Soundboard question

[Richard Brekne]

Thanks Nick and Will for your considered and well thought through 
responses.  These kinds of posts are very much appreciated. Nick points 
out a couple things, one especially that I have suspected and aired for 
quite some many years now. Namely that this whole concept of equating 
compression set per sé with "damage" in the most destructive of sense is 
very rightly questionable and long over due for considered discussion.  
He also points out something I've seen several places through the years 
in reading through different studies on wood properties. That wood under 
compression beyond its elastic limit to some point and in some 
directions actually initially gains in some strength properties before 
eventually weakening and failure occurs with continued increased 
compression levels.

Both Will and Nick point out the problem with the non-uniformity of 
wood, which of course is a basic point. Will points out that he believes 
that  a pre-compressive processes will identify and make acute any weak 
areas which when ribbed will react exactly like these same areas would 
had they become acute due to post(ribbing)-compressive processes that we 
know about.  Both he and Terry seem to think this would just hurry 
things along.  I am not quite sure thats what would happen... tho I 
admit being on thin ground here.  Its just there is something that seems 
a bit different. The pre-compressed panel has a different start state 
when ribbed. Without going into it (as I would like to think a bit more 
on the whole thing) it would seem on the surface of it that either Will 
and Terry are correct in thinking that checking would be hurried.... or 
the opposite would happen. I think its reasonable to assume in any case 
the pre-compressed panel would not behave identically to one that had 
not been.

In both areas of discussion, I am brought back to a discussion several 
years ago where it was stated out right that an old soundboard that had 
undergone as much as 100 years of compression set, re-ribbed to function 
as a rib crowned assembly would function quite as well and perform very 
much like a brand new panel. Two things about this claim struck me as 
more then a little significant. First... how could this be possible if 
the term compression set is to be equated with the idea of such 
destructive damage ?  Compression damage as it is often presented and an 
even acceptable performance of such an old panel are mutually exclusive 
states. One has to be flawed, and since it is very clearly possible to 
reconstruct an old panel into a very fine soundboard it strikes me as 
clear we need to re-think what compression damage really implies in our 
particular application. Again this echos some of what Nick writes about.

I am also brought to think about the basic procedure in refitting an old 
checked panel.  It is carefully de-ribbed, brought back together 
appropriately and re-glued into a single panel, then re-ribbed.  The 
weakened areas that were checks in the panel are removed and whats left 
is far more uniformly strong compressed wood. Such panels seem to 
exhibit a tendency towards increased stability and do not check. Strikes 
me that at the very least pre-compressive process could be contrived to 
create a similar state. Removing overly weak areas, and increasing the 
panels resistance to some of the problems relating to climatic change.  
Whether or not it is worth the effort (in the case the above reasoning 
holds) is another matter.

Thanks again for your considered replies

RicB