[ Richard Moody wrote:

> I am curious to know, how do you know this?  Can you hear it by ear
> or only by a tuning machine?  Or is this for pipes in close proximity
> (less than an inch apart with their speaking sides facing each other)?

I have noted this phenomenon by ear, without the aid of any tuning
device.  I used to have the care of several pipe organs in churches,
and one of them was an older electrified John Bergstrom former-tracker,
which had been shoehorned into really tight "chambers" built of old
doors, etc.  Pipes were mitered to fit, and many of the pipes were
really crowded.

Tuning this was a chore, as often just closing the access door caused
some of the close-by pipes to change their pitch.  Tuning was often a
guess as to what effect closing the door would have, as there was no
room to tune the organ with someone inside with the door closed.
Drawing can be a real pain in the ear...

Bob Loesch