Bridge design

[Barbara J. Fandrich]

----- Original Message -----
From: "Ron Nossaman" <RNossaman@cox.net>
To: <davidlovepianos@earthlink.net>; "Pianotech" <pianotech@ptg.org>
Sent: Tuesday, March 25, 2003 8:56 PM
Subject: Re: Bridge design


>
> >I notice on Steinway bridges (as well as some others) that the lower part
> >of the bridge root narrows in the treble section of the piano.   What is
> >the design purpose of that and does it serve its purpose?
> >
> >David Love
>
> It's to get the "footprint", or attach point of the bridge to the
> soundboard panel away from the rim as far as is practically possible. Yes,
> it's a good idea since a bridge sitting on the rim doesn't move the
> soundboard all that well. It would be nice to be able to get it even
> further from the rim, but there is a practical limit in a grand determined
> by hammer clearance of the belly rail, and the upper limit of the speaking
> length of C-8.
>
> Ron N
> _______________________________________________


David,

The idea was certainly to reduce the size of the footprint, but it was
thought to be helpful along the entire length of the bridge. The theory was
that the soundboard produced "tone" by "undulating" and anything that
inhibited this undulating would interfere with the tone production
capability of the soundboard. A positive side effect of this practice was to
move the attachment point of the bridge some away from the soundboard liner
through the treble region.

Taken to its illogical extreme it has the effect of reducing the stiffness
of the bridge leaving it somewhat inefficient in its task as a coupler
between the vibrating string and the soundboard panel. It can be a
contributing factor to short-sustain problems.

Typically we undercut a new treble bridge along the leading edge. This
undercut extends back as far as a perpendicular line drawn straight down
from the leading rows of bridge pins. We do not undercut the back side of
the bridge.

Del