However, these headphones are not suitable for all situations as noise-cancelling earmuffs. Thus, with ANC for low-frequency noise and PNC for high-frequency noise, noise can be insulated over a wide frequency range.Įarmuff-type devices with PNC and ANC are widely marketed as “noise-cancelling headphones”, which are useful only when the headphones cover the ears. At these frequencies, ANC becomes dominant over PNC. In earmuff-type sound insulation devices, ANC is generally effective at frequencies below 1.5 kHz, when the wavelength is sufficiently longer than the dimensions of the surrounding space. However, in principle, ANC still has an upper limit to its working frequency. Furthermore, recent studies have shown that subband ANC and frequency-domain constraint algorithms can solely cancel noise at specified frequencies. Improvements in the algorithm have increased the computational efficiency, providing a response to fast changes in signal characteristics. However, since PNC cannot select the frequency of sound insulation and does not provide sufficient sound insulation for low-frequency noise in principle, the combination of PNC and ANC was proposed. Earplugs and earmuffs are traditional sound insulation devices that utilize only PNC. In the latter, such as wearable devices, two methods are widely used: PNC alone and a combination of PNC and ANC. Hence, ANC has been employed for applications in confined spaces, such as car interiors and windows, using multiple microphones and loudspeakers. In contrast, it is not easy to apply ANC to sound insulation over a wide area because of the sound field. Over the past couple of decades, as PNC performance has evolved, several studies have presented improved sound insulation technologies via multiple materials, and sound insulation with perforated boards has been developed to ensure atmospheric permeability. In the former, PNC is commonly used because a large area has to be uniformly and permanently soundproofed. Two forms of sound insulation technologies are generally applied: wide walls (such as sound barriers) and small devices (such as those used for hearing protection). 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. 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) or active noise control (ANC). The experimental results confirm that the proposed device is a useful approach for insulating frequency-selective sound.Īcoustic 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. 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. In this research, the acoustic notch filtering performance of the proposed HR array plate is investigated in both simulations and experiments. 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.

A sheet-like sound insulating plate comprising HR arrays is realized in a honeycomb structure. Here, we propose an acoustic notch filtering earmuff utilizing Helmholtz resonator (HR) arrays that provides a sound attenuation effect around the tuneable resonant frequency. Thus, it has been difficult for traditional earmuffs to cancel out only high-frequency noise that people feel uncomfortable hearing. However, PNC is incapable of insulating selective frequencies of noise, and ANC is limited to low-frequency sounds. Two sound insulation technologies have been utilized: passive noise control (PNC) and active noise control (ANC). 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.

Parallel notch filter designer