Organs come in all shapes and sizes!
From the very large, to the quite small...
Organs, especially the larger ones, are often custom made to fit into a particular space. It is the custom nature of these instruments that could cause problems for organists if the organ controls were different for each instruments.
If every organ was designed to a different brief, organists would not be able to easily move between, and play, different instruments. It would, for example, be difficult to practice on a small 2 manual organ, before performing on a huge 4 manual organ in a cathedral.
The American Guild of Organists (AGO) and the Royal College of Organists have both tackled this problem by producing standards for organ builders. These provide a set of dimensions that define the relative positions of the main components of the organ (keyboards, pedalboards, swell pedal etc.).
PDFs of these configuration standards are available at the following locations.
(Source: Organ Works and Westminster Organ Works)
Unfortunately the standards do not match exactly. For example, the AGO has a 32 key pedalboard, while the BOC uses a 30 key pedalboard.
However, both standards take the horizontal surface of the lowest manual as the horizontal datum, and the front of the keys as the vertical datum. The organ is then dimensioned and 'built out' from these datums.
For the most part the various dimensions are with the tolerance zones of each other, the main difference is the distance from the front of the keys of the lower manual to the up stand of the sharp keys on the pedalboard (the set back).
- 2 or 3 manuals
Set back 215 - 254 mm
- 4 manuals
Set back 280mm
- 1 or 2 manuals
Set back 200 - 230 mm
- 3 or 4 manuals
Set back 240 - 270mm
The set back on the organ we're building will be set to 230mm. For our 2 manual setup, the organ will meet both AGO and BOC specs. When the design is eventually upgraded to 3 manual, this will be out by 10mm to conform to the BOC spec. I'm not going to loose too much sleep over 10mm!