Soundboard Torture

[Farrell]

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----- Original Message -----=20
From: "Richard Brekne" <Richard.Brekne@grieg.uib.no>
To: "Pianotech" <pianotech@ptg.org>
Sent: Sunday, March 30, 2003 10:21 AM
Subject: Re: Soundboard Torture
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> Farrell wrote:
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> > I'm not 100% sure I am understanding your comments correctly, but =
here goes: The board in my picture has very thin (about 3/8" thick) ribs =
and offer little resistance to bending. An unribbed panel will expand =
and contract with changing humidity without crushing - because it can =
expand freely. With my MC gauge in the photo, the wood is relatively =
free (compared to a piano soundboard in a strung piano) to expand and =
contract, so little, if any, crushing is going to occur with my MC gauge =
(likely no crushing because the level of compression force here is =
likely well below the failure level of spruce).
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> We are on the same page here.
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> > In the piano, when the soundboard panel is exposed to a similar high =
humidity environment, the panel will try to expand as much as the panel =
of my MC gauge. It will tend to crush though because the stiff ribs
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> Here's where my comment came in... I thought it (a real soundboard) =
would start crushing without the addtion of the string downbearing... =
especially if you are up to humidity levels as in your (very cool I =
might add) experiement.

If the ribs are more stiff than the compression strength of the panel, =
it would certainly make sense.
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> > and the string downbearing pressure prevent it from expanding (of =
course, it will expand a little bit, and that is why you might see a =
several millimeter increase in crown - ! but not 8 inches).
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> And then the addition of string bearing would simply compound, =
exasperate... further damage the cells with even more compression.
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> I thought this is what Del and Ron have been describing.

I have little doubt that if Del and Ron state that, it is likely true.=20

> > Does that address your comment? Are you asking whether panel damage =
can occur from the rib restraint alone? I don't know what the numbers =
are, but obviously if the ribs were big and numerous enough, the panel =
thin enough, and the humidity high enough, I'm sure you could set it up =
where the panel would fail in areas.
> >
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> Yes, thats what I thought has been argued... described by Del, Ron, =
and a few others.
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> >
> > The panel will crush if it is restrained enough. In a strung piano, =
I don't know what percentage of the restraint is from ribs and how much =
is from string bearing. I suspect the ribs play a much larger role.
> >
> > Terry Farrell
> >
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> I think we are pretty much on the same page Terry. What I dont know is =
just what combination of humidity and downbearing will push wood cells =
beyond their compression limits in a traditional compression crowned =
board. I do know, that S&S claim that as long as the humidity levels are =
kept within recommended tolereances the soundboard will perform and hold =
up well.  How they define this exactly is another matter :)

Agreed. And I wonder about the same thing.

Terry Farrell

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> Cheers, and thanks for the clarification
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> RicB
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> "Welcome to the Brave New World, may I see your passport please ?"
> Horiff Ikensaur Urlyf
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> --
> Richard Brekne
> RPT, N.P.T.F.
> UiB, Bergen, Norway
> mailto:rbrekne@broadpark.no
> http://home.broadpark.no/~rbrekne/ricmain.html
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> _______________________________________________
> pianotech list info: https://www.moypiano.com/resources/#archives
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