Date: Fri, 11 Oct 2002 12:23:38 -0400 (EDT)

Author: Richard Berg

Subject: Re: breaking a glass with a speaker

Post:

Erik,

You are going to get a large number of responses to this one.

If I understand what you are doing, I think it will not work.

First of all, use a cheap beaker or a wine glass with a nice ring.

You should put a microphone close to the glass, and display the signal
from the microphone on a scope while you trigger with the signal from the
wave generator. Use a very stable oscillator and a healthy horn driver
with an amplifier having around 25 Watts or more output.

Match the pitch of the oscillator to the pitch that you get by tapping the
brim of the beaker or wine glass, then tune very carefully until you get a
large increase in amplitude and a phase shift of the signal from the mic
as you pass through the resonant frequency. This must be done VERY
CAREFULLY. At this point you should be able to see the vibrations of the
beaker brim with a strobe after you have turned out the room lights.

Use a hearing protector muff. I think care in the setup will minimize the
noise and discomfort.

You can see ours at:

http://www.physics.umd.edu/lecdem/services/demos/demosh3/h3-61.htm

Best wishes,

Dick Berg



On Fri, 11 Oct 2002 erikh@email.arizona.edu wrote:

> 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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Dr. Richard E. Berg, Director Phone: (301) 405-5994
Lecture-Demonstration Facility FAX: (301) 314-9525
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