Spatial multizone soundfield reproduction over an extended region of open space is a complex and challenging problem in acoustic signal processing. In this paper, we provide a framework to recreate 2-D spatial multizone soundfields using a single array of loudspeakers which encompasses all spatial regions of interest. The reproduction is based on the derivation of an equivalent global soundfield consisting of a number of individual multizone soundfields. This is achieved by using spatial harmonic coefficients translation between coordinate systems. A multizone soundfield reproduction problem is then reduced to the reproduction over the entire region. An important advantage of this approach is the full use of the available dimensionality of the soundfield. This paper provides quantitative performances of a 2-D multizone system and reveals some fundamental limits on 2-D multizone soundfield reproduction. The extensions of the multizone soundfield reproduction design in reverberant rooms are also included.

/pdf/spatial-multizone-soundfield-reproduction-theory-and-design-5axcw0ohc6.pdf

Spatial Multizone Soundfield Reproduction: Theory and Design

Reproduction of a soundfield is a fundamental problem in acoustic signal processing. A common approach is to use an array of loudspeakers to reproduce the desired field where the least-squares method is used to calculate the loudspeaker weights. However, the least-squares method involves matrix inversion which may lead to errors if the matrix is poorly conditioned. In this paper, we use the concept of theoretical continuous loudspeaker on a circle to derive the discrete loudspeaker aperture functions by avoiding matrix inversion. In addition, the aperture function obtained through continuous loudspeaker method reveals the underlying structure of the solution as a function of the desired soundfield, the loudspeaker positions, and the frequency. This concept can also be applied for the 3-D soundfield reproduction using spherical harmonics analysis with a spherical array. Results are verified through computer simulations.

/pdf/theory-and-design-of-soundfield-reproduction-using-2ds6ksd5af.pdf

Theory and Design of Soundfield Reproduction Using Continuous Loudspeaker Concept

Minimization of interior cabin noise has been a key topic of research in the automobile industry for the last two decades. This problem was initially approached via passive noise cancelation methods, where physical treatments such as structural damping and acoustic absorption were used. However, with vehicle manufacturers striving for more economical and lightweight designs, the resulting car interiors invariably became noisier due to the increased structural vibrations. These noise fields are generally dominanted by low frequencies (i.e., 0-500 Hz) [1], [2], hence, the conventional passive noise cancelation approaches are less effective. In an attempt to resolve the aforementioned problem, active noise control (ANC) methods were developed where secondary sources were proposed to attenuate the noise inside the cabin. With modern in-car entertainment systems providing four to six built-in loudspeakers, the addition of an ANC system comes at a relatively low additional cost.

/pdf/recent-advances-in-active-noise-control-inside-automobile-3vwnq0p8gh.pdf

Recent Advances in Active Noise Control Inside Automobile Cabins: Toward quieter cars

In this paper, we consider physical reproduction of sound fields via planar and linear distributions of secondary sources (i.e., loudspeakers). The presented approach employs a formulation of the reproduction equation in spatial frequency domain which is explicitly solved for the secondary source driving signals. Wave field synthesis (WFS), the alternative formulation, can be shown to be equivalent under equal assumptions. Unlike the WFS formulation, the presented approach does not employ a far-field approximation when linear secondary source distributions are considered but provides exact results. We focus on the investigation of the spatial truncation and discretization of the secondary source distribution occurring in real-world implementations and present a rigorous analysis of evanescent and propagating components in the reproduced sound field.

Sound Field Reproduction Using Planar and Linear Arrays of Loudspeakers

This paper reviews the current state of loudspeaker-based spatial sound reproduction methods from technical perspective as well as perceptual perspective. A nomenclature is developed that allows for a strict separation between these two perspectives. The physical fundamentals, practical realization, and results from perceptual studies are discussed for a number of well-established and emerging reproduction techniques. Further, the paper outlines novel approaches to spatial sound evaluation in terms of perceived quality and provides a comparison of current approaches.

Spatial Sound With Loudspeakers and Its Perception: A Review of the Current State

Wave field synthesis is a spatial sound field reproduction technique aiming at authentic reproduction of auditory scenes. Its theoretical foundation has been developed almost 20 years ago and has been improved considerably since then. Most of the original work on wave field synthesis is restricted to the reproduction in a planar listening area using linear loudspeaker arrays. Extensions like arbitrarily shaped distributions of secondary sources and three-dimensional reproduction in a listening volume have not been discussed in a unified framework so far. This paper revisits the theory of wave field synthesis and presents a unified theoretical framework covering arbitrarily shaped loudspeaker arrays for twoand three-dimensional reproduction. The paper additionally gives an overview on the artifacts resulting in practical setups and briefly discusses some extensions to the traditional concepts of WFS.

Rudolph Rabenstein

Papers

The Theory of Wave Field Synthesis Revisited