[Fwd: Rocking bridges]

[Robin Hufford]

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At 1:48 PM -0600 12/22/01, Ron Nossaman wrote:

>
>John, Robin, try this with a strung piano.
>
>...strike the key as if you were demonstrating
>the sustain characteristics of one of your pianos to a skeptic...
>Now press down on the strings of the unison adjacent to the gage one
>about the same amount and observe the indicator dial. It will
>move....Oh, but that's not a fair test because you have to push too
>hard to get that 0.0005" deflection. Fine. Push less, get less
>deflection, and produce less air displacement, which would result in
>less volume from the instrument if the string were then allowed to
>vibrate from that displacement amplitude. No mystery there I
>trust....


>All sorts of compression waves and molecular level stress disturbances
can
>be immediately moving through every part of the bridge from the first
>movement of the string, but they're clearly not what moves the bridge.
The
>strings move the bridge, the bridge moves the soundboard.

Ron,

     Should the string be substantially, physically, moving the bridge
as a result of its cyclic behavior that  to any significant degree
contributes to the sound  then one has to contemplate a panorama of
immense complexity  regarding the tension in the strings as the bridge
supposedly flexes back and forth, rocks and ripples.  While I think it
obvious that putting pressure on the strings or pulling up on them will
move the board a little bit, and stipulating the string does so then if
your example were true
would this make a difference in the sound and how would you calculate
it?  0.0005 of an inch seems to be a rather small and very trivial
amount.  I emphasize again that I believe, in fact, that any rocking,
rippling or flexing motion is not a significant contributor to the
energy level acquired by the soundboard and that there must be a very
critical limit that such motion, if it existed, could not be allowed to
exceed.  In fact, I believe, historical, that the practical evolution of
soundboards has been precisely in the direction of minimizing and
elimanating any such motion.     Perhaps you, Del or Ron O.  could tell
us how such a small amount were its existence actually a fact,  could
make an audible difference.


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From: John Delacour <JD@Pianomaker.co.uk>
Subject: Rocking bridges
Date: Sat, 22 Dec 2001 22:39:04 +0000
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