Hi there, Robert Scott: > The soundboard all by itself > does have resonances, but they are not strong resonances. The tuning of these resonances is an important aspect to building fine string instruments. In fact, their top and back resonances should not be so defined as for pianos, since their 'rims' only are thin or kerfed liners joining ribs to the plates. > assuming you could find more > than one such resonance, there is no reason for two such resonances > to be even approximately harmonically related. For example, if you > found a soundboard resonance at 10 Hz and another at 28 Hz, what would > you conclude about inharmonicity? In the violin family these are carefully adjusted into a faintly harmonic order, but they also are inside the range of played pitches. Coincidences of a resonance and sounded pitch are another so-called wolf-tone which is audible as pronounced false beats. In "The Physics of Harpsichord Sound", John Sankey explores the effect of soundboards on the dissipation of string energy: "...the relative radiated power of each partial was calculated and is shown compared with the theory for a non-resonant 'piston' soundboard. The soundboard seems to be acting primarily as a non-resonant element. And, it seems close to being a rigid piston...the high partials [are] a bit higher in power than expected. That should be due the deviations of the soundboard from those of a piston, i.e its resonances." (from http://www.geocities.com/Vienna/Studio/1714/energy.html ) Another factor affecting the power of higher partials has been mentioned here in discussion of the Wapin bridge-pinning system. One version of the invention can be installed in recapped bridges, obviously which shouldn't much change the existing board resonances. Sankey explores a similar effect in "Bridge Pins of Harpsichords", where he concludes that differences in the apparent string lengths between horizontal and vertical modes had been exploited in antique instruments (i.e. two different, but phase-locked sets of partials). Ric: > But one quick (although abusive) experiment would be > to pull up on a string under the capo, or agraffe, or push down near the > upper termination in an upright as to alter its bend, then re-measure the > inharmonicity The higher effective wire stiffness at these points is described to cause an apparent elongation of the speaking length of a vibrating string; however, introducing the desired bend might cause a second. Clark
This PTG archive page provided courtesy of Moy Piano Service, LLC