Measurement of acoustic performance of PTFE microporous membrane

A new method of sound transmission loss measurement using a modified four-microphone impedance tube was proposed in this paper to investigate the microporous membrane's acoustic performance. Transmission loss matrix algorithm of the system was conducted with the physical meaning more clear than that of four-microphone impedance algorithm. The new algorithm effectively separated the transmission wave from the secondary reflected wave in the impedance tube and ensured the measurement result not to be influenced by absorbent end of the tube. Three types of microporous membrane were studied with new algorithm. The results indicate that the new method can raise the precision and repeatability of the measurement, especially in low frequency.