Soundboards: Thickness and Area

[Richard Brekne]

Delwin D Fandrich wrote:
> 
>
> 
> > 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?


The subject matter at hand is the gathering of sand around the edges of
the piano. The Chladni patterns reflect the vibrational modes of the
soundboard. 

I beg to differ ... these two things are independent of each other. Of
course they have in common that you bang the bridge with hammer, and
that sand is used to show where the board is not moving. But thats about
it.

RicB


> 
> 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
> 
> 
-- 
Richard Brekne
RPT, N.P.T.F.
UiB, Bergen, Norway
mailto:rbrekne@broadpark.no
http://home.broadpark.no/~rbrekne/ricmain.html
http://www.hf.uib.no/grieg/personer/cv_RB.html