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Possible acoustic phenomenon, very bizarre



Think about this: what happens when there is a standing wave in a pipe
with sealed ends? The pressure oscillation is maximum at the ends,
right? This is true regardless of which overtone is excited in the pipe?

OK, now what would happen if we excite multiple overtones of equal
pressure? (Say 1F, 3F, 5F, 7F, 9f, etc.) The pressure oscillation
at the
end of the pipe would be large for every overtone. WHen sine waves are
superposed like this, the result approaches a delta-function. The profile
of the pressure oscillations in the pipe would be very strange: low
amplitude everywhere except near the surfaces of the closed ends of the
pipe. With enough short-wavelength standing waves in the system, the
thickness of the high-pressure region would be very small. It would be
like a thin membrane.

With enough energy in the system, the absolute pressure at the ends of the
pipe while oscillating would approach two atmospheres... and vacuum. It
would become a sort of "cavitation bubble" or "standing shockwave" in
the air. (I've seen pictures of such things in books on Ultrasound, but
didn't realize that they might appear at lower frequencies.)

If we then remove the closures from the end of this pipe, what will
happen? Well, the thin "oscillating shockwaves" represent a nonuniformity
in the medium. The speed of sound is not normal within them. Since they
represent an impedance mismatch, it might be true that they will reflect
sound, and keep the standing waves trapped inside the tube. BIZARRE!
Remove the ends from the tube, and the waves continues to reflect... from
themselves?!!!

Now for the really weird part. (And you thought it was weird already?)
Slowly lower the frequency of the drive oscillator (the drive oscillator
would emit a kind of comb-spectrum +1 -3 +5 -7 +9...) As the frequency
goes down, the "shockwave membrane" should move out from the end of the
pipe as if a soap bubble was being inflated.

!

This is all speculation.

If this should really work in the real world, we would expect to see a
sort of silvery "membrane" because the pressure excursions within the
high-pressure region produces internal-reflection in the air. If this
should really work, what will happen if you stick your finger into the
"bubble"? Will it receive a burn? Resist penetration? Is this a "Star
Trek" device brought to life?

Where did this idea come from? I suppose it was just floating around in
the aether. :) While the closed mind resists penetration, a mind that is
open enough can sometimes act like a net, and catch a fish that would
otherwise never be encountered.


((((((((((((((((((((( ( ( ( ( (O) ) ) ) ) )))))))))))))))))))))
William J. Beaty SCIENCE HOBBYIST website
billb@eskimo.com http://www.amasci.com
EE/programmer/sci-exhibits science projects, tesla, weird science
Seattle, WA 206-781-3320 freenrg-L taoshum-L vortex-L webhead-L