Farrell wrote: > I'm not 100% sure I am understanding your comments correctly, but here goes: The board in my picture has very thin (about 3/8" thick) ribs and offer little resistance to bending. An unribbed panel will expand and contract with changing humidity without crushing - because it can expand freely. With my MC gauge in the photo, the wood is relatively free (compared to a piano soundboard in a strung piano) to expand and contract, so little, if any, crushing is going to occur with my MC gauge (likely no crushing because the level of compression force here is likely well below the failure level of spruce). We are on the same page here. > In the piano, when the soundboard panel is exposed to a similar high humidity environment, the panel will try to expand as much as the panel of my MC gauge. It will tend to crush though because the stiff ribs Here's where my comment came in... I thought it (a real soundboard) would start crushing without the addtion of the string downbearing... especially if you are up to humidity levels as in your (very cool I might add) experiement. > and the string downbearing pressure prevent it from expanding (of course, it will expand a little bit, and that is why you might see a several millimeter increase in crown - ! but not 8 inches). And then the addition of string bearing would simply compound, exasperate... further damage the cells with even more compression. I thought this is what Del and Ron have been describing. > > Does that address your comment? Are you asking whether panel damage can occur from the rib restraint alone? I don't know what the numbers are, but obviously if the ribs were big and numerous enough, the panel thin enough, and the humidity high enough, I'm sure you could set it up where the panel would fail in areas. > Yes, thats what I thought has been argued... described by Del, Ron, and a few others. > > The panel will crush if it is restrained enough. In a strung piano, I don't know what percentage of the restraint is from ribs and how much is from string bearing. I suspect the ribs play a much larger role. > > Terry Farrell > I think we are pretty much on the same page Terry. What I dont know is just what combination of humidity and downbearing will push wood cells beyond their compression limits in a traditional compression crowned board. I do know, that S&S claim that as long as the humidity levels are kept within recommended tolereances the soundboard will perform and hold up well. How they define this exactly is another matter :) Cheers, and thanks for the clarification RicB "Welcome to the Brave New World, may I see your passport please ?" Horiff Ikensaur Urlyf -- Richard Brekne RPT, N.P.T.F. UiB, Bergen, Norway mailto:rbrekne@broadpark.no http://home.broadpark.no/~rbrekne/ricmain.html
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