Patent GB-350947-A (GB)
Title: Improvements in or relating to electro-magnetic vibratory devices
IPC: H04R11/00
Filed: 1930-03-17
Abstract: 350,947. Loud-speakers. WIRELESS MUSIC, Ltd., 41, Whitehall, London, and IONIDES, A. G., Markyate, Dunstable, Bedfordshire. March 17, 1930, No. 8572. [Class 40 (iv).] Relates to electromagnetic vibratory devices, such as loud-speakers, employing an armature adapted to co-operate with a polepiece or polepieces rigidly or adjustably mounted on a fixed member and comprises methods of mounting the supporting member for the armature on the fixed member so as to obtain extreme accuracy in positioning the armature in relation to the polepiece or polepieces. Fig. 1 shows a construction employing a U-shaped magnet 2 secured to a base 3 and provided with polepieces 1. A reed 4 has its free end initially clamped to the polepieces, its outer end being fixed to a pillar 5 projecting into a cup 6 on the base 3. The rod 8 for connecting the reed to the diaphragm passes through a hole in the upper member of the clamp and is correctly positioned with respect to the polepieces by the projection 10 of the clamp engaging the polepieces, the right-hand non- magnetic side cheek 11 being of reduced depth. The non-clamped end of the reed is then depressed a predetermined amount by a weight 12 hung on the reed by means of a bridge-piece 13 and while the reed is thus stressed hot shellac or a fairly readily fusible metal or alloy 7 is poured into or melted in the cup 6. After cooling, the clamp and weight are removed. If desired, packing may be inserted between the reed and polepieces before clamping and a micrometer screw may be used for depressing the other end of the reed instead of the weight 12. According to the modified construction shown in Fig. 3, a member 14 projecting upwardly from the base 3 has its surface 15 machined substantially perpendicular to the upper surface of the polepieces and the pillar 5, after being depressed to the desired extent, is clamped to this surface by the plate 16 and screws 17. Fig. 5 shows the invention applied to a balanced armature type of unit. In this construction, the armature 18 is positioned between the polepieces 1 by a forked jig member and its axis is correctly distanced from the polepieces by rollers 22 against which it is pressed by springs 23. The armature pivots 19 are supported in position by jig 24 and springs 25, and shellac or other fusible material is then poured into the cups 7. According to the modification, Figs. 6 and 7, the armature 18 is carried on a cross-bar 26 provided with lugs 27 and is positioned between the polepieces 1 by a forked jig 20 and a spring 21 bearing against a jig member 28. This member is held in position by a yielding part 29 which presses the bar 26 against a packing piece 34 inserted between the back of the cross-bar and the polepieces. In this construction, the polepieces are also fixed by fusible material, and in order to support them in position they are pressed against jig 20 by springs 30. The assemblage is then supported over the base 3 so that the lugs 27 project into the cups 31 and the lugs 32 on the polepieces project into the cups 33, fusible material being then poured into the cups and allowed to solidify.