Stephen Birkett wrote: > My point (I think) was that older pianos (historical or otherwise) need > not automatically fall into that category 2), whether from 1800, 1850 or > 1900. That was where Del and I have disagreed in the past. There are > plenty of old (even really old) pianos with soundboards as good today as > they ever were in their prime (Enuf that these aren't "exceptions"). > > Stephen > > Stephen Birkett Fortepianos > Authentic Reproductions of 18th and 19th Century Pianos > 464 Winchester Drive > Waterloo, Ontario > Canada N2T 1K5 > tel: 519-885-2228 > email: birketts@wright.aps.uoguelph.ca ------------------------------------------------------------ Sigh... My point is simply that soundboards in pianos of so-called modern, "high tension," design, using what I have previously described, and now refer to, as a "compression-crowned" soundboard, installed in what is today considered to be a normal rim structure, and loaded with what is today considered to be a normal amount of string downforce, by design begin to undergo compression set from the moment they are installed in those normal rim structures. The evidence, both theoretical and empirical, overwhelmingly supports this assertion. These soundboards depend on the build-up of internal compression both to form and to hold crown. This compression is built up in the across-grain plane. Due to the nature of wood, compression set begins to occur in the wood forming these soundboard panels immediately after assembly. As compression set occurs, the ability of the soundboard to hold crown decreases -- hence crown decreases. Simple tests (see earlier posts and Journal articles) prove that the amount of internal compression built up within these soundboards is often above the wood's fiber stress proportional limit (fspl). When the amount of compression is above fspl, fiber failure occurs. And crown decreases. This failure becomes obvious in the form of compression ridges, and later cracks. And crown has decreased. The soundboards found in these pianos are not "as good today as they ever were in their prime...." And they never will be again no matter how much wishful thinking is applied to them. Since I don't build, rebuild, remanufacture, design, redesign, or even study in-depth, instruments of an earlier age every day, my comments may or may not apply to them. I have not studied the stresses that exist in the soundboards of these instruments. I'll leave that for others with that experience to determine. As well, even soundboards found in modern pianos that are fabricated in a different manner than the "traditional" compression-crowned soundboard described above are a whole other matter and are not, and never have been, a part of this discussion. They are subject to a completely different set of trials and tribulations. But, no matter what spin one wants to use, when wood is placed under compression across-grain, compression set occurs. And when wood is compressed across-grain beyond its fspl, wood fiber failure is inevitable. Del
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