Design charts and experiment for sound attenuation in a circular lined

In this paper, sound attenuation characteristics of a circular lined duct are studied generally by varying the value of a complex reflection coefficient at its inner surface. In this study, at first, eigenvalue equations are solved by using a complex reflection coefficient and and frequency parameter. Next, the sound attenuations between two cross sections of the duct are shown,after sound intensities are calculated. On the other hand,the above theoretical results are confirmed by the experiments. We measured the complex reflection coefficients and the sound attenuation of two kinds of lined ducts. The experimental results about sound attenuation approximately coincided with theoretical ones.