A measurement technique of sound absorption coefficient and impedance using an impedance tube and two cardioid microphones

摘要

Two omnidirectional microphones and an acoustic tube are usually used to measure the surface normal impedance and absorption coefficient of materials. This measurement technique is specified in ISO10354-2, JIS1405-2, and so on. In this paper, we tried to obtain the surface normal impedance of material using two cardioid micro-phones in the tube. As a result, it was clarified that the ratio of sound pressure and velocity effect on the value of impedance measurement. Therefore when the ratio is equalized, the values of impedance and absorption coefficient can be obtained as with the values using two omnidirectional microphones.