Soundboard stiffening

[David Love]

I don't have any deflection and load data, but, I can tell you that when
you insert wedges under the struts and start pounding on the board to get
the board partially loaded prior to setting downbearing, that the wedges go
in very easily at first and encounter increasingly more resistance the
farther the board deflects.  If the relationship were linear, I would
presume you would be able to insert the wedges without any increasing
resistance.

David Love
davidlovepianos@earthlink.net


> [Original Message]
> From: Phillip Ford <fordpiano@earthlink.net>
> To: <pianotech@ptg.org>
> Date: 2/3/2004 1:33:10 PM
> Subject: RE: Soundboard stiffening
>
> >Well, you're the engineer, but if it takes 100lbs to compress the
> >soundboard 1", doesn't it take considerably more than that to compress it
> >the next inch?
>
> I don't know.  Hence the reason for my initial post.  My inclination is
to 
> say no.  If you were to take a flat sheet or thin panel (or slightly
curved 
> or crowned sheet or panel - so slightly curved that curved beam effects
are 
> negligible), attach ribs to it, and support it at its ends (only vertical 
> support - allowing the ends to move in and out) then I would expect the 
> spring rate to be linear, as long as we were in the elastic range of the 
> material.  If it took 100 lbs to deflect this ribbed panel 1 inch, then
it 
> would take an additional 100 lbs to deflect it an additional 1 inch 
> (actually, this is not realistic - those deflections are huge and you
would 
> start having non-linear effects - but assuming real world deflections for
a 
> real world panel I would expect the spring rate to be linear).  Now
attach 
> this to a rigid rim or frame.  If the geometry of the panel is not such 
> that there can be any arch effects then I would expect the same result. 
If 
> the geometry of the ribbed panel is such that there could be arch type 
> loading, and if this arch loading did not cause the elastic limit of the 
> material to be exceeded, then I would expect the spring rate to be 
> non-linear, and I would expect the spring rate to be decreasing, not 
> increasing, as the arch flattened out under increasing load.  So, based
on 
> all this, I would not expect an increasing spring rate.  If there is one, 
> I'll have to see some data to be convinced.  And then my question would
> remain, what's causing that to happen?
>
> >  Doesn't that suggest a stiffening of the board as it's
> >compressed?
> >
> >David Love
> >davidlovepianos@earthlink.net
>
> If what you're positing actually occurred, then yes, it does suggest a 
> stiffening of the board as it's compressed.  Do you have any deflection
vs. 
> load data for a real board that demonstrates this?
>
> Phil Ford 
>
>
> _______________________________________________
> pianotech list info: https://www.moypiano.com/resources/#archives