Two inventors have staked competing claims to a potential audio revolution in which focused beams of sound could direct music or speech to a single person in a crowd.

Known as directional sound, it uses an ultrasound emitter to shoot a laserlike beam of audible sound so focused that only people inside a narrow path can hear it.

Both inventors say the ultimate goal is to replace a large number of the millions of loudspeakers sold each year for home entertainment and personal-computer systems with directional-sound devices.

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