----- 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
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