GB396990A - Improvements in loud speakers and other apparatus for interconverting electrical andacoustic vibrations - Google Patents

Abstract

396,990. Loud-speakers; gramophone pick-ups. LEWIS, J. H. W., 31A, Farm Lane, Fulham, London. Dec. 6, 1932, No. 34595. [Class 40 (iv).] ' Relates to a loud-speaker driving unit or gramophone pick-up comprising a permanent magnet and a reed adapted to vibrate in an air space between polepieces arranged on opposite sides thereof. According to the invention the magnet is L-shaped or substantially. L-shaped and the reed is secured at one end to the upturned end thereof. Fig. 1 shows one construction in which the reed 2 is secured by a screw 4 to the upturned end 3 of an L-shaped magnet 1, a T-shaped laminated polepiece 5 surrounded by a coil 6 being secured against the other end of the magnet. The leads 7 from the coil may be secured to terminals 8 as shown and the reed may be adjusted relatively to the polepiece by a screw 11 acting on a spring 10. A magnetic stirrup (not shown) having its ends secured to the side faces of the magnet is arranged to span the polepiece 5 and the free end of the reed or alternatively a magnetic hood or shroud 21 may be provided, as shown in Fig. 14. This hood, which may have side-pieces extending around the extremity of the reed, Fig. 12 (not shown), may either be screwed to the magnet or may be clamped or wedged against the magnet, as shown in Fig. 14, by forcing the parts into a box-like baseplate 22 having a pair of spaced abutments 23. If desired, the polepiece may be mounted/on the upper surface of the magnet, as shown in Fig. 14, whilst in a further modification, Fig. 15 (not shown), the polepiece is E-shaped with the coil 6 arranged around the centre limb. Fig. 5 shows a modified means for securing the reed to the magnet, the end of the reed being bent round the end 3 of the magnet, passed through a slot therein and secured against its inner surface by a screw 16. According to further modifications, the end 3 of the magnet may be formed with a horizontal portion so as to form a substantially Z- or J-shaped magnet, Figs. 3 and 4 (not shown), and various means are described for clamping or wedging the end of the reed against the upper or lower surface of this upper horizontal portion, Figs. 6, 7 and 8 (not shown). In order to reproduce the low notes efficiently the reed is made as long as possible and its mass and weight are reduced by providing it with a triangular aperture 20, as shown in Fig. 9. According to a further modification, Fig. 16, the reed 2 has its free end bent as shown at 26 and 27 so as to enter the upper end of the coil 6 and a polepiece 28 shaped as shown is secured together with the reed by a screw 29 to the upturned end 3 of the magnet.