Motion Picture News (Jul - Sep 1930)

July 5, 1930 Motion Picture News 31 Moreover, in substituting incandescent lamp for the arc, the humming due to the rapid expansion and contraction of a heated gas. such as an arc flame, is substantially eliminated. In addition to this the entire superimposed alternating energy of the talking circuit, impressed upon the normally high candle-power lighting direct current, is effectively employed in alternately raising and lowering the normal candle power of the lamp. This variation, it will be seen, occurs in that part of the spectrum in which the slightest addition or subtraction of electrical energy (such as would be caused by a very small to and fro movement of the transmitter diaphragm,) will produce a considerable fluctuation in candle power and in its resultant actinic or photo-chemical action upon the film. Since the induction coil and condenser used by me cause the setting up of induced currents flowing alternately in opposite direction's through the lamp filament, those currents that flow with the normal lamp current serve to reinforce it and augment the candle pcwer, while those that flow against the normal lamp current oppose it and cause a diminution of the normal luminosity. If this action took place while the filament were burning at a very low candle power, say a bright red, the effect of the superposed telephone current would scarcely be noticeable. But if the filament were burning at a brilliant white, or a bluish white incandescence, such superposition of the telephone current, I have found, will produce a verv decided and sharply defined variation in candle power, a variation that is entirely too rapid to be perceptible to the eye, hut which is quite strongly marked when produced upon a moving film. However, since by the use of ray focusing lens 1 concentrate a considerable amount I%gr9. JZgr:8 of light upon an exceedingly small surface, I find that it is not essential to overstrain the lamo-filament. The strength of the source of light and the photographic materials and speed of photography are adjusted to each other for this purpose in accordance with the well known practice in the photographic art. In fact, a very small tungsten filament lamp using an almost insignificant amount of current will more than suffice to produce a strong, well defined and powerful record, a record that is practically free from all scratching and other extraneous mechanical sounds inseparable from the use of ordinary phonographic records. Coming now to the method and appliances I have devised for reproducing my sound records, reference is made to Fig. 2, which, with certain modifications, shows on a larger scale the sound reproducing apparatus illustrated in Fig. 1, and already partially described. In Fig. 2, the light climber, 51, (corresponding with 24 in Fig. 1,) contains a small tungsten or other suitable metal-filament incandescent lamp, 52. This lamp is supplied with direct current from a battery or other source 53. Behind the lamp is mounted a standard, S\ carrying an adjustable reflector 55, which may be secured upon the standard by thumb-screw 56. In front of the lamp, mounted in the wall of the lamp chamber, is a flanged cylinder, 57, which supports an adjustable lens tube provided with a lens, 58, and a rack and pinion, 59, for focussinc the lens 58, tinlatter being shown as secured in its tube by a flanged clamping ring 60. This clamping ring is adapted to enter within a hood, 61, the two forming a light-tight and dust-proof connection between the light-chamber and that part of my sound-reproducing apoaratus which co-operates with the film. This last named apparatus, as shown, consists of a closed, box-like chamber having top and bottom walls 62, 63, two side walls (not shown,) and a rear wall. 64. The top and bottom walls are provided with slots 65, 66, through which the vertical section 21 of the developed film, 1, is free to pass, this section of the film extending between the two lower sprockets 14 and 16, as shown in Fig. 1. The front of the box is closed by the perforated plate 67, (see Figs. 3 and 4), which may if desired be held in position by a removable clamping frame 68 to facilitate changing the plate to form a wide or a narrow sound record. Secured to the inner face of the rear wall 64, and preferably covering its entire surface, is a variable, electrical resistance, 69, adapted to be influenced in its conductivity when impinged unon by light. I may employ as such variable resistance a "selenium cell" of any desired or appropriate construction, but I prefer to use a selenium cell or grating, 69, of a special type that I have invented for this purpose, the design and construction of which is illustrated in detail in Fig. 5. This consists of two thin, interlaced sheetmetal stampings, 70 and 72, marked + and — respectively, the space between and around the uniformly spaced, interlaced prongs of which is completely filled with melted selenium, 71. Usually, if flesired, a very thin layer of selenium may also be spread over the top surface of the grating 69, that is formed by the two conducting grids 70 and 72. These grids terminate in a pair of binding posts, marked + and — , respectively, secured to the back of the rear wall 64. Within the chamber, suitably placed between the film section 21 and the variable resistance grating 69, is a small double-concave lens, 73, mounted upon a fixed support, 74, so that its focal axis is opposite the light-opening, 36 or 36', in the plate 67. Upon the shaft of the lower guide roll 16, which if desired may be in the form of a sprocket wheel, I place a small belt 75, arranged to drive a centrifugal governor 76, whose disc, 77, is adapted to raise and lower a lever 78, so as to make or break the circuit of battery 53. The purpose and function of this governor, 76, and its associated parts, as will be apparent, is automatically to open the circuit of battery, 53, and thus to extinguish the lamp 52, if for any reason the speed of the film 1 is unduly reduced, or when the projecting machine comes to a stop, or again during the starting up of the same from a position of rest until it has gained its minimum or normal operative speed. In this manner, I eliminate all possibility of accidently overheating or burning the him by reason of any prolonged focusing of the light from the lamp 52, upon any given spot on the same. I will say, in passing, that I may also use the same governor to extinguish the picture-projecting lamp, particularly if this be of the high candle-power incandescent type which under certain operating conditions I rind it feasible to substitute for the arc, and thereby dispense with the usual fire-shutters now generally employed. The use of this automatic lamp extinguishing safety device will serve, incidentally, to insure a more correct and uniform operation of the projecting apparatus on the part of the attendant. The operation of the remaining devices described with reference to Fig. 2 are as follows. The rearwardly extending light-rays from the incandescent lamp 52. impinge upon the reflector 55, which in some cases I may make in the form of a parabolic reflector having the lamp, 52, in the focus thereof. From this reflector they are projected against the lens 59, as indicated by the arrows. The forwardly extending rays from the lamp filament are in like manner directly projected upon the same lens, being added to those coming from the reflector 55. The lens 59 concentrates and brings the combined rays thus falling upon it to a focus directly upon that given spot of my sound record, usually located near one edge of the translucent film-section 21, (as indicated more clearly in Figs. 8, 9 and 10,) which at the moment is passing behind the narrow slit or light-opening 36 It will thus be evident that this spot, which niay represent, say a portion of a single sound wave, is very highly illuminated, and that the amount of lght transmitted through the film at this spot will depend directly upon its relative degree of translucency, which changes rapidly from moment to moment with each succeeding wave that passes the slit. The light rays pass, preferably through a small double-concave lens 73, which is placed close to the fi'm causing them to diverge and to spread preferably over the whole of the large area of my selenium grating 69, as shown by the dotted lines. By this novel means I produce a wide and uniformly distributed variation in the electrical resistance of the selenium between the + and — grids, 70 and 71, which variation will be in substantially direct proportion to the varying intensity of the distributed light. It may he mentioned here that in reproducing my photophonic sound records, it is not essential to have the emulsion side of the translucent film face the light rays coming from the lamp 52. It suffices merely to transmit the convergent rays at the desired focal intensity through the film so that the plane of the photographically developed sound-record surface will intersect and pass through the concentrated light rays. I prefer to place my sound-reproducing lamp 52, together with its light concentrating and projecting system, on the opposite side of the film from that shown in the drawings, thus reversing the position, with reference to the film 1 at the point 21, of the lamp 52 and the selenium grating 69. Moreover, in the reproduction of my photographic sound records, unlike the reproduction of an ordinary photograph, the sound is the same whether it is reproduced from a negative or a positive print. On referring to Fig. 1, the manner in which the variation in the electrical resistance of the grating 69 is utilized in the present application of my invention, will now be made clear. To the + and — binding posts of the selenium grating 69, are attached the conducting wires 81 and 82. These wires extend, let us assume, from a picture-projecting booth located on or above the balcony of a theater, — in which booth the entire projection apparatus shown at the left hand portion of Fig. 1 is placed — to the stage of the same theatre. The location of this stage is represented at the right-hand portion of Fig. 1 by the talking-picture screen. 91, and the sound -reproducing horn 90, of my photophonoscope. The dotted lines 83, 84, represent a continuation of the conducting wires 81, 82, and are run from the aforesaid balcony and joined to the remaining circuit wires, 85, 86, located on the stage, a primary battery. 87, being included at any convenient point in the sound reproducing circuit. Ordinarily, I may connect the wires 85 and 86 directly with one or more telephone receivers placed on the stage, generally behind the screen 91, and in this case the battery 87 is alone sufficient, without any additional appliances, to cause an absolutely pure reproduction of the photographed voice-record, by virtue of the changing resistance of the selenium grating 69, and the automatic corresponding increase and decrease of the current which the battery 87 sends through the telephone or telephones. However, in order to increase the volume of the reproduced sound, especially when my apparatus is used in large auditoriums, I preferably introduce in J&rJO this circuit any suitable amplifying device or devices, by which speech may be intensified to fill the entire auditorium. I have illustrated as one type of such amplifying device that I find useful for this purpose, a loud-speaking electrochemical telephone receiver of a well-known type, to the terminals of which the wires 85 and 86 are connected. This apparatus consists essentially of a diaphragm of relatively large diameter, which 1 place within the base of the megaphone, 90, said diaphragm having a flexible, springpressed metallic arm, preferably of palladium, 89, extending from the center thereof and bearing upon the surface of a uniformly driven rotating cylinder, 88, preferably of compressed chalk, that is kept in a moistened condition by any suitable means, as by an occasional wetting of its surface about once or twice a week, from the liquid-containing receptacle 92. With the shaft of cylinder 88, one of the wires leading from the battery, 87, is in electrical contact, the other wire being connected with the arm 89. In some cases I may also introduce an induction coil in this circuit to augment the effect. The passage of a variable current between the moistened cylinder and the arm, by its electrolytic action, effects a corresponding and very pronounced variation in the mechanical friction between the two surfaces. In this manner, oscillations of large amplitude are produced in the diaphragm, in exact accordance with the density of the photographic sound record on the film. 1. The effect of these oscillations upon the column of air contained within the megaphone, 90, is such as to still further augment the volume of sound emitted, so that it becomes possible with this arrangement of the various parts of my apparatus, audibly to reproduce and amplify the sound record on the film to such an extent, if necessary, that the reproduced speech, vocal, instrumental and other sounds will be louder and carry farther than the original sound vibrations themselves. Although I have herein shown and described one specific type of sound amplifying apparatus, I desire it understood that I do not limit myself to this type, as I may employ any other form of telephonic relay or other sound amplifying devices. It will now be clear how the original atmospheric sound waves incidental to a given act or scene are automatically converted into light waves, the light waves into a chemical sound record upon the film, and which, together with a similar record of the series of pictures of the scene taken therewith upon the