Is it possible to change stops while the organ is sounding?

Of course if it's a modern organ...
But what if it's an old tracker-action organ? (Like the Bovenkerk Hinsz organ in the Real World)
Is it possible to pull or push stops, while the keys are held down and the instrument is sounding? Will it damage the instrument?
For example: with some stops already pulled out, I play a chord and hold, now I want to pull another stop whose pipes may be on ANOTHER wind chest. Is it OK to do so?

Thank you!

Best Regards,
Christian Liu

Yes: I can't think of a design where this would cause a problem. Historic and traditional organs (slider or pallet) would be fine since the key action is completely independent of the stop action. I can't think of any organ that would actually be damaged by pulling stops while the keys are depressed. Nor can I imagine anyone would be content to keep repairing the damage that would inevitably ensue.

Maybe some early 20th century cinema and extension (unit chest) designs might have done something unexpected - they did some crazy things with electromechanical relays as they were discovering how to use them.

EDIT: On reflection, your question might be about couplers rather than stops. The designs of inter-manual, octave and manual-to-pedal mechanical couplers used for the last 250 years have allowed them to be brought into use easily and safely while keys are depressed. (They may or may not have any effect on these notes depending on mechanism). Before that, this was not always true: it took some time for workable designs to emerge.

I've had significant experience playing 19th-century tracker-action organs. With the ones I played it was no trouble to change anything at all during performance. However in earlier times the coupling actions could easily cause problems if they were operated while playing.

The so-called "shove" coupler involved grasping two large brass knobs - one at each of the keyboard - then pulling the entire keyboard forward a short distance to engage a coupling link to the keyboard underneath. This type of coupler mustn't be operated with keys depressed. Although it's difficult to play keys while moving the coupler mechanism - since both hands are needed on the coupler - it's still important not to be holding a coupled pedal note at that time if the pedal coupler physically moves the keys.

Some two-manual reed organs (Estey in particular) use a Swell to Great coupling action which shouldn't be drawn if any keys are depressed on the Great. This type of coupler uses short stickers mounted on a rotating spindle fitted between the key tails. The entire assembly rotates when pushed off so that the stickers move to the horizontal and thus don't touch the key tails. When drawn, the mechanism turns through 90 degrees to bring the stickers into the vertical position. Then, when the long centre-pivoted Great keys are pressed, the key tails lift up (like a see-saw), and the little stickers now create a direct link from them to the underside of the Swell key tails. The rear ends of the Swell keys are then pushed up, pivoting in the middle and thus forcing the fronts down, causing the Swell to sound when the Great is played upon. This type of coupler should only be operated without keys being played upon the Great, and without any coupled pedal notes sounding. Some pipe organs with mechanical key action also use this type of coupler.

Andrew

On some old instruments, because of the mechanics of the the action, the stops might sometimes be too far away from the player to operate from the console. See http://www.jacobus.de/neu/english/index_2_5.html An assistant would be need to add stops whilst playing.
Iain

In regard to 19th c type mechanical actions, it is generally possible to change couplers while playing, It is, however, decidedly not good practice. Changing the couplers while playing drags the activating jack across the leathered surface of the key, which most assuredly will damage the leather, at least when it's older and dried out. When doing restoration work on these instruments it's always evident when this has occurred (and conversely when it hasn't). Modern (non reproduction type) couplers don't present this problem as they couple on the actions rather than the keys and don't involve dragging jacks across the leathered surfaces.

References: 19c mechanisms : excellent drawings in Audsley, Modern mechanisms: Laukhuff catalog 8.13 et seq - concept drawings of various configurations and some photos give the idea.

Just to be complete, there is no problem doing this on theater (cinema) pipe organs. In fact, holding down keys and moving stops on and off is a standard technique - often used to accent chords or bring on percussions momentarily.

Also, any organ for which a crescendo mechanism exists should support this - since that's exactly what these mechanisms do.

Les