GB339205A - Loudspeaker and circuit therefor - Google Patents

Abstract

339,205. Farrand Inductor Corporation, (Assignees of Farrand, C. L.). Feb. 26, 1929, [Convention date]. Loud-speakers.-A loud-speaker having a magnetic system comprising four or more poles, at least two of which have single speech coils, and an armature between the poles such that equal currents through the coils produce no movement of the armature, while unequal currents cause the armature to move, is associated with a circuit for each of the speech coils including a direct current source, whereby the direct current flowing through both coils produces like flux changes with no resulting movement of the armature, and. means for producing fluctuating currents cf unequal value in the coils with consequent movement of the armature. The figure shows a pushpull output stage, in which the primary of the usual output transformer is replaced by two coils 39, 40 forming the speech coils of a loud speaker unit, the junction of the coils being connected to the anode battery 24. The permanent magnet 8 of the loud-speaker has pole pieces 31, 32, each with two or more poles 33, 36. Each pole 33 - - 36 may carry a coil, but as shown coils are placed only on the poles 33 and 36. With this arrangement the steady current through coils 39, 40 from the battery 24 produces equal and opposite effects on the armature 37, while speech or other fluctuating currents amplified by the valves produce additive effects, swinging the armature sideways in the gap.