Soundboard stiffening-thanks Ron-N ( Here's that response I promised. )

[gordon stelter]

Dear Mr.Nossaman,
     I thank you for attempting to empirically
demonstrate the effect of downbearing, on a "mock-up"
of a soundboard panel and rib. And I thank you for
your very polite description, which has added to my
understanding of the forces involved.
     Still, I remain skeptical of your explanation.
     You claim to have seen the board ends come INWARD
as pressure is applied to the crown's apex---- and I
would never call an eyewitness a liar! But I am sure
that you realize this contradicts common perception
and observation, to say nothing of the laws of
physics. Unless something else is at work here!
     Therefore, I can imagine such a possibility IF
the naturally outward forces of downward pressure on
an arch were confounded by the glue joint in a built
up system, such as panel and rib, causing the board's
cellular structure to compress as pressure is applied
from above, and causing the top of the panel ends to
draw inward.
     But ONLY at the top edge of the panel ends, as
the bottom corner of the panel/rib laminate is acting
as a fulcrum and rotational point.
     And I suspect that the bottom  corner, while
rotating, does NOT actually draw away from the end
blocks, and probably even extends very slightly
outward, if even a few thousanths of an inch, as per
the famous Mason and Hamlin  "Business Card"
demonstartion.
      And your demonstration setup , while quite
useful, also fails to replicate actual piano
conditions. For in a real piano the first inch or so
of the board is glued to the canted surface of the
inner rim. And in such a set-up the rotational energy
you observed in your lab would be constrained, as the
inner edge of the inner rim becomes the fulcrum, and
as the board-to-rim glue joint prevents the panel ends
from rotating upward and inward at this point,
regardless of pressure applied at the bridge.
Therefore, some of the force of downbearing will now 
be transferred to an outward direction. N'est pas?
     The only (legal) way to end this debate may be to
put a very large micrometer across a piano rim and
load the board, watching for expansion. ( Or
contraction, as your prior assertions would seem to
indicate.)  
     Your response will be most sincerely appreciated.

     Thank You!
     Thump          


 --- Ron Nossaman <RNossaman@cox.net> wrote:
> 
> >Thanks for the patient re-explanation, although my
> >mind hasn't fully processed this, which seems
> >improbable. But you claim to have tried this
> >empirically, and I would not call you a liar as I
> >would not be called one, myself.
> 
> Then try it for yourself. You can call yourself a
> liar all you like and 
> nobody will care.
> 
> 
> >      But to accomodate this I must imagine that
> the
> >rigidity of the glue line between rib and panel
> forces
> >the cellular structure of the panel to compress
> from
> >upward pressure, before it has a chance to spread
> >outward, thereby drawing the upper edge of the
> panel
> >ends inward, and away from the end blocks.
> >      I'll think about this overnight and provide a
> >snotty retort tomorrow.
> >      Thump
> 
> Read my post to Phil and you shouldn't need a snotty
> retort. Then build a 
> couple of test models and try it.
> 
> Ron N
> > _______________________________________________
> pianotech list info:
> https://www.moypiano.com/resources/#archives
> 



__________________________________
Do you Yahoo!?
Yahoo! Finance: Get your refund fast by filing online.
http://taxes.yahoo.com/filing.html