Soundboards: Thickness and Area

[Delwin D Fandrich]

----- Original Message ----- 
From: "Richard Brekne" <Richard.Brekne@grieg.uib.no>
To: "Pianotech" <pianotech@ptg.org>
Sent: October 20, 2003 1:50 PM
Subject: Re: Soundboards: Thickness and Area


> No... Banging with a hammer or something on the bridge to see where sand
> gathers has nothing to do with Chladni patterns.
>


Of course these are Chladni patterns. What do you think banging on the
soundboard with a hammer or something is doing?

This hammer or something constitutes a broadband impulse tone generator.
The act of hitting the soundboard with any reasonably hard object sets up a
broad spectrum of vibrating energy (along with the resulting resonances) in
the soundboard. The energy spectrum can be altered by varying the hardness
and velocity of the striking object. When used to generate Chladni patterns
this process tends to emphasize the fundamental because the upper
resonances damp out so quickly the sand doesn't have time to find and
settle into the smaller nodes. But these are Chladni patterns all the same.

Striking an object with a carefully calibrated steel hammer is generally
how vibrating energy is set up in an object under test for a modal
analysis. It's then called a modal hammer and its price goes up by an order
or two of magnitude.

Del