Linear enhancement of mechanical compliance by zeolite filling in a compact loudspeaker

Abstract

The zeolite filled in the rear cavity of compact loudspeaker enhances sound pressure amplitude of loudspeaker system with a frequency range up to ~500 Hz, while its intrinsic mechanisms remain elusive. We theoretically consider the gas adsorption-desorption behaviors on zeolite that can be dynamically perturbated by sound pressure from diaphragm of loudspeaker. By merging equivalent circuit theory with gas thermodynamic theory, a linear relationship between mechanical compliance and zeolite volume in the rear cavity is quantitatively modeled. Confirmed by electro-acoustical impedance experiments, the linear relationship with a slope of 1.92 mF/cm3 reveals the intrinsic ability of porous material to enhance mechanical compliance by gas adsorption onto the zeolite in the rear cavity. This study correlates the kinetic behavior of air molecules on zeolite and acoustic behavior, not only offering a novel insight to improve the performance of the compacted loudspeaker by simple filling of porous material, but also introducing a comprehensive method to evaluate gas adsorption-desorption dynamics in porous media.