----- 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
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