Study on the Performance Improvement Mechanisms of Expansion Chamber Water Mufflers with Reacting End Walls

This paper investigated the effect of wall compliance on the noise attenuation performance of a water muffler. Firstly, the sound transmission loss (TL) of an expansion chamber with a piston-spring element located at one end wall of the chamber was derived using the transfer matrix method. It is found that transmission loss of a water-filled expansion chamber can be noticeably improved by introducing a reacting element, especially for the low-frequency range and frequency range around the resonance of the reacting element. A further lumped model established using acoustical–electrical analogy reveals that the reacting element functions as a volume amplifier of the expansion chamber for the low-frequency range, while the resonant behavior is dominated by the area and impedance of the reacting element. Then, the model was extended by replacing the piston-spring element with a circular plate. A 1.5-dimensional model was developed in which the fluid–structure interaction was regarded as an added mass effect, and a FEM model was used to verify the accuracy of the theoretical model. Finally, the effects of material properties, thickness, radius, boundary conditions, surface area, and length of the expansion chamber on the sound attenuation performance of reacting expansion chamber mufflers have been examined and discussed.