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Re: Singing pipes




On Fri, 26 Dec 1997 09:30:35 -0800 (PST) William Beaty <billb@ESKIMO.COM>
writes:
On Tue, 18 Mar 1997, Leigh Palmer wrote:

Greetings everyone! I saw an advertisement a while ago
about a
singing pipe. You place a pipe that has a wire mesh inside of it
over a
bunsen burner. When you remove the pipe from its heat source, it
lets
off a tone/moan.

I found this ancient while cleaning out old mail in my inbox.

If anyone here can quickly set up a Rijke Tube demo, I have something
for
you to try out. The Singing Pipe normally goes silent when turned
horizontally. Two theories popped up after some debate on the SAS
forum:
the sound being driven by sudden density changes and gravity, versus
the
sound being generated by a sort of Stirling Engine effect, with the
air
acting as the engine's piston, and the resonant mass acting as the
flywheel.

To further investigate this, I'd like to find out if the Rijke Tube
still
makes noise if positioned horizontally while being provided with a
gentle
air flow from a nearby fan. If the effect comes from gravity, then it
will always fail when the tube is horizontal, even if the "convection"
wind is supplied with a fan. If the effect is driven by a heat
engine,
then the "howl" will appear as long as there is slow wind through the
tube, even if the tube is horizontal.

These are called "Rijke tubes". The gauze is optimally placed one
quarter
of the length from the bottom of the tube. The ones I've made are
also of
50 mm diameter glass, with about 3 mm spaced brass wire gauze. I've
made
quite a few of these and have kept a set which is tuned to a major
triad
plus the octave. They are deafening!

I cannot explain simply (or otherwise) how these tubes work. Brian
Pippard (former Cavendish Professor of Physics at Cambridge) and I
had a
go at trying to understand them during his visit to Simon Fraser
thirty
years ago. After he left we continued a correspondence about them,
and
he believed that he did understand them, but I was incapable of
understanding his explanation, which was nonmathematical. I saw
quite a
bit of Brian during my stay in Cambridge a couple of years ago, but
I
didn't renew the discussion. Brian told me that schoolboys in
Britain
had made drainpipes sing by shoving lighted newspapers up into them
from
below. I was unable to duplicate the feat, even with his help. He
had
never done it himself.

What can be said confidently is that the tubes are powered by
convection.
When mine are laid over sideways they become utterly silent. After
being
left that way for ten seconds or so I can turn them vertical and
they
sing loudly again, seemingly with no energy source. It is quite a
dramatic effect.

I, too, would like to know how these things work.

Leigh

This sounds like one of Tom Hudson's famous "magical" physics
experiments. If there is interest, I'll try to find Tom's *new* e-mail
address and you can get a list of experiments, supplies, and directions.
- TLW