Sound Absorption Measurement in a Circular Tube Using the Echo-Pulse Method

An alternative method for measuring normal-incidence sound absorption coefficients of materials or structures was examined, that is based on the echo-pulse method in a circular tube. The so-called Butterworth impulse was generated in a standing wave tube with a flat frequency response over a wide frequency range. The inverse filtering principle was adopted to compensate for the loudspeaker frequency response at higher and lower frequencies. Two types of acoustical material and structure were employed: glassfibre material and tube exit. Through comparison with the traditional, well-established transfer function method, it can be seen that the new method can be as accurate as the established method. The main errors of this new method result from the accuracy of the measurement of the amplitude of the reflection coefficient of the sample.