Soundboard Torture - and Understanding!

[Farrell]

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Comments below:

Terry Farrell
 =20
----- Original Message -----=20
From: "Delwin D. Fandrich" <pianobuilders@olynet.com>

> I was debating with myself as to whether or not I should warn you =
about
> this, ultimately deciding that experience is a really great teacher =
and you
> weren't jeopardizing any priceless pianos on your road to discovery. =
You can
> use a spruce panel as a humidity indicator but you have to allow it to
> free-float. I.e., you cannot allow it to come under compression.

Gee whizz. Nice guy! It was a very good educational experience. Now how =
can you free-float a gauge? The only way I can imagine that is to not =
put a rib on it, and simply measure the change in length across the =
grain. Is that what you have in mind?
=20
> Yes, what you are witnessing is 'compression set.' This phenomenon =
takes
> place any time wood cells are placed under compression and are =
particularly
> observable when the compression is applied perpendicular to grain. It =
is
> difficult for people who have a nearly religious belief in viability =
of the
> compression-crowned soundboard to understand just how devastating
> compression set can be to the stability of the completed soundboard =
panel.
> Or how quickly compression set can occur. Your little experiment =
graphically
> illustrates both the speed and extent to which compression set can =
occur.

I be a believer! I be seen it with my own eyes!

This quickly brings to my mind the sight of several semis full of =
(compression-crowned-type) new pianos for a local "University Sale" that =
sat for a week in a blacktop parking lot in Tampa Florida in the full =
sun during the hot monsoon month of July. Not a pretty thought.

Is it possible this had anything to do with the negative 1/4" of crown =
in MY new "famous NY manufacturer" piano?

"Ideally, your S%$#*&y piano should reside in a temperate atmosphere =
where relative humidity ranges from 45% to 65%. Don't position it in the =
path of an air conditioning outlet or a heating outlet. Don't put it =
near an evaporator cooler or a room humidifier. Don't put it close to an =
uninsulated outside wall. .....the instrument subjected to such =
environmental insult may be permanently damaged."
Again, I be a believer! I be seen it with my own eyes!

> Actually, compression set follows a log curve. If you place a sample =
under a
> given amount of compression, compression set starts to deform the wood
> fibers immediately. This, of course, reduces the amount of compression
> (pressure on the fibers) and the rate of compression set decreases.
> Ultimately, the pressure against the wood cells will deform them to =
such an
> extent that further compression set is reduced to virtually (though =
not
> exactly) nothing.

So, like, check the weather report before you have the movers put your =
piano in their truck - pick a good humidity day!
=20
> Keeping a piano with a compression-crowned soundboard in a =
hermetically
> sealed environment would not relieve the problem unless the atmosphere =
in
> the hermetically sealed environment were maintained at such a level as =
to
> keep the soundboard panel at 4% MC.

Does a semi in an August Florida monsoon meet this criteria?

> In this environment, of course, the
> soundboard assembly would not have any crown. The problem of =
compression set
> is present any time a panel such as a spruce soundboard panel is =
placed
> under perpendicular-to-grain compression and this occurs immediately =
upon
> returning the newly-ribbed soundboard assembly to normal atmosphere. =
It is
> only exacerbated by installing a bridge, gluing the assembly into a =
piano
> and loading it with some amount of string bearing.

Ouch! Hurts just thinking about it.
=20
> Del
=20
> ----- Original Message -----
> From: "Farrell" <mfarrel2@tampabay.rr.com>
> To: "Pianotech" <pianotech@ptg.org>
> Sent: Wednesday, April 09, 2003 7:00 PM
> Subject: Re: Soundboard Torture - and Failure!
> >
> > 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!
> >
> > 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.

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