Reducing interior noise in a cylinder using micro-perforated panels

Sound absorption inside a cylindrical enclosure using micro-perforated panels (MPP) is investigated. Attention is focused on analyzing the effect of backing cavities on the sound absorption capabilities of various MPP configurations both numerically and experimentally. A model is used to analyze the acoustic coupling between the cylindrical acoustic domain enclosed by the MPP and the annular cylindrical acoustic domain forming the air space behind it. It was shown that the sound field in the backing cavity of the MPP plays an important role in determining the energy dissipation efficiency of the MPP construction, and thereby affects the degree of attenuation of the standing waves inside the enclosure. Conventional MPP construction with a backing air layer was shown to only provide limited noise reduction, but fail at certain frequencies associated with the acoustic resonances of the cylindrical acoustic field. The problem can be tackled by adding proper partitions in the baking cavity, as a result of the alteration of the acoustic coupling across the MPP panels.