Soundboard grain angle (was Negative bearing)

[Delwin D Fandrich]

----- Original Message -----
From: "Phillip L Ford" <fordpiano@lycos.com>
To: <pianotech@ptg.org>
Sent: December 04, 2001 12:07 AM
Subject: Soundboard grain angle (was Negative bearing)


>
> Why does the grain have a positive effect in the highest part of the
treble?
>
> Phil
>

Because the soundboard assembly wants (needs) a relatively large amount of
stiffness there to avoid dumping energy into the soundboard overly fast. The
proximity of the bridge to the bellyrail/soundboard liner uses the
with-the-grain stiffness to help raise the mechanical impedance of the
system enough to maintain a reasonable amount of sustain. Thinning the
soundboard in this region detracts from this effect--one reason why post
1930s Steinway pianos often have sustain problems through the sixth and
seventh octaves. Thinning the board down to approximately 5 mm considerably
reduces the soundboard stiffness as felt by the bridge through that region.
It also reduces the ability of the soundboard panel to hold the compression
needed to support crown.

Del