Membrane sound absorber with a granular activated carbon infill

Abstract

An impervious membrane sound absorber with an air cavity partially filled with a porous material is a viable alternative to perforated panels when impermeable surfaces are required. On the other hand, due to its unusually high sound absorption properties at low frequencies, using activated carbon (AC) in granular form as an absorbing material has recently received attention. This paper reports the sound absorption performance of a novel system consisting of a thin stretched impervious circular membrane made of silicone, backed by an air cavity partially filled with granular AC. The system is analyzed theoretically using the impedance translation theorem. The normal-incidence sound absorption was measured in an impedance tube for combinations of cavity depth, membrane tension, and membrane surface density. The results of using an AC and a fiberglass infill material of the same thickness in the air cavity were also compared. The findings validated the advantage of AC as porous infill material of a membrane sound absorber in the low-frequency range. Furthermore, the outcomes of the impedance tube experiments were in good agreement with theoretical predictions. The findings reported in this work could be used to design new innovating sound-absorbing metamaterials based on activated carbon and stretched membranes.