I have been following this discussion on organ pipes, and just have
a couple things to add.

I worked on pipe organs for 15 years, with some time in a pipe shop.
The gentleman that ran the pipe shop had some interesting thoughts
about pipe work, which lead us to do some interesting experiments.

One of these was to make a set of pipes which were of flute tone, but
mixed in the construction of the pipes.  This rank was 50/50 wood and
metal pipes and not every other one, but a very random pattern, i.e.,
c could be wood, but c# would be metal then d and d# wood, then 3 more
metal, but no particular order.

A sample of people that came by the shop were then asked if they could
spare a couple of minutes, and we gave them the "test".  The pipes were
behind a screen and thus you could not see them, and the subject was
then told to play for a few minutes, and then tested as to which were
wood and which were metal.  We found that generally people (even highly
educated) could not tell the difference.

We also constructed the larger pipes of aluminium, in these cases
the ones usually made of "zinc" (G.W.F. Hunt, not Matters).  In general
I would have to say that aluminium pipes do sound similar, but a little
more on the flute-like side, rather than stringy.

These pipes would also experience "tuning shock", which usually
happened while tapping the slide or stopper down (the note would jump
to the next harmonic, until you stopped playing the note.  The pipe
would return to the correct pitch when played again.

We also did some experiments using aluminum tongues on reed pipes,
rather than brass, this resulted in a much louder pipe than with the
brass tongue.  We even made a couple of other experimental pipes.  One
was a 4-foot aluminum tibia clausa pipe with a domed cap, to try for
the scooped languid effect.  (Check out some of the better tibias, that
are scooped out just behind the flue.)  Another experiment was a 2-foot
diaphone, with a brass beater -- this pipe would not play until we feed
it 15 PSI (pounds per square inch, not inches water gage)!

I noted that one gentleman who contributed mentioned that theatre organ
strings were wood.  I haven't seen a theatre organ with wood strings
yet, but it would be interesting to see and hear.  I know that band
organs have wooded strings, and I have worked on some church organs
with wood 16' violone stops, a couple of which were rather good
examples.

Just my input for the moment.

Edward "Dan" Copeland
edcplnd@thebestisp.com
See "Our Musical House":  http://www.ourmusicalhouse.com/index.html