A Laser Interferometer Technique for Measuring Sound Harmonic Distortion in the Acoustic Output of a Transducer

摘要

A Michelson laser interferometer technique is developed to measure the second harmonic distortion in the acoustic output of a transducer. The only prerequisites to such a technique is that the fundamental displacement be no larger than 2000A, and that the second harmonic displacement be at least 20 dB less than the fundamental. Measurements were taken to prove the feasibility of such a technique. A transducer was driven with a simulated distorted signal by driving the transducer with a 1 kHz and 2 kHz mixed signal supplied by two audio oscillators. The displacement measured at both frequencies agreed well with those displacements determined by two other independent methods. The two other independent methods used to verify the measurements were (1) measurements taken optically using a laser interferometer while the transducer was vibrating at one frequency only, and (2) displacements that were calculated using the specification sheets provided with the transducer. (Author)