Patent GB-353439-A (GB)
IPC: G03B21/56
Filed: 1930-04-22
Abstract: 353,439. Projection screens ; kinematograph apparatus. BANNING, E., 140, South Dearborn Street, Chicago, U.S.A. April 22, 1930, No. 12490. Convention date, April 22, 1929. [Class 97 (i).] An electrostatic loud-speaker has one of its electrodes adapted to constitute a picture projection screen. The rear electrode may comprise a number of diaphragm elements responsive to different frequency ranges and means may be provided for controlling the relative sound volumes emitted by these diaphragm elements. Such controlling means may be manually operated or automatically controlled by prearranged enlarged slots in the side of the kinematograph film. Figs. 1 and 1a show a construction of combined kinematograph screen and electrostatic loud-speaker comprising a front electrode 7 consisting of overlapped strips of aluminium foil secured on a dielectric 2 of empire cloth by japan varnish gold size, the electrode 7 serving also as the light reflecting surface. Electrode 7 is also preferably coated with lacquer, such as a cellulose base lacquer coloured white with a tinge of orange or blue or aluminium bronze pigment. The dielectric 2 is stretched on a frame 1 by providing it with a canvas web rim 8 attached by eyelets 8a and loops 9 to hooks 10 on the frame. The frame 1 has extended side portions strengthened by truss members 1b and covered by black fabric 1c, the frame being adapted to be hoisted by ropes 12 co-operating with eye rings 13. Electrode 7 and dielectric 2 co-operate with differently sized rear electrodes 3, 4, 5, 5a, 6, 6a in the form of diaphragms of Dutch woven fine textured metal cloth secured on sub-frames, such as 4b, 6b, Fig. 1a, mounted on supports 11d. These supports are mounted by gaskets 11b and screws 11c on sub-frame supports 11 secured across the main frame 1, the gaps 26a, 26b being initially adjusted by means of screws 11c. Each back electrode sub-frame may be further adjusted in normal tension with respect to its diaphragm by means of small wedges 4d. Fig. 2 shows a modified construction of small size for home or school use in which the dielectric 2 and conductor coating 22, 24 are secured on frame 1 by tacks 15 and co - operate with a rear porous electrode diaphragm 28. This diaphragm is constructed from a piece of metal tinsel cloth 19 overlaid with sets of perforated metal cross strips 20,18. The diaphragm 28 may be in one piece or may be divided into a number of insulated sections. A rim sheet 27 of loosely stretched fabric placed between the diaphragms 2, 28 and a fabric sheet 16 stretched at the back of member 19 serve to damp the vibrations of the diaphragms. Fig. 3 shows a synchronized kinematograph and gramophone apparatus in which the relative outputs of the differently sized back electrode diaphragms 28a, 28b are controlled by means of an arm 31 passing over a resistance 30 to vary the amount of this resistance in the respective speaker unit circuits. The arm 31, which works between stops 58, 59, may either be manually operated or automatically as shown by providing the film 33 with prearranged enlarged slots 62, Fig. 4, through which spring-controlled members 45, 46 can make contact to close the circuit of relay 50 which closes contacts 51 to energize solenoid 52 and actuate the spring-controlled lever 56 carrying arm 31. If desired, enlarged perforations may be provided in both margins of the film and two or more control contactors such as 45, 46 may be arranged to operate a theatre organ or an electromagnetically controlled stage thunder and lightning producer apparatus.