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Chladni musings
http://luthiersforum.com/forum/viewtopic.php?f=10101&t=31192		 Page 1 of 1
Author:  mhammond [ Sat Feb 19, 2011 11:37 pm ]
Post subject:  Chladni musings
Good evening everyone:
I purchased the Alan Carruth video about Mr. Chladnis' theories, VERY interesting. I had an old top that was damaged and removed during construction and figured it would be a perfect victim for my first tests. The first picture is of a pattern that popped up almost immediatly. This pattern looks to me (a Chladni beginner) to be just about right. The frequency was a little bit low at 214 hz., so I am figuring the top might have been a little bit too thin but the bracing was about right. About ten seconds after I got that pattern the speaker exploded in a small flash of light and large cloud of stinky smoke.

SO... Am I reading the pattern right? Is the top a little tight just above my signature on the back side? Also, can anyone recommend a speaker that might survive this abuse?

Attachment:
Chladni 001.jpg

Just dumb luck? idunno
Attachment:
Chladni 002.jpg


Thanks for bein here....
Mikey
Author:  Andy Gamble [ Sun Feb 20, 2011 12:54 am ]
Post subject:  Re: Chladni musings
That looks to me like a fairly good ring-and-a-half mode. It is a bit jagged in the lower treble side, but with the frequency that low I don't know if I'd try to fix it. None of this is entirely straightforward.

You need a speaker rated for at least 20 watts or so RMS, with decent bass response. I've been using the old speakers from a 2000 Mustang, but one has died and the second is starting to smell bad, so I actually just ordered a couple new speakers from Parts-Express.

I got one of these: http://www.parts-express.com/pe/showdetl.cfm?Partnumber=292-404 (That's a 40 watt 4" woofer for under $5, so I figured it's worth a try.)
and one of these: http://www.parts-express.com/pe/showdetl.cfm?Partnumber=292-405 (A 70 watt 5-1/4" woofer under $6; it might be a little bigger than I'd like, but it should last a while).

The pure sine waves that we use for Chladni patterns tend to break speakers faster than the wattage would suggest, especially at low frequencies. 15 watts is about what you need for plate tuning, so you want to exceed that significantly in the speaker's rating. It also needs to put out frequencies down to 70 Hz or so with some volume without maxing out the speaker's range of motion. Since we normally want fairly small speakers for this, that means a high Xmax. Both of the speakers I mentioned have a larger-than-average Xmax. Really, it seems to me that a miniature subwoofer might be the best way to go, but these speakers were dirt cheap.
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