US1877034A - System for transmitting sound-carrying and field currents to remotely located dynamic loud speakers - Google Patents

Description

Sept. 13, 1932. L. o. PAINTER ET AL 1,377,034

SYSTEM.FOR TRANSMITTING SOUND QARRYING AND FIELD CURRENTS To REMOTELY LOCATED DYNAMIC LOUD SPEAKERS Filed June 14, 1930 '00 OTHER SELE TIVE SWVI'CHING DEVICES Ioweniom v Patented Sept. 13, 1932 UNITED STATES PATENT OFFICE LAWRENCE O. PAINTER AND HOWARD L. JOHNSON, OF ST. PAUL, MINNESOTA, ASSIGNORS TO PROGRAM SERVICE COMPANY, OF ST. PAUL, MINNESOTA SYSTEM FOR TRANSMITTING SOUND-CARRYING AND FIELD CURRENTS T BEMOTEL'Y LOCATED DYNAMIC LOUD SPEAKERS Application filed June 14, 1930. Serial No. 461,095.

This invention relates to transmission and distribution systems for sound programs, such as musical programs, addresses and the like and relates particularly to systems wherein sound-carrying currents are transmitted and distributed by conductors from a central station to a number of distantly located dynamic loud speakers.

Such systems, while capable of wide general use, in the distribution of sound programs, are especially well adapted for profitable, commercial use by telephone companies. Telephone oflices or exchanges may constitute central stations, wherein several sources of sound-carrying currents may be amplified and these currents may be transmitted to distantly located dynamic loud speakers at the homes of the telephone subscribers, thereby offering to said subscribers a selection of sev eral programs.

At least one of the independent telephone companies in this country has used a system of the general class above described, but up to this time where dynamic loud speakers are served by the system, it has been found expedient to employ amplifiers at the location of the dynamic speakers and it has been necessary to energize the field coils of said speakers from currents supplied from the amplifiers or from lighting or power supply circuits available at the subscribers home or location of the speakers, and in the latter instance, expensive apparatus, such as rectifiers, and transformers or batteries were required.

In addition to the substantial original expense of amplifiers for each dynamic speaker, and/or the other'apparatus above described the same had to be occasionally serviced an parts replaced by the company supplying the program entertainment to prevent the apparatus from losing its efliciency and to insure roper volume at the subscribers home.

urthermore, the subscribers voften ob'ected to the increase in their electric light an power bills, because of current consumed in operating the amplifiers at their homes and/or in supplying currents for energizing the field coils of the dynamic speakers.

It is an object of our invention to rovide a program transmission system of t 0 class described, wherein remotely located dynamic speakers are utilized in connection with the system and wherein the said objectionable features of the systems heretofore used may a supplied from the central station and simultaneously transmitted over the same conductors.

It is a further object to provide a multiprogram system of the class above described, wherein any one of a number of sources of sound carr ing current may be selected by a person at t e remote location of the dynamic oud speaker by means of a controlling circuit and a selective switching device which is located at a point convenient to the central station and wherein the sound-carrying currents, the current for energizing the field coil of the dynamic speaker and the current for remotely controlling the selective switch ing device are all transmitted from the central station by a single pair of conductors.

Another object is to provide a system of the type described, in the preceding paragraph,

wherein a momentary operation 'of a device for changing the magnitude of the current flowing in the said controlling circuit for 0 rating the selective switching device will simultaneously effect the complete or partial de-energization of the field coil of the dynamic speaker and the actuation of the selective switching device to connect a different source of sound-carrying current with the dynamic speaker.

These and other objects and advantages of the invention will be fully set forth in the following description made in connection with the accompanying drawing, wherein reference characters are applied to the several parts andwherein an embodiment of our system is diagrammatically shown, the elements and apparatus above the dotted line XX being located at the central station and g aevaoea the elements below said dotted line being located at a remote point, such as a subscribers home.

As schematically shown in the drawing, three different sources of sound-carrying currents are available at the output terminals of three amplifiers A A andA located at the central station. These amplifiers may be secondary amplifiers of an amplifying system (not shown) and the sources of said sound-carryin currents may be derived from the outputs o microphones, electrical phonogra hs or an other suitable source. The amplifiers A 2 and A may serve a multiplicity of distantly located dynamic speakers, as indicated in the drawing and for each dynamic speaker or subscribers station a suitable selective switching device B is provided, located at the central station or if desired at some point convenient to the central station and to a number of subscribers homes. The selective switching device utilized may be of any suitable type where a momentary change of the magnitude of a 25 controlling current will progress or step over the moving element of the switching evlce,

and wherein the momentary change in magnitude of said current may be controlledat the distantly located loud speaker. An en- 30 tirely satisfactory selective switching device is disclosed in our co-pending application for U. Ei. Letters Patent entitled Selective multiprogram system for distribution of soundcarrying currents, S. N. 449,271, filed May 2nd, 1930.

A pair of conductors 7 and 8 extend between the central station and the distantly located dynamic speaker for transmitting sound-carrying currents and other currents necessary for operating the system, as will hereinafter be more fully set forth. These conductors may constitute a air of wires in a =::onv'entional telephone ca le.

The output terminals of amplifiers A A and A are connected with the conductors 7 and 8 through the contacts of the selective switching device B and through condensers 2 and 3, said condensers preventing flow of direct current though the output trans 50 formers of the amplifiers. As illustrated, the

selective switching device includes a stepping magnet provided with the usual magnetic coils 5 and 6 and operating a spring actuated armature bar Y which is equipped 55 with a pawl P engaging a ratchet R for progressively rotating the selective switch control shaft S. A battery or other source of direct current is connected to the conductors 7 and 8, through the two stepping magnet coils and 6. The high reactance of said magnet coils prevents the flow oi: audio frequency current through the batterv 1. In the type of tivc switching din illustrated, each ill the controlling circuit through the coils i tle eoergized or partially ole-energized, the spring actuated armature bar Y will move from left to right causing a different source of sound-carrying current to be connected with the conductors 7 and 8.

At the subscribers home or location of the dynamic speaker, which is indicated as an entirety by the letter E, a coupling transformer C consisting of three separate coils 9, lO'and 11 is wound on a single core D. One terminal of coil 9 is connected to conductor 7 and the other terminal of coil 9 is connected to one terminal of a condenser 12. The other terminal of condenser 12 is connected to one terminal of coil 11 and the other terminal of coil 11 is connected to the conductor 8. The two terminals of condenser 12 are also. connected respectively to the two terminals of the field coil 15 of a dynamic loud speaker E, and the contacts of a key or push button 13 are connected in series with one of the conductors used in making the above described connection between the condenser and field coil. The key or push button 13 is preferably of a type in which thecontacts are normally held in the closed position by a spring and open only momentarily while the key or push button is depressed. The two terminals of the coil 10 of coupling transformer C are connected respectively to the two ends of the resistance element 14 of a volume control potentiometer. One end of the above mentioned resistance element 14 and the movable contact 14a of the volume control potentiometer are connected respectively to the two terminals of the voice coil 16 of dynamic speaker E.

Operation In operation, sound carrying current will follow a circuit starting from one of the output terminals of one of the amplifiers A A and A and continuing through the appropri ate connected contacts of the selective switching device 13 through condenser 2, conductor 7, through coil 9 of the coupling transformer at the location of the dynamic speaker, through condenser 12, through coil 11 of the coupling transformer and back to the amplifier through conductor 8, and the appropriate connected contacts of the selective switching device B. Sound carrying current tendint, to fiow through the condenser 12 at the subscribers station or location of the dynamic speaker will not be diverted through the key 13 and field coil 15 due to the high inductive-reactance of said field coil. Audio frequency or sound-carrying current flowing in the coils 9 and 11 of coupling transformer C, due to transformer action, will set up a substantially similar sound carrying current flowing in the closed circuit, which includes the two terminals of the secondary coupling transformer coil 10, this circuit being formed by the resistance element 14 of the volume control. potentiometer and the conductors connecting the volume control potentiometer to the secondary winding 10 of the transformer.

Sound-carrying currentflowing in the resistance element 14 of the volume control causes an audio frequency potential to exist between the two ends of the resistance element. All or a part of this potential depending upon the position of the movable contact 14a of the potentiometer, is impressed upon a circuit comprising the voice coil 16 of the dynamic loud speaker E and the sound-carrying current flowing through said voice .coil 16 of the dynamic speaker has substantially the same wave formand characteristics as the sourd-carrying current delivered by the amplifier A. .The field coil of the dynamic speaker is energized by direct current transmitted from the central station over the cable pair of conductors 7 and Sin the following manner:

Current flows from the positive terminal of battery 4 and continues through coil 6 of the stepping magnet through conductor 7 of the cable pair to the location of the speaker, through coil 9 of the coupling transformer C through the contacts of key 13 to one end of the field coil 15 and through the field coil and coil 11 ofthe coupling transformer and back over the conductor 8 of the cable pair and through coil 5 of the stepping magnet, back to the negative terminal of battery 4. It will be obvious that the direct current delivered to the field coil 15 cannot be diverted through condenser 12 which is associated with the coupling transformer C. It will also be obvious that the said direct current for energizing the field coil will have no effect upon the sound-carrying circuit fed from coil 10 of the coupling transformer.

In the embodiment of the invention illustrated, it will be seen that the function of the key or push button 13 is to momentarily interrupt when depressed, the flow of direct current through the stepping magnet of the selective switching device, thereby causing the switching device to step over to a new connection for connecting a different source of sound-carrying current with the cable pair 7 and 8 and simultaneously de-energize the field coil 15 of the dynamic speaker, thereby eliminating at the location of the speaker, undesirable clicks or sounds during the operation of the selective switching device. It will be seen that with the type of selective device illustrated, when the entering circuit is opened or the magnitude of currents flowing therein considerably reduced, the armature bar of the stepping magnet, due to the spring, will move away from the magnet progressing the rotative actuating element of the switching device one step.

It will further be seen that the coupling I transformer in combination with the connamely that of impedance matching transformer. The transformer windings" preferably have such a ratio that the impedance loo ing into the primary of the coupling transformer C from the line will be precisely that into which the amplifier is designed to operate. a

With our system, all sound-carrying currents and direct currents for energizing the field coil and the dynamic speaker, as well as for operating the selective switching device are conveniently supplied from the central station over a single pair of conductors, which conveniently may be a cable pair disposed in a conventional communication cable. Amplifiers at the locations of the dynamic speakers are dispensed with and the necessity for lighting and power supply circuits at the subscribers homes to energize the speaker and/or to control the selective switching mechanism, including the use of rectifiers, transformers or batteries 1' s obviated. The central ofiice or company supplying the program service, with our system, furnishes all currents for operating the system and, the charge made to subscribers will include the entire subscribers expense, whereas formerly with dynamic speakers at the subscribers home, the subscriber had to pay for the current necessary to operate his amplifier and energize the field coil in addition to the service charges made by the company supplying the program service.

It will, of course, be understood that various changes may be made in the form, details, arrangement and proportions of the parts without departing from the scone of our invention, which, generally stated, consists in a device capable. of carrying out the objects above set forth, in the novel parts and combinations of parts disclosed and defined in the appended claims.

What is claimed is 2- 1. In a system for transm tting sound-carrying current, a central station, a distantly located dynam c loud speaker having a. field coil and a voice coil, a number of sources of sound-carrying currents available at said central station, amplifiers for each of said sources of sound-carrying current, a selective uni-directionally progressive switching device located at a point convenient to said central'station and having a series of switch unitseach connected with one of said sources of sound-carrying current, a pair of conductors extending between said central station and said dynamic loud speaker, a source of direct current at said central station connected with said conductors for supplying current for energizing the field coil of said distantly located dynamic loud speaker, and for also magnetically operating said selective switching device, said same pair of conductors transmitting sound-carrying currents from said central station to said distantly located dynamic speaker,

2. In a system for transmitting sound-carrying current, a central station, a distantly located dynamic loud speaker having a field coil and a voice coil, a number of sources of sound-carrying currents available at said central station, amplifiers for each of said sources of sound-carrying current, a selective uni-directionally progressive switching device located at a point convenient to said central station and having a series of switch units each connected with one of said sources of sound-carrying current, a pair of conductors extending between said central station and said dynamic loud speaker, a source of direct current at said central station connected with said conductors for supplying current for energizing the field coil of said distantly located dynamic speaker and for also magnetically operating said selective switching device, said same pair of conductors transmitting sound-carrying currents from said central station to said distantly located dynamic speaker, and means at the location of said dynamic speaker for momentarily changing the magnitude of the controlling current for said selective switching device and to simultaneously at least partially de-ene-rgize said field coil of the dynamic speaker.

3. In a system for transmitting sound-carrying current, a central station having available a number of sources of sound-carrying currents, a distantly located dynamic loud speaker having a field coil and a voice coil, :1 selective uni-directionally progressive switching device located at a point convenient to said central station and having a series of switch units each connected with one of said sources of sound-carrying current, a pair of conductors extending between said central station and said dynamic speaker, a source of direct current available at said central station and connected with said conductors for supplying current for energizing the field coil of said distant dynamic speaker and for also magnetically operating said selective switching device, said same pair of conductors transmitting sound-carrying currents from said sources to said distantly located dynamic speaker and means at the location of said dynamic speaker for momentarily changing the magnitude of the controlling current for said selective switching device.

4. In a system for transmitting sound-carrying current, a central station having available a number of sources of sound-carrying currents, a distantly located dynamic loud speaker having a field coil and a voice coil,

an electro-magnetically operated selective switching device, the moving element of which moves a predetermined distance each time the current through the magnetic element is momentarily interrupted, said switching device being located at a point c0nvenient to said central station and having a series of switch units each connected with one of said sources of sound-carrying current, a pair of conductors extending between said central station and said dynamic speaker, a source of direct current available at said central station and connected with said conductors for supplying current for energizing the field coil of said distant dynamic speaker and for also magnetically operating said selective switching device, said same pair of conductors transmitting soundcarrying currents from said sources to said distantly located dynamic speaker, and means at the location of said dynamic speaker for momentarily interrupting the controlling current for said selective switching device.

In testimony whereof we afiiX our signatures.

LAWRENCE O. PAINTER. HOWARD L. JOHNSON.

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