A robust error sensing strategy for global active noise control in car cabins.

Global active noise control (ANC) systems reduce noise over the entire car cabin with robust performance even as the human head moves; however, they have not been implemented in real-world applications. A robust error sensing strategy is proposed in this paper that is based on which a feasible global ANC system is realized in an electric car, and real-time ANC experiments demonstrate its effectiveness. Simulations based on measured road noise show that using evenly distributed error sensors is a robust error sensing strategy for different car speeds and the upper limit frequency of 3 dB global control is inversely proportional to the equivalent distance between error sensors.

A further study on coherence between virtual signal and physical signals in remote acoustic sensing (L).

A recent paper by Zhang, Wang, Duan, Tao, Zou, and Qiu [(2022). J. Acoust.

Active control of sound transmission through a floor-level slit.

The floor-level slit between the door and the floor is one weak point in building noise insulation. In this paper, an active noise control system is proposed to reduce the sound transmission through a floor-level slit with evenly distributed secondary sources on its top boundary. The system performance is first investigated based on the analytical and numerical models, and simulation results indicate a decrease in active control performance with increasing frequency.

Transmission loss and directivity of sound transmitted through a slit on ground.

An analytical model is proposed for sound transmission through a slit on a rigid ground based on the modal superposition method to investigate the transmission loss (TL). A simple formula is derived for estimation of the TL for plane waves with and without the ground, which gives a more precise prediction than existing approaches. It is found that a larger slit height generally decreases the TL, except at the resonant frequencies of the slit.

A study on coherence between virtual signal and physical signals in remote acoustic sensing.

Remote acoustic sensing can be used to estimate the error signals in human ears without placing any physical microphones there. In this paper, the coherence between the signals picked up by physical microphones over a sphere surface and the signal obtained at the sphere center is investigated. Based on the multiple channel coherence formulas in the time domain and frequency domain, the relationship between the coherence and the placement of physical microphones is analyzed by numerical simulations first, then the experimental results obtained in a reverberation chamber and a car cabin are presented to verify the simulation results.

Improving the performance of an active staggered window with multiple resonant absorbers.

The active noise control (ANC) technique has been applied in staggered windows to improve the noise reduction at low frequencies. The control performance of such a system deteriorates significantly at some frequencies where the secondary source cannot radiate effectively due to the reflection at the boundaries of the staggered window. A resonant absorber consisting of a perforated panel and coiled up tubes is proposed to solve the problem.

Ultra-sparse metamaterials absorber for broadband low-frequency sound with free ventilation.

An absorptive device for broadband low-frequency sound with ventilation is essential but challenging in acoustic engineering, which is subjected to the narrow-band limitation and difficulty of balancing high-efficiency absorption and excellent ventilation. Here, we have theoretically and experimentally demonstrated an ultra-sparse (with filling ratio of 53.7%) broadband metamaterial absorber which can efficiently absorb (absorptance  >90%) sound energy ranging from 307 to 341 Hz, while enabling air to flow freely.

Broadband noise insulation of windows using coiled-up silencers consisting of coupled tubes.

It has been demonstrated that a staggered window achieves better noise reduction performance than a traditional single glazing one at middle to high frequencies while maintaining a degree of natural ventilation. There is, however, little improvement in the low frequency range. In contrast, this work proposes to apply coiled-up silencers consisting of coupled tubes on the side walls of staggered windows to obtain noise attenuation in a broad band, especially in the low frequency range.

Dual frequency sound absorption with an array of shunt loudspeakers.

Transformer noise is dominated by low frequency components, which are hard to be controlled with traditional noise control approaches. The shunt loudspeaker consisting of a closed-box loudspeaker and a shunt circuit has been proposed as an effective sound absorber by storing and dissipating the electrical energy converted from the incident sound. In this paper, an array of shunt loudspeakers is proposed to control the 100 Hz and 200 Hz components of transformer noise.

The performance of active noise control systems on ground with two parallel reflecting surfaces.

This paper investigates the performance of active noise control (ANC) systems with two reflecting surfaces that are placed vertically on ground in parallel. It employs the modal expansion method and the boundary element method to calculate the noise reduction of the systems with infinitely large and finite size reflecting surfaces, respectively. Both experimental and simulation results show that the noise reduction of the system can be significantly increased after optimizing the surface separation distance and their locations with the sound sources.

Increasing the performance of active noise control systems on ground with two vertical reflecting surfaces with an included angle.

This paper investigates the feasibility of increasing the noise reduction performance of active noise control (ANC) systems on ground by introducing two vertical reflecting surfaces with an included angle. By using the image source method, the theory of sound wave propagation in a wedge-shaped reflector and the integral equation method, the noise reduction of the ANC systems with two infinitely large or finite size reflecting surfaces with different included angles are studied. It is demonstrated that the noise reduction of the system can be increased significantly with two reflecting surfaces after optimizing their included angle and size.

A near-field error sensing strategy for compact multi-channel active sound radiation control in free field.

Noise reduction performance of a compact active sound radiation control system is significantly affected by locations of the error microphones which are required to be installed near the primary source. In this paper, near-field error sensing for multi-channel active radiation control systems in free field is investigated, and it is found that the optimal locations of error sensors for minimizing the sum of squared sound pressure are between the primary source and the secondary sources distributed uniformly on a sphere surface surrounding the primary source. Both simulation and experiment results show that the optimal locations of error microphones are independent of the type of primary source when there are sufficient secondary sources.

A boundary error sensing arrangement for virtual sound barriers to reduce noise radiation through openings.

Previous work has demonstrated that sound radiation through a cavity opening can be reduced with secondary sources at the edge of the opening, but the error microphones are implemented over the entire opening, which might affect the natural ventilation, lighting, and especially the access through the opening in some applications. A boundary error sensing arrangement is proposed and investigated in this paper. It is found that a double-layer error microphone arrangement achieves better performance than a single-layer one.

Mechanisms of active control of sound radiation from an opening with boundary installed secondary sources.

Previous work has demonstrated that installing secondary sources at the edge of a cavity opening can reduce sound radiation through it, but the mechanisms are not clear, which is investigated in this paper by using the modal decomposition method. It is found that a double layer edge system achieves better performance than a single layer system because secondary sources at the edge of the same layer cannot excite some modes effectively and those at different heights compensate this. There exists an upper limit frequency for the systems with boundary installed secondary sources, which is mainly decided by the length of the short side of the opening.

Controlling sound radiation through an opening with secondary loudspeakers along its boundaries.

We propose a virtual sound barrier system that blocks sound transmission through openings without affecting access, light and air circulation. The proposed system applies active control technique to cancel sound transmission with a double layered loudspeaker array at the edge of the opening. Unlike traditional transparent glass windows, recently invented double-glazed ventilation windows and planar active sound barriers or any other metamaterials designed to reduce sound transmission, secondary loudspeakers are put only along the boundaries of the opening, which provides the possibility to make it invisible.

Performance of a planar virtual sound barrier at the baffled opening of a rectangular cavity.

This paper proposes to reduce the radiation of a sound source inside a cavity through the baffled opening by using an array of loudspeakers and microphones. The system is called a planar virtual sound barrier because it acts like a concrete sound barrier to block the transmission of sound but does not affect light and air circulation. An analytical model for the planar virtual sound barrier is developed based on the modal superposition method to calculate the sound field in and outside a rectangular cavity with a baffled opening.

Sound absorption of a finite micro-perforated panel backed by a shunted loudspeaker.

Deep back cavities are usually required for micro-perforated panel (MPP) constructions to achieve good low frequency absorption. To overcome the problem, a close-box loudspeaker with a shunted circuit is proposed to substitute the back wall of the cavity of the MPP constructions to constitute a composite absorber. Based on the equivalent circuit model, the acoustic impedance of the shunted loudspeaker is formulated first, then a prediction model of the sound absorption of the MPP backed by shunted loudspeaker is developed by employing the mode solution of a finite size MPP coupled by an air cavity with an impendence back wall.