Violin normal mode radiative properties

Abstract

Calibrated far-field pressure measurements of violin radiation excited by force hammer impact at the G-string corner of the bridge were performed at 266 microphone positions over an r=1.2 m spherical surface inside an anechoic chamber. These were combined with simultaneous mobility measurements over the violin surface using a scanning laser to extract radiation efficiencies for violin normal modes below 4000 Hz. For favorable cases it was possible to compute experimental values for radiation damping, and the companion fraction of vibrational energy lost to acoustic radiation. As an example, preliminary results for the lower of the first corpus bending modes of a violin by A. Schroetter were the following: radiation efficiency of ∼0.12, total damping of ∼1.15 (percent critical) for a Q of ∼43, radiation damping of ∼0.41 (percent critical). For this mode ∼35% of the vibrational energy was radiated as sound. Radiation patterns measured for each mode were corrected for anechoic chamber reflection/interference effects. [Research supported by the NSF DMR-9802656.]