Soundboard stiffening

[Phillip Ford]

> >At the risk of oversimplification, isn't a crowned soundboard just a big
> >spring, the more you compress it, the more rigid it becomes?
> >
> >David Love
> >davidlovepianos@earthlink.net
> >
>
>David,
>
>This is the point that I was trying to make.  I believe that the
>soundboard is essentially just a big spring.  A spring doesn't get
>more rigid or stiff the more you compress it.  Within its working
>range it has a constant spring rate or stiffness. ... If the board is
>actually getting stiffer as a result of applied load then it's not
>acting like a spring or a beam, and I would like to understand what
>mechanism is causing that to happen.
>
>Phil Ford
>
>   Phil
>   If this is true then why can I measure a predictable amount of residual 
> bearing at the bridge after the board is string?

You could do that whether the spring rate was linear or non-linear.  Let's 
say you put on 1 1/2 degrees of bearing everywhere.  Let's say that the 
bridge sinking 1/10 inch would decrease that to 1/2 degree bearing.  Let's 
say for the sake of argument that the spring rate of the board is uniformly 
a linear 1000 lbs/in. everywhere.  Let's say total downward load from the 
bearing is 100 lbs.  This would result in a predictable and measurable 1/2 
degree bearing after stringing.

I don't see that the board spring rate has to be non-linear (the board 
doesn't have to be stiffening as you load it) in order to end up with 
bearing after stringing.


>    I thinkthe boards compression rate is non linear. At least that's the 
> wya it behaves in my hands.
>    DAle


You may be right.  But I'm going to have to see some measurements to be 
convinced.

Phil