Acoustic notch filtering earmuff utilizing Helmholtz resonator arrays

Abstract

In recent years, noisy bustling environments have created situations in which earmuffs must soundproof only specific noise while transmitting significant sounds, such as voices, for work safety and efficiency. Two sound insulation technologies have been utilized: passive noise control (PNC) and active noise control (ANC). However, PNC is incapable of insulating selective frequencies of noise, and ANC is limited to low-frequency sounds. Thus, it has been difficult for traditional earmuffs to cancel out only high-frequency noise that people feel uncomfortable hearing. Here, we propose an acoustic notch filtering earmuff utilizing Helmholtz resonator (HR) arrays that provides a sound attenuation effect around the tuneable resonant frequency. A sheet-like sound insulating plate comprising HR arrays is realized in a honeycomb structure. Since the resonant frequency is determined by the geometry of the HR arrays, a highly audible sound region can be designed as the target frequency. In this research, the acoustic notch filtering performance of the proposed HR array plate is investigated in both simulations and experiments. Furthermore, the fabricated earmuffs using the novel HR array plates achieve a sound insulation performance exceeding 40 dB at the target frequency, which is sufficiently high compared to that of conventional earmuffs. The experimental results confirm that the proposed device is a useful approach for insulating frequency-selective sound.

Open planar acoustic notch filter using a film-integrated Helmholtz resonator array

“…In a previous study, an acoustic notch filtering earmuff was achieved using large HR arrays molded into one piece using a 3D printer. 18) The proposed design of the layered structure can be easily extended in a plane and almost eliminates the restrictions of materials, substantially reducing the fabrication cost. However, the coincidence effect on acoustic filter performance should be considered in large scale panels.…”

“…Previous studies have exploited HRs as sound absorbers or insulators. [15][16][17][18][19] HRs are also used for open acoustic metamaterials with high ventilation 20,21) and impedance control of acoustic filters. [22][23][24] In such metamaterials, the working frequency is a function of the structural dimensions.…”