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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. Finally, a placement of physical microphones for active control of road noise in car cabins is discussed. Both the numerical and experimental results show that an upper limit frequency exists for accurate sound pressure estimation at the center of a sphere with the sound pressure on the sphere surface. For a sufficiently complex sound field such as that in a reverberation room or in a car, half the wavelength of the upper limit frequency is about the average distance among the physical microphones. [ABSTRACT FROM AUTHOR]

A steerable parametric array loudspeaker (PAL) can electronically steer highly directional audio beams in the desired direction. The challenge of modelling a steerable PAL is to obtain the audio sound pressure in both near and far fields with a low computational load. To address this issue, an extension of the spherical wave expansion is proposed in this paper. The steerable velocity profile on the radiation surface is expanded as Zernike polynomials which are an orthogonal and form a complete set over a unit circle. An expression for the radiated audio sound is then obtained using a superposition of Zernike modes. Compared to the existing methods, the proposed expansion is computationally efficient and provides a rigorous transformation of the quasilinear solution of the Westervelt equation without paraxial approximations. The proposed expansion is further extended to accommodate local effects by using an algebraic correction to the Westervelt equation. Numerical results for steering single and dual beams are presented and discussed. It is shown that the single beam can be steered in the desired direction in both near and far fields. However, dual beams cannot be well separated in the near field, which cannot be predicted by the existing far field models. [ABSTRACT FROM AUTHOR]

• Leakage detection was conducted by generating special crests of sound with a cavity-shaped whistle. • The occurrences of crest were independent from leakage rate, leakage channel size, and sensor location. • Leakage detection sensitivity and accuracy of our method exceeded acoustic emission method. Currently, on-line leakage detection of sealed surfaces is being researched to improve detection accuracy. This study presents a new method of leakage detection by generating sounds with two crests at frequencies of 11.0 kHz and 32.7 kHz using specially designed cavity shaped whistles. The sound pressure levels (SPLs) that are generated were significantly greater than the pressure levels of the leakage jet noise at the sealing surface. In addition, the occurrence of the crests (11.0 kHz and 32.7 kHz) was independent of the leakage rate, leakage channel size, and sensor location. The experimental results showed that the leakage detection sensitivity and accuracy of the presented method exceeded those of the commercial acoustic emission (AE) method. The simulations revealed that the frequency crests resulted from strong fluid pressure oscillations and symbolic opposite radiation reactance of cavity shaped whistle. The proposed leakage detection method shows great potential in real industrial applications due to its anti-disturbance and good accuracy. [ABSTRACT FROM AUTHOR]