Thoughts on soundboards...you out there Ron?

[Ron Nossaman]

At 07:30 AM 3/18/99 -0500, you wrote:
>Hi,
>
>I had the opportunity to dismantle an old 1915 Baldwin "E" (5'8") over
>the last couple of days that I'll be rebuilding. Looks like it'll be a
>Nice piano!
>
>I've been reading a little on soundboards, and from what I've read so
>far, most soundboards are too rigid in the bass, and not rigid enough in
>the treble.  (Over generalized, I know, but it's a start?)  

* Hi Brian, sounds, generally, like a pretty good start to me.

>On this
>Baldwin, I noticed that the lower half (aprox.) of the long bridge was
>notched out on the bottom so that it only touched the soundboard by way
>of about 4 inch and a half squares of what would be the bridge body
>spaced evenly along the bottom of the long bridge.  I was thinking that
>maybe that was to encourage the soundboard in that end of the piano to
>vibrate more freely.?

* I think that was the idea, though I'm not sure why they would think that.
Most of the diaphragm action of a soundboard is along the ribs, not the
bridge, though bridge weight and stiffness is a factor. I wouldn't think
there would be much action between the ribs, along the bridge line, and
parallel to the panel grain, that the notches would help.  


>I haven't taken notice of the bottom side of the soundboard yet, but I
>wondered if my thinking is on the wrong track to think that perhaps (in
>general), if the soundboard is not rigid enough in the upper end, that
>either an extra rib or two, or adding to the thickness of the ribs might
>accomplish this stiffening effect?

* That's the basic idea. Consider a rib a center loaded beam. The stiffness
and mass of the rib/panel/bridge assembly is what controls impedance in
different parts of the board. The idea is to keep the mass relatively low,
and control the stiffness with the panel thickness and rib configuration.
Since beam stiffness increases directly with the width, and with the cube of
the height, you can make a rib stiffer, without increasing it's mass, by
making it taller and narrower. Make sure you have bottom brace clearance.
Crown the ribs, instead of relying on panel expansion to supply crown to
flat ribs, and you gain a lot more control of the result, and a longer lived
soundboard.    



>I know I'm rambling a bit, but if anyone has a thought they'd like to
>pass along, I'm interested.  (Ron, I know you're light years ahead of me
>on this, so that's why I thought of you in particular.)
>
>Hope you all have a great day!
>
>Brian Trout
>Quarryville, Pa.
>

* It's all Del's fault. <G> He got me interested in this stuff, and I'm
trying to catch up. It truly does work, and there are plenty of things to
learn yet.

 Ron