Re: Singing pipes

[Leigh Palmer <palmer@sfu.ca>]

Richard W. Tarara wrote:
> > From the vast amount of traffic on this topic, it seems clear that many do
> this demo, but from the lack of a coherent explanation (or the complexity
> of such explanations) I fail to see the pedagogical value.  Only George
> Spagna's lab seems to make any real 'use' of the phenomenon.  This seems to
> me to be one of the many 'gee whiz' demos that we often get into but that
> fail to educate in proportion to the time, effort, and expense invested in
> them.

When I teach the physics of music course I talk about Sabine's work on
architectural acoustics. 1990 Canadian sensibilities would be offended
if I used his technique of firing off a pistol in the lecture hall to
measure reverberation time, so I use a Rijke tube instead.

While I do that, I also show Rijke tubes to any class in which I discuss
acoustics. I do let the students know that I don't quite understand the
mechanism by which they are driven by the gauze, but they oscillate at
the same fundamental frequency as any open pipe. The information that a
Rijke tube has oscillated with a component at the first overtone (in
this case the octave) comes as a great surprise to me because that would
place the gauze at a *node* of the oscillation, certainly a clue I did
not have before. If it is true it is very surprising.

Leigh