More on soundboard crown

[Richard Brekne]

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Ron Nossaman wrote:

>
> >>>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."
>
> What do you find that's conflicting, and how can you possibly interpret
> this to mean that I said compression crowned boards are categorically
> stiffer than rib crowned? How about the real stuff instead of the game?

First off.. I said nothing about categorically.. nowhere.. not even closely or
remotely or anything else..In fact I quite obviously placed several conditions and
qualifiers to get at what I thought was a simple little point I had a question
about.  Second... since you asked, I find it conflicting to say in one sentence
that "the one with the higher panel compression level will have the steeper
spring rate gradient, and will be stiffer." and then say "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,..."

Jimmenees there Ron.. I'm not attacking you or anything... Just trying to sort out
on my own what some of the justification for using a CC board must be in the minds
of its advocates. There is no game here... no competition... nothing except a
simple question.

> >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.
>
> Yes, do remember the qualifiers. Or better yet, go back up and read it
> again and you will see that the rib crowned board I proposed was assembled
> without drying the panel at all. While you're at it, re-acquaint yourself
> with the fact that this is one specific example, put forth to John Hartman
> indicating that there is more to what determines assembly stiffness than
> merely cross section and mass of the components, and that identical looking
> assemblies aren't necessarily equally stiff. That's what I meant to say,
> that's what I said as far as I'm concerned, and if you think there's
> anything there (in context) indicating that I said compression crowned
> boards are categorically stiffer than rib crowned, make your case. Again,
> the real stuff please.

Again... the real stuff is that I said nothing about catagorically.. I went out of
my way to isolate a bunch of factors out of the picture.... which you for some
reason just ignore. There is no catagorically thingy here. And the qualifiers were
not origionally your own.. they were Johns...  he said on thursday last...


     "O.K. I will say it again. If two or more soundboards have the same
     dimensioned ribs and the same panel thickness and THE SAME CROWN at the
     same EMC. Then the two Soundbaords assemblies will have the same
     stiffness even if the method of crowning is not the same."

This quote followed your example experiement that specifically mentioned the same
EMC ... and while we are on that post  you state

     "Of the three, the rib crowned assembly  with the non-compressed panel
     will be the least stiff, the compression
      crowned with straight rib will be stiffer, and the combination
     compression and rib crowned assembly will be stiffest."

Again... you seem to say one thing here and the other there.... And YES... I know
better then to think this in anything else then something that just needs
clarifying... at least to me... which is why I asked.... for christs sake.

>
> >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.
>
> We're still putting the qualifiers back in my original statement before we
> go anywhere with yours. Derogatory or not, compression set still exists,
> and is still real science.

Nobody said or hinted at anything else.

>
>
> >>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 ?
>
> Of course not. Nothing can survive any conceivable climate condition. If
> you need that kind of absolute, I'll leave you to it. I sure don't know how
> to build anything that's utterly indestructible.

Thats a cop out.

>
>
> >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.
>
> And that's the question I answered.

No it isnt... but no bother...Del already took care of most of this, in an
appreciated fashion as well.

>
> 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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