Hi John The whole reason for compression boards is an involved, to say the least, discussion. Compression ridges in themselves do little or nothing to the sound of the instrument... nor do the cracks that eventually show themselves because of these or because of a lack of enough compression when the board was assembled. What compression ridges show are lengths of the soundboard where the wood has been compressed beyond its tolerance.. the cells are destroyed in the sense that their ability to swell or grow if you will with RH increases to. They are simply crushed. That in itself is not a big problem when it comes right down to it either... at least acoustically. A board with severe compression set could be reused as an RC & S panel quite successfully... which makes one ponder a bit on what is actually implied by compression damage. A board fails to respond acoustically because of other developments in the panel... that can very well be related to compression damage... or because the support against crown may not be sufficient in a given area... or because of other reasons. As such... a compression ridge simply shows a weakness in the soundboard that may (and probably will) develop eventually into a crack... and may or may not turn into an acoustic problem given enough time and large enough climatic instability. At least... thats what I hear from most holds, and it seems to match well with my experience through some 30 odd plus years of working with pianos. Cheers RicB Speaking of compression boards. What I can't comprehend, is the fact that compression ridges, are apparently ok, by some. How can they figure out the crown? Do they know how much of a compression ridge there is going to be, and allow for it? This seems to me to be impossible. Or is there something, I am missing? John M. Ross Windsor, Nova Scotia, Canada jrpiano at win.eastlink.ca
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