Doug Richards wrote: > Stephen, > I agree that a yardstick (simple beam) stiffness should have linear > deflection for some range. I think we are discussing an over-constrained > beam though. If a soundboard has crown and glued at the perimeter, the > downward force of the string may not give a linear deflection due to the > soundboard edge constraints. I haven't tested this, but would go out on the > limb far enough to say that I wouldn't be surprised to find a > non-proportional deflection for increasing force. Any takers? -------------------------------------------- Doug & Stephen, A specific rib may well act as a center-loaded, end-supported beam on a test bench and my own calculations treat it as such. However, every test I have ever conducted on actual soundboards installed in piano rims -- regardless of how they are designed and/or bellied -- has shown that their deflection under load is not linear. This includes my own designs which, with their curved ribs and relatively high panel moisture content are about as purely rib-crowned as any I've ever encountered. The measured deflection of these soundboards is not directly proportional to the loading force. To the best of my knowledge I am not stressing any of the wood members or fibers beyond their proportional limits. I'm certainly making every effort to avoid this little problem. Regards, Del
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