I think I am beginning to see what you are saying (asking).

While one can in theory make a round metal or square or rectangular
wooden pipe that have similar characteristics, in reality the end
result when you compare them is similar in sound, but also different.

This could be the result of the shape of the area directly inside the
mouth extending to the back of the mouth.  With a wood pipe where you
could have the mouth on the long side of the pipe (like a hohl flute),
the space behind the upper lip to the back of the pipe is short, but
the full width of the pipe.

When you turn it around, and put the mouth on the narrow side you get
the standard issue concert flute which is similar to the hohl flute,
but yet different.  When you look at metal pipes the cross section at
the mouth is round with one side flattened (like the wheel on a flat
car which had the brakes on when a train moved).  This means that the
space behind the mouth is actually wider that the mouth, in some cases
much wider and the back is not flat, but rather curved.

With this in mind, the wave which will be the sound of the pipe, will
be re-enforced and influenced by the area around the mouth.  Think of
a bowl of Jello.  If one has a rectangular bowl of this dessert and
shakes it back and forth first with the narrow side on the front and
then with the wide side on the front, and observes the way in which it
wiggles, one would see that it is much different.

Now if the same person (at the same table) has a round bowl and shakes
it, no matter which way the bowl is turned it wiggles in a similar
manner.  I suppose if you made Jello cubes and discs the way in which
it wiggled would be more similar to the air in an organ pipe.

Then you look at the material of which the pipe is made.  For instance,
take the Murray M. Harris Tibia, made of redwood.  Redwood is soft;
if you break a redwood board the ends tend to have long tongues on them
(in contrast break a piece of balsa).  Pine is similar, but harder, and
poplar is a little harder yet.  The entire body of the pipe vibrates
(if you hold one while it is playing the pitch changes, both from heat
and the fact that you hand is causing a node).  Another factor is
sympathy, however, I would state that you need two pipes, of a similar
pitch playing to notice.

Think of a pipe organ as a group of waveform generators.  The usual
groupings being 8' pitch (unison, 1st harmonic), 4' pitch ( 2nd har-
monic), 2-2/3' ( 3rd harm.), and 2' (4th harm).  If all these are in
tune, it would be louder than if they were slightly detuned, and this
is because of the re-enforcing factors of the sound waves.

Now when I have noticed pipes drawing to each other is when I am
tuning, and it is usually if I am using a 8' diapason to tune an 8'
flute.  This can be avoided if you use the 4' octave instead of the 8'.
I think this has to do with a similarity in the sound wave.  If you try
this with an 8' string (a loud one) rather then the diapason the two
tones may still try to pull together, but not as much.  I have seen
examples of this with both metal and wood bourdons and other flutes.

To sum up, all these factors add into the way in which an organ pipe
produces sound.  One can see why one type of pipe sounds different than
another of theoretically similar dimensions, but made in a different
manner, with a different material.  This is because they are different.
I feel it is more the power of suggestion that causes us to perceive
a sound a certain way.

There was a small residence Kimball player pipe organ I use to take
care of.  It had a French Horn on the great.  When I first went to tune
it, I could not find the French horn pipes in the chamber, just this
big open melodia.  I had my key-holder hold down a note on the French
horn, only to find that the large melodia _was_ the French horn.  I had
been fooled.

Ed Copeland
edcplnd@thebestisp.com
www.ourmusicalhouse.com