GB1236007A - Microphone - Google Patents

Abstract

1,236,007. Microphones. RCA CORPORATION. 12 Dec., 1969 [23 Dec., 1968], No. 60676/69. Heading H4J. In a moving conductor microphone such as a ribbon microphone a labyrinth for providing an acoustic termination is made from an outer shell member 11 and an inner member 12. Each member 11, 12 has an open end and a closed end. The open end of each member is spaced from and faces the closed end of the other member. The ribbon 4 is of aluminium and is held by a brass clamp 38 secured to opposite polepieces 3 respectively cemented to opposed magnets 5. A magnetically conductive bottom plate 7 is provided. Sound waves enter the microphone through a screen 2 and impinge on ribbon 4. Sound waves also enter through a side screen 15 and pass through an aperture 9 for providing unidirectional characteristics. The sound waves pass through a labyrinth connector 8 of rubber and through a hole 17 in plate 7 to reach the labyrinth. The labyrinth has its entrance in the lower wall of plate 7. In the labyrinth the sound waves are guided through passages 18, 19, 20 to the opening in inner member 12. This member 12 is located by screws 14. It houses a transformer 13. The members 11, 12 are of electrically conductive material to shield the transformer 13. Open cell polyurethane foam material fills the labyrinth passages and locates the transformer 13. It also fills the labyrinth connector 8. There may be a series of more than two labyrinth members and alternate members may have their closed ends formed by one common closed end. The members 11, 12 need not be cylindrical. The "ends" may be in the long dimension of elongate bodies or in the curved parts of cylinders or spheres.