Date: Fri, 11 Oct 2002 21:17:24 +0200

Author: "Simcha Segev"

Subject: RE: breaking a glass with a speaker

Post:


Hi Erik, red-headed (or Gingi in Hebrew)

Breaking a glass is a very delicate and not easy to perform. From my
experience, the most important thing to do is adjust exactly the
function generator frequency.
I will try to describe the necessary steps to successfully perform this
demo.

First, the glass should be with a very thin wall. I use laboratory Pyrex
beaker, 100 or 250 Ml.

With a directional microphone and scope, I find the natural vibration
frequency of the beaker. (~1200Hz in 100 Ml beaker) I place the beaker
on a soft base ( foam ).

Then I start to change the frequency of the function generator ( In a
medium level power, 70 - 80 Db or about 30 - 40 Watt of the amplifier )
and look on the oscilloscope to see the level of the sound reflected
from the beaker until I see the enlargement of the signal.

The MOST IMPORTANT thing now is to adjust the correct frequency to the
exact frequency of the glass or beaker. For that, you will need a
digital function generator that can be adjusted to +/- 0.1 Hz.

Now you can increase the power of the loudspeaker ( 120 - 150 Db ) and
the glass will break.

Another way to see the natural vibration frequency of the beaker is to
put a small amount of water inside the beaker ( it change a little bit
the frequency) and in the resonance frequency the water start to "boil"
.
You may also glue a small aluminum foil to the upper side of the beaker
and aim a laser light so it will be reflected to a wall and it will
start to shake in the resonance point.

I hope that my description will be helpful to you.
Good luck, Simcha

Simcha Segev - Demo Lab
School of Physics and Astronomy
Tel Aviv University - ISRAEL
Tel. 972-3-6408077 Fax. 972-3-6429306
E-mail: simcha@post.tau.ac.il
http://minerva.tau.ac.il/physics/demolab


-----Original Message-----
From: owner-tap-l@listproc.appstate.edu
[mailto:owner-tap-l@listproc.appstate.edu] On Behalf Of
erikh@email.arizona.edu
Sent: Friday, October 11, 2002 6:03 PM
To: tap-l@listproc.appstate.edu; tap-l@listproc.appstate.edu
Subject: breaking a glass with a speaker

Hello everybody, I'm new to the listserv but you might remember me from
Boise--the
red-headed guy from the University of Arizona.

Anyway, I want to show my students what they've all seen on TV--that you
can break a glass with sound energy.

I tried it on my own & it didn't work by just matching the pitch with a
frequency
generator, turning it up 'till I couldn't take anymore, then fine tuning
it in both directions.

Where am I going wrong? glass thickness? more power? finer tuned
frequency?
'Focusing' the sound somehow?

As it was, I could smell my speaker beginning to burn afterwards.

Also, has anybody ever been able to do this with just a mic, amp, &
speaker
so that it creates a feedback loop?

Erik Herman

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