GB399016A - Improvements in and relating to signal receiving systems - Google Patents

Abstract

.399,016. Loud-speakers; circuits for magnetic instruments. BRITISH THOMSON-HOUSTON CO., Ltd., Crown House, Aldwych, London.-(Assignees of Whelan, D. O.; 504, Avondale Avenue, Haddonfield, New Jersey, U.S.A.) Sept. 15, 1932, No. 25723. Convention date, Sept. 15, 1931. [Class 40 (iv).] The output of a loud-speaker is controlled by varying the flux density of an auxiliary gap forming a magnetic shunt to the main gap. Fig. 1 shows a moving-iron loud-speaker unit comprising magnet energizing coils 12, 13, and speech coils 17, in which the main air-gap in which the armature 14 works is shunted by an auxiliary gap 21 associated with a winding 22. The winding 22 constitutes the output choke of the final amplifier 24, Fig. 2, of a receiver, so that the current through the winding will increase with increasing signal input and vice versa. The flux across the auxiliary gap 21 will thereby increase, shunting the main gap and reducing the loud-speaker output, so that the arrangement constitutes an automatic volume control. In Figs. 3 and 4 the same principle is applied to a moving-coil loudspeaker, the auxiliary coil 38, associated with an auxiliary air-gap 37, being in this case connected in series with the primary of the output transformer 41. Manual control is additionally provided at 43, and the winding 38 may be made to assist the main coil 34 by a reversing switch 42 to give added sensitivity. The invention is also applicable to loudspeakers having permanent field magnets. Specification 240,528, [Class 40 (iv), Telephones &c.], is referred to. The Specification as open to inspection under Sect. 91 states that instead of using an auxiliary field coil for control purposes the current through the whole field winding may be controlled e.g. by shunting or reversing part of the winding. This subject-matter does not appear in the Specification as accepted.