A modified electro-acoustical reciprocity method for measuring low-frequency sound source in arbitrary surroundings

The reciprocity principle provides a possible means of measuring the low-frequency volume velocity of a sound source in arbitrary surroundings; however, the auxiliary transducer in the reciprocity experiment is required to be absolutely reciprocal, which means that the radiation property and the receiving property of the transducer are identical. However, it is not always easy to obtain such a low-frequency reciprocal transducer, because some issues like nonlinearity would lead the transducer to be non-reciprocal. In this study, a modified method is proposed to conduct the reciprocity measurement using an ordinary loudspeaker instead of a strictly reciprocal one as the auxiliary transducer. Firstly, the relationship is established between the measurement error and the inconsistency of auxiliary loudspeaker's radiation property and receiving property. Furthermore, a modified reciprocity method is proposed to compensate the inconsistency. Finally, experiments are carried out with the modified reciprocity method in both an anechoic room and a reverberation room with two different auxiliary loudspeakers. The experimental results of the modified reciprocity method agree with the results obtained with the free field method very well.