2015 Volume 9 Issue 5 Pages JAMDSM0065
This study estimates the sound-absorption coefficient and transmission loss for the dimensions of clearances among the close-packed cylinders by theoretical analysis and compares these estimates with experimental values. In the analysis, we performed an elemental breakdown of the clearance configuration, and then approached each element as the clearance between two planes. Considering the effects of sound wave attenuation in each element of clearance, we found the propagation constant and characteristic acoustic impedance using three-dimensional analysis. By connecting these elements in parallel, we treated them as a one-dimensional transfer matrix. We then calculated the sound-absorption coefficient and transmission loss through the transfer matrix method. No sound-absorption coefficient could be obtained with calculations that did not account for attenuation. In addition, calculations that approached the clearance as an equivalent circle and a triangle did not match experimental values well. On the other hand, calculations using the method that accounted for clearance shape, that is the method used in this study, closely matched experimental values. Estimations of transmission loss expressed all clearances by connecting their transfer matrices in parallel. In calculations, these estimations did not account for attenuation, and the falling curve for transmission loss greatly diverged from experimental values. In the three calculations that accounted for attenuation, the falling segment of transmission loss showed frequency characteristics that were close to experimental values. Calculations through the methods that accounted for clearance shapes and that analyzed clearance as an equivalent triangle also had peak transmission loss values that closely matched experimental values.
