Sound waves(The behavior of soundboards)

[Ron Nossaman]

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