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

Partial enclosures are a common way to reduce machinery noise emissions, but unfortunately can amplify the noise at low frequency resonances. The most commonly used metric to assess enclosure performance is insertion loss and low frequency resonances manifest themselves as a trough in the insertion loss. A plane wave approach has been developed to determine the insertion loss and to especially identify low frequency enclosure resonances. The plane wave approach has been validated by comparison with boundary element method simulation and direct measurement. Following this, the method is then used to strategically add muffler elements to an enclosure to improve the performance at selected frequencies. Improvements in performance of up to 20 dB at selected frequencies were observed.