Date: Sat, 29 Oct 2005 21:43:16 -0700

Author: "Chuck Patten"

Subject: RE: Beaker Breaking Demo Question


More Power. No trouble when using 4 12" subs driven by 3800W stereo Amp
system... 159db!


-----Original Message-----
[] On Behalf Of Urs Lauterburg
Sent: Saturday, October 29, 2005 12:57 PM
Subject: Re: Beaker Breaking Demo Question


As glasses to break usually oscillate around the rim forming
characteristic nodes in a kind of analogy to the Schroedinger
equation quantum states could the following have taken place? :

If the oscillation took place in a node forming four knots and four
bellies and if the mike is located near a belly oriented 90 degrees
away from the direction of excitation, the amplitude there would be
180 degrees out of phase in respect to the excitation. Maybe with the
mike picking up about the same amplitude from the glass as of the
original signal it could lead to total cancellation at the place of
the mike.

You should be able to test this by moving the mike farther away but
still maintain the 90 degree angle and you should have a signal again.

This is my hypothesis to what you observe.


Urs Lauterburg
Physics demonstrator
Physikalisches Institut
University of Bern

PS: As European winos we would of course use nice sounding wine
glasses to break. Anything else would be considered barbarian. I have
found a reasonably cheap brand which breaks fairly easily. I would
observe the glass vibration with a mike on an oscilloscope and adjust
the frequency of my SR Function synthesizer in mHz steps for maximum
response. As Wolfgang has pointed out it is necessary to readjust for
perfect resonance when increasing the excitation volume. If done well
the glasses break at a fairly low sound volume. We have never managed
to break a glass by a human voice though :-))

Doug Johnson wrote:
> The other day, I was setting up our Beaker Breaking Demo and ran across
> something I never noticed before. Using a microphone, when I looked for
> peak resonance(or volume) on the oscilloscope, I got one frequency like
> 1263.4 Hertz and when I tweaked it up bit, I got almost total sound
> cancellation on the microphone (outside the sound chamber it was still
> loud) at 1264.2 Hertz. At both high and low settings I have broken
> beakers. The microphone is positioned 90 degrees instead of the 180
> degrees (or opposite side) to the beaker and horn driver.
> Any idea why these two frequencies work? ...Doug J.
From Sun Oct 30 08:26:14 2005