Multizone wideband sound field reproduction

This thesis deals with the problem of multizone wideband sound field reproduction using an array of loudspeakers. A pressure matching approach is researched to control the sound field within the zones through the calculation of loudspeaker weights. The loudspeaker weights are computed first using a regularized least-squares (LS) approach and then a least-absolute shrinkage and selection operator (Lasso). It is demonstrated that the single-stage LS technique outperforms the single-stage Lasso in multizone wideband sound field reproduction, while the single-stage Lasso enables the judicious placement of loudspeakers. To improve the multizone sound reproduction performance of wideband sources using a limited number of loudspeakers, it is assumed that the virtual sources are fixed in positions. A new two-stage Lasso-LS pressure matching approach is then proposed to optimize both the loudspeaker locations and weights. In the first stage, a Lasso algorithm is used to select the loudspeakers' positions for all sources and frequency bands. A second stage then optimizes reproduction using all selected loudspeakers on the basis of a regularized LS algorithm. The results show that a horizontal array of limited number of loudspeakers (e.g. 52) can be used to effectively create personal audio spaces for multiple users of variable heights. The proposed method is then extended to a nested Lasso-LS method which employs harmonic nested arrays in the first stage Lasso to reduce the computational complexity. Effectively, the nested arrays provide a priori knowledge of prospective loudspeaker locations based on the frequency bands of interest. The final loudspeaker locations and weightings are then estimated during the two-stage Lasso-LS optimization

An approach to generating two zones of silence with application to personal sound systems

An application of current interest in sound reproduction systems is the creation of multizone sound fields which produce multiple independent sound fields for multiple listeners. The challenge in producing such sound fields is the avoidance of interference between sound zones, which is dependent on the geometry of the zone and the direction of arrival of the desired sound fields. This paper provides a theoretical basis for the generation of two zones based on the creation of sound fields with nulls and the positioning of those nulls at arbitrary positions. The nulls are created by suppressing low-order mode terms in the sound field expansion. Simulations are presented for the two-dimensional case which shows that suppression of interference is possible across a broad frequency audio range

Generation of half-space sound fields with application to personal sound systems

A method is presented for generating a sound field that is significantly attenuated over half of the reproduction region, which has application to the generation of two independent sound fields for two listeners. The half-space sound field is produced by attenuating the negative or positive modes in the cylindrical or spherical expansion of a plane wave or point source sound field. It is shown that this is equivalent to adding to the original sound field, in quadrature, a second field which is the Hilbert transform of the original field. The resulting analytic field has a small magnitude in one half of the plane. Methods are presented for controlling the attenuation in the unwanted half-space. Finally, a simulation is presented showing the generation of a wideband pulse that propagates across half of the area within a circular array of sources

An efficient approach to dynamically weighted multizone wideband reproduction of speech soundfields

This paper proposes and evaluates an efficient approach for practical reproduction of multizone soundfields for speech sources. The reproduction method, based on a previously proposed approach, utilises weighting parameters to control the soundfield reproduced in each zone whilst minimising the number of loudspeakers required. Proposed here is an interpolation scheme for predicting the weighting parameter values of the multizone soundfield model that otherwise requires significant computational effort. It is shown that initial computation time can be reduced by a factor of 1024 with only 85dB of error in the reproduced soundfield relative to reproduction without interpolated weighting parameters. The perceptual impact on the quality of the speech reproduced using the method is also shown to be negligible. By using pre-saved soundfields determined using the proposed approach, practical reproduction of dynamically weighted multizone soundfields of wideband speech could be achieved in real-time

Acoustic contrast, planarity and robustness of sound zone methods using a circular loudspeaker array

Since the mid 1990s, acoustics research has been undertaken relating to the sound zone problem—using loudspeakers to deliver a region of high sound pressure while simultaneously creating an area where the sound is suppressed—in order to facilitate independent listening within the same acoustic enclosure. The published solutions to the sound zone problem are derived from areas such as wave field synthesis and beamforming. However, the properties of such methods differ and performance tends to be compared against similar approaches. In this study, the suitability of energy focusing, energy cancelation, and synthesis approaches for sound zone reproduction is investigated. Anechoic simulations based on two zones surrounded by a circular array show each of the methods to have a characteristic performance, quantified in terms of acoustic contrast, array control effort and target sound field planarity. Regularization is shown to have a significant effect on the array effort and achieved acoustic contrast, particularly when mismatched conditions are considered between calculation of the source weights and their application to the system

Generation of isolated wideband sound fields using a combined two-stage lasso-LS algorithm

The prohibitive number of speakers required for the reproduction of isolated soundfields is the major limitation preventing solution deployment. This paper addresses the provision of personal soundfields (zones) to multiple listeners using a limited number of speakers with an underlying assumption of fixed virtual sources. For such multizone systems, optimization of speaker positions and weightings is important to reduce the number of active speakers. Typically, single stage optimization is performed, but in this paper a new two-stage pressure matching optimization is proposed for wideband sound sources. In the first stage, the least-absolute shrinkage and selection operator (Lasso) is used to select the speakers' positions for all sources and frequency bands. A second stage then optimizes reproduction using all selected speakers on the basis of a regularized least-squares (LS) algorithm. The performance of the new, two-stage approach is investigated for different reproduction angles, frequency range and variable total speaker weight powers. The results demonstrate that using two-stage Lasso-LS optimization can give up to 69 dB improvement in the mean squared error (MSE) over a single-stage LS in the reproduction of two isolated audio signals within control zones using e.g. 84 speaker

Optimizing Source and Sensor Placement for Sound Field Control: An Overview

International audienceIn order to control an acoustic field inside a target region, it is important to choose suitable positions of secondary sources (loudspeakers) and sensors (control points/microphones). This paper provides an overview of state-of-the-art source and sensor placement methods in sound field control. Although the placement of both sources and sensors greatly affects control accuracy and filter stability, their joint optimization has not been thoroughly investigated in the acoustics literature. In this context, we reformulate five general source and/or sensor placement methods that can be applied for sound field control. We compare the performance of these methods through extensive numerical simulations in both narrowband and broadband scenarios. Index Terms-source and sensor placement, sound field control , sound field reproduction, subset selection, interpolation

Spatial Multizone Soundfield Reproduction Design

It is desirable for people sharing a physical space to access different multimedia information streams simultaneously. For a good user experience, the interference of the different streams should be held to a minimum. This is straightforward for the video component but currently difficult for the audio sound component. Spatial multizone soundfield reproduction, which aims to provide an individual sound environment to each of a set of listeners without the use of physical isolation or headphones, has drawn significant attention of researchers in recent years. The realization of multizone soundfield reproduction is a conceptually challenging problem as currently most of the soundfield reproduction techniques concentrate on a single zone. This thesis considers the theory and design of a multizone soundfield reproduction system using arrays of loudspeakers in given complex environments. We first introduce a novel method for spatial multizone soundfield reproduction based on describing the desired multizone soundfield as an orthogonal expansion of formulated basis functions over the desired reproduction region. This provides the theoretical basis of both 2-D (height invariant) and 3-D soundfield reproduction for this work. We then extend the reproduction of the multizone soundfield over the desired region to reverberant environments, which is based on the identification of the acoustic transfer function (ATF) from the loudspeaker over the desired reproduction region using sparse methods. The simulation results confirm that the method leads to a significantly reduced number of required microphones for an accurate multizone sound reproduction compared with the state of the art, while it also facilitates the reproduction over a wide frequency range. In addition, we focus on the improvements of the proposed multizone reproduction system with regard to practical implementation. The so-called 2.5D multizone oundfield reproduction is considered to accurately reproduce the desired multizone soundfield over a selected 2-D plane at the height approximately level with the listener’s ears using a single array of loudspeakers with 3-D reverberant settings. Then, we propose an adaptive reverberation cancelation method for the multizone soundfield reproduction within the desired region and simplify the prior soundfield measurement process. Simulation results suggest that the proposed method provides a faster convergence rate than the comparative approaches under the same hardware provision. Finally, we conduct the real-world implementation based on the proposed theoretical work. The experimental results show that we can achieve a very noticeable acoustic energy contrast between the signals recorded in the bright zone and the quiet zone, especially for the system implementation with reverberation equalization