Ron Nossaman wrote: > > In a rib crowned and rib supported board, maybe 95%-100% of the > stiffness comes from the ribs. In a compression crowned board, probably > somewhat over 120% of the stiffness comes from the panel, since the ribs > supply negative stiffness and crown support. A rib crowned but panel > supported board is somewhere above 0%, and under 100%. I'm sorry but I am not swallowing this one. This is very misleading. If this were true a strip of cross grain soundboard panel say 5" wide and 30" long with a rib glued on using the panel crowning method would have the same stiffness (or less) than the panel alone. This is just not true. Using your theory we can draw all sorts of faulty conclusions. Ribs made from laminated strip were the crown is formed by cold gluing in curved forms would then be less stiff than ones cut from solid wood. Laminated chair backs would be a public health concern with the potential to let go at any time releasing negative stiffness! I am going to go out on limb here and predict that from a stiffness point of view it doesn't much matter whether the crown is formed by the shape of the ribs or whether the crown is formed by an expanding panel. The main factor when it comes to stiffness is the cross section and length of the ribs. There are many advantages to rib crowned soundboards (God knows we've heard plenty) but the kind of things reported above just muddies the water with absurd claims. You make it sound like a panel crowned soundboard will be as flimsy as an un-ribbed panel. And what the heck is negative stiffness? John Hartman RPT John Hartman Pianos [link redacted at request of site owner - Jul 25, 2015] Rebuilding Steinway and Mason & Hamlin Grand Pianos Since 1979 Piano Technicians Journal Journal Illustrator/Contributing Editor [link redacted at request of site owner - Jul 25, 2015]
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