Effects of Expansion-Chamber Muffler on High-Frequency Sounds in Circular Duct.

Abstract

Sound attenuation in a circular duct through an expansion-chamber muffler was studied theoretically and experimentally for high-frequency sounds. In the calculation, the higher-order mode waves, the order of which is sufficiently high, are taken into account even if they are nonpropagating modes. In the frequency range where the plane wave theory is usually applicable, the calculated results using the method in this study were different from the calculated results using the plane wave theory. Upon comparsion with the measured values, the accuracy of the calculated results in this study was confirmed. We also examined the effects of the expansion-chamber muffler in the frequency range where the plane wave theory is not applicable and in the case that the higher-order mode wave enters the expansion-chamber muffler. In both cases, the calculated results were sufficiently consistent with the measured values. The method of calculation in this study is expected to be valid for the design of an expansion-chamber muffler for high-frequency sounds.