Investigation on acoustical performances of micro-perforated panel with soft boundary backing cavity

Abstract

Low-frequency noise control is still an issue due to its characteristic of having a long wavelength. Therefore, attenuation requires a bulky noise control component, including an acoustic absorber. Conventional absorber materials, such as micro-perforated panels (MPP), are a candidate to circumvent such a problem. However, the requirement of backing cavity depth causes the MPP to work under a quarter wavelength constraint. Eventually, the bulky characteristic of the absorber is persistent. Therefore, this study introduces a soft boundary condition to the MPP to enable the system to work at a lower frequency while the associated dimensions reduce. Open gaps between the backing cavity and rigid surface realize the soft boundary conditions and double-layer MPP is considered to test such a system. The experimental result shows that the soft boundary can enhance at low frequencies (<250 Hz) by 0.3-0.6 points. At the same time, the open gap can slightly increase the resulting absorption performance deficiency at mid-frequency.