RC vs CC again

[Delwin D Fandrich]

----- Original Message ----- 
[link redacted at request of site owner - Jul 25, 2015]
To: "Pianotech" <pianotech@ptg.org>
Sent: October 06, 2003 7:20 PM
Subject: Re: RC vs CC again


>
> The soundbaord we inherited has evolved to have equal stiffness both
> along the ribs and along the grain of the panel. This makes sense
> because it assures that the vibration modes of the soundboard will be
> fairly circular in shape to best utilize the soundboard area. If you
> start to design the ribs to be more stiff than the panel the vibrating
> areas (modes) of the soundboard will begin to elongate in the direction
> of the ribs. At some point if you continue to design the ribs to support
> all the bearing load you will make a soundboard less able to project
> tone. The board will break up into smaller less efficient vibrating
> areas and this defeats the whole purpose of supporting bearing in the
> first place.
>
>
> John Hartman RPT


One of these days I'll show you the slides I have of some Chladni sand
patterns taken on a compression-crowned soundboard. (When I find them again
I'll get a few of them digitized.) The resonance patterns are anything but
"fairly circular." They are scattered all over the board in a variety of
patterns ranging from seemingly random to more-or-less rectangular patterns
outlining various ribs. With the exception of a couple of patterns down in
the lower frequencies there are very few "fairly circular" patterns to be
seen.

Which is probably a good thing. Soundboard resonances are voicing problems.

Del