Sound absorption of double porosity material backed with air cavity

The widely used porous materials commonly have good sound absorption performance at high frequencies, but with bad performance at low frequencies. To improve the low frequency sound absorption of porous materials, we propose a sound absorber design which consists of a double porosity material obtained by perforating slits in homogenous porous materials and a back air cavity. A theoretical model based on the double porosity theory and impedance transfer method is developed to study the sound absorption of this material. Also, a finite element model is established to validate the theoretical model, with good agreements achieved between these two models. Results show that the introduction of the air cavity can supply a larger space for sound energy storage and change the sound energy transmission path, which significantly improves the low-frequency sound absorption of porous materials. Moreover, the influences of structural geometry parameters on sound absorption performance are analyzed. This work is helpful for the novel design of porous material sound absorber with low-frequency and broadband sound absorption performances.