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

Abstract

A zeolite filling in the rear cavity of a compact loudspeaker enhances the sound pressure amplitude of the loudspeaker system with a frequency range up to ∼500 Hz, but its intrinsic mechanisms remain elusive. We theoretically consider the gas adsorption–desorption behavior on zeolite that can be dynamically perturbed by sound pressure from the diaphragm of the 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 electroacoustic impedance experiments, the linear relationship with a slope of 1.92 mF cm−3 reveals the intrinsic ability of porous material to enhance mechanical compliance by adsorption of gas onto the zeolite in the rear cavity. This study correlates the kinetic behavior of air molecules on zeolite and acoustic behavior; it offers a novel insight to improve the performance of a compact loudspeaker by simple filling with porous material and introduces a comprehensive method for evaluating gas adsorption–desorption dynamics in porous media.