Tangent line method (TLM) is a loudspeaker array technique for producing curvilinear acoustic beams. As the name implies, a curvilinear beam is produced as an envelope of its tangent lines. The beam length can be specified by the envelope. This is contrast to conventional straight beams produced by delay-and-sum beamformers, in which a plane wave is imitated, and the beam length cannot be specified. Curvilinear beams are more convenient to deliver sounds to specific regions and keep silence elsewhere. In this study, a TLM-based loudspeaker array is used to perform multi-spot sound reproduction. Two regions are specified as listening areas. Different sounds, i.e., two circular beams, are delivered to the individual areas, while reducing sound leakages to surrounding areas. Simulation results and experimental results measured in an anechoic room are presented.
Terada et al. (Wed,) studied this question.