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A recent paper by Zhang, Wang, Duan, Tao, Zou, and Qiu [(2022). J. Acoust. Soc. Am. 152, 2840–2848] proposed that the average distance between physical microphones in remote acoustic sensing should be no larger than half the wavelength to ensure the coherence between the virtual signal and physical signals no less than 0.9 in complex sound fields. In this letter, the effects of the sound sources' distance on the coherence between the virtual signal and physical signals are further investigated, and it is found that the required average distance among physical microphones becomes smaller when sound sources are closer to the microphones. [ABSTRACT FROM AUTHOR]

The movement and rotation of the human head can significantly degrade the control performance of active headrests with virtual microphones. This paper investigates the performance robustness of an active headrest with virtual microphones against the head rotation in a pure tone diffracted diffuse sound field. A physical model of a headrest system with a diffractive sphere is firstly developed, based on which the influence of acoustic transfer responses on the performance robustness against head rotation is analyzed. Then, the multi-objective optimization with constraints is developed to improve the performance robustness of the system, by designing optimized plant responses. Simulation results show that the method is effective in improving the robustness of single and dual channel systems. For a dual-channel headrest system with the proposed arrangements of secondary sources and microphones, the promotion of the minimum noise reduction is more than 7 dB after optimization when the head rotates from −90 degrees to 90 degrees at 125 Hz, 250 Hz and 500 Hz. In addition, the influence of different parameters on the optimization method is discussed for this dual-channel system. Finally, experiments carried out in an ordinary room validate the effectiveness of the proposed method. [ABSTRACT FROM AUTHOR]

Abstract: Virtual sound barrier (VSB) is an array of loudspeakers and microphones forming an acoustic barrier, which creates a quiet zone without blocking air and light. A 16-channel cylindrical VSB system has been developed and its feasibility is verified by both numerical simulations and experiments. Experimental results in a normal room show that it can create a quiet zone larger than the size of a human head in the low-middle frequency, with a total sound pressure level reduction of more than 10dB in the quiet zone. The control performance of the system with respect to the frequency, the distribution of the error sensors and the control sources are discussed. [Copyright &y& Elsevier]