Patent GB-302161-A (GB)
Title: Improvements in or connected with sound reproducing devices
IPC: H04R1/42
Filed: 1928-12-08
Abstract: 302,161. British Talking Pictures, Ltd., (Assignees of Forest, L. de). Dec. 10, 1927, [Convention date]. Loud-speakers; magnetic instruments; diaphragms. - A sound reproducing device, more particularly a loud-speaker, comprises readily flexible means operated by or in synchronism with sound controlled electric currents so as to control the issue of compressed gas. Fig. 1 shows a construction in which a coil 17, wound on a spool 17' secured to an annular corrugated diaphragm 12, moves in the air gap of an electromagnet comprising a casing 1, central core 2, coil 3, and annular pole 9. A ring 10 secured to the pole 9 carries a horn member 11. The core 2 is bored centrally at 8 and is connected at its lower end to a hollow tube 7 to which a compressed air source is connected. At its upper end, the core 2 has a reduced threaded portion 14 on which in mounted a turret 15 having a plurality of fine horizontal or angularly disposed slits 16. A sleeve 13, formed by the cut-away central portion of the diaphragm, engages the outer cylindrical surface of the turret 15 so as to control the amount of compressed air passing through the slits 16 in accordance with the varying telephonic currents in the coil 17. The sleeve 13 may have horizontal slits therein and its upper edge may be serrated. The diaphram 12 is preferably provided near its periphery with a number of small holes. In the modification, Fig. 3, the sleeve 13 is dispensed with, the diaphragm 12 lying in a plane with the slits 16 in the turret 15 which is screwed into a recess in the enlarged end 2<1> of the core 2. The coil spool 17<1> is formed with a series of hole's and a cock 21 is provided for drawing off air below the diaphragm. Fig. 4 shows a construction in which the upper end of the core 2 is formed with a concave depression 22, the turret 15 being provided with a corresponding convex portion to which is attached a piece of cushioning material 25. The diaphragm is formed with a circular concave portion, the surface thereof adjacent the cushioning material on the turret being provided, if desired, with similar cushioning material. The turret is formed with a threaded integral stud 23 mounted in a perforated support 24 secured to the horn member 11. The diaphragm is provided with a hole adjacent the bore 8 and a short tube may project from the bore and extend through the hole in the diaphragm. Fig. 5 shows a further modification in which a brass casing 30 with integral horn 33 is provided with an annular recess 31 whch opens to the interior of the casing as shown. A closure member 34 threaded into the bottom of the casing carries a two-piece magnetic member 35, 35 and conical cap 36, the direct current winding 3 and telephonic current winding 17 being accommodated in the magnetic member as shown. A magnetic diaphragm 12 is mounted between the magnetic pieces 35 so that its free ' peripheral edge is in alignment with the opening in the recess 31. Passages 38 in the wall of the casing 30 connect the recess 31 by means of pipes 39 to the tube 40 which is connected to the fluid pressure source. A cock 50 is attached to the casing as shown. Fig. 9 shows a modified arrangement for mounting the moving coil and sleeve valve in which the valve is in the form of a cylinder 58 having the coil 17 mounted on its lower half and provided with a flange 59 adapted to be attached to a rubber, leather &c. diaphragm 60. The periphery of the diaphragm is clamped between rings 61, 62, the ring 61 being formed with an upwardly projecting lip for stretching the diaphragm. Slots are formed in the upper half of the cylinder 58 and in the flange 59. Fig. 6 shows a moving coil construction employing a different type of valve. A short piece of pipe 51, Fig. 11, closed at its upper end and provided with longitudinal slots 53, is mounted in the upper end of the passage 8. Stacked discs 54 surround the pipe 51 and rest on the diaphargm 12. A soft rubber disc 56 mounted on the top of the sack and a thumb nut 55 engages the threaded end 52 of the pipe so as to vary the pressure on the discs. Movements of the diaphragm 12 in accordance with currents in the coil 17 vary the amount of air issuing between the discs into the cap member 11. In the construction shown in'- Fig. 15 both the coils 3 and 17 are stationary. The core 2 in the magnetic casing 1 is slightly reduced in diameter at its upper end and externally threaded to receive the conical turret 71 provided with openings 71<1>. Beween the turret and core is clamped a non-magnetic cup 72, the free edges of which closely engage the under surface of the magnetic ring 9 and magnetic flakes 74 are confined in the space between the ring 9 and turret 71 by perforated rings 70. In operation, when the coil 3 is magnetized, the flakes 74 are more or less compacted together and the compactness of the flakes is varied in accordance with currents in the coil 17 so as to vary the amount of air passing therethrough. Fig. 18 shows a construction in which no constant magnetic field is provided, the speech coil 17 surrounding the gas tube 80 which opens into a casing 82 formed integrally with a horn member 83. The casing 82 is filled with magnetic flakes and provided with a non-magnetic partition 84, perforated ring 86, and perforated partitions 85 and discs 85<1>. In the modification, Fig. 19, the speech-winding 17 is mounted between the poles of a permanent magnet 87, an insulating tube 88 which passes through the coil being formed at one end as a horn member whilst its other end is provided with the compressed gas inlet 7. A number of perforated discs 90, 91 break up the space in the tube 88 which is filled with magnetic flakes. In the further modification, Fig. 20, a non-magnetic casing 92 formed with the horn member 97 supports a conical member 95 above the gas inlet 7 which is surrounded by the speech coil 17. The space 93 between the member 95 and coil 17 is filled with magnetic flakes which are prevented from being blown out by a perforated ring 94. Fig. 21 shows a construction in which the compressed gas is supplied through a tube 100 mounted in the horn member 11 and connected at its inner end to a fabric chamber 102 which supports the speech coil 17. The coil 17 is located in an annular magnetic field formed by the casing 1, core 2, coil 3 and disc 9. The upper and lower portions of the chamber 102 are cemented so as to limit the escape of gas to the equatorial zone. In operation, movements of the coil 17 cause an up and down movement of the chamber 102 so as to vary the amount of gas escaping therefrom in accordance with the strength of the currents in coil 17. Fig. 22 shows a further modification in which both coils 3 and 17 are stationary and surround the core 2 of the casing 1. The core 2 is provided with the passage 8 communicating at its lower end with the gas inlet 7 and opening at its upper end into a brass chamber 107 perforated radially at 109. The chamber 107 is surrounded bv a magnetic fabric casing 108, movement of which in accordance with the currents in the coil 17 controls the amount of gas issuing into the horn member 11.