Re: [Phys-l] Tuning fork to drive a speaker

[Bernard Cleyet <bernardcleyet@redshift.com>]

Aaaa,  before piezoelectric oscillators such devices were a very good  
oscillator (clock), not as good as a pendulum, but much more portable  
and much higher frequency possible.  The better ones were in an  
evacuated box to increase their Q.  I have an old one that uses a  
carbon microphone as the feedback detector.  Not in a vacuum  
chamber.  While I was a student at UCSB, they had one (evacuated).

According to a Scientific Am. article (IV '64) they typically have a  
Q of 6K.  The better pendula have ~ 10k

bc, reminded of the time he had a friend drop coins in a pay phone  
while he looked * at the signal, then duplicated it by rubbing a wire  
on a file.  Admits to stealing many nickels from the 'phone company.

*O'scope borrowed from physics dept. while a grad. student at USC.  
(c. 1961)



On 2008, Mar 03, , at 14:28, Joseph Bellina wrote:
> You just reinvented a device used in the 19th century to drive  
> electromagnets that in turn drove tuning forks in front of  
> resonators.  The device was a mechanical acoustic synthesizer.
>
>
>
> cheers,
>
> joe
>
>
> Joseph J. Bellina, Jr. Ph.D.
> Professor of Physics
> Saint Mary's College
> Notre Dame, IN 46556
>
> On Mar 3, 2008, at 4:51 PM, Folkerts, Timothy J wrote:
>
> > I was playing around with speakers for some class demos and come  
> > up with
> > a new (to me, anyway) idea.
> >
> > The old idea ...
> > If you connect a battery directly to a speaker, it will either  
> > move in
> > or out depending on the polarity of the battery.  Pretty clearly, you
> > can relate this to an attraction of repulsion of the electromagnet on
> > the cone interacting with the permanent magnet in the base.
> >
> > If you repeatedly touch the wire to the battery, you can make the
> > speaker vibrate.  But it is hard to touch the wire to the battery  
> > more
> > than a few times per second.
> >
> > The New Idea! ...
> > Enter the tuning fork.  The students can clearly see the tuning  
> > fork is
> > vibrating (especially if you dunk it in water).  Well I touched the
> > vibrating tuning fork to the battery.  One of the wires was  
> > brought up
> > close to the tuning fork, making intermittent contact with each
> > vibration.  The speaker immediately resounded with the pitch of the
> > tuning fork. (At least until the vibrations died down too much in  
> > a few
> > seconds.)  The intermittent connection to the tuning fork is, I  
> > think,
> > much more "visceral" than a function generator for a square wave  
> > input
> > to the speaker.
> >
> >
> > Depending on the situation, you could use this to demonstrate  
> > something
> > about sound or something about electromagnets and speakers.
> >
> > Tim Folkerts
> > _______________________________________________
> > Forum for Physics Educators
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>
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