Negative bearing

[Delwin D Fandrich]

----- Original Message -----
From: "Greg Newell" <gnewell@ameritech.net>
To: <pianotech@ptg.org>
Sent: December 01, 2001 8:16 PM
Subject: Re: Negative bearing


> Ron,
>     What are you doing with a new board to eliminate the need for a
cantilevered
> bass bridge? Are you thinning the board or routing it in proximity to the
> location of the bass bridge to make it more flexible in that area? Is not
the
> reason for the cantilevered design to get the bulk of the bridge away from
the
> edge of the board? Just trying to gain understanding.
>
> Greg
> -----------------------

I'm not Ron, but...

The cantilever was introduced to allow the mounting point of the bridge to
be placed away from the inner rim and out toward a "more resonant portion of
the soundboard" while allowing the longest possible speaking length in a
shorter piano. (And we'll leave the idea of soundboard resonance alone for
now.)

Since designing a piano of any size with the longest possible speaking
length is going to place the bridge well back toward the plate hitchpin
riser, the string backscale is going to be very short. It is not just the
inefficiency and filtering effect of the bridge cantilever that is the
problem, an even bigger problem is the shortness of the backscale tying the
bridge down to the plate. To produce any kind of fundamental energy in the
waveform, the bridge must have some degree of mobility. That means it must
be able to move, and with it the soundboard. If the string backscale is
tying the bridge to the plate it does not have this mobility.

Converting to vertical hitch pins through the bass will partially alleviate
this problem, but an even better solution is to shorten the speaking length
somewhat and move the bridge forward some. A typical change in say, a 179 cm
(approx. 5' 10 1/2") grand will yield a backscale length of from just under
50 mm up to approximately 100 mm.

If it is still considered desirable to free the bridge from the soundboard
in some way it can always be undercut somewhat. This serves the same
function without the filtering effect, the distortion and the mass added by
the cantilever. I used this expediency in both the Baldwin 148 and the
Walter 190.

Yes, the back of the soundboard can also be cut away--'floated'--to free up
the board more than is possible by just thinning out the soundboard panel.
We are now doing this on almost all pianos under 190 cm (6' 3") and,
occasionally, on somewhat longer pianos. It depends on the configuration of
the bass bridge relative to the inner rim. It's a bit scary the first time
you do it--the problem is possibly making the soundboard assembly too free,
or flexible--but after a while you get a feel for what you're doing and the
results are quite predictable. (A note, our upright piano had a
fully-floating soundboard across the bottom of the piano.)

Del