[CAUT] Re: Restringing Treble

[James Ellis]

I won't repeat the previous posts, because I don't believe it's necessaty.
Ron Nossaman is mostly correct.  The drastic change in pitch of one section
when the tension is off an adjacent section has more to do with the plate
than it does the soundboard.  But it's not so much "compression" of the
plate as it is "deflection".  It's the fact that the plate wants to bow up
when it's under tension.  Release the tension of one section, and the plate
straightens out a little.  Put the tension back, and the plate bows up
again.  That's what the nose bolts and the "horn" are for - to minimize the
upwatd bowing.  It may not be obvious to the eye, but if you will put a
rigid beam across the piano, and some dial indicators measuring both plate
and board deflection at different places as you change overall tension, you
will see what's happening.  I have done that, and the dial indicators tell
the story.

It's both plate and board, but as Ron says, I believe in this case, it has
more to do with the plate than it does with the board.

Another point missed here.  If you look at one string only, and see changes
in neighboring strings, a part of that change will be coming from
compression in the bridge itself - i.e., forces on bridge pins being
reflected to neighboring bridge pins.  If you look at the bridge on a
microscopic scale, you will see that it is not a rigid body at all.  On the
cell-to-cell scale, it is somewhat springy too.

Conclusion:  Because of the obvious plate deflection, you can't assume
anything about the board.  When you change the tension, everything moves
just a little bit, but not in the same direction.

Sincerely, Jim Ellis