Speaker
Description
Array design typically aims to direct the beam towards or away from a given direction. However, certain applications — such as surround channels in sound reproduction or acoustical measurements — require a wide polar pattern. This paper describes a method for achieving such a pattern using arrays in which individual transducers are fed with randomly phased signals.Traditional array design relies on precisely optimised phase and amplitude for each transducer. Established approaches to wide polar patterns include frequency-dependent shading applied to edge transducers, adjustment of element spacing, and delay-based processing. The extreme case of delay-based processing is wave field synthesis, in which the sound field of a virtual source is emulated. Bessel arrays offer an alternative approach, defining transducer weights via Bessel functions; in notable special cases, these weights are unity magnitude with alternating sign. The properties of these existing methods are reviewed.The method proposed applies a unity-magnitude, random-phase filter individually to each transducer. The resulting polar pattern varies with frequency; however, its frequency average approaches that of a single transducer, regardless of the number or spacing of transducers. The smoothness of the average polar pattern within a given bandwidth is influenced by array properties and filter length. The random-phase array can further be interpreted as an ideal distributed mode loudspeaker (DML). Numerical examples illustrating array behaviour are presented and discussed.