At 10:35 AM 12/3/98 -0500, you wrote: >If the "crystal" soundboard was not deflected at all by the vertical >component of the stringband loading it can only be explained if the board >was much *stiffer* than an oridinary spruce board. So the thing is both too >stiff and too heavy. * I didn't read that the panel wasn't deflected by the string load, I read that he hadn't built any crown in. I either missed that, or you're assuming. >Agreed, as Ron points out, it is an impedance >question. I don't agree, though, that the stiffness parameter is affected >by the loading. It is not functioning as a "hardening spring" such as a >car suspension or the hammer coverings, in both of which the stiffness >parameter changes with applied force. A soundboard stiffness is constant >and pre-designed before any loading. >Stephen * Absolutely not so, and easily enough proven. When you load any wooden beam, like a rib, it will deflect to some degree. If it deflects at all, and the resistance to deflection (stiffness) didn't increase as deflection occurs, the beam (rib) would simply continue deflecting until it breaks. The fact is that a given load will deflect the beam a certain amount, but double the load will not deflect it twice the distance. You can prove it in the shop in a couple of minutes with an old wooden yardstick and your set of gram weights, or in a piano with a couple hundred pounds of lead. You can also prove it with a simple beam deflection formula in a computer program or spreadsheet. It doesn't matter, in principle, whether the board is compression crowned, or supported by machine crowned ribs. The results are similar. A positively crowned soundboard assembly is stiffer under load than it is in an unloaded state. Ron
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