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
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