Compression Question

[Delwin D Fandrich]

----- 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