----- Original Message ----- From: "Bill Ballard" <yardbird@vermontel.net> To: "Pianotech" <pianotech@ptg.org> Sent: August 28, 2003 5:45 AM Subject: Re: Compression Question > I look forward to this answer, but at the same time would also like > the guidelines the question is based on confirmed. I heard somewhere, > maybe on this list, maybe in a convention classroom, that there was > at most a 6% EMC range (from belly-room dry to living-room full > summer humidity), through which a soundboard panel glued into a piano > rim could go before serious compression ridge damage occurred. IOW, > the board in Ric's example should be allowed to rise to no greater > than 10% EMC. That depends on where you live (more properly, where the piano lives). A compression-crowned soundboard assembly is typically ribbed at 4% MC. According to most weather charts RH inside houses located in various parts of the U.S. can range from about that (4%) up to about 13% or 14%. All depending on the individual house and whatever HVAC systems may or may not be in place. > > Correct me. I have a customer with a 2-year-old Petroff grand, which > at one year had serious compressions ridges, a separation between > board and ribs, and a crack (closed during summer humidity) at the > location of the separation. Both the dealer and the company regional > rep downplayed the effectiveness of the Dampp-Chaser system, which > the owner had in the Yamaha vertical traded in for the grand. If seasonal variations in RH were not a problem Dampp-Chaser would have gone out of business decades back. As it is they are still with us. I don't know the precise soundboard crowning method used by Petroff but I've seen enough of them to suspect it is some form of compression-crowning technique. It's a moot point anyway. The whole point of a Dampp-Chaser system is to stabilize things, especially the movement of a solid-spruce soundboard and even more especially the high MC swings. Of course a Dampp-Chaser system will help. Del
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