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.
Highlights
Acoustic noise is one of the most serious environmental problems due to its variety of negative effects on people’s health and lives; for example, acoustic noise is responsible for causing sleep disturbances, hearing impairment, and heart disease [1,2,3]
We proposed an earmuff-type acoustic notch filter using Helmholtz resonator (HR) array plates
We designed two types of HR array plates: HR array (A, B) plates with a diameter of 108 mm, the necks of which were connected to the inner side of each hole, and HR array (C) plates with a diameter of 57 mm, the necks of which were connected to the front surface of the plate
Summary
Acoustic noise is one of the most serious environmental problems due to its variety of negative effects on people’s health and lives; for example, acoustic noise is responsible for causing sleep disturbances, hearing impairment, and heart disease [1,2,3]. To protect ears from acoustic noise and provide a comfortable acoustic environment, various sound insulation technologies have been developed; these technologies are mainly classified as either passive noise control (PNC) [4,5,6,7,8,9,10] or active noise control (ANC) [11,12,13,14,15,16,17,18,19,20,21,22,23]. PNC is based on physical sound insulation using a sound insulating material without a power supply, whereas ANC attenuates acoustic noise by generating waves of the opposite phase to the noise (i.e., anti-noise) from a loudspeaker.
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