---------------------- multipart/mixed attachment >> >>I'm honestly not sure about that. It seems like to me it's both. >> Was Ron Os demonstation on a board glued to the case liner? For the=20 >> board will certainly react differently if the test is out of the piano=20 >> with out the edges glued down > >It was not glued to a rim. But it was clamped so that the edges could not= =20 >move out. It should be in the archives. I sort of remember this, but not the details. I'll try to find it.=20 Incidentally, the edges won't move out - they'll move in as the board is=20 depressed. It's not an arch, it's a cable suspension. Remember? >> >> And too much makes for a stingy sound especially in the treble > >Yes. Good point. If it was just about increasing stiffness while not=20 >increasing mass, then it would seem that one wouldn't so quickly reach an= =20 >upper limit. So how much of that is due to restriction from the short back scale lengths= =20 of a tuned duplex, and how much is the soundboard? >This gets back to one of my original questions. Is it increasing=20 >stiffness that matters or stress (or strain as you put it) in the=20 >board? Or something else altogether? This is a semantics problem, more than a mechanical one. Take two=20 soundboards, one with a low crown and stiff enough that it deflects 1mm, to= =20 produce a 1=B0 bearing angle at a certain point in the scale. The other has= a=20 higher crown, but is less stiff (lower spring rate), so that it deflects=20 3mm to produce a 1=B0 bearing angle at that same point in the same scale.=20 Both are supporting identical loads at identical heights. Which is stiffer?= =20 Depends on whether you're talking about load capacity, or spring rate. Why would a soundboard assembly spring rate get higher as it is loaded?=20 Panel compression will make the difference, in my opinion. I've done=20 deflection tests on model assemblies consisting of one rib and a strip of=20 panel, both compression crowned and rib crowned. The spring rate does=20 increase as the board is deflected. It's not linear like a beam, at least=20 in my testing. >>If the crowned board is not getting stiffer as it >>deflects down, then a flat board would be just as stiff as a crowned >>board. So, the reason for the crown would not be 'stiffness'. >> >>Phil But if the panel compression is what is responsible for the increasing=20 spring rate, and the board is already flat, that means the panel is already= =20 too crushed to bend the rib into a crown, much less provide the compression= =20 resistance to increase spring rate as it is loaded. >> >> But I think it is getting stiffer. >> Dale Me too. Ron N ---------------------- multipart/mixed attachment--
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