Sound waves(The behavior of soundboards)

[Robin Hufford]

John,
     We the proviso that the superposition of traveling waves  develops
the
standing wave patterns in the soundboard this seems to be pretty much
the way I
see it too.
Regard Robin Hufford

John Delacour wrote:

> At 11:28 PM +0100 12/16/01, Richard Brekne wrote:
>
> >John Delacour wrote:
> >>....If the solenoid of a speaker is jammed, no sound at all will be
> >>emitted from the cone.  The two cases are completely different.
> >
> >Touche'. In otherwords.... the diaphram analogy is far from adequate to fully
> >describe all of the sound producing elements of the soundboard ??.
>
> As another illustration of what I've been saying about the bridge, we
> might hark back to the Kundt experiment that you, Richard, drew our
> attention to during the Great Compression Wave Debate.
>
> You will recall that a thick metal rod was clamped firmly at its mid
> point and made to vibrate longitudinally by means of a resin-covered
> chamois leather pulled along its first half.  At the end of the
> second half was fixed a disk which fitted quite closely, like a
> piston, in a long air-filled glass tube.  The compression wave
> travelled along the rod and caused the disk to set up a compression
> wave in the air whose length could be measured using a scattering of
> cork granules, etc.
>
> The rod is firmly clamped and rigid; it cannot move longitudinally
> and yet it can carry a compression wave thoughout its length and
> excite vibrations at the same frequency in the disk, to which it is
> attached at a right angle, just as the bridge is attached to the
> soundboard.  The disk creates a compression wave in the air in the
> tube by its _transverse_ vibrations, just as our soundboard does.
> Thus a compression wave in a static body is converted into more or
> less complex transverse vibrations of a flat body, whether the disk
> or the soundboard.
>
> In the case of the bridge/soundboard pair, the bridge is "clamped"
> only in so far as it is held firmly in equilibrium between two equal
> and opposite forces.  The bridge is the locus of the points where
> these forces oppose each other and is roughly speaking at a location
> where the system is the most flexible, a good distance from the rigid
> fixings of the perimeter.  The tranverse movements induced in the
> board disturb this equilibrium and the whole structure of board, bars
> and bridges etc. is set in vibration of a complex nature.
>
> I'm not handing this out as gospel, but merely as the very simplified
> view that I currently have of the way things work, which seems to be
> logical.  I'd very much appreciate any educated comments on this view
> from the more qualified.
>
> JD