Calculation method of acoustic impedance from sound absorption coefficient by Hilbert transform

摘要

The purpose of this study is to estimate acoustic impedance as complex by sound absorption coefficient as real. In causal linear systems, the real and imaginary parts or the amplitude and phase of the transfer function are related. The amplitude and the phase parts form the Hilbert pairs according to the minimum phase property. Using this relation, the phase characteristics can be obtained from the amplitude. The amplitude on reflection is determined by the sound absorption coefficient of material, and the transfer function is given by the amplitude and phase. The transfer function on the reflection surface is equal to the reflection coefficient of surface, and the acoustic impedance is the function of reflection coefficient. In this paper, we show the numerical calculation technique of the transfer function from the amplitude values by these relationships, and conduct an experiment to validate the present technique. As a result, the measured acoustic impedance of absorbing material are good agreement with the calculated one by the present technique.