US2383594A

US2383594A - Electromagnetic sound reproducer

Info

Publication number: US2383594A
Application number: US471132A
Authority: US
Inventors: Verter Walton De
Original assignee: Individual
Current assignee: Individual
Priority date: 1943-01-02
Filing date: 1943-01-02
Publication date: 1945-08-28
Anticipated expiration: 1962-08-28

Description

Aug. 28, 1945. w DE VERTER 2,383,594

ELECTROMAGNETI C SOUND REPRODUCER Filed Jan. 2, 1943 Patented Aug. 28, 1945 zssssai UNITED STATES PATENT oFjFicE fmacraomcns'r 'ffsi r xsnanraonvcm I I Ap lleat lonlzlnz'i 2,-( r;:s1,::i:iwo; 411,132.

This invention relates'to sound reproducers or loud speakers, more particularly to electrodynamic sound reproducers in which a movable dynamic or voice coil, excited with sound-representlngor voice currents, isprcvlded' for inter-' action with anintense unidirectional magnetic field, and the invention has for an-biect the provision of improved sound character.

In, the usual radio receiveror electric piano graph adapted for operation on commercial alternating current, the field producing winding of the electrodynamic sound reproducer'assoreproducers 01 this ciated with such apparatus is excited with unidirectional pulsating currentpsuch as may be obtained from the rectifier circuit utilized for supplying the plate and grid energy to the amplifier tubes or the receiver or phonograph. Thefluctuations or periodic variations of the magneticfield produced by such excitation have been found to produce, by interaction with the,

dynamic coll, an undesirably intense and annoying hum in the loud speaker.

In order to minimize or substantially eliminate this undesirable hum, it has heretofore been i proposed to provide such sound reproducersor -loud speakers with a second or bucking coil dis-' posed in the magnetic field and connected di-- rectly in series with the voice coil and the source of sound-representing or voice currents. This minimizing means in trodynamic type.

In' carrying out'the invention in one form, a

loud speakersof the eiec loud speaker is provided having" the usual field,

producing winding and a or voice coil disposed in the magnetic field and energized from a suitable source of sound-representing currents.

as to'oppose and minimizecurrents induced in the voice coil by fluctuations-in: the strength of the magnetic field. The .parallel bucking coil, which may be designed so as to carry only a small component of the sound-representing currents supplied to the voice coil, may be iormedtoi second series coil is 01' opposite polarity to the 7 voice coil, and therefore tends to produce in the voice coil voltages opposite in phase to those induced directly in the voice coil by thefiuctua- I tions of the magnetic field.

While inmost respects electrically satisfactory, .mechanical diificulties are encountered in the economic construction and proper location of such series bucking coils. Ordinarily such series coils are wound on separate forms or tubes and may be placed either over the core oi the horn Iii, a field winding ii, a dynamic or voice very fine gauge wire. and the area occupied thereby and the costs of fabrication and materials are considerably less than for the heretofore known series bucking coils. 7

- For a more complete understanding of the invention, reference should now be had to the drawingin which the single figure is a diagrammatic' representation of a sound reproducer or loud speaker embodying the present invention.

In the drawing, the invention is shown as embodied in a loud speaker comprising the usual coil i2, and a bucking coil ll. Since the magnet circuit or the sound reproducer is entirely conventional, only the electrical circuits have beenshown.

loud speaker, or inside of the field winding, or-

around the outer periphery of the field In any event, the series coil, which must carry all of the voice or sound-representing currents supplied to the dynamic, coil, must be formed of relatively heavy wire, "and thus difiiculties are introduced into fabrication and excessive costsare encountered. In addition, the heavy wire I series-coil takes up space which could otherwise be devoted to better use in constructing the loud speaker. Accordin ly. something is yet to be desired in providing compact, inexpensive and electrically satisfactory .loud speakers of this character, and it is a further object 0'! this in- Thefield winding II is connected, as shown,

to a pair of terminals M which may represent a sourceoi periodically fluctuating unidirectional current such as may be obtained from the usual rectifier circuit. .The voice coil I2 is connected to be supplied with sound-representing currents from the secondary winding II ot'a suitable transformer I, the primary winding I! of which is connected to suitable terminals II which may, 7

. ior, example, be the output terminals of an ampliiier system such as is contained'in a radio receiver or an electric phonograph. The voice coil I2 is of course disposed in the intense magnetic field produced by the winding l I, so that upon the dew oi sound-representing currents through the voice cell it, movement thereoi will be produced andthevoice-coilmaybaconnected in anysuitable manner to the diaphragm oi the-horn Ill.

small component of the voice-representing currents from the transformer winding l5 flows through the bucking coil I3.

In addition to the parallel circuits the two coils l2 and I3 constitute a local-series circuit which may be traced from one terminal of the winding l3, through the conductors l9 and 20, the coil l2, and the conductorsZl and 22, to the opposite terminal of the coil l3. The coils l2 and I3 are, as previously indicated. of opposite polarity so that the inductive effect of the magnetic fieldon these coils tends .to produce, in the two coils of the local series circuit, voltages and currents of opposite polarity. Thusthe direction of the voltages and currents induced inthe coil 13 is represented in the drawin by the'broken arrows extending about the local series circuit, while the direction oi the voltages and currents induced in the coil 12 is'represented by the solid line arrows extending about the local series circuit. v

Byproperly adjusting the locations of the respective coils l2 and Hand the electricalcharacteristics of each coil, it is possible substantially to eliminate or greatly minimize the flow of current inth'e localseries circuit due to the inductiv'e eflect of the fluctuations in the magnetic otherwise appear. in the hom ID of the loud i speaker. is reduced to a satisfactorily low value.

While I have shown a particular embodiment of my invention. it will be understood, of course, that I do not wish to be limited thereto since many modifications may be made, and I, therefore, contemplate by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention. 1

Having thus described my invention, what I claim and desire to secure by Letters Patent is:

1. In an electrodynamic sound reproducer, the combination of a field winding energized by unidirectional current to produce a magnetic field,

a source of sound representing current, a dynamic coil connected across said source and disposed in said magnetic field, and a bucking coil disposed in said field and connected across said dynamic coil in parallel relation thereto with respect to said source to form a local series circuit includin said two coils, said bucking coil and directional current to produce a magnetic field,

a source of sound representing current, a dynamic coil connected across said source and disposed in said magnetic field,'and a bucking coil disposed in said ffield and connected acros s said dynamic coil in parallel relation thereto with respect to said source tofformfa local series circuit including said two coils, said bucking coil being arranged to-produce in said local series circuit, by the inductive efiect thereon of variations'in the strengthiof said field potentials opposite in a polarity to the potentials induced in said dynamic coil by said variations.

WALTON on ,VERTER.