Re: chladni plates

["Prof. John P. Ertel (wizard)" <jpe@nadn.navy.mil>]

Sorry --- in my haste to get to work on other things, I forgot to answer
the second part of this question. (:^)

On Fri, 14 Mar 1997, Dwight K. Souder wrote:

> 	I was wondering if someone could assist me.  We are currently
> covering waves and I've been trying to get a chlandi plate to work.  I've
> put the plate above a speaker, which is connected to a wave generator.  I
> can get some vibrations in the plate, but nothing to great.  I've tried a
>  wide variety of plates and wavelengths, but I'm still getting poor to no
> results.  I know many times this demo is done with violin bow strings,
> but I've also heard of using speakers.  My guess is that maybe my
> amplitude is to low.
> 	Also, I showed my students a picture of the "quiet room", the
> room where there is very little sound reflection from the wedge shaped
> material that is all over the room.  Does anyone know what type of
> material they are using?  Any chance I can get some for my underclassmen
> study hall?  Or better yet, a large enough speaker to generate a complete
> destructive interference for the entire room.  :^)

We have an "anechoit chamber" here at the Academy.  The wedges are filled
with simple loose packed (and wire mesh covered) fiber glass --- nothing
more complecated than that.  The anechoit system relies upon sound moving
into the space between the wedges and getting trapped and absorbed after
multiple reflections.

> Dwight
> dsouder@juno.com

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