Soundboard stiffening

[Phillip Ford]

>>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. ...
>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
>

The measurements I had in mind were from pressing down on the bridge at a 
few spots with known, incrementally increasing loads.  Measure deflections 
at these same spots for each load increment.  You could then put together 
some deflection vs. load curves to see if things were stiffening up as load 
was increased.  Also, doing this to the same piano both strung and unstrung 
might be informative.

Phil