Modulus of Elasticity ...Ron

[Ron Nossaman]

At 12:36 AM 11/20/1999 -0600, you wrote:
>Hi Ron,
>    Thank you for your most helpful response to my inquiry about the modulus
>of elasticity for spruce.  What are the proper units on each of the
>variables in the nice-and-simple formula for beam deflection?  To answer
>your questions:

*Of course, sorry, inches. If you prefer working in millimeters, change E*4
to E*0.0062. 


>1) Why decrease rib width?  My impression was that the gentleman intending
>to install the soundboard was not real comfortable working with ribs so wide
>and with so little height as originally on this old piano, which if I recall
>correctly are in the neighborhood of 1.5" wide, closely spaced (15 ribs, 7'+
>grand), and only about 0.5" in height.  At this point he is not committed to
>changing the rib dimensions, only proposing that this be done.
>2) How does he know he doesn't want to change the stiffness of the
>soundboard assembly?  He doesn't, and neither do I, but I dearly wish I did.

*You're both probably justified in wanting to make changes. Rib dimensions
like these indicate to me that the board is (was) compression crowned at
birth. If you are going to convert to a rib supported crown, the ribs will
have to be stiffer to support the string bearing load. Since the panel
isn't dried so severely for assembly of rib crowned systems, the panel
doesn't add a lot of stiffness across the grain (like the compression
crowned does) and the assembly as a whole can have about the same stiffness
as the original, even with the stiffer ribs. This means you can pre
determine how stiff you want the panel to be in any given area and pretty
much build what you want. Unfortunately, with the power of control comes
the burden of responsibility. You have to try to figure out what you have,
and what changes will get you where you want to be. Starting with the
string scale, compute downbearing load for every unison in the scale.
Determine which rib is holding up which group of unisons and assign the
cumulative load to that rib. Repeat for all the ribs, and chart the
resulting deflection in a spreadsheet so you can clearly see what's
happening. Burn enough brain cells to decide what to use for a crown
radius, or radii, and why. Change whatever dimensions and placement you
think might improve what you see and observe the result. Repeat as
necessary until you think you've made an adequate improvement. During this
process, mix in everything Del's told us about impedance, rib lengths,
active soundboard area, and stiffness requirements in the bass, killer
octave, and treble. Make sure you have beam and nose bolt clearance for
your improved rib design (this is rather important), and roll the dice. You
can probably get an improvement by just crowning the ribs and re
proportioning them to be a little stiffer, but you won't really know what
you've got until you build a few and see if the finished product
corresponds to your graphed expectations. The first one is a definite crap
shoot... a ranging shot, if you will.   


>In the absence of further knowledge (or educated guesses), I thought the
>best bet would be to duplicate as precisely as possible the original
>stiffness.  How can I get a handle on this so that I don't duplicate faults,
>but instead improve the piano (with respect to the soundboard assembly) to
>whatever degree this might be possible?  Any hints, guidelines, or rules of
>thumb you can share?  You (and Del) have given us all hope (in previous
>posts and in Del's Journal articles) that there is generally room for much
>improvement in soundboard design, especially as it relates to the mid
>treble/"killer octave" area of the scale.  What do I need to know,
>calculate, measure, determine, buy, borrow, or sacrifice in order to wind up
>with soundboards in my pianos of which you would be proud?  Within reason,
>I'm willing to do whatever it takes, because I'm sooo sick of dealing day in
>and day out for over 20 years with various shades of mediocrity where
>scarcely 1 piano in 100 could be called "fun and exciting" to play.
>    Hope you have a great weekend and an uneventful finish to this
>millenium.
>
>Wasson Kerrick, RPT
>Owensboro, KY


Noble ambition. It was the inevitability of that lousy killer octave,
wretched crossover, and "dink" in the treble, and the utter hopelessness of
voicing them away that got me primed... then along came Del with some real
R&D produced cause and effect relationships. So I figured, what the heck,
I'm already cursed, and he's done a lot of the hard work already. There
isn't really a "reasonably" quick and relatively painless way to get into
this stuff. It took me a lot of months of heavy brain burn to absorb the
concepts and integrate them into something I could make sense of. Most of
it's in the archives, and the Journal, and by the time you can figure out
the right questions, you'll have a pretty good idea what the answers are. 

Ron N