Precision of reference sound source hemianechoic sound power calibration using a fixed microphone array: Relation to ISO 6926 revision

Abstract

Reference sound source calibration by the hemianechoic ISO 3745 method allowed a course array of 10 measurement microphone positions on a hemisphere. Draft revision of ISO 6296 provides for a difficult meridional arc constant vertical velocity microphone scan. An improved array of multiple fixed microphone positions is proposed as an alternate to the meridional scan method. Bias of the improved array was simulated with Mathcad 4.0. Agreement was predicted to be within 0.2 dB up to 4 kHz for 10 points and up to 8 kHz for 20 points. Experimental results for three microphone position arrays were compared to reverberation room results over the limited frequency range of 125 to 8000 Hz. The standard deviation of the difference was 0.84 to 0.89 dB (0.81 dB predicted) for the old ISO 3745 array. For an array having 10 fixed height difference positions from 0.15R to 0.95R, the standard deviation was 0.62 dB (0.61 dB predicted). For 20 fixed heights from 0.025R through 0.975R the standard deviation was found to be 0.63 (0.18 predicted). Calculated results and experimental test results, compared with reverberation room results, will be presented.