Killer Octave

[Delwin D. Fandrich]

----- Original Message -----
From: "Joseph Garrett" <joegarrett@earthlink.net>
To: <pianotech@ptg.org>
Sent: Monday, April 14, 2003 8:42 AM
Subject: Killer Octave


> Del, Ron & Ron,
> Someone mentioned the physical difference of where the bridge is, in
> relation to the crown of the board. The killer octave is usually right
where
> the bridge(s) is/are at the top of the crown, as it crosses from being on
> the back side of the arc, to being on the front side of the arc. The
> question is: Is there a relevance here? I know there are many factors in
> what makes a "bad" area in the soundboard, but could this factor be part
of
> the equation? Just wondering.

This is only true with rib-crowned soundboards. With compression-crowned
soundboards the crown radius is anything but uniform after the piano is
strung. String pressure pushes the bridge down but the internal cross-grain
pressure of the wood cells continues to force a stress-interface between the
soundboard panel and the ribs. This stress has to be relieved until some
equilibrium is reached. It does this by bowing up on either side of the
bridge(s). You end up with an elongated and squished "m" shape. There is a
drawing in one of my old Journal articles.

Del