二次元マイクロホンアレー構造が計測音場に及ぼす影響の解析的検討(機械力学,計測,自動制御)

Abstract

A two-dimensional microphone array is used to acquire spatial sound field distributions. The spacing between the microphones in the array should be shortened when the sound field would be acquired at the high frequency. The narrower spacing of the microphones would be also employed to acquire evanescent wave components of the sound field near the source. These components are utilized in the applications of the NAH (Near-field Acoustic Holography). This condition might causes some deviations included measured values because of the cylindrical bodies of the neighbor microphones closely located each other. Authors have already presented in the former experimental study that there are some deviations because of the existence of the structure of the microphone array in the measured sound field. In this study, analytical method based on the boundary element method has been developed, and verified with the experimental results mentioned above. Then characteristics of the deviations are investigated, that are caused respectively by the set of the bodies of all the microphones or the outer frame that holds the microphones. Finally, the maximum frequencies are defined to measure the sound field that is compromised as the true values with the various types of the microphone holders. It is also shown that the deviation caused by the small frame designed as a practical size is larger than the deviation by the set of all the microphones.