Soundboard stiffening

[Erwinspiano@aol.com]

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In a message dated 2/1/2004 11:38:00 PM Pacific Standard Time, 
fordpiano@earthlink.net writes:


If the crowned board is not getting stiffer as it
deflects down, then a flat board would be just as stiff as a crowned
board.  So, the reason for the crown would not be 'stiffness'.

Phil
>> But I think it is getting stiffer.
     Dale


Well, you've done it many times, so your opinion means more than mine.  But 
if it is getting stiffer I'd like to know why.  Have you tried the same thing 
with an initially flat board?  Did it get stiffer as you wedged it down?  Was 
the increase in stiffness comparable to a crowned board?  If so, then why 
bother with the crown?  I think it's time for some measurements.  I guess I'm going 
to have to do some deflection vs. load measurements on a few pianos.  Another 
thing to put on the list of things to do.


Phil
 Phil
    Me too. It's getting stiffer because of a sum total of the component 
forces that exists in the system.  Some compression, the stiffness of the crowned 
or uncrowned rib, mass of the ribs,the stiffness  caused by  laminating grain 
angles at right angles (plywood) & the whole system anchored to the case, 
thickness of the soundboard & Backscale lengths as Ron Mentioned.  I think this is 
as close as I can come.
 Typically  flat boards don't get stiffer unless your putting tension against 
the ribs & then it's going into a reverse crown mode.  In some case this may 
not really be a bad thing ie uprights.You know my thoughts about reverse 
crowned boards, but that,s another story. My Mason AA for example is stiff without 
much crown or bearing it also has longer backscale lengths. You heard it
  What kind of measurements?
   Dale
     

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