Impedance problem

[David Ilvedson]

So is this like on some small grands and the first tenor note or so kind of booms out...?

David I.



----- Original message ----------------------------------------
From: Ron Nossaman <rnossaman@cox.net>
To: Pianotech <pianotech@ptg.org>
Received: Fri, 21 Jan 2005 18:31:20 -0600
Subject: RE: Impedance problem



>>I didn't weigh it but it was a very small one that I use for making
>>loops for string knots.  On second thought it seems like not enough mass
>>to have an influence on impedance so soundboard resonance makes sense.

>Right, and an impedance change wouldn't be so note specific, but rather 
>more general to the area.


>>What is it that causes that to happen and how is it generally avoided in
>>design?
>>
>>David Love

>Consider a soundboard a driven harmonic oscillator. A sprung mass system. 
>When the resonant frequency of the assembly at the driven point is the same 
>or close to the same as the driver, the soundboard moves in phase with the 
>driver, increasing in amplitude and draining the driver's energy quickly. 
>It sounds loud and short. Lower the resonant frequency of the soundboard by 
>making it either heavier or less stiff, and something different happens. 
>The phase of soundboard movement lags behind that of the driver, opposing 
>movement rather than reinforcing it, so the soundboard moves at a lower 
>amplitude, and absorbs the driver's energy more slowly. It sounds less loud 
>for longer. Avoiding it in design is partly luck, depending on the 
>soundboard construction method, and partly ignoring it when it happens. 
>Adjusting it after the fact by mass loading the bridge  is easy enough, and 
>doesn't otherwise muck anything up.

>Ron N

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