Audio spotlight system based on formation of multiple focused sound sources via loudspeakers

We propose a new audio spotlight system which uses focused sound sources arranged in an arc shape, and we evaluate its suppression performance and frequency responses. Audio spotlight systems use ultrasonic waves to produce sharp directional sounds without any external disturbances. However, such systems contain two problems: (1) low efficiency of the electro-acoustic conversion and (2) distortion of the reproduced sound. Therefore, we attempted to form an audio spotlight system by using focused sound sources based on wave field synthesis. A single focused sound source is designed to harmonize the phase of the driving signal at an arbitrary position. Thus, the driving signals that correspond to the number of the optional focused sources can be superimposed and reproduced from a loudspeaker array in order to form multiple focused sound sources. By arranging the focused sources in arc shape, we produced the audio spotlight. A numerical simulation revealed that the sound volume difference between the center of an arc and at 1 m away from the center was approximately 10 dB. Moreover, because a flat frequency response was maintained at the center of the arc, the proposal is expected to be able to control optional sounds with minimal distortion.