Date: Mon Dec 1 10:06:34 2008

Author: Dale E. Stille

Subject: Re: Breaking glass with sound

Post:

Van and all,

One quick note. I had been using 1000 ml Pyrex beakers with very
consistent results. Then biochem stores where I got the beakers
switched to the VWR 1000 ml beakers because they were cheaper. No
matter how I tuned, turned, or positioned, I could not get a one of them
to break. Ended up having them order me the old beakers again.
I also burnt out a couple of driver coils when setting up my demo and
trying to tune by ear. Ended up using the Pasco digital function
generator to tune up with. No failures since.
A word of caution......tune carefully and when you ramp up the power, if
the glass doesn't break, ramp the power down quickly. Holding at high
power for any length of time will blow the driver.

Later,
Dale

Van Bistrow wrote:
> Thanks again, Guys!
>
> I hear you on the necessity of finding the resonance frequency.
>
> I would also like to design a system that does not blow drivers. I
> believe the failure mode is burning up the coil, since I can smell that
> lovely burning scent after the speaker dies. Also, the speaker
> resistance goes to infinity after the failure. So, I think I know the
> failure mechanism.
>
> It is unclear to me why it should make a difference whether the
> frequency is narrow or broad-band. I would think that over-heating the
> coil wouldn't depend on that, but rather, the overall power dissipated
> in the coil. (??)
>
> Thanks to all your help, I have ordered the new driver you've
> recommended and will do a better job of finding the resonance. BUT I
> still haven't figured how to protect the speaker, since I am unclear
> what the power specs actually mean.
>
> Thanks again!
>
> Van
>
> Van Bistrow
> Director, Instructional Laboratories
> and Lecture Facilities
> Department of Physics
> University of Chicago
> Phone: 773-702-7013
> Fax: 773-702-7018
>
> On Nov 25, 2008, at 12:03 PM, Richard Berg wrote:
>
>> You need to get better at fine tuning resonance so you don't need to use
>> such high power to break the glass.
>> Keep the glass very, very close to the horn driver.
>> Be sure to find the phase shift of the signal at resonance. - JZ
>>
>> Amen, brother. Say what?
>>
>> Dick
>>
>> ***********************************************************************
>> Dr. Richard E. Berg, Professor of the Practice
>> Director, Physics Lecture-Demonstration Facility
>> U.S. mail address:
>> Department of Physics
>> University of Maryland
>> College Park, MD 20742-4111
>> Phone: (301) 405-5994
>> FAX: (301) 314-9525
>> e-mail reberg@umd.edu
>> www.physics.umd.edu/lecdem
>> ***********************************************************************
>



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