US1804295A

US1804295A - Sound reproducing apparatus

Info

Publication number: US1804295A
Application number: US417248A
Authority: US
Inventors: Dow O Whelan
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1929-12-28
Filing date: 1929-12-28
Publication date: 1931-05-05
Anticipated expiration: 1948-05-05

Description

y 9 193% n. d. WHELAN- 1,804,295

SOUND I QERRODUCING APPARATUS Filed Dec. 5%, 192

HLs'Attor'ne .atented ay 5, i931 Mam "rArEN OFFEE DOW O. OF SCOTIA, YORK, ASSIGNOR TO GENERAL ELEOTRIO COMPANY, A CORPORATION OF NEW YORK scum) nnrnonocrnearramrus Application filed December 28, 1929. Serial No. 417,248.

I My invention relates to apparatus for reproducing sound from a film record. Apparatus of this character now in common use employs the Well known arrangement comprising an incandescent lamp operated from a storage battery or motor-generator set, an Optical system for projecting a light beam therefrom in a narrow band on the sound record portion of the moving film, a photoelectric device behind the film and an amplifying means and a loud speaker connected with the output circuit of the photo-electric device. Under certain conditions where such qualities in the equipment as lightness, portability, space requirements, simplicity and cost are import-ant considerations as for example in apparatus intended for use in the home or in apparatus intended to be assembled in small compass and to be transported by hand, it becomes highly desirable to dispense with he storage battery or motorgenerator set and to operate the lamp from the house or commercial lighting circuit which also is usually employed in such apparatus to drive the film. Such lighting circuits almost invariably supply alternating current and although the frequency, usually 60 cycles, is too high to produce any visually perceptible flicker of the lamp, theresulting intensity variations in the light produce an objectionably' loud bum in the loud speaker unless the amplifyingcharacteristic thereof is modified for the purpose of eliminating the lower range of frequencies. It is the object of my invention to provide an improved sound reproducing apparatus with which the frequency hum resulting from an alternating current energization' of the lamp is largely, if not entirely, eliminated without sacrificing the low frequency characteristics of the amplifying and sound reproducing system. Referring to the drawing wherein I have illustrated my invention in a diagrammatic manner, the lamp 1 having the filament 2 is shown connected through the-step-down trans former 3 to the alternating current line 4;. Light from the lamp 1 is focused by the optical system 5 to a narrow beam on the sound record portion of the film 6 which is caused to move through the beam at a uniform speed; Where the film passes through the light beam it is shownby way. of example as supported by the rotatable drum 7 and on that side of the film opposite the lamp is the photo-electric cell 8 arranged to receive the light as modulated by the sound record. Con

nected in the usual manner with the output circuit of the photo-electric cell 8 are the translating device 9, shown for example as a loud speaker. and suitable current amplifying means. The latter I have illustrated as comprising the two units 10 and 11 which may be of any well known construction. Connected with the output circuit of the photo-electric cell 8 is the mechanically resonant filter 12 which in the form I have'illustrated comprises the core 13 having two lgs provided with the winding l i shown series-connected in the output circuit between the photo-electric cell and the first amplifier unit 10. The armature15- which for example may be constructed of spring steel is shown secured at one end to one leg of the core and is adapted to vibrate freely at .the other end adjacent to the other core leg. -The armature is carefully tuned to have 'a natural period of vibration equal to the number of alternations or half waves per second of the alternating current supply circuit 4'. llhe temperature of and hence the radiation from the filament 2 of the lamp undergo periodic variations-which if the supply has the standard cycle frequency will be 120 per second .since each cycle produces two light impulses. These light impulses as well as the sound impulsesare transformed into current impulses by the photo-electric cell.

Assuming a 60 cycle line frequency, the armature is tuned to makelQO vibrations per second and in so vibrating, the filter greatly increases the impedance which it offers to waves having the same frequency. By this lamp variations which component is dissipated mechanically in the v brating element.

In the event that the sound made by the vibrat-ing armature is objectionable it may be overcome by well known means such as by a suitable damping of the armature or by arranging the filter in a sound proof receptacle. If desired the armature may be resiliently supported so that thg entire armature vibrates relativeto the core; in any case, the

specific construction of the filter is not essential to my invention. While I have shown the filter arranged between the photo-electric cell and the first amplifier ilO it may under certain conditions be found desirable to arrange it between the two amplifiers or even between the second amplifier 11 and the loud speaker.

I have; chosen the particular embodiment described above as illustrative of my invention and it will be apparent that various modifications may be made without departing from the spirit and scope of my invention whichtmodifications I aim to cover by the appended claims. I

What I claim as new and desire to secure by Letters Patent of theUnited States is:

1. An electrical amplifying and sound reproducing system having an alternating current supply and having means for eliminating an undesirable frequency, due to said supply comprising a mechanically resonant filter provided with an armature tuned for movement in unison with said frequency.

2. Sound reproducing apparatus comprising a light source adapted to be energized by an alternating current, means for passing a sound record through a'narrow beam of light from said source, aphoto-electric device arranged to receive the light beam modulated by the sound record, a translating device con- 55 ing a light source adapted to be energized by nected with the output circuit of said photoelectric device, and a mechanically resrinant filter connected with said output circuit tuned to the alternation frequency of said current.

3. Sound reproducing apparatus comprising a light source adapted to be energized by an alternating current, means for passing a sound record through a narrow beam of light from said source, a photo-electric devicearra'ngedto receive the light beam modulated by the sound record, translating and amplifying devices connected with the output circuit of said photo-electric device and a methereby, said member being tuned to the frequency of alternation of said current.

5. Sound reproducing apparatus comprising a light source adapted to be energized v by an alternating current, means for passing a sound record through a narrow beam of light from-said source, a photo-electric device arranged to receive the light beam modulated by the sound record, an amplifier and a sound producing device connected with the output circuit of said photo-electric device and a filter comprising an electro-magnet having a winding connected with said circuit and having a vibratory armature tuned to the alternation frequency of said current.

6. Sound reproducing apparatus comprising an incandescent lamp having circuit connections with a source of alternating current, means for supporting a moving sound record film, optical means for focusing a narrow beam of light from said lamp on the sound record of the film, a photo-electric cell arranged behind the film, an amplifier and loud speaker connected with the output circuit or" the cell and a filter in the output circuit of the cell comprising a core having a winding thereon and an armature tuned to vibrate in unison with the alternation frequency of the alternating current.

, In witness .whereof,:1 have hereunto set my hand this 27th day of December, 1929.

DOW O. VVHELAN.

chanically resonant filter connected with said output circuit having a vibratory member tuned to the frequency of alternation of said current. v

4. Sound reproducing apparatus comprisan alternating current, means for'passing a sound record through a narrowbeam of light from said source, a photo-electric device arranged to receive the light beam modulated by the sound record, a sound producing device and an amplifier connected with the output circuit of said photo-electric device, and a filter having a winding connected with said 5 circuit and a vibratory member actuated.