With the recent emergence of surround sound technology, renewed interest has been shown in the problem of sound field reproduction. However, in practical acoustical environments, the performance of sound reproduction techniques are significantly degraded by reverberation. In this paper, we develop a method of sound field reproduction for reverberant environments. The key to this method is an efficient parametrization of the acoustic transfer function over a region of space. Using this parametrization, a practical method has been provided for determining the transfer function between each loudspeaker and every point in the reproduction region. Through several simulation examples, the reverberant field designs have been shown to yield a reproduction accuracy as good as conventional free-field designs, and better than multipoint least squares designs when loudspeaker numbers are limited. The successful reproduction of sound over a wide frequency range has also been demonstrated. This approach reveals the appropriate choices for fundamental design parameters.
Sound rendering is increasingly being required to extend over only certain regions of space for multiple listeners, known as personal sound zones, with minimum interference to listeners in other regions. In this article, we present a systematic overview of the major challenges that have to be dealt with for multi-zone sound control in a room. Sound control over multiple zones is formulated as an optimisation problem and a unified framework is presented to compare two state-of-the-art sound control techniques. While conventional techniques have been focusing on point-to-point audio processing, we introduce wave-domain sound field representations and active room compensation for sound pressure control over a region of space. The design of directional loudspeakers is presented and the advantages of using arrays of directional sources are illustrated for sound reproduction, such as greater control of sound fields over wide areas and reduced total number of loudspeaker units, thus making it particularly suitable for establishing personal sound zones.
Abstract-This paper proposes an efficient parameterization of the Room Transfer Function (RTF). Typically, the RTF rapidly varies with varying source and receiver positions, hence requires an impractical number of point to point measurements to characterize a given room. Therefore, we derive a novel RTF parameterization that is robust to both receiver and source variations with the following salient features: (i) The parameterization is given in terms of a modal expansion of 3D basis functions. (ii) The aforementioned modal expansion can be truncated at a finite number of modes given that the source and receiver locations are from two sizeable spatial regions, which are arbitrarily distributed. (iii) The parameter weights/coefficients are independent of the source/receiver positions. Therefore, a finite set of coefficients is shown to be capable of accurately calculating the RTF between any two arbitrary points from a predefined spatial region where the source(s) lie and a pre-defined spatial region where the receiver(s) lie. A practical method to measure the RTF coefficients is also provided, which only requires a single microphone unit and a single loudspeaker unit, given that the room characteristics remain stationary over time. The accuracy of the above parameterization is verified using appropriate simulation examples. I. INTRODUCTIONThe room transfer function (RTF), demonstrates the collective effect of multipath propagation of sound between a source and a receiver within a given room enclosure. Accurate modeling of the RTF is useful in soundfield simulators as well as many other applications such as sound reproduction, soundfield equalization, echo cancellation, and speech dereverberation. These applications use appropriate RTF deconvolution methods to cancel the effects of room reflections (reverberation), and therefore, are highly dependent on the accuracy of the RTF model.The theoretical solution to the RTF based on the Green's function [1] was derived assuming a strict rectangular room geometry. It can only be applied to highly idealised cases with reasonable effort. The rooms with which we are concerned in our daily life however are more or less irregular in shape and the formulation of irregular boundary conditions will require extensive numerical calculations. For this reason, the immediate application of the classical model to practical problems in room acoustics is limited.In practice, RTFs are usually estimated as FIR filters, or as parametric equations based on the geometrical properties of the room. In the FIR filter approach, the RTF is assumed to behave as a linear time-invariant system, and then modeled as either an all-zero, all-pole, pole-zero [2] or a common pole-zero [3] system. The coefficients of these models are estimated as variable parameters of the RTF, and since the
Multi-zone sound control aims to reproduce multiple sound fields independently and simultaneously over different spatial regions within the same space. This paper investigates the multi-zone sound control problem formulated in the modal domain using the Lagrange cost function and provides a modal-domain analysis of the problem. The Lagrange cost function is formulated to represent a quadratic objective of reproducing a desired sound field within the bright zone and with constraints on sound energy in the dark zone and global region.
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