Noise reduction from large machineries by using sound enclosures

Abstract

A sound enclosure is an effective measure to reduce the noise emitting from the large noise sources such as diesel engines and gas turbines. In this study, insertion loss prediction of the large enclosure is presented. Inside the enclosure, diffuse sound field is assumed, and there exist no air leakages. Insertion loss is predicted by using SEA (Statistical Energy Analysis). From the energy equilibrium equations, sound pressure inside the enclosure is derived in terms of the acoustic power from the machinery. Insertion loss is defined as the ratio between acoustic power inside and transmitted power outside the enclosure. It is shown that sound radiation from the panel vibration can be neglected compared to that transmitted through panel. Insertion loss predictions are compared to the measurements. The enclosure size is 6.4 m x 2.65 m x 4.8 m (L x W x H) and 4.5 m x 2.5 m x 2.0 m, where panel consists of 1.5 mm steel plate and 70 mm mineral wool. The comparisons show good agreements. It is concluded that to increase the insertion loss, panel must have a large sound transmission loss and sound absorption coefficient inside the enclosure must be high.