Sound waves(The behavior of soundboards)

[Richard Brekne]

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Ron Nossaman wrote:

> >Askenfelt
> >clearly addressed thot point and said the rocking motion the bridge
> >experiences was
> >caused by longitudinal waves.
>
> No, clearly to anyone who read and understood his message, he did not. He
> said a longitudinal force component.
>
> Ron N

I recopy below  what he actually said Ron. And ok... I shouldn't have said
"longitudinal waves" which is something else entirely and not what I was
getting at to begin with.

Yet there is no doubt that he attributes the rocking motion to longitudinal
movement in the strings vibration. I doubt seriously he would choose this
word unless he meant to use it.  The point is, no matter how you cut it this
is a different kind of force then the one you applied with your "finger on a
string" bit . As I said then, your finger experiment did nothing more then
prove you could deflect the bridge in this manner. It said nothing about
exactly how the strings vibrations could accomplish that.

Your finger example was much more analogous of a purely transverse action.
And I think it was the kind of mental picture this purely transverse action
creates that loosed Johns counteraction.

What Anders says looks more like a pulse moving in directly from the side,
applied at the top of the bridge, which literally pushes and pulls (sideways)
at the bridge.

And again, I'd like to get a better grip also on this "frequency dependent
velocity of waves" thing in the panel. How does that fit with the description
of the SB's movement as it had been presented up to early Dec last year ?

Curious minds want to understand how this all fits together.



     1. The force from the string tries to drive the sound board up and
     down
     mainly. This gives bending waves (transversal waves) in the sound
     board
     which in turn radiates sound into the air. (Surface waves occur
     mainly
     in water and other liquids.) There is also a much weaker
     longitudinal force
     component which tries to tilt (rock) the bridge back and forth (as
     the
     force is applied at the top). This force also gives bending waves
     in the
     sound board.

--
Richard Brekne
RPT, N.P.T.F.
Bergen, Norway
mailto:rbrekne@broadpark.no
http://home.broadpark.no/~rbrekne/ricmain.html


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