Facts and nots : was Recommend Rebuilder?

[David Love]

Not exactly.  While there are no "compression ridge" or "crack" noises as
such, it's not quite true that they do nothing or mean nothing for the sound
of the instrument.  That they exist indicates a weakening of the soundboard
spring which was supported by nothing more than the compression of the
panel.  The weakening of that spring does have implications for tone.
Moreover, they have implications for the tonal stability of the system over
time.  

David Love
davidlovepianos at comcast.net 
www.davidlovepianos.com

-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of RicB
Sent: Friday, March 23, 2007 3:12 PM
To: pianotech at ptg.org
Subject: Facts and nots : was Recommend Rebuilder?

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