GB1371338A - Loudspeakers - Google Patents

Abstract

1371338 Moving coil loudspeakers EMI Ltd 9 Dec 1971 [9 Dec 1970] 58373/70 Heading H4J A moving coil loudspeaker includes a magnet 1, a central pole piece 3 and an apertured plate member 4, the inner periphery of which is bent to form a lip 5. Between the inside circumference of the lip 5 and the pole piece 3 is a cylindrical air gap for the voice coil 8. The coil 8 is carried by a diaphragm 9 mounted on a centrally apertured support 10 which fits the outside of the lip. The ceramic magnet 1 and pole piece 3 are mounted on a back plate 2. The front plate 4 having the lip 5 is formed by pressing or turning. It is aligned in a jig with the pole piece 3 to provide an accurate gap 12 and the plate 4 is then secured to the magnet 1, e.g. by adhesive. The diaphragm 9 has a fixing portion 13 at its periphery and this secures the diaphragm 9 and coil 8 to the support washer 10. To effect this the coil 8 and diaphragm 9 are centralized relative to washer 10 using a jig and are then secured to washer 10 by the fixing portion 13. The washer 10 is a push fit over the lip 5. Washer 10 and plate 4 are spaced from one another by a spacer washer 11. Four screws 15, 16, etc. pass through a moulded front cover 14, washers 10, 11 and into tapped spigots 17, 18, etc., attached to plate 4. If desired, the pole piece 3 may have a constant diameter throughout its length. The spigots 17, 18, etc. may be integrally formed with front plate 4, or formed separately and attached thereto. Alternatively the spigots may be dispensed with and cooperate with tapped holes in plate 4. The spigots, if provided, may be used to achieve the required spacing of washer 10 from plate 4 by the provision of steps or ridges, the washer 11 then being omitted.