A sound telescope: a control of zone of interest

For hands-free audio communication, a beamforming has been widely used to focus a broadband signal. Algorithms of conventional beamformers are based on focusing received signals from sensor array toward the location of a target single source. However, conventional beamformers cannot be directly applied when we desire to focus on multiple sound sources inside a zone of interest. The design issue of our interest is how to control the beamformer’s beamwidth, from which we can change zones of interest (bright zone and quiet zone) and listen to any possible sound source located inside the bright zone with small amount of distortions. For the case of multiple sources, integration of array gains within desired directions of interests can be applied, and it is a direct approach of using a conventional beamformers. The results are the moving average of a beam power in controlled regions. To extend the ideas of conventional beamforming, a concept of regional focusing is suggested. The algorithm is based on the inverse approach of acoustic contrast control which has been used for designing a desired sound field by using loud speakers. The performance of two, direct approach and inverse approach, are compared. To simulate proposed algorithms in a practical situation, an array of microphones placed in circular positions is used, and the performance of proposed algorithms is tested. In the case of direct approach, the solution basically has the same problems of the conventional beamforming technique. In the case of inverse approach, remarkable reduction of any sound came from quiet zone is expected.