Patent GB-371446-A (GB)
Title: Improvements in or relating to electro-magnetic vibratory devices such for example as loudspeakers
IPC: H04R11/00
Filed: 1931-01-23
Abstract: 371,446. Loud-speakers. WIRELESS MUSIC, Ltd., 41, Whitehall, London, and TROUTON, M., Dadbrook House, Cudding- ton, Buckinghamshire. Jan. 23, 1931, No. 2318. [Class 40 (iv).] An electromagnetic vibratory device, such as a loud-speaker, comprises an armature mounted on a support and adapted to vibrate relatively to a polepiece and means for adjusting the relative positions of the support and the polepiece about an axis which is displaced from the working surface of the pole piece, the adjusting means engaging the support and polepiece, or a member rigidly connected therewith, closer to said plane than said axis. As shown, a pair of polepieces 1, 2 surrounded by coils 13 are riveted to a central member 3 upon the lower surface of which is clamped by a strap 4. and bolts 5 a cantilever 6, the bolts 5 also serving to secure the whole to a base 24. The free end of the cantilever 6 carries a pin 7 adapted to be soldered in an extension 8 of a support 9 on which the reed 10 is secured by screws 11. A screw 12 threaded through a projection on the strap 4 and bearing against the member 6 allows for a final factory adjustment of the relationship of the armature to the polepieces. The rod 27 for connecting the reed 10 to a diaphragm is arranged so that when the armature is in contact with the polepieces, this rod is located centrally with respect to the polepieces. The magnet 14 is secured by screws 15, 16 in a slot in the member 3, the arrangement being such that the magnet can be removed and replaced without affecting the adjustment of the armature and polepieces. The means for adjusting the air gap comprises a cam 17 carrying a screw 18, the cylindrical portion of the cam bearing in two places on the member 3 whilst the tip of the screw bears against the reed support 9. To the cam is fixed a pair of arms 19 between which is pivoted a part 21 adapted to receive an adjusting screw passing through the base 24 and provided with a knob 23. If desired, a spring may be provided between the part 21 and base 24. Rotation of the cam 17 in a clockwise direction forces the reed support 9 away from the polepieces thus flexing the lever 6, the movement of the armature in the direction indicated by arrow 25 at right-angles to the direction of vibration being much greater than its movement in the direction of vibration indicated by arrow 26, the effective axis about which the support 9 is moved being in the neighbourhood of point 28. The position of the screw 18 in the cam may be initially adjusted by a screw-driver inserted through a hole 30 in the member 3, and, if desired, the operating means for the cam may consist of a cranked lever 29 projecting through a slot in the base 24. According to a further modification, the cam arrangement may be replaced by an adjusting screw threaded horizontally through hole 30 and bearing with its tip on support 9. If desired, the adjustment axis may be arranged on the opposite side of the air gap to that shown, the reed being made of such length that it just reaches the further edge of the polepieces when adjusted for maximum intensity and the rod 27 projecting downwardly through the gap between the polepieces. The Provisional Specification describes constructions in which the reed is secured to the base, preferably in the manner set forth in Specification 350,947, and adjustment of the air gap is effected by movement of the magnet and polepieces. Such means may also be combined with another form of adjusting means comprising a spring of variable tension connected to the reed or a variable magnetic shunt across the polepieces. Specification 299,537, [Class 40 (iv), Telephones &c.], is referred to.