Soundboard Torture - and Failure!

[Ron Nossaman]

>My gauge has been in the shop now for a week at 45% RH. It did not settle 
>back at the two/three-inch crown position. It is nearly straight, with 
>only about ONE INCH of crown. I thought that because the ribs are so thin 
>it would bend quite a bit (which it did) at high humidity, but not crush 
>the spruce panel. Apparently, the panel suffered quite a bit a damage 
>(compression set I suppose) with just the one several day exposure to high 
>humidity. Just imagine what that would do to a piano soundboard that has 
>one-inch by one-inch ribs and all the strings only allowing it to expand a 
>tiny bit. CRUSH, CRUSH, CRUSH!


Left unconstrained, your 48" panel going from the original 5%MC to 16%MC of 
that 80%+RH would have expanded around 0.8". The side glued to the rib 
can't go much of anywhere, and the side that's "free" to expand can't go 
much further. Seems like most of the life of compression crowned boards is 
used up just by assembly and the first chip tuning.


>I'm getting the to the point where I think a good piano should spent its 
>life with museum-like environmental control - nothing less will do.
>
>Terry Farrell

Rib crowning sure buys a whole lot of tolerance.

Ron N