Measurement of sound absorption using a single fixed microphone in a circular pulse-tube

This study presents a method for measuring the normal incidence sound absorption coefficient of acoustical materials by separating the incident and first reflected waves in the time domain using a pulse-tube with only a single microphone whose position is fixed. Based on the pulse generation technique, the effect of the characteristics of tube termination can be eliminated, and the drive signal used for the measurement is obtained. A moveable piston is used to move the sample to a certain position in the tube, which renders the recorded incident and first reflected waves separated. As a validation of the proposed method, two different materials are investigated. Good agreement is found between the proposed method and both the well-established two-microphone transfer function (TMF) method and the verified pulse separation method.