Soundboard question

[Will Truitt]

To Ric and Nick:

Thanks particularly to Nick for shedding so much light on this, based on a
depth of knowledge that not many of us here have.  It moves the discussion
forward, and we all can benefit from his "just the facts, M'am" approach. I
am now enlightened to know that, up to a point, the compression set will be
non-destructive - which my previous post did not consider.  

I have read that it is a more common practice in Europe to re-rib a panel.
That is rarely done here in North America, probably for two reasons.  I can
only speak in general terms.  One reason being that our pianos exist in a
(comparatively) more destructive environment, both climatically and how they
are housed.  We heat our homes to higher temperatures and they are drier, so
the wood goes through larger EMC swings.  The other reason is that European
rebuilders believe that old panels have attained some valuable acoustic
properties from aging and seasoning that new panels do not have.  While some
American rebuilders hold these beliefs, they are not as widespread as in
Europe.  

One of the reasons that I would be reluctant to re-rib a piano (at least one
that comes from our North American environment)is that the cellular damage
is not always obvious when it has already occurred.  The example from my
last post is more extreme in that we see the obvious manifestation of that
localized cellular collapse in the pressure ridges that form and ultimately
become cracks.  Allow me another lake piano example.

About 10 years ago we rebuilt a 7' Henry F. Miller grand built in 1889 for a
customer.  This piano had sat in her unheated summer home for over 50 years.
These pianos exhibit some typical properties:  They are remarkably stable
year in and year out as far as tuning and pitch goes.  You come by once a
year and dust the unisons, and little more than that.  But it is a bit of a
hidden bomb.  They exist in an intensely humid environment, but one that
little changes.  So when she called me to do the estimate to rebuild her
piano, I found a pristine board with no cracks, decent bearing, and some
crown.  

We got the piano to redo over the winter just after Labor Day.  By the end
of September, the first cracks were already appearing, and we had hardly
touched the heat.  More in October, more in November.  By December, there
were 30 cracks in the board, even in our humidified shop.  We tried to
convince the customer to let us put in a new board, but she didn't want to
go to the expense on this second home piano for her.  The piano sounds ok
now, but it sounds like a piano with an old, tired, flat board; which it is.


I am not going to argue the point that you can re-rib an old panel and get a
fine sounding piano, I believe that is possible.  My point here would be
that one would have to be very careful in doing this in America.  To borrow
a phrase, "Don’t touch that - you don't know where it has been!"

It's the same amount of work or slightly more to re-rib a panel as it is to
make a new one.  But there is more risk attached to doing that for the above
kinds of reasons.  There are no identifiable acoustic properties that would
obviously make the old panel superior to the new one, only the belief that
it is so.  We don't have the same confidence that the old panel would have
an increased tendency towards stability.  

Ric, you make the point that this compressed would is going to be stronger.
A fair question then, is:  How much stronger?  And, how important is this
extra strength?  While the strength of a soundboard comes as a system - the
strength comes from the ribs, the panel, and the bridges acting together; it
is fair to say that the panel is the lesser of these components and the ribs
by far the greater.  If you have held an unribbed panel in your hands it is
pretty flimsy at that stage.  So I think whatever extra strength your old,
compressed panel might have is of relatively little importance - practically
speaking.  

As rebuilders we have a limited amount of time, money, and energy to devote
to our tasks.  We are all dedicated to making a better piano, howsoever we
go about that.  But because I have finite resources, I want to devote my
energies where they will give me the most bang for the buck so to speak. For
me, your question is academically interesting, but little more than that.   

Will Truitt


 



-----Original Message-----
From: pianotech-bounces at ptg.org [mailto:pianotech-bounces at ptg.org] On Behalf
Of Richard Brekne
Sent: Thursday, August 21, 2008 4:15 AM
To: pianotech at ptg.org
Subject: Soundboard question

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