Compact Spherical Loudspeaker Arrays

Abstract

This chapter introduces auditory objects that can be created by adjustabledirectivity sources in rooms. After showing basic positioning properties in distance and direction, we describe physical first-and higher-order spherical loudspeaker arrays and their control, such as the loudspeaker cubes or the icosahedral loudspeaker (IKO). Not only static auditory objects, but such traversing space by their timevarying beam forming are considered here. Signal dependency and different practical setups are discussed and briefly analyzed. This young Ambisonic technology brings new means of expression to sound reinforcement, electroacoustic or computer music. While surrounding Ambisonic loudspeaker arrays play sound from outside the listening area into the audience, compact spherical loudspeaker arrays play sound into the room from a single position. Directivity adjustable in orientation and shape can be used to steer sound beams in order to excite wall reflections in the given, acoustic environment. The directional shapes and orientations of such beams are all controlled by-guess what-Ambisonic signals. Despite the huge practical difference, both applications do not only share the spherical harmonics that lend their shapes to Ambisonic signals: The control of radiating sound beams employs nearly the same model-or measurement-based radial steering filters as those of compact higher-order Ambisonic microphones. The works of Warusfel [3], Kassakian [4], Avizienis [5], Zotter [6, 7], Pomberger [8], Pollow [9], Mattioli Pasqual [10] established the electroacoustic background technology required to describe compact spherical loudspeaker arrays built with electrodynamic transducers. The early works on auditory objects were written by Schmeder [11], Sharma, Frank, and Zotter [2, 12, 13]. And some contemporary results were found in the project "Orchestrating the Space by Icosahedral Loudspeaker" (OSIL) between 2015 and 2018 [14-19].

Accurate time-domain simulation of spherical microphone arrays

“…The modal transfer function A n (s) is modeled by a discretetime system whose z-transform is denoted by Ân (z). The linear time-invariant system is modeled by a digital filter which can be built either based on cascade (7) or partial fraction expansion formulation (8). Bilinear transform or matched z-transform can be used for the former, and impulse invariance method for the latter.…”

“…The authors proposed a time-domain approach in [6], where the acoustic impulse responses are modeled with digital IIR filters. This method is inspired by earlier studies in array signal processing [7][8][9][10]. The filter coefficients are derived from an analytical representation of the system function.…”

How Spherical Loudspeakers Came Into Auralization

“…The achievable spatial resolution is limited by the number of loudspeakers used, similar to what we find with limited sampling rates and corresponding aliasing effects. Due to the physical size of the single transducers and the requirement for different membrane sizes for a full spectral coverage, the resolution is usually severely limited with these speakers, see also [3,4,5].…”

Measuring the Acoustical Properties of the BBC Maida Vale Recording Studios for Virtual Reality

“…The use of spherical loudspeaker arrays has also been proposed by Farina [37] and Zotter [38] for modeling the directivity of sound sources. Farina demonstrates how complete directional information can be obtained by measuring sweeps with spherical harmonic emission due to manipulation of the individual loudspeaker feeds in a docdecahedron [37].…”