Highly directional response patterns can be obtained by connecting microphones or loudspeakers with tubular coupling path structures. The coupling paths comprise a plurality of elements (110,111 . . . 157) arranged in pairs (110,111; 112,113; . . . 156,157) so that for every element (110) below a center...http://www.google.de/patents/US4421957?utm_source=gb-gplus-sharePatent US4421957 - End-fire microphone and loudspeaker structures
