On 7/15/2011 1:57 PM, John Delacour wrote: > At 07:27 -0700 15/07/2011, David Love wrote: > >> The discussion was whether a rib bent and clamped to the rim while >> bent supports load before it goes negative. > > There are two things I don't understand here. First, what has > "supporting load" got to do with the function of a soundboard? In the days before carbon fiber, a working traditional crowned (by whatever method) board is typically expected to have both positive crown and positive bearing. If a board is maintaining crown under positive bearing, it's supporting load. >and > second, why would anybody put a piano together in such a way that it was > possible for the soundboard to "go negative"? Beats me, but it's been done forever, and still is. > Probably the ideal situation is a soundboard which gives the proper > pressure (admittance) at the bridge when it is almost flat. What degree > of crown that soundboard will have when the strings are off will depend > on its compressibility, and that is not an easily measurable quantity. Which is why I said I find unloaded crown measurements in old boards to be of no use to me. >I > can't see any virtue in having any considerable degree of crown on the > board when the tension is on. Personally, I want the loaded crown to be at least as high as the bearing offset - so it can't go negative. Other than that I don't find any clear evidence that it makes a difference. Ron N
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