Hybrid passive noise control on a plate silencer with micro-perforations

Abstract

A theoretical study has been carried out for investigating the use of micro-perforation in the plate silencer. A plate silencer consists of two side-branch, rectangular cavities covered by plates. Previous study showed that if properly selecting the parameters of the plate, there would be three resonant peaks in the low to medium frequency range and the transmission loss (TL) between adjacent peaks remained above 10 dB. Modal analysis pointed out that the first two vibration modes of plate in vacuo play the important roles in reflecting sound, and the peaks of TL are contributed by different combinations of the first two modes. Besides, an optimal performance requires a high bending stiffness of the plate which helps lifting the dip between 2nd and 3rd peak of the TL to achieve a broad bandwidth. This study introduces absorption by adding micro-perforation into the plate. By combining the reflection and absorption. this research aims at achieving a wider stopband. Theoretical model has been established and the vibro-acoustic coupling mechanism between the micro-perforation plate, the duct and the cavity has been investigated. It is found that the micro-perforation is beneficial for releasing the bending stiffness and widening the stop band by 20%.