Image derived directional microphones
US4965775A · kind A · utility
Assignee
Inventors
Key dates
| Filing date | May 19, 1989 |
| Grant date | Oct 23, 1990 |
| Priority date | — |
| Expiry date | May 19, 2009 |
Classification
- Technology area (CPC H)Electricity
- CPC primaryH04R2499/13
- WIPO fieldAudio-visual technology
- WIPO sectorElectrical engineering
Abstract
Second-order gradient (SOG) toroidal and unidirectional microphones derived using a first-order gradient sensor (FOG) and a reflecting plane are described. The FOG 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 FOG'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 SOG unidirectional microphone. The perfect match between the sensor and its image from a good acoustic reflector results in an ideal SOG microphone with 3 dB beam width of .+-.33.degree. and no grating lobes below about 3 kHz for a spacing from the reflecting plane of about 2.5 cm. A wall-mounted toroid can be formed by using two FOGs at right angles to each other and with the axis of each sensor at 45.degree. to the reflecting surface and a spacing between transducers that is twice the height of the transducers fr…
Source: USPTO / EPO open patent data. Objective bibliographic and citation counts.