US2124030A

US2124030A - Stereophonographic apparatus and method

Info

Publication number: US2124030A
Application number: US759854A
Authority: US
Inventors: William L Douden
Original assignee: RCA Corp
Current assignee: RCA Corp
Priority date: 1934-12-31
Filing date: 1934-12-31
Publication date: 1938-07-19
Anticipated expiration: 1955-07-19
Also published as: DE650116C

Description

Jul 19, 1938. L DOUDEN 2,124,030

STEREOPHONOGRAPHIC APPARATUS AND METHOD Filed Dec. 31, 1934 5 Sheets-Sheet l [:k EII INVENTOR W/LL/AM A. DUUDf/V ATTORNEY July 19,1938. w. DOUDEN Filed Dec. 31, 1934 5 Sheets-Sheet 2 INVENTOR mama/Z0005 BY ATTORNEY July 19, 1938.

W. L. DOUDEN STEREOPHONOGRAPHIC APPARATUS AND METHOD Filed Dec. 51, 1934 3 Sheets-Sheet 3 INVENTOR W/l. L/AM L. 00005 ATTORNEY section of the sound reproducing apparatus,

Patented July 19, 1938 STEREO-PHONOGRAPHIC APPARATUS AND METHOD William L. Douden, New York, N; Y., assignor to Radio Corporation of America, a corporation of Delaware Application December 31, 1934, Serial No. 759,854

plifiers 3 and 4 of conventional type which serve to amplify the electrical impulses received from the microphones. The amplifiers 3 and 4 are connected to the usual mixer and power amplifier indicated at 5, which may be of any usual commercial type, and the acoustically modulated electrical output from the amplifier 5 actuates' the galvanometer B in the known manner used in variable width sound recording, and is described and claimed in Kellogg Patent 1,740,406.

Connected to the output from the amplifiers 3 and 4 are rectifying amplifiers 6- and l which provide a direct currentoutput corresponding to the envelope of the audio frequency input to each of the microphones. These amplifiers may be constructed, for example, as shown and described in MacDowell Patent 1,855,197.

The output from the amplifiers 6 and 'l is fed to solenoids 8 and 9 which operate upon cores NJ and I I connected to the mask I2. It will be apparent that if the currents through the solenoid's 8 and9 are equal, the mask l2 will remain stationary in midposition while variations in the currents through the solenoids 8 and 9 will shift the mask l2 laterally by a corresponding amount.

The optical system used is of any convenient commercial type such, for example, as that shown in the Kellogg patent above referred to, and consists of an exciter lamp 13 from which the light is condensed on the mask [2 by the condenser lens M. An optical system i5 is provided together with a lens It for condensing the light upon the mirror of the galvanometer 6 which vibrates about a horizontal axis, and an additional optical system I! is provided which; together with [5 and I6, images the aperture in the member [2 upon the slit member I8 as indi-'- cated at 19. An additional lens 20'is provided between the slit member I 8 and the film 2| for imaging the slit 22 in the member I8 upon the film.

It will be apparent from the foregoing that sound impressed on the microphones l or 2, or both, is converted into electrical impulses which vibrate the mirror of the galvanometer fi about a' horizontal axis, thereby moving the triangular image l9 over the slit 22 and illuminating correspondingly varying lengths of the slit;' and this varying illumination is imaged upon the film- Zl by the lens 20 thereby producing a variable width sound record of the type having modulationabout both sides of an axis.

If the sound input is entirely to the microphone I, it will be apparent'that theramplifieri'l will give a correspondingly difierent current 9 Claims.

This invention relates to an apparatus for so recording and reproducing sound that the listener can tell the direction of origin of the sound, and involves both a new apparatus and a new method for accomplishing said result. Heretofore there have been attempts to stereophonographically reproduce sound by the use of two or more soundtracks or sound records operating corresponding sound reproducers, and in some instances the procedure has been successful but has never been commercially adopted due to the great expense involved in the multiple sound records and the multiple recording and reproducing equipment. The present invention involves such sound recording and reproduction with a single record, and I efiect the shifting of the apparent point of sound reproduction by a shifting of the axis of recording in relation to the axis of the soundtrack.

One object of the invention is to provide a method and apparatus for stereophonographically recording sound.

Another object of the invention is to provide a method and apparatus for stereophonographically reproducing sound.

Another object of the invention is to provide a novel photographic sound reproducer.

Another object of the invention is to provide an improved sound recorder.

Another object of the invention is to provide a sound record which may be reproduced either stereophonographically on the apparatus for such purpose or on a standard sound reproducer.

Another object of the invention is to provide a stereophonographic sound record occupying the minimum practical space.

Other and incidental objects of the invention will be apparent to those skilled in the art from a reading of the following specification and an inspection of the accompanying drawings, in which:

Fig. 1 is a diagrammatic illustration of my sound recording apparatus.

Fig. 2 is a diagrammatic illustration partly in Fig. 3 is an illustration of the soundtrack.

Fig. 4 is an illustration of a special form of galvanometer for use in my apparatus, and

Fig. 5 is an illustration of a second form of galvanometer.

Referring first to Fig. 1: l and 2 indicate microphones located at the outer limits. of the sound recording stage. These microphones may be of any convenient type capable of giving'high quality response, andare connected to the ammicrophone than to the other, the member I2 will be shifted a proportionate amount. This, obviously, will shift the image l9 longitudinally of a slit 22 and will shift the axis of the sound record in relation to the soundtrack 2| on the film. The position of the sound record in relation to the soundtrack area will accordingly indicate the position of the speaker in relation to the microphones.

The soundtrack produced by Fig. 1 is shown in Fig. 3 where 2| indicates the film and 25 indicates the sound record. It will be apparent that in this case the source of sound moved from near one microphone toward the other and became slightly louder as it approached the second microphone as is indicated by the movement of the sound record from one side of the soundtrack to the other and with slightly increased modulation.

In order to reproduce the sound so that it will appear to come from the direction or position of its original source, I use the apparatus shown in Fig. 2. In this apparatus, an exciter lamp 313 and condenser lens 3|, a slit member 32 and an objective lens 33, all as customary in commercial sound reproducers are used to produce a brilliantly illuminated image of the slit 32 upon the film 2| in the form of a. narrow line of light. Light passing through the film 2| is directed by the lens 34 to the reflector 35. This reflector is coated with a layer of silver 36, 31 of varying thickness, being sufiiciently thick at 36 to give complete reflection of the light and tapering to substantially no reflection and complete transmission at 31, and with 50% reflection and. 50% transmission at its mid-point. Any equivalent type of reflector may, of course, be used provided it has complete transmission at one edge and complete reflection at the other edge with a gradually varying reflection and transmission between. The mirror reflects light to the lens 38 Which collects it upon the photocell 39, while light transmitted by the mirror 35 is collected by the lens 40 upon the photocell 4|. The photocells 39 and 4| actuate amplifiers of any usual commercial type indicated at 42 and 43 which in turn operate the

loudspeakers

44 and 45 located in substantially the same relative positions on the stage as were occupied by the microphones and 2.

It will be apparent that this apparatus will reproduce an ordinary sound record having the variable density type or a sound record of the variable area type having the modulation equally about the middle axis of the soundtrack in the usual manner, the sound being equally reproduced by the

loudspeakers

44 and 45. If, however, a soundtrack of the type shown in Fig. 3 is reproduced in the apparatus when the soundtrack is imaged primarily upon the portion 31 of the mirror, the light will be substantially transmitted thereby and will be focussed upon the photocell 4|, thereby actuating only the loudspeaker 44 and causing the sound to come from the corresponding side of the stage. As the soundtrack reaches mid-position, half of the light will reach the photocell 4| and the other half will reach the photocell 39, thereby equally actuating the

loudspeakers

44 and 45, and causing the sound to appear to come from the middle of the stage; while when the soundtrack image is adjacent the point 36 of the mirror 35 substantially all the light will be reflected to the photocell 39 and cause the sound to appear to come from the other loudspeaker 45.

It will be apparent that with this arrangement I can use modulation through either recording amplifier amounting to the full capacity of the soundtrack as when the axis of the sound record is shifted to coincide with one side of the soundtrack the modulationbecomes of the single or saw-tooth type and may extend over the entire width of the soundtrack. The one loudspeaker reproducing all the sound from one half of the soundtrack and the other loudspeaker which reproduces the sound from the edge of the track opposite to the axis of the record reproducing the peaks of the modulation and thereby giving good quality sound reproduction.

Instead of using the movable diaphragm I2 and the galvanometer 6 as shown in Fig. 1, I may use a galvanometer such, for example, as that shown in Egerton Patent 1,605,930 in which the mirror is capable of movement about two perpendicular axes, but I prefer to use a galvanometer of the type shown in Fig. 4. In this galvanometer, indicates a metallic frame mounted pivotally on a vertical axis on the pivots SI and 62. This frame carries two

independent coils

63 and 64 which are respectively connected to the amplifiers 6 and of Fig. 1, and this entire assembly is mounted between the pole-

pieces

65 and 66 between which there is an appropriate magnetic field. It will be apparent that any lack of balance in the current through the

coils

63 and 64 will evidence itself as a corresponding movement of the frame 60 in one direction or the other. Mounted within the frame 60 on appropriate pivots 6'! and 68 is a shaft 69 carrying a mirror 10. To this mirror is connected a driving rod H which serves to vibrate the mirror about a horizontal axis in response to audio frequency currents. ing rod H by a vibrating reed 13 of an appropriate. driving motor such, for example, as that shown in Dimmick Patent 1,936,833. The driving rod 1| is reduced in thickness at 12, as indicated, to permit it to flex about the vertical axis defined by the pivots 6| and 62. It will be apparent that in this construction the mirror 10 will be capable of rapid vibrations about the horizontal axis in response to audio frequencies while the frame 60, which would not readily oscillate at such high frequencies, follows the movement of the source of sound.

In the form of galvanometer shown in Fig. 5, the unit is a complete galvanometer of the type shown and described in Dimmick Patent 1,936,833, and is mounted to pivot about a vertical axis on the pivots 8| and 82. An appropriate arm 83 is connected to the pivot 82 for the purpose of moving the galvanometer about the vertical axis about which it is maintained in approximate position by the spring 83. Solenoids 84 and 85 actuate the tension members 86 and 81 which are connected to opposite ends of the member 83, and thereby serve to move the galvanometer about a vertical axis. The

solenoids

84 and 85 are connected to the amplifiers 6 and I, while galvanometer 8!! is connected to the amplifier 5 in the same manner as the galvanometer 6.

It will be apparent that in conjunction with The modulation is supplied to the drivmy apparatus I may also use a ground-noise reduction system of the same general nature as shown in the MacDowell patent. above referred to, and connected to the mask 12 to shift it vertically in the manner shown, described, and claimed in Maurer application Serial No. 602,135, filed March 31, 1932 and Kellogg application Serial No. 621,787, filed July 11, 1932. In such case, of course, the ground-noise reduction apparatus would be connected to the output of the amplifier 5 in the manner there described.

Likewise, I may use the ground-noise reduction system of either Robinson Patent 1,854,159, or Hewlett Patent 1,853,812, or Hanna Patent 1,888,724, in which case the ground-noise reduction amplifier will be connected to the galvanometer 6, the vibrating means for the reed 12 or the galvanometer Bil, so as to shift the spot of light l9 vertically in relation to the slit 22.

Having now described my invention, I claim:

1. Sound reproducing apparatus comprising means for illuminating a photographic soundtrack, a plurality of photocells and a, mirror for directing light passing through said soundtrack to said photocells, one edge of the surface of said mirror being substantially completely reflecting for directing said lights to one of said photocells and the other edge of said mirror surface being substantially completely transparent for transmitting said light to another of said photocells.

2. In the method of sound recording which comprises the imaging upon a film of an illuminated portion of a slit which is illuminated by the image of a triangular aperture, the steps of vibrating said triangular image transversely of said slit in accordance with the acoustic vibrations to be recorded, and shifting the image longitudinally of the slit in accordance with the position of the acoustic vibrations to be recorded.

3. In the method of sound recording which comprises the imaging upon a film of an illuminated portion of a slit which is illuminated by the image of a triangular aperture, the steps of vibrating said triangular image transversely of said slit in accordance with the acoustic vibrations to be recorded, shifting the image longitudinally of the slit in accordance with the position of the acoustic vibrations to be recorded, and shifting the mean position of said image transversely of the slit in accordance with the average amplitude of the vibrations to be recorded.

4. Sound reproducing apparatus comprising means for illuminating a sound track varying in transparency along its length, a plurality of photocells, a mirror for directing light passing through said sound track to said photocells, one edge of the surface of said mirror being substantially completely reflecting and the other edge of the surface of said mirror being substantially completely transparent, amplifiers connected to said photocells and loudspeakers connected to said amplifiers, whereby the amplitude of response from each of the speakers is determined by the position of the sound recorded laterally of the sound track.

5. Sound reproducing apparatus comprising means for illuminating a sound track varying in transparency along its length, a plurality of photocells, a mirror for directing light passing through said sound track to said photocells, one edge of the surface of said mirror being substantially completely reflecting and the other edge of the surface of said mirror being substantially completely transparent, amplifiers connected to saidphotocells, loudspeakers connected to said amplifiers, a sound record having its axis shifted in proportion to the position of the sound recorded thereon between said illuminating means and said mirror whereby the response of each of the loudspeakers is determined by the position of the said sound track.

6. Sound reproducing apparatus comprising means for illuminating a sound track varying in transparency along its length, a plurality of photocells, means for directing light passing through said sound track simultaneously to said photocells in a ratio of illumination determined by the position of the illumination on said directing means, amplifiers connected to said photocells and loudspeakers connected to said amplifiers, whereby the amplitude of response from each of the speakers is determined by the position of the sound recorded laterally of the sound track.

7. Sound reproducing apparatus comprising means for illuminating a sound track varying in transparency along its length, a plurality of photocells, means for directing light passing through said sound track simultaneously to said photocells in a ratio of illumination determined by the position of the illumination on said directing means, amplifiers connected to said photocells, loudspeakers connected to said amplifiers, a sound record having its axis shifted in proportion to the position of the sound recorded thereon between said illuminating means and said directing means whereby the response of each of the loudspeakers is determined by the position of the said sound track.

8. Sound reproducing apparatus comprising means for illuminating a photographic soundtrack, a plurality of photocells and a mirror for directing light passing through said soundtrack to said photocells, one edge of the surface of said mirror being substantially completely reflecting for directing said light to one of said photocells and the other edge of said mirror surface being substantially completely transparent for directing said light to another of said photocells, the pro-portion of light reflected to that transmitted varying uniformly between the said two edges.

9. Apparatus of the classdescribed including two photocells, means directing a beam of light toward said photocells and a mirror for directing light from said beam to said photocells, one edge of the surface of said mirror being substantially completely reflecting for directing said light to one of said photocells and the other edge of the surface of the mirror being substantially completely transparent for directing said light to another of said photocells, the ratio of reflection and transmission being graduated between said edges.

WILLIAM L. DOUDEN.