Sound waves(The behavior of soundboards)

[Delwin D Fandrich]

----- Original Message -----
From: "John Delacour" <JD@Pianomaker.co.uk>
To: <pianotech@ptg.org>
Sent: December 16, 2001 7:43 AM
Subject: Re: Sound waves(The behavior of soundboards)


> The vibrations cause by the transverse movements of the taut string
> are passed into the bridge at a point equivalent to the point of the
> tuning fork pressed against the bridge, and this point in both cases
> is static and not mobile.  From this point the vibration, or
> molecular disturbance, radiates into the elastic medium that is the
> beech or box or maple + the steel of the pin and travels as
> compression waves in all directions as fast as the medium, the grain
> direction etc. allow.  Virtually every molecule of the wood or steel
> will be displaced and oscillate in response to the kicks and shoves
> from its neigbours.  It is the oscillation of the molecules next to
> the glue line, excited by kicks and shoves from all directions within
> the bridge, that will now raise a rumpus in the soundboard.  The
> bridge so far remains unmoved, its internal tranquility severely
> disturbed but outwardly unmoved, unrippled, unfurrowed.
>
> Serious comments only please.
>
> JD
> --------------------------------------------

The accelerometer doesn't care at all about the molecules inside the bridge,
the bridge pin or the glue line. It measures only the physical acceleration
and motion of the object it is fastened to. And when an accelerometer is
mounted to a bridge excited by a string it--when connected to the proper
measuring and/or indicating equipment--indicates that physical motion is
clearly taking place. The bridge is physically moving predominately in the
vertical direction with some fore and aft motion and even a little side to
side motion thrown in for good measure. Whatever else might be taking place
inside the bridge might be open to some speculation, but the bridge is
definately and physically moving.

Del