R,C&S question

[Jude Reveley/Absolute Piano]

Ron said:

> 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 board.

Jude:
Ok so I propose that the RC&S is more about the rib design than the emc at rib glue-up. Why can't an RC&S panel be ribbed at a lower emc for the sake of a given climate. There would be some compression in the panel but it wouldn't be necessary to support the panel. Then I could join the club and wouldn't have to skate the issue with my hybrid. Seems it's more about matching a given load with a given resistance. 
>
> 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?


Since I didn't hear the pianos in question nor get any real specifics, it is just hearsay which I wish to publicly retract. I was just very surprised at the source but no matter. Maybe it was an RC board or maybe an RC&S with a mismatched scale design. Can you say that RC&S unto itself precludes that there are other factors that could render tonal problems? 

 
> 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.

Again it seems to be about the ribs not the panel, so what difference does the emc really make in this regard. I think Ric might be right to suggest that post-loading crown Sag is a more noteworthy topic. 

And on that note, my board assemblies sag about 30%. 

25% crown retention seems a tad soft to me but maybe it's just a different sound if it will hold up.

Ron, you're always the warrior that takes the time to dicuss this and I really appreciate it.

Best,

Jude Reveley, RPT
Absolute Piano Restoration, LLC
Lowell, Massachusetts
(978) 323-4545


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