Noise Reduction Techniques for Close-fitting Enclosures at Structural/Acoustic Resonance

Abstract

In this paper, a close-fitting enclosure model is used to prove the existence of a common structural-acoustic coupling experimentally, which deteriorates the insertion loss performance but was not considered in the formulas developed by Refs.(1)-(3) and the classical formula used in Refs.(4)-(6). The experimental results show that an enclosure, which first anti-symmetric structural and acoustic resonant frequencies do not coincide or nearly coincide, can avoid strong structural-acoustic couplings within the air cavity. At the acoustic resonance frequencies, the insertion loss performance of an enclosure can be improved by using the aluminum fiberboard, porous aluminum, and perforated aluminum panel to absorb the sound energy. Stiffener is useful to enhance the insertion loss ability of an enclosure if the dominant frequency bands of the noise are below the first structural resonant frequency. For having good damping effect to suppress the noise radiation at structural resonant frequencies, an enclosure should be mounted with both stiffeners and damping treatments.