voicing

[Ron Nossaman]

>Exactly my point. Personally, tho not an accomplished rebuilder myself, I
have not
>seen a soundboard that has both too little downbearing and at the same time
plenty
>of crown.

* They're out there. I've seen negative bearing on a board with about 6mm of
crown at the longest rib, and between 2 and 3mm in the killer octave. It
looked like the plate had just been set too high in the first place, and
lowering it a little should work wonders in that piano. If it was one of
those where the tension could be dropped and the plate, pinblock, and
strings could be lifted out as a unit, it wouldn't have been that hard to do.



>Hmm.. I guess I need to be more precise. String deflection at the bridge is
measured
>before easing off string tension, and then again afterwards. The difference
gives a
>reading of how much the board rises with tension off. ie. crown. Does this
jive with
>your meaning of crown ?

* Yes, sort of, but I meant crawling underneath with a string and
flashlight, stretching the string from rim to rim against the underside of
the board - parallel to and between two ribs. The gap between the string and
the board in the middle is the crown. If there is no gap, slowly pull one
end of the string away from the board and see if the board is flat, or even
low in the center (negative crown). Personally, I like to see measurable
crown when the strings are still on and under tension. Downbearing force
diminishes rapidly as the deflection angle nears zero. If there is very
little bearing at tension, and there is no, or negative measurable crown in
the board, the board has nothing to give you since it's already flat with
only a very light loading. Even if it springs back some when you take the
strings off, it doesn't have any load carrying capacity left. If there is
very little to zero crown (maybe even a very slight negative crown), and
high string deflection angles, the bearing was set too heavy in the first
place. If the board springs back to a decent crown when the string tension
is taken down, raise the plate or shim under the aliquots and  it will
probably do well under the more moderate bearing load when you restring it.
See how this works? The more a board is deflected, the harder it pushes
back. At the same time the string bearing angle that pushed the board down
in the first place decreased as the board was deflected, and the lesser
resulting angle resulted in a lighter bearing load. It's sort of self
correcting, within limits. At a certain point, equilibrium is reached.
Setting bearing is the process of trying to pre determine where that
equilibrium point will occur and what the resulting crown, deflection, and
bearing angle will be. If the bearing is set so that, *if* you were to force
the bridge down by clamps or weight (but don't do it) until the soundboard
was flat, and the resulting string deflection angle wasn't over zero, there
would be no way the downbearing could push the board below flat in actual use.  

I hope this makes sense. I'm pretty helpless at trying to explain most
things without pencil and paper, and lots of hand gestures (gesticulating
wildly, occasionally scratching, often befuddled).

 Ron N