Bridge design

[David Love]

Del:

Is there an ideal dimension (height, width and width at the footprint) in
the treble section of the piano?  It seems that the two requirements are at
odds, one of flexibility to allow the soundboard to move, and one of
stiffness to increase impedance in that section and improve sustain. 
Wouldn't it be better to support the board in that section with an
additional rib, say, and leave the bridge more flexible?  Or is it six of
one...

David Love
davidlovepianos@earthlink.net


> [Original Message]
> From: Barbara J. Fandrich <pianobuilders@olynet.com>
> To: Pianotech <pianotech@ptg.org>
> Date: 3/26/2003 6:07:19 PM
> Subject: Re: Bridge design
>
>
> ----- 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
>
>
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