Ih J., Kang J.

The air cleaner filter in engine intake system filtrates various dirt in inbreathing air, but also the box attenuates the noise reactively. The noise attenuation by the air filter itself, however, has been regarded as negligible by the field engineers. In this paper, for the analysis of the acoustical performance of air filter, acoustical models are suggested and the characteristics of air filter system are investigated. Fibrous structure of the filter element is modeled as a micro-perforated panel using the flow resistivity and porosity. The pleated geometry of the filter element is modeled as two coupled ducts that have permeable walls, in which each duct area is assumed being constant. Using such simplified geometry, a mathematical model is developed for the analysis of sound propagation within the narrow duct system. Visco-thermal effect is considered in modeling the sound propagation through the tubes: the filter box is modeled as a rigid rectangular box. By combining two models, a transfer matrix is derived. For the validation purpose, transmission loss of a plastic rectangular box containing an air filter is measured. A noticeable effect of the air filter element is observed by including the filter into the box: enhancement of TL at troughs and shift of troughs to low frequencies. By comparing the predicted and measured data, it is found that the predicted TL agrees well with experimental results, in particular, for magnitude and frequency at TL troughs.