Soundboard Thoughts

[Ron Nossaman]

Having just finished scraping my shoes free of the vast pile of ... posts
this otherwise fine Sunday produced, I thought it might be time for a non-
"Prozac withdrawal" technical discussion.

The other day as I was lowering a plate into a piano after the last bearing
height adjustment, I got to thinking about crown and ribs and such. I was
wondering what there was about that wonderful octave 5-6 range that made it
such a bear to tune, voice, and keep a crown in. I was imagining the ribs
underneath, and where they started, stopped, and intersected the bridge.
Then it occurred to me how asymmetric the support is along the ribs going
under that area. The longest ribs in the piano go under there, and the
bridge isn't anywhere near the center of these ribs. Maybe it's not stable
because it's not balanced. It fights against itself through every humidity
swing from the day it's strung to the day it dies, about two weeks later.
Well, OK, maybe a little longer, but it's never in equilibrium in that area.
Maybe it sounds so bad because the frequency response is different on each
side of the bridge because of the asymmetry of the loading. It seems to me,
also, that a transducer ought to be tuned to the frequencies it's expected
to transduce. If that's right then the width of a soundboard ought to taper
(curve following the bridge, with the bridge(s) fairly centered) from wide
at the bass, to narrow at the treble, proportional to the frequency produced
at each point on the bridge. Thicker heavier and more flexible in the bass
graduating to thinner, lighter  and stiffer (more, thinner ribs) in the
treble. Looking closer, I could see that a big curved tone bar cutting off a
MAJOR portion of the front bass corner of the board, and maybe a smaller bar
cutting a bit of the corner off the tight outside curve in the treble would
do just that, without the rib and thickness changes. Picturing all this in
my fevered little head, I started tapping around on the soundboard to
crudely map out the areas of more or less volume and "ring". The sounds
produced differed pretty dramatically on either side of the line along my
imaginary bass tone bar! I couldn't tell much in the high treble (5' 3" piano). 

If any of this is real, I would expect changes along these lines to result
in a better sounding instrument, through the whole scale, and much improved
tuning stability. Since the board is moving proportionally to it's width,
which is (sort of) proportional to the frequency, and the length along the
bridge, the tuning should all move in the same direction at a similar rate
in each section with a humidity change. Yes? No? Maybe? Help?

I don't have any answers here, just observation and conjecture. Does any of
this mesh with real world experience? Anybody got any compelling reasons why
this wouldn't work? Let's play.

 
 Ron Nossaman