# Acoustic Enhancement Performance of Hierarchical ZSM-5 Zeolites with Different Si/Al Ratios

## TL;DR

This paper explores how hierarchical ZSM-5 zeolites with different Si/Al ratios can improve the acoustic performance of microspeakers in small devices.

## Contribution

The study introduces a novel approach to acoustic enhancement using hierarchically structured ZSM-5 zeolites with controlled SiO2/Al2O3 ratios.

## Key findings

- ZSM-5 zeolite with SAR of 614 showed a resonance offset of 199.53 Hz and sound pressure level enhancement of 4.74 dB.
- Mesopores in zeolites improve air molecule diffusion and sorption during microspeaker diaphragm vibration.
- Supermicropores complement micropores by adsorbing air molecules during vibration.

## Abstract

Size restrictions pose increasing challenges to the acoustic performance of microspeakers in portable devices as the size of such devices, and thus the back volume of microspeakers, continues to shrink. Filling the back volume with porous materials, such as zeolites, has been proved to be an effective strategy for improving acoustic performance. In this work, hierarchically structured ZSM-5 zeolites with abundant mesopores were synthesized via the traditional hydrothermal method by adjusting the SiO2/Al2O3 ratios (SAR), and their pore structures and morphologies were systematically investigated. Their acoustic enhancement performance was evaluated using a commercial microspeaker. Based on their acoustic properties, the influence of pore structure on acoustic performance was further studied. The ZSM-5 zeolite sample with an SAR of 614, which exhibited the maximum mesopore volume, demonstrated exceptional acoustic enhancement performance with a resonance offset of 199.53 Hz and an enhanced sound pressure level of 4.74 dB at 500 Hz. The presence of mesopores significantly facilitates diffusion within the zeolite crystals, enabling air molecules to access more micropores for efficient sorption–desorption processes during diaphragm vibration in microspeakers. Furthermore, supermicropores were found to contribute to improved performance by adsorbing air molecules during diaphragm vibration, complementing the role of micropores.