GB1295790A - - Google Patents

Abstract

1295790 Moving coil transducers INTERNATIONAL STANDARD ELECTRIC CORP 24 June 1971 [29 June 1970] 29576/71 Heading H4J A moving coil telephone receiver comprises a cup-shaped plastics housing containing at least three projections which define a centering space for a permanent magnet system, and a plastics thrust collar fits between the housing and the magnet so as to hold the latter against the bottom of the casing. The housing 1 which may be an injection moulding of polystyrene modified with butadiene and aryl nitrile, has three inward, box-like projections 18, of which only one can be seen, that define a central space for receiving a permanent magnet consisting of an axially magnetized cylindrical metal block 5 and a soft iron cup 3 having a rebated rim for receiving polepieces 4. The magnet may alternatively be a plate or ring-shaped oxide-ceramic magnet. To further assist positive location of the magnet, a centering ring 23 having resilient legs 19 may be moulded with the housing. The magnet is retained in position by a collar 2, made of the same material as the housing, which is seated on steps formed round the rim of the magnet and the housing and is attached to the latter by ultrasonic welding. A generally conical-shaped diaphragm 7, formed in a circular shape of a sheet of stretched polystyrene and having glued thereto a self-supporting coil 8 consisting of a cylindrical copper wire coil whose turns are insulated and bonded together by thermovarnish, is rim clamped by a ring 10 and a cover 9. The latter is held off the casing 1 by means of a plurality of noses 20 projecting outwardly therefrom so that differences in their coefficients of expansion are accommodated at least in the range - 40‹ to + 70‹ C. The cover is attached to the casing by bending over lugs into recesses 21 formed therein. Terminals 11 are sealed into one of the inner projections 18. The thrust collar 2 defines with the magnet and casing a resonant chamber to which access is had from the rear of the diaphragm via openings 15 which are covered by damping plates 12 for the purpose of linearizing the frequency response of the transducer.