More on soundboard crown

[Richard Brekne]

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Ron Nossaman wrote:

> >snip.... Given a panel crowned assembly with a severely dried
> >panel, and one rib crowned with a non dried panel, both to identical crowns
> >at room EMC, the one with the higher panel compression level will have the
> >steeper spring rate gradient, and will be stiffer.
> >
> >
> >Now correct me if I am wrong.. but I understand this to mean that a CC
> >board will be stiffer, both unstrung... and increasingly so when
> >downbearing is applied.
>
> Wrong. As we've discussed specifically and often, the RC board can be made
> much stiffer, both unstrung and strung, though the CC board will often have
> a steeper spring rate progression under deflection, at least while the
> crown lasts.
>

Well.. you'll excuse me if I find this directly above in direct conflict with

     "the one with the higher panel compression level will have the steeper
     spring rate gradient, and will be stiffer."

and please remember the qualifiers for this example so as to keep it in
context.... it was  equal crown at same RH, and further we were to leave all
other compression damage issues aside for a moment.


>
> >Assuming that is correct, and putting aside all other compression damage
> >discussion for a second or two... I have a question about this long term
> >so called compression set.
>
> It's not so called. It is a real thing, backed by that real science that
> you so often peripherally refer to lately. See "Understanding Wood" by R.
> Bruce Hoadley, for a start. Reading up on some of that real science you
> recommend will answer your questions.

Real science Ron... means also answering a question in the context it was given
with qualifiers intact... and do me a favour... dispence with the scolding
routine.  And FWIW the term "so-called" isnt a derogatory.

>
> >On the side of this... and please forgive whatever lack of knowledge I
> >display in the asking,  if compression from ribs being glued cross grain
> >to the panel is such a problem...even in RB boards.. is there no way of
> >contriving a rib such that it is a bit less constraining ?
> >
> >Just musing again
> >
> >RicB
>
> Yes, if you design the ribs to support the crown without needing panel
> compression to do so, and don't dry the panel to extremes, panel
> compression is no longer a problem. This should start sounding familiar
> about any time now.

Again.. thats not the question I asked.... Or perhaps you are saying that under
no circumstances can the constraint placed by the ribs on the panel cause
problems regardless of climatic conditions ? I asked if there was a way of
contriving a rib such that it was a bit less constraining to the panel ... as in
either compression or tension.

>
> Ron N
>

--
Richard Brekne
RPT, N.P.T.F.
UiB, Bergen, Norway
mailto:rbrekne@broadpark.no
http://home.broadpark.no/~rbrekne/ricmain.html
http://www.hf.uib.no/grieg/personer/cv_RB.html


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