GB1045807A - Loudspeaker - Google Patents

Abstract

1,045,807. Loud-speakers. W. F. EWALD. June 16, 1964, No. 24870/64. Heading H4J. A loud-speaker speech coil 4 (Fig. 1a comprises a flat plate 4<SP>1</SP> of insulating material and a metal foil on the plate etched in the form of a flat spiral 16. Preferably congruent spirals 16 on opposite sides of the plate 4<SP>1</SP> are interconnected at 13 with outer ends at 14, 15, and are wound so that current flows in the same direction in the corresponding limb of each spiral. Tabs 17 are fastened to a diaphragm at the top and to a guide spring at the bottom. A plurality of such speech coils 4 may be secured side-by-side with interposed insulation. Pole plates may be disposed on either side of the plate 4<SP>1</SP> opposite the upper and lower limbs of the speech coil 4 to form two gaps across which magnetic fields are directed in opposite directions by two oppositely directed magnets (Fig. 2a, not shown). The speech coil is connected to the junction of two rectangular diaphragms with stiffening ribs perpendicular to the junction. Alternatively the diaphragm may be conical (not shown) in which case its apex will be provided with a closed keel the length of the speech coil 4. In another arrangement, permanent magnets 5<SP>1</SP>, 61 (Fig. 3a) are provided, together with rear stirrup-shaped polepieces 7<SP>1</SP>, 8<SP>1</SP> and flat front polepieces 9<SP>1</SP>, 10<SP>1</SP>. The speech coil 4 may be centred through a slot 2 and is secured to end guide springs 11, 12 (Fig. 3b, not shown). In a further arrangement, a single permanent magnet 5<SP>2</SP> (Fig. 4a) magnetized perpendicular to the direction of the plane of the speech coil 4 has a stirrup-shaped polepiece 7<SP>2</SP> extending round the magnet 5<SP>2</SP> and a polepiece 9<SP>2</SP> to define with the latter an air gap in which the speech coil 4 lies. The magnet 5<SP>2</SP> also has a stirrupshaped polepiece 8<SP>2</SP> and a channel-shaped polepiece 10<SP>2</SP> defining a second air gap. In a modification (Fig. 4c, not shown) the two lower polepieces 8<SP>3</SP>, 10<SP>3</SP> are each of U-shape and are interdigitated.