Tweakers' Asylum

Posted by Steve Eddy (M) on November 21, 2006 at 19:05:25

In Reply to: I suspect there are 2 resonance characteristics at least in play posted by bartc on November 21, 2006 at 15:54:30:

I was speaking in terms of the open mouthed bowl a la a Helmholz (sp?) resonator, not the resonant frequency of the solid material of the bowl and stand.

That's what I'm referring to as well. When I said "the device's resonant frequency" I simply meant the device being used as a resonator.

The Greeks learned to use open bowls and open mouthed jars (Greeks and Romans embedded these in walls of arenas I'm told) as resonators to amplify specific frequencies related to speech.

Except that they don't amplify. They absorb. At least at the resonant frequency. What they don't absorb they re-radiate and accoring to my reference (Everest's Master Handbook of Acoustics) it was this property that they were used for:

In Helmholz resonators, we have acoustical artifacts that far antedate Helmholz himself. Resonators in th eform of large pots were used in ancient times by the Greeks and Romans in their open-air theaters. Apparently they were used to provide some reverberation in this nonreverberant outdoor setting. Some of the larger pots that have survivied to modern times have reverberation times of from 0.5 to 2 seconds. These would also absorb sound at lower frequencies. Groupings of smaller pots supplied sound absorption at the higher frequencies.

And just for additional trivia:

More recently (that is, in medieval times) such resonators were used in a number of churches in Sweden and Denmark. Pots like thos of Fig. 9-30 were embedded in the walls, presumably to reduce low-frequency reverberation that is often a problem in churches. Ashes have been found in some of the pots, undoubtedly introduced to "kill the Q" of the ceramic pot and to broaden the frequency of its effectiveness.

se