Reflektionsretningsmikrofoner

Second-order gradient directional microphones, both toroidal and unidirectional, derived using a first-order gradient sensor and an acoustically reflecting surface are disclosed. The sensor is positioned with its axis illustratively orthogonal to and suspended a few centimeters from a large acoustically reflecting surface. The resulting sensor image is phase reversed resulting in a transducer that is a linear quadrupole. The linear quadrupole can be described by two dimensions; the distance corresponding to the sensor's dipole distance and twice the distance from the reflecting plane. If the reflecting surface is large enough or if the wall of an enclosure is used, the resulting microphone becomes a second-order gradient unidirectional microphone. A perfect match between the sensor and its image from a good acoustic reflector results in an ideal second-order gradient microphone with 3 dB beam width of +/-33 DEG and no grating lobes below about 3 kHz for a spacing from the reflecting plane of about 2.5 cm. Toroidal directional microphones are formed using two or more sensors and an acoustically reflecting surface.