Computerized measurement and tracking of acoustical resonances.

Abstract

A system is described which incorporated a Hewlett-Packard 85 "desk-toe" computer to control a frequency synthesizer and read the output of a lock-in analyzer to measure, display and record the resonant frequencies, amplitudes, and quality factors of several modes of an acoustical resonator. The system is capable of locating, measuring, and tracking the resonant modes as parameters which affect sound speed and attenuation are varied. An algorithm for rapidly fitting "good quality" measured data to a resonance lineshape is described which determines quality factors to precisions cf better than 9.1 percent, amplitudes to better than 0.01 percent ind center frequencies to better than 0.01 ppm. Sample output is provided for the lowest three plane wave modes of a n air filled cylindrical resonator in the temperature range of -15 to 25 degrees Celsius.