The Film Daily (1929)

Wednesday, September 4, 1929 DAILY 32nd Instalment, 'Sound Patent9 Series CONCLUDES ANALYSES OF SOUND-ON-FILM SYSTEMS This is the thirty-second instalment in "Sound Patents," a series of articles dealing with the patent history of sound and synchronization devices in the United States, England, France and Germany. British patent No. 253,226 issued to Robertson Cottnam on June 17. 1926, sets forth that the speed of the motion picture film is not as fast as is required for the best results in reproducing sounds from a magnetized wire. This patent, therefore provides four magnetized wires and four recording and reproducing solenoids with commutators so arranged that each of the solenoids is connected ' to the amplifiers and loud speakers at successive intervals. The arrangement is shown in Figs. 2 and I of the drawings as applied to the intermittent film advancing mechanism. In this arrangement one solenoid (la) is connected to the amplifying apparatus so as to receive varying magnetic impulses from the wire (1) while the film is in motion Other recording or reproducing electro-magnets (2a, 3a and 4a) are mounted on a rotating drum which, when the film is standing still, rotate in a direction opposite to the movement of the film, thus moving the solenoids (2a, 3a and 4a) past the Fig. 2 magnetized wires (2, 3 and 4) with the same relative speed as the wire (1) passes the stationary solenoid (la). The solenoids (2a, 3a and 4a) are connected to the amplifying apparatus at the proper intervals so that a continuous sound is reproduced and an effective speed of the magnetized wires about four times that of the film is attained. United States patent No. 1,590,694 issued to William W. McLaren on June 29, 1926, illustrates a device in which a film (8) and wire (4) arc separately drawn from a common reel having .special film guides (9) and wire or ribbon guides (5), thus attaining a uniform movement of the wire and making the wire independent of the film. Photographic Sound Records In this type of apparatus, which is now in use in certain types of talking pictures, the sound waves or vibrations are recorded in a strip of film or on the edge of the picture film in the form of short, parallel transverse bands or of a lengthwise band of varying color or opacity. These bands may be formed by controlling or varying the intensity of a beam of light that is directed onto the passing film during the recording of the sound. In reproducing the picture a beam of light is directed through the sound record onto a light sensitive element of an electric circuit. The light sensitive element is of such a character that its resistance or conductivity varies with the amount of light directed onto it and thus the flow of current through the A British sound-on-film system, devised by Robertson Cottnam and patented on June 17, 1926. Patent No. 253,226 Use of selenium cell in sound-on-film system. British Patent No. 18,057 circuit varies in accordance with the photographic sound record on the passing film. The making of a photographic sound record had been disclosed in patents for forming permanent records of telephone conversations. An example of such apparatus is shown :n British patent No. 19,901, issued to Christian Hulsmeyer on May 14, 1903, as shown in Fig. 1 of this patent, the sound waves strike a microphone (a) in the telephone circuit, causing variations in current which vary the electro-magnetic strength of the solenoids (d, d1) also included in the telephone circuit. The varying magnetism of the solenoids (d and d1) tilt an armature (e) having a mirror (h) to a greater or less extent against the tension of a spring (f) in accordance with the changes in the current flowing throuRh the telephone circuit. A beam of light from a lamp (i) is directed at an angle onto the surface of the mirror (h) and is reflected through a plate (1) and through a lens (o) towards a point (q) on a passing photographic film (r), the amount of light passing through the plate (1) depending upon the deflection of the reflected beam of light by the mirror (h). As the mirror (h) tilts and deflects the reflected beam in one direction or the other, a greater or less quantity of light is projected onto the film (i) and thus varies the intensity of the photographic effect. The phonographic record after developing is then passed between a fixed light and a selenium cell positioned within a telephone circuit. This apparatus is not shown in the patent. Selenium is an element somewhat similar to sulphur but having the peculiar property that its electrical resistance or conductivity is affected by light, the resistance decreasing and the conductivity correspondingly increasing in proportion to the intensity of the light. If a small strip of selenium is thus included in an electric circuit, the conducting power of the circuit may be made sensitive to light acting upon the selenium. Selenium when used in this connection sometimes is called a selenium cell. In British patent No. 18,057 issued to Robert T. Haines, John St. Vincent Pletts and Eugene Lauste on Aug. 10, 1907, this principle is applied to the simultaneous making of a sound and picture record on a single strip of film. As shown in Fig. 1 of the patent, a strip of film (in) is drawn over a number of rollers (m1) from an unwinding reel to a winding reel. The picture record is made on the film through a lens (n) in the lower part of the apparatus, the film being drawn intermittently through this part of the apparatus. Above the picture-recording lens the film (m) is drawn at a constant speed and in position to receive light reflected from a lamp (j) by a reflector (k). The light from the reflector (k) passes through a fixed screen (C) and a movable screen (C1) shown in Figs. 3 and 4, before reaching the film. The screens (C and C1) are provided with slits through which the light passes, the quantity of light being greater when the screens are shifted to bring the slots into perfect alignment, and being decreased as the movable screen (C1) is shifted in one direction or the other. The shifting {Continued on Page 12) H'tlsmeyer system uses photographic sound record, b.itish Patent No. 19,901