Attaining "Free-free" Normal Mode Frequency and Damping Conditions for the Violin, #237
Ke Ye, D. G. Bissinger · SPIE eBooks · 2000
A recent re-examination of free-free support conditions using an idealized two-degree-of-freedom mass-spring system showed that support damping could cause significant errors in measured structure damping values even if frequency errors were small. Numerical simulations with this model indicate companion support conditions that produce small damping errors along with large frequency errors. General concepts necessary to achieve reliable frequency and damping values were applied to optimizing support conditions for simple metal structures with inherently low damping. By modifying support conditions to minimize measured frequencies and dampings, this optimized system could then be used with confidence for wood structures with considerably higher damping. Finally our prototypical complicated wood structure, a violin, placed in the optimized support system was utilized to examine the effects of various methods of suspension, or damping of unwanted rigid body motions, or damping of string motion, on its normal mode frequencies and damping. An outline is given for how general support system concepts were evolved by steps into a workable support system/fixture consistent with automated hammer-impact modal/acoustic analysis of the violin, without excessive rigid body motion.