Low frequency noise reduction by acoustic coupling with membrane

Abstract

A strategy of low frequency noise reduction by vibroacoustic coupling between membrane and fluid is proposed. The main advantage of the proposed method is that it can reduce the low frequency noise considerably in comparison with the previous noise reduction methods by absorption material. In the membrane-fluid coupled system, there exists resonant mode which is due to stiffness effect of enclosed fluid and inertia effect of membrane. It results in evanescent mode in the low frequency. Cutoff frequency and decay ratio can be controlled by membrane density and membrane tension. Low density makes broader band of noise reduced frequency than the high density membrane does, and low tensioned membrane is more effective to noise reduction than high tensioned one does. In real situation, there is another coupling between membrane and external fluid as well as internal fluid. The main effect of external fluid is mass loading. Therefore external fluid results in narrow noise-reduced-frequency range in comparison with the case that is without external coupling.