GB678766A - Improvements in or relating to microphones - Google Patents

Abstract

678,766. Microphones; diaphragms. FORTIPHONE, Ltd. April 26, 1951 [May 24, 1950], No. 13076/50. Class 40 (iv). A variable resistance microphone primarily intended for hearing aids comprises an element coated with stress sensitive resistance material which has sound-varied stress imparted to it by a diaphragm. As shown in Fig. 1, the element consists of a mica disc 1 which is provided at the centre region with a stresssensitive carbon or metallic coating 2 and is held between threaded casing parts 5, 6. The disc is coupled by a rod 8 to a rim-clamped diaphragm 7 and is backed by a stiffening ring 10 which concentrates the imparted stress at the centre. Flexible leads 3 provide electrical connection to the coating. In an alternative arrangement, the disc 1 may constitute the diaphragm. In an alternative arrangement, Fig. 4, the element comprises a mica strip 21 having a carbon track coating 22. Metal stiffening strips 210 are arranged on either side of a centre point D to which the diaphragm is attached. In a modification, Fig. 5 (not shown), a single stiffening strip is provided, the strip being weakened at the diaphragm attachment point by a transverse saw cut. A further arrangement, Fig. 6, utilizes a carbon impregnated string or cord 61 of glass fibre, natural or artificial silk or asbestos. In this embodiment the cord is tensioned by a bowed spring 62 and is attached to a diaphragm 67 through a connector 68. Adjustable spring tension is effected by a screw 65 co-operating with a fixed nut and collar 66, 69.