An Improved Technique for Measuring the Vibration Sensitivity of Subminiature Microphones

Abstract

Presented is a test methodology for characterizing the vibration sensitivity of miniature microphones. An ordinary vibration sensitivity experiment becomes difficult because vibrating surfaces are also sources of sound. This sound is picked up by the microphone being tested, changing the result. The sound pressure will be correlated with the vibration signal such that averaging will not serve to increase the accuracy of that result.The previously described techniques reduce the correlated pressure using custom experimental equipment and have geometric limitations. In the improved technique, the microphone is treated like a linear two-input-one-output system. The two input signals (vibration and acoustic pressure) are measured, and the vibration sensitivity is determined using two different spectral analysis techniques. These techniques have good agreement between one another, and the measured values fit well into a simple acoustic model of the microphone. A technique for estimating the major source of measurement error indicates that this error is small enough for a reasonable estimate of vibration sensitivity to be made.