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Re: chladni plates



Dwight,

Try driving the plate directly with a wound coil instead of by
directing sound on it. A tinplate (steel) sheet will couple
much better than a nonmagnetic material to the coil. You will
need an amplifier.

At my Alma Mater (Mount Allison Univ in Sackville, NB Canada) they
built a dirt-cheap anechoic chamber by carving stiff fibreglass sheets
into the spikes, and by cutting and gluing stiff fibreglass triangles
onto still fireglass backing. It was a lot of work, but it worked
really well. However, you have to wear masks while cutting and a lot of
nasty dust flies about (making clothing pretty itchy), then you have to
spray the assembled chamber walls ceiling and floor with something to fix
the fibres in place for safety.

There are a number of commercial sources for anechoic panels & spikes,
one of the best known is SONEX, who sell most of their wares to radio
stations and concert halls to shape studio acoutics by 'deadening'
regions. These are brutally expensive sources, in my experience.

Best regards,

Dan M

PS -- if you ever get to visit an anechoic chamber, try dropping a
set of keys on a plate or rattling your keys. Very enlightening.

Dan MacIsaac, Assistant Professor of Physics and Astronomy, Northern AZ Univ
danmac@nau.edu http://www.phy.nau.edu/~danmac/homepage.html

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. :^)

Dwight
dsouder@juno.com