Patent GB-349111-A (GB)
Title: Improvements in or relating to apparatus for recording and reproduction of sound
IPC: H04R3/12
Filed: 1930-02-10
Abstract: 349,111. Transmitting music. ELECTRICAL RESEARCH PRODUCTS, Inc., 195, Broadway, New York, U.S.A., NEILL, H. J., 2, Elm Close, Leatherhead, Surrey, and CALVER, B. G., Lla Oidar, Sunbury-on-Thames. Feb. 10, 1930, No. 4496. [Class 40 (iv).] Relates to apparatus, for use in talking motion picture projections, whereby the position of the main source of sound is varied in accordance with the changing positions upon the screen of the image representing the sound source. According to the invention, an operator follows with a sighting device such as a telescope the movements of the image, and by the movements of the telescope switching mechanism is operated to vary selectively the input to a number of loud-speakers arranged behind the screen. Alternatively, instead of using such manual control, the distribution of current to the loud-speakers may be automatically controlled by means of a specially prepared record of the changes in position of the actual source of sound. Such a record is made, synchronously with the sound recording and the taking of the kinematograph pictures, by the use of a sighting device with which an operator follows the movements of the source of sound. In the system shown in Fig. 1, nine loud-speakers 14 .. 22 are arranged, in three horizontal and three vertical rows, behind a kinematograph screen. Each horizontal row is associated with an impedance network or potential divider 30, 31, or 32, one terminal of each loud-speaker being connected to a particular point on its own potential divider. Three multi-contact switches 26, 27, 28 are associated severally with the devices 30, 31, 32, the fixed contacts of each switch being connected to equally spaced points on the resistance associated therewith. A fourth impedance network 24, 25 is similarly connected to another nine-point switch 23, and the ends and a centre tapping of the resistance 24 are connected respectively to the movable contact arms of the switches 26-28. A source of electrical variations 11 derived from the sound record, such as a photo-electric cell or a gramophone pick-up, is connected to an amplifier 12, the output side of which is connected as shown to the movable arm of the switch 23, the potential dividers 24, 30, 31, 32, and to one terminal of each of the loudspeakers. The switches 23, 26, 27, 28 are connected mechanically with a telescope 36 in such a manner that angular movements of the telescope in a vertical plane alters the setting of the arm of the switch 23 on its contact studs, and the arms of the switches 26-28 are moved together over their contact studs in accordance with horizontal swinging movements of the telescope. With this arrangement, as an operator keeps the telescope directed upon the image of a speaking character on the screen, current from the amplifier 12 is so distributed to the loud-speakers that at any instant it is fed mainly to the one nearest to the image which constitutes the apparent origin of the sound. Instead of controlling the distribution of current through the impedance network by manual operation of a sighting device, such control may be effected automatically by using a record such as a film having thereon photographic traces the density of which varies in a manner representing the changes in position of the original source of sound. An arrangement of this kind is shown in Fig. 2. A film 37 having a photographic record varying in accordance with a co-ordinate of the source of sound with reference to a chosen axis is moved across a light beam which falls on a photo-electric cell 43. The output from the cell is amplified by a system of valves (shown as a resistance-coupled direct current amplifier such as is described in Specification 289,217, [Class 40 (v), Wireless signalling &c.], the last one of which, 48, is connected to a marginal or selective relay arrangement of the kind described in Specification 308,789, [Class 40 (v), Wireless signalling &c.]. The relays 52 .. 59 perform the same function as the switch 23 of the arrangement shown in Fig. 1, and they comprise contacts which, like the studs of the switch 23, are connected to a resistance 24. A conductor 50 connects all the relays to an output terminal of the pick-up amplifier. In operation, the density of the record on the film 37 passing across the light beam determines at any instant the value of the anode current in the valve 48, and thus the relays 52 .. 59 are selectively operated. Consequently, the point on the resistance 24 to which the conductor 50 is connected through the relays is varied accordingly. To replace the manual switches 26, 27, 28 of Fig. 1, as well as the switch 23, two systems such as that shown in Fig. 2 are required, one having three banks of contacts. Instead of using a record of varying density, a record may be used in which the changes in position of the moving source of sound are represented as rhythmic variations of a predetermined frequency. A system for employing such a record is described, embodying an ordinary resistance-capacity coupled amplifier. A record may also be used combining in one trace modulated rhythmic variations of one frequency to represent changes in one co-ordinate of the source of sound, and variations of another frequency to represent changes in another co-ordinate. Such a double record may be used with the circuit arrangement shown in Fig. 4, comprising a photo-electric cell 43, coupled through an amplifier to a transformer 65 having two output windings ; these are connected through appropriate band-pass filters 66, 67 to valves 61a, 61b, respectively, each of which is in turn connected to a valve such as the valve 48, Fig. 2, associated with a marginal relay arrangement. Further, there may be used a record incorporating in a single trace not only the records of one or more co-ordinates of the original source of sound, but also a record of the sound itself, the changes in position of the source being represented by variations of frequencies outside the audible range. It may, however, be preferred to use one film having three separate traces thereon, two being co-ordinate records and the other a record of the sound; this film would be run synchronously with a separate picture film. A further alternative consists in representing the co-ordinates of the source of sound as rhythmic variations, recorded mechanically on a wax blank (in the manner in which a gramophone record is produced), or in the form of a magnetized wire record. Fig. 5 shows apparatus for making two record traces of varying density representing horizontal and vertical co-ordinates of the source of sound. A telescope 70 is so mechanically connected to two contact arms 71, 78 that vertical movements cause corresponding movements of the arm 78, and horizontal movements similarly affect the arm 71. The two arms are movable over resistances 72, 79, each of which is connected to a valve as shown. The valves separately control neon or like lamps 76, 83, the light from which is recorded on films 87. During the production of a talking film, an operator follows with the telescope the movements of a speaking character, and thereby the arms 71, 78 are moved so that potential variations are impressed on the grids of the two valves in accordance with the changes in the two co-ordinates, and the fluctuations in the light from the lamps 76, 83 are recorded on the films. A system is also described in which two valves generate oscillations of predetermined frequencies, and variations corresponding to the changes of position of the source of sound are, by means similar to that shown in Fig. 5, impressed upon these oscillations and recorded photographically in a single trace.