Craig Brougher wrote:

> Metal pipes don't seem to intervibrate when they play, but wooden
> pipes definitely do.  You can even feel their next-door neighbors
> vibrating in response, but you can't feel a metal round pipe next
> to the playing pipe doing that.

In church organ design it is bad practice to place two four-foot open
metal ranks next to each other.  Another rank, usually of different
pitch, is usually placed between them.  The reason for this is that
when tuning one of the ranks (say, a principal) the tuning is often
"pulled" by the pipe of the same note on the other rank, thus making
tuning accuracy impossible.

This phenomenon is caused by the close proximity of two pipes of the
same pitch (or more accurately, the mouths of the two pipes) inter-
acting with each other.  I have tried tuning an organ with this
problem, the only solution being to interrupt the resonance of the
adjacent pipe by placing cotton wool inside its open top.  This can
be very difficult, given the contortions one gets into when reaching
into some small organs.

I may add that this problem does not seem to exist with eight-foot
ranks because their very size dictates them to be further apart.
Similarly, smaller ranks (two-foot etc.) would have more space between
them because of practical limitations of the chest on which they stand.

John Page, U.K.