Bridge pressure bar

[Delwin D. Fandrich]

----- Original Message -----
From: "Alan Forsyth" <alanforsyth@fortune4.fsnet.co.uk>
To: "Pianotech" <pianotech@ptg.org>
Sent: Saturday, April 12, 2003 9:04 PM
Subject: Bridge pressure bar


> Del wrote
>
> >"This system would certainly maintain good string contact with the
bridge,
> but that is not the function of string bearing. These are two quite
> different issues. String bearing provides a way to increase soundboard
> impedance without adding mass to the system."
>
> Del,
> Can you please explain to me or define soundboard impedance.

Not in a sentence or two. Basically impedance is a measure of how readily
the soundboard assembly is able to accept energy from a vibrating string (or
strings). A soundboard having low impedance will accept energy very easily
and the resulting tone will be short and percussive. A soundboard assembly
having high impedance will not accept energy as readily and the sound will
be less loud but with longer sustain.

It is a frequency-dependent function of the soundboard's overall stiffness,
mass and mechanical resistance. The overall stiffness of a soundboard is
dependent on the design of the assembly and physical characteristics of the
materials used for the panel, the ribs, the bridges, etc., its mounting
system (the characteristics of the rim, bellyrail, etc.) and whatever string
loading exists.

If you're a real glutten for punishment you can refer to my article,
"Soundboard Damage Part I--A Guide to Soundboard Cracks and Other Maladies,"
Piano Technician's Journal, December 1997.

Del