Baldwin SD-10

[Delwin D Fandrich]

----- Original Message -----
From: "Farrell" <mfarrel2@tampabay.rr.com>
To: <pianotech@ptg.org>
Sent: September 06, 2001 4:48 AM
Subject: Re: Baldwin SD-10


> > The soundboard was designed to leave it approximately 5/8" short of the
> > outer rim all along the perimeter. The rationale, if I remember
> > correctly, was to give the sound board room for expansion or contraction
> > depending on the season.
>
> So is the soundboard not glued to the inner rim so as to allow it to
expand
> to the outer rim? Or is it glued, and they simply designed the inner rim
to
> compress as the soundboard expands toward the outer rim? Kinda hard to
> figure.
---------------------------------------------

This subject keeps coming up in one form or another from time to time.

There is simply no way any potential soundboard expansion is going to be
felt between the edges of the soundboard and the outer rim. This notion
doesn't even make any theoretical sense, let alone any practical sense.

Most pianos have an inner rim that is somewhere on the order of 35 to 45 mm
thick. Even if the inner rim is coved in a misguided attempt to 'increase
the radiating area' there is still a minimum of about 20 to 25 mm of glue
surface around the inner rim. The glues or adhesives used to bond the
soundboard to the inner rim are typically quite rigid--that is, they do not
creep under load. They will fail before they will allow any creep. For any
soundboard expansion to be felt around the outside parameter of the board
there would have to be some slip across the glue line but, since the
adhesives used do not allow that, the only possible way the gap between the
edge of the soundboard and the outer rim could change after assembly is for
the adhesive to fail catastrophically--and that's a whole other issue.

The same logic applies to the notion that the edges of the soundboard must
contact the outer rim to somehow 'reflect' sound back into the
soundboard--or whatever it is that's supposed to happen out there. As long
as the soundboard remains glued to the inner rim it simply doesn't matter if
the edges contact the outer rim or not. This may be an aesthetic
consideration to some, but it is neither a performance nor an acoustical
consideration.

Del