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.

Total harmonic distortion (THD) plays an important role in the performance of miniature loudspeakers used in mobile phones. Traditional nonlinear models fail to predict THD in the higher frequency domain. Significant discrepancies can be found between the prediction and measurement. In this study, an extended model considering nonlinear acoustic damping is proposed to address this issue. Flow separation occurring near the orifices of the sound port is of particular interest. Two velocity-dependent parameters were derived to model the nonlinear damping effect. Based on the extended model, the dynamics of miniature loudspeakers are described using the state-space method. Experiments and calculations confirm the validity of the extended model. The influence of nonlinear acoustic damping on THD is also discussed.

Personal Sound Zone (PSZ) allows listeners to enjoy their individual sound without being disturbed by sound from other zones. Acoustic contrast, signal distortion, and array effort are the most frequently used metrics for measuring the performance of a PSZ system. However, usually, the three metrics cannot be optimized at the same time. A trade-off between the three metrics has to be made when designing a PSZ system. In this paper, two generalized methods based on multi-objective optimization are proposed for dealing with all possible trade-off problems between the three metrics in PSZ. Optimality analysis of the two proposed methods is taken, and the relationship between the two proposed methods is investigated. Numerical simulations are presented to validate the efficacy and flexibility of the two proposed methods.

The multimodal method is used to develop an approach for optimizing the shape of axisymmetric acoustic horns for both well-controlled directivity and high radiation efficiency over a wide frequency range. A horn with an arbitrary profile can be efficiently modeled with the multimodal method by projecting the wave field over transverse modes in connected short cylinders; the radii of the cylinders are used directly as design variables. Many design variables are employed in the optimization process to ensure design flexibility and computational accuracy. The relative weights for the design objectives of constant directivity, high radiation efficiency, and acceptable shape smoothness are adjusted by two coefficients in the objective function. The optimization problem is solved with a gradient-based algorithm, which takes advantage of algebraic gradient expressions. Numerical experiments demonstrate that the optimization procedure generates smooth horn contours that exhibit considerably improved performance over the target frequency band. Interestingly, a high-quality horn produced with moderate weight coefficients is similar in shape to constant-directivity horns invented earlier while having good low-frequency loading properties. The proposed method provides an attractive alternative to conventional horn design approaches.

Sound field reproduction aims to reconstruct a desired sound field in a listening area by using multiple loudspeakers. To improve sound field reproduction performance, several loudspeaker placement methods have been proposed to select suitable loudspeaker positions. However, most conventional loudspeaker placement methods do not consider the distribution characteristic of the desired sound fields such as the distribution of directions from where the sound wave emanates, making these methods not optimal when the prior knowledge of the distribution characteristic of the desired sound fields is known. In this paper, a weighted loudspeaker placement method is proposed, which considers optimizing the objective function that depends on a set of desired sound fields with different weights. This paper formulates the optimization problem for weighted loudspeaker placement, presenting three alternative discretization methods to obtain a more practical optimization problem, after which the group greedy method is used to solve the optimization problem to find the near-optimal loudspeaker setup. To validate the proposed method, numerical experiments aiming to reconstruct the desired sound wave from a restricted range are conducted. The results indicate that the proposed method performs well in both narrowband and broadband cases, because it can use prior knowledge of the distribution characteristic of the desired sound fields.