US1801472A - Sound-reproducing system - Google Patents

Description

Apri! 21, 1931.

D. A. WHITSON 1,801,472

SOUND REPRODUCING SYSTEM Filed July 50, 1928 2 Sheets-Sheet 1 ,qr-rozlvsy April 21, 1931. D. A. WHITSON SOUND REPRODUCING SYSTEM Filed July 30, 1928 2 Sheets-Sheet 2 erraervsy 1 15 commonly usedloud s Patented Apr. 21, 1931 UNTTED STATES PATENT? OFFICE DELMLAB WHITSON, LOS ANGEIOES, CALIFORNIA, ASSIGNOB TO WHI'ISON PHOTO- PHONEOORPOBATION, OF LOS ANGELES, CALIFORNIA, A CORPORATION OF NEVADA BOUND-BEPBODUGING SYSTEM Application filed. July 80,

This invention relates to sound reproduction, and especially to reproduction from photo aphic records. A

uch records are now "well known. In on form, for example, the record is produced on g a film, the density (or degree of translucency is longitudinally variable in accordance wit the sound to be reproduced. Now if such a record he passed between a steady source of light and a photo-electric device, this device can control the current in a circuit, and-the resultant current variations can be caused to operate a device thattranslates cur-rent variations into sound; such for exam le as the now akers. ince such reproducing systems as ust outlined are now in quite general use, and especially in connection with talking movies, it is considered unnecessary to detail them further.

My invention is in the nature of an improvement over a system of this character; and accordingly it is one of the objects of my invention to improve the reproduction of sound by this means.

It is obvious that in a record of this character (the so-called variable density record), the record carrying medium should, for perfect results, have its density continuously and accurately variable along its length; in other. words, for each increment of length theremust be a corresponding increment or decrement of density. Practicalconsidemtions'iminediately show that the length increments cannot be reduced to a mathematical infinitesimal, such as are treated for example in differential calculus; and consequently, this theoretical perfection is lost.

Nevertheless, the human ear being itself incapable of discriminating between perfection and near perfection, highly satisfactory results can be obtained when the density variations occur in widths of say of the order of one or two thousandths of an inch where the rectilinear speed of the record is approximately fifteen inches per second at any given point. Consequently when such a density rec 0rd is viewed with the naked eyes, it appears as a series of very closely spaced bars of vary ing widths and of varying darkness or density. These bars are the result of passing the 1928. Serial No. 298,298.

light that produces the record through a correspondin'gly narrow slit or iris onto the recorddwhich is later photographically develope For reproduction purposes, the density of each individual bar should theoretically be caused to affect in succession, the photo-electric device, so that the device may faithfully follow the density variations of the whole record. In order to accomplish this result, it has been customary to provide a narrow slit or iris across which the record is passed. However, -1t was found that dirt or other foreign matter soon clogged up at least a portion of the opening, and interfered with the transmission of light therethrough. Even if the reproduction were not entirely lost, yet due to the irregular blurrin of the optical path occasioned by the foreign matter, a serious distort1on would result. Consequently it has been proposed to fill'the slot with a transparent 'plug, such as a crystal or glass, that would eifectively keep out the foreign matter.

Such an arrangement is nevertheless far from ideal. The film, travelling in contact with the iris, is rubbed thereb and a scratching of the record is caused by fine dust or particles trapped between the film and the slot. It is another object of my invention to obviate all these disadvantages and yet secure the highly desirable accurate reproduction.

I accomplish this result by passing the light through an iris that is comparatively wide; of the order of an eighth of an inch, and by maintaining the film record entirel out 0 contact with the structure in which the opening is rovided. The image of a lar e number 0? striations or density lines is t en projected in magnified form onto a baflle, which has a slot or an elongated transparent window just wide enough to pass only a very small fraction of a single striation onto the photo-electric device. Since the ima e is optically projected and fractionate by a slot or light passage remote from the film, the slot can be kept easily free of interfering foreign matter, and may be provided with a transparent coverin such as a glass plate or plates on both sides thereby Insuring a clear light path at all times.

The advantages of such an optical system are important. In prior devices, the photoelectric device was subjected at frequent points on the record to the light intensity roduced by a small group of density lines, own as harmonic groups, the combined or total width of which was much smaller than the width of the fractionating slot; and accordingly, attempts to record and reproduce variations in tone volume could not be readily accomplished, for the individual density variations were lost. In my scheme the tone volume can readily be recorded and reproduced, for a very much finer subdivision of the'lines is provided, and the density variations, which occur over the entire width of the individual lines being the volume factor, can be reproduced by making the magnification sufiiciently large, and the opening or window in the baflie plate suificient narrow, so as to scan across the width of the line from one edge to the other. Such scannin is practicall impossible where a slot having a width 0 .001 of an inch is directly employed to fractionate fundamental tone lines more or less of that width, and harmonic lines are present possibly as narrow as .0005 or even .0002 of an inch, which condition now obtains in other devices for reproducing sound.

'My invention possesses many other advantages, and has other objects which may be made more easily apparent from a considera tion of one embodiment of my invention. For this purpose I have shown a form in the drawings accompanying and forming part of the present specification. I shall now roceed to describe this form in detail, which illustrates the general principles of my invention but it is to be understood that this detailed description is not-to be taken in a limitin sense, since the scope of my invention is Eest defined by the appended claim.

Referring to the drawings:

Figure 1 is a diagrammatic view of a reproducing system incorporating my invention; the optical system and its associated structure being shown mainly in section.

Fig. 2 is a side elevation of the optical system and its associated structure, some of t 0 parts being broken away to illustrate the structure more clearly.

Fig. 3 is a plan view thereof; and

Fig. 4 is a diagram of a ortion of the ma ified image with the batle plate.

ig. 5 is a magnified view of an individual tone line or photograph showing the density variation, or graduation over its entire width, characteristic of the volume factor.

The record film 11 in this instance is shown as carrying not only the sound record 12, but also the frames 13 of a motion picture for the purpose of producing talking pictures. This film has a series of s rocket tooth engaging apertures linear 021(1 edge;

. adjacent support 28, can

in the present instance, only the apertures at the right hand edge (Fig. 3) are engaged by a sprocket wheel 15. This wheel as most clearly shown in Fig. 1, can be used as a driven wheel, as by the provision of a drive shaft 16. Optionally one or the other sprocket wheels 17 (Fig. 2) can be used as a driver; otherwise it can serve, as sprocket 18, merel as a tensionin idler. Other idlers, suc as 19, 20, 21, canie used to maintain the film 11 in proper arcuate configuration with respect to wheel 15.

\Vheel 15, as shown in Fig. 2, is provided with an undercut flan e 22 that is of considerably less width than film 11, so that the free edge of the film projects beyond the narrow rim 23 and is supported thereon. The film 11 is urged sidewise to maintain it in correct position with relation to the optical system, as by a ring 24, urged resiliently as by a series of springs 25, against that edge of the film which is nearest the sprocket wheel. To adjust the spring pressure, an adjustable rin 26 is used, against which the springs 25 a ut, and which is adjustable by having it threaded onto the screw threads 27 shown as formed as an extension of wheel 15. Wheel 15 has sufficient weight to produce a fly-wheel effect, and to maintain the speed thereof substantially uniform. This uniformity is quite essential for accurate reproduction.

That part of film 11 which projects beyond rim 23 carries the sound record. The optical system whereby light shines through the record will now be described. A stationary support 28 is used, that has an offset portion 29 extending beneath flange 23. This portion has an arcuate segment 30 in which is formed a comparatively wide slot 31 to permit li ht to shine through the projecting edge of lm 11 as it travels past. This slot, as shown in Fig. 2, can be stepped in order to prevent difl'raction at the inner edge; and it is furthermore so wide as to preclude the possibility of it clogging. In fact, glass windows can readily be placed on each end of the slot if necessary.

As shown most clearly in Fi 1, the film 11 is spaced from the slot opening, so that it cannot be scratched or injured by the slot edges. Light can be passed through the slotin any desired manner; for example, an in candescent lamp 32, appropriately supported be used. A lens 33 concentrates the light onto a prism reflector 34 supported in the offset portion 29 of support 28. Lens 35 in this offset portion then concentrates the rays to pass it through aperture or slot 31. After the light passes through film 11, the image of the record thereon is magnified by anyl desired arrangement, as by lens 36, and t e magnified image is proj ected onto a baflie plate 37 As shown most clearly in Fig. 1, the image of the record covering slot 31 at any instant image is allowed to affect the light sensitive device 40, such as a photo-electric cell. For

this urpose, bafile 37 has a central slot 41, or s win ow wide enough to pass only such rays as correspond to a portion only of a density line. These rays can then be again diverged to affect the electron emitting'electrode 42. This device can then be used to afl'ect, in a well known manner, one or more stages of electronic emission amplifiers such as 43, and finally the amplified electrical im ulses can pass to a loud speaker 44 or equiva ent device that translates these impulses into sound waves. 7

The baflle plate 37 is shown as having an exaggerated slot opening 44. As a matter of fact, the slot is made very narrow, as indicated by the line 45 in Fig. 4, so that it serves to fractionate or scan the individual bars. In this way, the variations in volume of the sounds ori nally recorded can be faithfully reproducetf The slot in bafile plate 37 may be equipped with transparent windows, such as a sheet of glass or mica, cemented on either or both sides of the battle as shown at 37a, thereby preventing the accumulation of dirt or foreign matter in the light passage, or the baflle plate may be made of a transparent solid such as glass or quartz coated or covered on one face with an opaque substance, that is heavily silvered or painted and a very narrow line ruled through the covering to the glass surface thereby permittin light to pass, as if it were an open slot. T 's arrangement permits easy cleaning when, if ever, any dirt should accidentally accumulate at that point. In view of the fact that the bafile plate is remote from the accumulated dirt adhering to the film, this elementary trouble is entirely overcome.

I claim:

In a structure defining a slot for photo- I graphic sound records, a wheel over which the record can be placed, said wheel having a flange beyond which the record can project, a stationary support having a part projecting beneath said record, and forming wlth the wheel an opening over which the record travels, a lens structure arranged to pass radiations radially through the opening, and supported on said part, and a reflector also supported thereon, for directing radiations from a source through the lens.

In testimony whereof I have hereunto set in hand.

y DELMAR A. WHITSON.

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