R,C&S question

[Ron Nossaman]

> What is it about the 6-6.5%emc at rib glue-up that causes the panel to 
> be supported, all else being equal in terms of rib crowning & rib 
> dimensions, panel thickness etc.?

I don't understand the question. All else is NOT equal, which 
is the whole point. The choice of panel MC at assembly is a 
result of RC&S design, not a cause. Just gluing up any old 
crowned rib set at 6%MC doesn't make it an RC&S board. In 
RC&S, panel compression isn't needed at all to support crown, 
because the number and stiffness of the ribs will support 
bearing without it, so you can leave the panel under less 
(little) compression without compromising longevity. A RC 
design rib set that needs panel compression will, if it 
doesn't get it at assembly, or the panel compression sets with 
time (say 5-10 years?????) and loses the needed support, tonal 
and killer octave problems will develop just like in CC boards.

So was that "RC&S" board you trashed just a while ago actually 
an RC board that didn't get or retain the panel compression it 
needed to function, or a true RC&S board, designed as such? Or 
is there something we need to know?


> I've read notes from classes taught by Del and Ron N. and while I get 
> the stiffer rib assembly, I don't get why the extra emc makes for a more 
> stable soundboard?

It's more stable because the ribs don't react all that much to 
humidity swings, but panel compression does. If panel 
compression is what's holding up the board, you'll have a more 
reactive soundboard than one in which the ribs are holding it 
up. In other words, the reactivity of the component that's 
supporting the board and supplying stiffness will determine 
the stability of the assembly.
Ron N