Ultradirectional microphone

Claim 1

A unidirectional microphone comprising: a second order bigradient uniaxial microphone including two first order uniaxial microphone units coupled in series opposition, said microphone units having substantially the same directivity and sensitivity along a first axis and being spaced apart facing substantially the same direction along said first axis, said second order microphone having a response symmetrical about said first axis, said second order microphone including means coupled to said units for causing said second order microphone to have second order directional characteristics in a lower portion of the audio frequency range whicH overlaps an upper portion of the audio frequency range, an elongated acoustic pipe structure for imparting highly directional characteristics to waves in said upper portion of the audio frequency range along a second axis which substantially coincides with the longitudinal axis of said acoustic pipe structure and having a response symmetrical about said second axis, and means for coaxially coupling said acoustic pipe structure to said bigradient microphone such that the directivity of said pipe structure faces substantially the same direction as the directivity of said bigradient microphone and said first and second axes coincide such that the responses of said acoustic pipe structure and said bigradient microphone are symmetrical about a single axis whereby said second order microphone and said acoustic pipe have substantially the same acoustic axis, said microphone units each including a microphone element which is spaced from the other element a distance that is less than the acoustic length of said pipe structure, said acoustic pipe being coupled to the microphone unit which is forward the other unit in a direction towards said same direction and said second order means includes means for acoustically cancelling the rear microphone unit in said upper portion of said frequency range.