crescendo pedal, or simply "crescendo pedal" draws or pushes back the stops one by one. Their only real interest is that they enable to study the way in which the stops are drawn, and thus to know about registration at the time the crescendo pedal was built.
The most widespread system consists in placing a whole division in a box,
which can be (smoothly) opened and closed by shades which are controlled by
a pedal on the console.
wedge-shaped bellows, parallel reservoir, wind conduit, postage
The wind supply has to produce the wind, to regulate the pressure and to stock the wind when not used. Thick pipes, called wind conduit bring the wind to the wind-chests, from where it is then dispatched to the pipes.
The difficulty is to keep a constant pressure, although the instrumental part uses more or less wind according to the number of notes and stops which are currently played.
Wind was formerly produced by wedge-shaped bellows, which were in fact (very)
slightly modified fireplace bellows.
Obviously, as the bellow is either pumped up or pushed down, at least two bellows were needed in order to have a steady pressure.
Until the 15th century, there was no reservoir : the bellows fed directly the wind-chests. Obviously, the wind was not so steady.
This had two major drawbacks :
After the 15th century, some rigidity has been given to the bellows, and, by putting a weight on them, it was possible to fix the inner pressure, as this weight would substitute for the operator during "emptying" phase. However, the operator had to give a great effort in order to pull the bellows up, as the weigh was added to the effort necessary to let the air in.
In year 1677, Christian FOERNER invented a very useful accessory : the wind meter, which enables to measure very accurately the pressure. Actually, the pressure has not only to be very even, but has to keep a given value in order to keep a good voicing.
But the former approximately, about the pressure being even in the
wedge-shaped reservoir, is important, because in a wedge-shaped reservoir, the
pressure does depend on the way it is open.
However, parallel reservoirs did not immediately give complete satisfaction, because there were too much folds directed to the inside, and they would produce an over pressure when the reservoir was nearly empty. The English clock-maker CUMMINS inventor in 1814 the modern reservoir, when he got the idea to put as many entering as outgoing folds.
Up to the invention of the electric blower, the reservoir was fed by wedge-shaped
bellows (then called pumps), operated by levers (either pulled by hand or by the feet).
Other small reservoirs, called concussion bellows are sometimes present in the organ itself (near the wind-chests), in order to prevent the wind from "shaking".
The pressure and amount of wind provided by the wind supply is very important. Wind has to be steady, because all the pipes are voiced for a given pressure. When the pressure is artificially increased, the organ sound louder, but, as it was not designed for this pressure, it looses its tuning, and some pipes began to "octaviate", i.e. play an octave too high, as a result of the modification of the vibration mode in the pipe.
There is a Zimbelstern in Marienthal
Besides the "real" stops, there are some "non-speaking" stops on the organ consoles :
The couplers enable to play a division from another keyboard than the usual one. It enables two or more divisions to be played simultaneouly from the same keyboard. If the "choir to great" coupler is enabled, each note played on the great will also be played by the choir division. (On the other hand, if the choir keyboard is played, the great does not).
In the dispositions descriptions, if the second keyboard can play the first division, the following code appears : I/II (II plays both, I plays alone).
Keyboards are numbered from the lower to the upper.
The oldest coupler device is the sliding keyboard. It is still widespread among
mechanical action, "classical" organs with a choir organ : the corresponding keyboard is
the lower one (it is called "the first", and numbered "I"), and the great organ keyboard
is just above (and numbered "II").
I/II (Sliding keyboard)
A manual / pedalboard coupler has often special names ("Tirasse" in French).
Some small organs do not have any stop specific to the pedalboard (they have no pedal division). The pedalboard always plays the notes on the great (or the single) division. This is called permanent pedal coupler".
As soon as non-mechanical actions have been invented for stops (pneumatic, electric...) it became possible to call stops combinations corresponding to given volumes (pp, p, mf, f, ff, tutti). This is called a preset. The study of presets is often interesting, because they teach a lots of things about the way of registering at the time of their design.
A (free) combination is a way to select a set of stops, and to call
them later. This is done with a little lever near the stop tilting button, or by
turning the register, or with completely electronic devices.
There are also mechanical devices enabling combinations, but these devices are often limited to small organs. In order to make the registration easier on large instruments with mechanical stops action, but also in order to enable different wind pressures, the wind-chests are sometimes split in two or three parts :
Thus, it is possible to cut the wind supply of the mixtures or the reeds. This is called "reeds canceling" or "mixtures canceling", or reciprocally "reeds call" or "mixtures call".
If the wind pressure stability is essential to get a sustained, regular sound, it is also possible to vary it on purpose, to get a "vibrato" effect. This is done by the tremulant (or tremolo). It is designed to be used with soloist stops (a vox humana for example, shall always sound properly with the tremulant).
A nightingaleis a set of (generally 3) pipes, which are partly immersed in a water box. The device produced a sound which is very like the bird's song. Very common in the old times (it appeared in the 16th century), it is now very seldom. This "musical toy" was adapted to organs not designed for virtuoso performance, but to give to the audience very differentiated sounds and effects.
A Zimbelstern is a set of bells, usually taking the form of a crown of a star. These devices were extremely popular in the Middle-Ages and the Renaissance. They were usually completed by automatons and animated puppets.
Until the 17 th century, the organs were often built with percussion stops : chimes, spherical bells, drum. Today, they have also nearly completely disappeared.
The short octave is not a device, but a key disposition enabling to spare 4 large (expensive) pipes from the first octave. This disposition has been used until the 17 th century (and even later, almost in Italy). The lowest octave lacks the C#, D#, F# and G# :
For a very long time, even during the 18 th century, the manual keyboards
compass was 4 octaves (49 notes). A compass of 44 or 45 notes is characteristic of
a short octave keyboard.