Patent GB-324698-A (GB)
Title: Improvements in and relating to telephonic microphones and gramophonic microphone appliances, electrical "pickups" and the like
IPC: H04R21/04
Filed: 1928-10-30
Abstract: 324,698. Cauthery, S., Smith, S. C. Winfield-, and Burovox, Ltd. Oct. 30, 1928. Microphones; gramophone pick-ups; diaphragms. - A carbon microphone appliance comprising a vibratory diaphragm and a resilient granule containing chamber, has the walls of the chamber and the granules themselves directly abutting against the diaphragm whilst the chamber is attached to an insulating disc mounted on a support by a conducting stud having a granule contacting surface provided thereon. Fig. 1 shows a telephone transmitter comprising a casing 5 which houses three granule chambers and has a carbon diaphragm 4 secured thereto by a perforated protective disc 2, the whole being mounted within a casing 1 and perforated cap 3. The casing 5 is provided with a central opening 6 in which is mounted an insulator 7 and a nut 8 having a cylindrical projecting portion 9 adapted to engage a screw 10 which secures a metal plate 11 to the bottom of casing 5. The granule chambers comprise cotton wool, glass wool &c. annuli 12 mounted on mica or other insulating discs 13 which are secured to plate 11 by means of spacers 14 and the screwed shanks 15 of electrodes 16. Carbon discs 17 mounted in these electrodes form contacting surfaces with the granules 18. Contact from discs 17 is made by means of electrodes 16, shanks 15, plate 11, screw 10 and spring 19 to a terminal 21 mounted on casing 1 but insulated therefrom. Contact with granules 18 is also made by diaphragm 4, casings 1, 5 and terminal 22. The elements 12 are preferably manufactured by cutting or shearing annuli from a layered sheet or web of wool &c. Fig. 3 shows a similar construction of microphone, but having only one granule chamber, employed in a gramophone pick-up. The mica disc 13 is in this case mounted directly on the casing 5, the electrode 16 being secured to casing 5 by a stud 15<a> and nut 27. The carbon diaphragm 30 is spaced a short distance from the stylus-operated diaphragm 31 by a ring 32, the parts being clamped to casings 1 and 5 by a ring 33. A rubber &c. damping gasket 34 may be provided as shown. The diaphragm 30 instead of being of carbon may be of metal, with or without a non-metallic coating, or of a material, such as compressed or prepared paper, rendered conducting either by applied metal foil or impregnation or coating with a suitable material, such as metallic powder or graphite. The casing 1 is supported by a rubber &c. tube 26 on the arm 25. The electrode 16 may be made adjustable, as shown in Fig. 4, bv securing the disc 13 to casing 5 by an internally threaded bush 44 secured by nut 45, the electrode 16 being provided with a screwed stud 46 which engages in the bush 44. The stud 46 may be rotated by the engagement of a screwdriver with slot 47 or alternatively a locking nut 48 may serve to secure the electrode in a predetermined position. The Provisional Specification states that metal, e.g. steel, granules may be employed and also describes a somewhat modified form of gramophone pick-up, which may, if desired, employ only one diaphragm.