Abstract
There are engineering benefits if we can predict the acoustic properties such as the sound absorption coefficient of a sound incident on the clearance of such an annular cross-section based on the geometric dimensions of the tubes and the physical properties of the gas. However, a successful theory for the sound absorption coefficient of narrow tubes of the abovementioned shapes has not yet been presented, and the comparison between experimental and theoretical values has not been made. Further, the propagation constant and characteristic impedance in the clearance in a double cylinder have not yet been derived in the cylindrical coordinate system or by other methods. Therefore, in this paper, the propagation constant and characteristic impedance were derived by approximating clearance of an annular cross-section with clearance between two parallel planes. And the sound absorption coefficient was calculated, then compared with experimental results. The theoretical values, according to this method, agreed well with the experimental values, and practically sufficient accuracy was obtained. It was experimentally confirmed that the eccentricity of a round bar in a circular hole does not appreciably influence the sound absorption coefficient. Even when this calculation method is applied to a circular hole, the results agree with the theoretical and experimental values for the circular hole. Therefore, this method is effective even if the diameter of the internal cylinder is considerably smaller than that of the external cylinder.
