Soundboard stiffness variances

[John Delacour]

However a spruce soundboard (not laminated in any way) is 
constructed, the force that resists the down-bearing of the strings 
is due almost entirely to compression and what fraction of it is not, 
is due to tension.  I refrain utterly from using the meaningless 
terms used to distinguish three construction methods -- though I 
notice one of these methods, which is the most common in my 
experience, is now omitted from the discussion and presumably being 
considered as indistinguishable in character, and as totally 
inferior, to "CC".

The un-barred soundboard is flaccid across the grain to the point of 
worthlessness for the purpose of a soundboard.  That essential 
flaccidity will not diminish or increase significantly with any 
change in moisture content.  I am now reading here that the stiffness 
of the soundboard assembly (across the grain, I assume is meant?) 
varies with moisture content.  First I can't see how this hypothesis 
is arrived at and secondly, even if the mysterious new phenomenon 
that causes this strange behaviour is identified and quantified, I 
can't imagine that the degree of reduction in flaccidity would have 
the slightest effect.

I take the soundboard out of a piano, take off the bars, leave it in 
a dry atmosphere for a day or two, shake it like a thunder-board and 
record what happens.  I then expose it to 90% humidity, make thunder 
with it the next day nd note the difference or sameness.  According 
to this new science, there will be a marked difference in the quality 
of the thunder.  According to my experience, the board will be as 
floppy after the moisture uptake as before.  How could I expect it to 
be stiffer or more flaccid?!

The lack of stiffness of the assembly in the direction across the 
grain of the board is supplied by the bars, by whichever construction 
method is used.

I have just spent the weekend 160 miles away preparing an 1890 7'4" 
Aliquot Blüthner, with the original Erard-Herz type action, for a 
concert with a world-famous singer and a very exacting accompanist. 
The piano has been "rebuilt" in Poland to a higher standard than some 
I have seen.  As regards the soundboard, nothing has been done except 
to put in a couple of slivers and make the top look like new.  Not 
having seen the piano, I went up prepared for the very worst.  I was 
even more concerned since the piano lives in a refectory where not 
only is the temperature kept too high but the humidity fluctuates 
from 25% to 60%.  A small Dampp-Chaser was fitted last year and I 
told them to make sure this was operational before I came and 
interrogated them as to the maintenance and water consumption of the 
device.  When I arrived it was practically bone-dry and I was told it 
used about one tank-ful per month, which seemed rather little to me.

The piano was rightly adjudged inadequate to a series of high-class 
concerts by the pianist.  When I left after 12 hours' work spread 
over 2 days, he was delighted, the piano was transformed and I would 
happily have taken it home with me.

Although the bars had not come loose, as I have seen on many 
Blüthners, they were not screwed to the board as they were in later 
years.  I've no idea how the soundboard was made but I presume it was 
made in the usual English way as most were at the time.  There was no 
measurable crown on the board nor any dishing, and that was 
indifferent to me, since many good pianos I know have no crown.  As 
to the string deflection I didn't even bother to measure it.  So I 
have obviously experienced a miracle : here is a piano, built 120 
years ago according to principles that we are being strongly urged on 
this list to regard as totally out-dated and laughable, that is now, 
after a little essential maintenance, adequate to the needs of a very 
exacting musician and, more significant, a great delight to me.

Let us suppose that the piano is designed so that when strung the 
soundboard will be flat, or nearly so, as is common to many 
fine-sounding pianos here in Europe -- of American pianos I have no 
useful experience.

Q. What will happen when the soundboard takes on moisture?
A. It will try to expand across the grain, but, inhibited by the 
irresistable downward force of the strings and by its connexion to 
the bars that are not expanding, it compresses itself to a degree.

Q.  Why does it not push the strings up and become crowned instead of 
compressing itself?
A.  Because the direction of the expansive/compressive force is 
practically horizontal and whatever vertical component it may possess 
is ineffectual against the comparatively large vertical force of the 
strings.

Q. What will happen if I then take the strings off?
A. The board and bars, being elastic, will use the compressive force 
to expand as far as contrary forces allow and a crown will develop.

Q. What will happen if the board was too dry or the crown too high on assembly?
A. The weakest of the summer growth of the spruce may become crushed.

Q. What harm will this do to the tone and structure?
A. None, since the stiffness of the assembly will be barely altered

etc. etc.