Smart Digital Loudspeaker Arrays

0INTRODUCTIONThis paper considers from a theoretical stance the fun-damental requirements of a programmable polar response,digital loudspeaker array, or smart digital loudspeakerarray (SDLA), which consists of either one-dimensionalor a two-dimensional array of micro radiating elements.The principal problem addressed here is the design of a setof digital filters which together with a uniform array ofsmall drive units, achieve a well-defined directional beamthat can both be steered over a 180° arc and be specifiedin terms of beamwidth such that it remains constant withthe steering angle. Intrinsic and critical to the SDLA is therequirement that the beam parameters remain stable overa broad frequency range. In addition to addressing theproblem of coherent radiation, the theory is extended toinclude the synthesis of directionally controllable diffuseradiation that is similar although not identical to the classof sound field produced by a distributed-mode loud-speaker (DML) [1], [2]. DML behavior can be emulatedusing an array of discrete radiating elements with excita-tion signals calculated to model panel surface wave prop-agation and boundary reflections using techniques such asfinite element vibration analysis [3]. However, for theSDLA a different approach is taken where each elementdrive signal is derived by convolution of the input signalwith an element-specific but stochastically independenttemporally diffuse impulse response (TDI) [4]. Each TDIis calculated to have a constant-magnitude response but aunique random-phase response, where for loudspeakerapplications it is formed asymmetrically to have a rapidinitial response and a decaying “tail” exhibiting a noise-like character.The conceptual structure of an SDLA is shown in Fig.1, where each mircodriver within the array is addresseddirectly by a digital signal that has been filtered adaptivelyto allow the polar response to be specified and controlleddynamically. It is proposed to configure the transducerarray with a large number of nominally identical acousticradiating elements, where the overall array size andinterelement spacing (referred to here as interspacing)