GB1294960A - - Google Patents

Abstract

1294960 Audio transducers STANDARD TELEPHONES & CABLES Ltd 26 Feb 1970 9273/70 Heading H4J [Also in Division H2] In an electro-acoustic transducer in which a rocking armature electromagnetic unit is connected to a diaphragm, the connection is offset such that the distances from the connection to the periphery of the diaphragm in directions parallel to the length of the armature are unequal and least in the direction away from the armature and the electromagnetic unit includes a single coil located on the polepiece nearest the diaphragm connection. The arrangement allows a relatively large electromagnetic unit to be mounted within the limits of the diaphragm. A deaf aid set with a pocket microphone having a rectangular diaphragm and an earpiece having a circular diaphragm are described. Both transducers operate in generally similar fashion. The microphone unit (Fig. 5) comprises a permanent magnet 110 secured to a yoke 100 which carries a single coil 130 on one of four bent-up arms 101 of the yoke. A rocking armature 141 (see also Fig. 1A) has two tortion arms by which it is supported by welding ends 144 to the tops of two arms of the yoke. The armature has projections 143 which act as roller bearings on the top of the magnet. A rectangular diaphragm (made from polycarbonate material) having a trapezium shaped portion dished out to form a shallow cone is welded or stuck to a rectangular frame (made from glass-filled polycarbonate material) having a groove 183 which extends along one side of the frame and is vented at one end by a bore 184 into the electromagnet chamber and is vented at the other end through a hole in the diaphragm to provide a Thuras tube. A connecting rod 150 in the form of a flat strip 150 welded to the end of the armature extends through the apex of the diaphragm cone and is secured thereto by adhesive 172.