Different numbers of pipes per rank in different divisions

[cpistel]

I was just looking at an organ spec and noticed that some divisions had 61 pipes and others had 68. What's the reason behind 68? I understand ranks extended by full octaves but I'm curious where the extra 7 pipes end up in this scenario.

[majestique]

It's a partial super-octave so that when octave couplers are used the pipes continue through G5 rather than stopping at C5. Many builders did a full octave (73 pipes) but some found it an unnecessary expense to go to that extent.

[myorgan]

cpistel,

I suspect it might be to extend the range of a mutation stop or use it in the upper 5^th or upper 6^th of an octave so a "normal" stop can be also borrowed as a mutation. I'm not sure how much I like this, as the "normal" stop is probably not voiced or scaled appropriate to be used as a mutation. One also loses certain harmonics when the pipe is duplicated.

Recently, I played on an organ with 4' super-couplers, and on one piece, I ended up missing about 5 notes on the high end. I'm not sure if the audience noticed it, but I certainly did. Oh, the joys of borrowing and unification!

Michael

[cpistel]

Unfortunately, the spec I was looking at did not include a list of couplers. It would be interesting to see if the divisions that had 68 note ranks had super couplers and if the ones with 61 didn't.

[myorgan]

@cpistel,

Not all organs have couplers. Borrowing and unification use different stop names/tabs/drawknobs to call on non-unison pitches from the same pipe as another rank. Hence the need for an additional 7 pipes (7 half-steps) above the end of the unison rank.

Michael

[davidecasteel]

I understand that some reed Stops use multiple flue pipes per key in the very top octaves, due to the difficulties in building reed pipes for the very high notes. This practice would make for unusual pipe numbers (not the usual values for octaves). Most of the reed Stops in our Klais instrument have an unusual number of pipes, usually 5 or 6 more than typical for other Stops. Our builder (Phillip @ Orgelbau Johannes Klais) explained that to me.

David

[michaelhoddy]

A very typical practice in "American" organs of the 20th century was to have 73 note or 68 note compasses in the enclosed divisions, especially the Swell, but often also the Choir and Solo. Unenclosed divisions with independent vertical choruses, usually the Great and Positiv, would have conventional 61 note compasses because they would be unlikely to be super-coupled, or at least would have complete choruses to the top of the keyboard.

This practice is separate from unit organs and unit ranks, which had extensions for different reasons.

[cpistel]

The spec I was looking at was an Aeolian Skinner and the split between 61 and 68 pipes was exactly on those divisions as you described.