Soundboard crown

[Delwin D Fandrich]

----- Original Message -----
From: "gordon stelter" <lclgcnp@yahoo.com>
To: "Pianotech" <pianotech@ptg.org>
Sent: August 13, 2003 2:58 PM
Subject: Re: Soundboard crown


> That was in reference to the previous inquiry.
>      It seems to me that a board built flat, with no
> crown but with plenty of bearing, will soon collapse.

This was done deliberately by Rippen. The string bearing simply bent the
system back to form "negative" crown. With a laminated soundboard they were
quite stable. And, within the limitations of their rather crude scaling,
they sounded rather nice.

Why do you suppose they would "collapse?" Assuming this starts out with
positive bearing it is a pretty stable system.


>
>      With some strings pulling up against their bridge
> pins ( as others cave the board in through forces
> exerted elsewhere on the bridge ) their force vector,
> normally pressing primarily downward on the bridge,
> will be transferred to an "up and against" direction.
> With more force thus on the bridge pin pulling it up
> and away from the bridge, it seems to me that widening
> of the bridge pin hole and general loosening would be
> accelerated. In other words: the force vector would be
> further from the bridge surface, creating more of a
> fulcrum at the surface itself.
>      Am I in error?

Yes. Initially you say the bridge has "plenty of bearing." Where does all
this up force come from? The soundboard is going to simply bend to a
so-called negative crown configuration until the stresses equalize. There
will still be positive bearing on the bridge. Unless you're assuming that
with the soundboard bowed back initially increasing the MC of the wood
would somehow cause it to bow back even further. I doubt this would happen.
Witness the number of pianos out there with dead flat soundboards that
don't do this.

Del