Sound attenuation in triple panel using locally resonant sonic crystal and porous material

Abstract

The present work combines the properties of sonic crystal (SC), locally resonant sonic crystal (LRSC) and porous material in the triple panel to increase the overall sound transmission loss through the combined structure. SC is a periodic structure which is mainly used for sound reduction in a particular frequency range. In the present work, sound transmission loss through the triple panels is investigated using an analytical method. Finite element simulations are also performed using acoustic structure interaction to predict sound transmission loss. The simulation predictions are validated by the analytical results. Multiple panels separated by the air gaps offer high sound reduction due to multiple reflections and discontinuities in the path of wave propagation. However, due to the 1D periodic structure made by multiple panels, there can be sudden losses in the sound attenuation, also referred to Bragg’s dip in the sound transmission loss curve. The results show that there are two types of sudden dips in sound transmission loss i.e. Bragg’s dip and dips due to the panel vibrations. To get rid of sudden dips in sound transmission loss, a porous material is filled in the air cavities. It is found that insertion of porous material in the air cavities between the triple panels does not alter the sound transmission loss curve except at certain frequencies. For enhancement of sound transmission loss, SC and LRSC are inserted along with glass wool in the triple panel. It is found that the panel with SC-glass wool assembly performs well in a specific frequency region around Bragg’s frequency whereas the panel with LRSC-glass wool assembly performs better in low frequency region as well as in high frequency region.