Presence is used to assess the subjective experience of being in one place when physically situated in another. Recently, the research on presence has gained increasing attention due to the wide use of immersive audio technologies. Currently, the most widely-used measurement of presence is based on post-experiment self-report questionnaires. It is reliable but imperfect due to the psychological changes caused by the act of answering the questionnaire when immersed in the virtual environment. Therefore, the present work aims to find an objective way to measure presence, and electroencephalography (EEG) was investigated as a possible tool for this objective measurement. In this study, two listening tests were conducted, where eight loudspeakers were used to reproduce urban soundscapes to stimulate auditory presence. Presence was measured by both questionnaires and EEG. Results showed a significant correlation between T/B (Theta/Beta Ratio) extracted from EEG and subjective presence levels assessed by questionnaires, suggesting the possible use of EEG to measure presence objectively. This study could bring some insight for the research of presence, and related technologies, such as VR, video games and immersive audio production.

In practical active noise control systems, saturation nonlinearity is one of the most common nonlinear effects, which can occur at the electronic circuits in the secondary path. Adaptive algorithms designed for linear systems, such as the filtered-x least mean square (FxLMS) algorithm, may diverge in nonlinear systems with a saturated secondary path and result in limited noise reduction performance. Various nonlinear algorithms with improved stability have been proposed; however, a trade-off between noise reduction performance and computational complexity exists when selecting a satisfactory algorithm. This paper therefore proposes a simple algorithm that can achieve significant noise reduction with low computational complexity. The proposed algorithm adopts the same update equation as the FxLMS algorithm, but uses an intermittent update strategy to avoid unnecessary fluctuations of the weight vector when the output of the control filter lies in the saturation region. Simulation results under different conditions demonstrate the effectiveness and advantages of the proposed algorithm.

The aim of multizone sound reproduction is to reproduce different sound programs to different spatial zones in a common space using a set of loudspeakers. Several multizone sound reproduction methods have been developed over the past few decades, and most of them assume that there are no listeners in the listening area. However, when listeners enter the listening area, the scattering effects will reduce the performance of the multizone sound reproduction system. In this paper, an adaptive control method of scattering effects is proposed for multizone sound reproduction. The proposed method models the scattering effects based on the equivalent source method and uses adaptive filters to estimate the scattering effect by a small number of additional microphones. To validate the proposed method, several simulations are presented. The results of the simulations indicate that the proposed adaptive method exhibits good performance when used in multizone sound reproduction with the scattering effects.

This paper presents a method for the shape optimization of an acoustic horn with respect to the impedance matching property based on the discrete multimodal method. The method models the horn as a series of short cylinders and takes mode coupling across the discontinuities into account. The optimization employs a gradient-based algorithm, and allows for analytical derivation of the objective function and its gradient in a numerically workable manner. A case study followed with an experimental validation is presented. With appropriate parameter settings, the method is capable of rapidly finding a smooth and convex horn design that behaves like a high-pass radiator with near-ideal wideband transmission in small dimensions.

Piezoelectric microelectromechanical system (MEMS) loudspeakers have received extensive attention in recent years. In particular, the piezoelectric cantilever MEMS loudspeaker, which uses multilayer piezoelectric cantilever actuators (MPCAs), has attracted attention because of its small size, low cost, ease of manufacture, and desirable piston movement. However, owing to the complex driving principles of MPCAs, no adequately efficient and appropriate method currently exists that can be used to analyze and predict the performance of piezoelectric cantilever MEMS loudspeakers. In this study, the equivalent circuit method (ECM) is adopted to theoretically model piezoelectric cantilever MEMS loudspeakers, and an ECM model with a special MPCA transformer for electromechanical conversion is proposed. With the proposed ECM model, the performance characteristics of piezoelectric cantilever MEMS loudspeakers, such as the displacement and sound pressure response, can be calculated efficiently and conveniently. To verify the accuracy of the ECM model, the finite element method is adopted for simulation, and the simulated results are compared with those of the ECM models. A satisfactory agreement was found, which verifies the accuracy of the proposed ECM model.