GB455682A - Improvements relating to sound reproducing devices - Google Patents

Abstract

455,682. Sound-transmitting devices; loud-speakers. CHRISTENSON, O., 108, E. Madison Street, Baltimore, U.S.A. Dec. 13, 1935, No. 34644. [Class 40 (iv)] A sound-reproducing device comprises a diaphragm rigidly connected to a magneto-strictive member in the form of a plate maintained under a compressive or tensile stress and subjected to changes caused by magneto - striction. The magneto-strictive plate is constituted by a sheet 30 of zinc soldered to a sheet 31 of nickel or of a cobalt-iron alloy which are pressed together when at a temperature sufficient to melt the solder and allowed to cool so that the plate 31 is subjected to permanent compressive stress. Alternatively, a sheet of an iron-nickel alloy may be secured to a sheet of the alloy known under the Registered Trade Mark " Invar " at a high temperature so that the cooled plate is under a permanent tensile stress. The magneto-strictive plate passes through formers on which the speech coils 45, 46 are wound and is held between blocks 17<a> of soft steel, the lower blocks being carried on the polepieces 17 of a permanent magnet 15 located in a groove 11<a> in the base of the casing 11 which houses the unit. A rubber strip 35 is interposed between the plate 30 and the upper blocks 17<a> and the assembly is clamped to the casing by screws 16. A diaphragm 62 supported by a flexible ring 63 is secured to the magneto-strictive plate 30, 31 by a bolt 14. In a modification, Fig. 7, applied to a loudspeaker, the bolt 14 passes through a hole in the cover 12 of the casing and is secured by plates 67, 68 to a cone diaphragm 65 having a flat apex portion. The lower supporting block 17b has a tapered lip 75 and the plate 30<a>, 31 is formed with an inclined end 76 to facilitate the clamping of the plate and to increase its flexural characteristic. Opposite faces of the plate are cushioned by rubber washers. The magneto-strictive plate may be formed by a single sheet of metal or alloy mounted in the casing so that it is subjected to tensile or compressive stress. The sheet 30 may be of lead, tin, aluminium, or of an alloy known as herculoy comprising zinc, copper, silicon and tin, in lieu of zinc. Each coil former comprises insulating plates 22, 23 joined by an apertured core 24 and having reduced ends 25, 25<a> connected by insulating blocks 26 provided with holes for screws 28 securing the former to the base member 10.