Low Frequency Determination of Partial Enclosure Insertion Loss using a Plane Wave Simplification

Partial enclosures are used to reduce machinery noise emissions, but can have the adverse effect of amplifying the noise at low frequency resonances which manifest themselves as a trough in the insertion loss curve. A plane wave approach has been developed to estimate the insertion loss and identify low frequency enclosure resonances. The plane wave approach has been validated via acoustic finite element analysis and direct measurement, and is utilized to strategically add muffler elements to a test enclosure. Improvements in performance of up to 20 dB are observed at selected frequencies. The paper concludes with a suggested methodology for investigating the airborne path of partial enclosures.