Sound waves(The behavior of soundboards)

[Robin Hufford]

Ron,
     Very interesting.  I am not implying an infinite stiffness anywhere and am
aware of the standing waves generated in the plate but maintain that they occur
as a result of the superposition of the traveling waves.   I am not the least
bit suprised that a ten pound weight would cause the case and plate to flex.
What would be more interesting would the deflection be at far lower weights,
for example that of a tuning fork.  Even this I think is much greater than the
pressure change exerted on the bridge by a string or a tuning fork.  This is
the point of contention.
Regards, Robin Hufford
Ron Nossaman wrote:

> Robin,
> I just stepped out in the shop and did a little experiment of my own that
> might help to clarify. Using what was a recently abandoned and not terribly
> informative attempt at a monochord as a beam, and clamping a dial indicator
> to it, I laid it across the rim of an unstrung piano. In the last treble
> section, where the plate is most heavily braced, and the struts and
> unsupported spans are shortest, I took a gage reading and set a 10lb box of
> tuning pins on the plate next to the dial indicator. The plate deflected
> about 0.0015". I then set the same box of tuning pins on the rim next to
> the beam and got a similar change - just over  a thousandth of an inch.
> Being relatively stiff doesn't make either of these things infinitely
> stiff, and that seems to be the presumption in your approach. If not,
> please correct me. As it is, they will both support a measurable transverse
> vibration, and will produce audible sound as a result. The same applies to
> the soundboard, only it's far easier to induce transverse vibrations in.
>
> Ron N