Unidirectional microphone

Claim 1

A MICROPHONE RESPONSIVE THROUGH A FREQUENCY RANGE COMPRISING AN ELECTROACOUSTICAL TRANSDUCER HAVING A DIAPHRAGM, SAID TRANSDUCER GENERATING AN ELECTRICAL SIGNAL RESPONSIVE TO THE DIFFERENCE IN PRESSURES EXERTED ON OPPOSITE SIDES OF THE DIAPHRAGM, A CASING ENCLOSING SAID TRANSDUCER AND HAVING A PORTION DEFINING AT LEAST ONE ACOUSTICAL TRANSMISSION LINE EXTENDING FROM ONE SIDE OF THE DIAPHRAGM, SAID CASING HAVING MEANS LOCATED AT A PLURALITY OF DISTANCES FROM THE DIAPHRAGM TO ADMIT SOUND INTO THE TRANSMISSION LINE, THUS FORMING A PLURALITY OF SOUND PATHS TO THE DIAPHRAGM OF DIFFERENT LENGTHS, THE LONGEST OF SAID PATHS BEING LESS THAN A HALF WAVELENGTH LONGER THAN THE SHORTEST OF SAID PATHS AT THE LOWEST FREQUENCY OF THE RESPONSE RANGE, SAID CASING INCLUDING MEANS DEFINING AN ACOUSTICAL PATH EXTENDING FROM THE OTHER SIDE OF THE DIAPHRAGM HAVING A CAVITY AND AN OPENING ON SAID OTHER SIDE OF THE DIAPHRAGM SPACED FROM THE DIAPHRAGM BY A DISTANCE LESS THAN ONE-HALF THE LENGTH OF THE LONGEST PATH OF THE TRANSMISSION LINE, SAID PATH HAVING AN ACOUSTICAL IMPEDANCE DISPOSED THEREIN AND A BAND PASS EXTENDING FROM THE LOWEST FREQUENCY OF THE RANGE OF THE MICROPHONE TO THE FREQUENCY AT WHICH THE LONGEST OF THE PATHS OF THE TRANSMISSION LINE IS A HALF WAVELENGTH, THE VOLUME OF SAID CAVITY AND THE MAGNITUDE OF SAID IMPEDANCE COMPRISING MEANS FOR PRODUCING AN ACOUSTICAL PHASE SHIFTAPPROXIMATELY EQUAL TO THE SHIFT IN PHASE OF A SOUND WAVE IN SAID PASS BAND TRAVELING BETWEEN THE DIAPHRAGM AND OPENING WHEREBY THE MICROPHONE ACHIEVES A DIRECTIONAL RESPONSE IN THE PORTION OF THE FREQUENCY RANGE OF THE MICROPHONE COVERED BY THE BAND PASS OF SAID ACOUSTICAL PATH TO SAID OTHER SIDE OF THE DIAPHRAGM.