Realization of a broadband low-frequency plate silencer using sandwich plates

A broadband low-frequency plate silencer is realized experimentally using sandwich plates. The silencer consists of an expansion chamber with two side-branch cavities, each covered by a light but extremely stiff plate. The requirement for high bending stiffness and low density of the plate is satisfied with a sandwich construction by adhering two high-rigidity thin sheets with a relatively thick and light foam core. A test rig is built with a square duct of 100mm in dimension, and each cavity is 100mm deep and 500 mm long. Three types of sandwich plates with different mechanical properties are tested. The plate having the highest bending stiffness and lowest density results in a measured stopband from 133 to 274 Hz in which the transmission loss is higher than 10dB over the whole frequency band. Comparisons between the three sandwich plates partly confirm the theoretical findings on the effect of plate properties on the silencer performance. It is also shown that the mathematical model based on homogeneous plates can provide satisfactory prediction on the performance of a sandwich plate silencer in the low-frequency range of interest. Experimental and theoretical results are found to be in fair agreement.