US2328836A - Loud-speaker and circuit therefor - Google Patents

Description

. INVENTOR; :c/OHN u. MoY /IHAM BY 1 ATTORNEYJ.

2 Sheets-Sheet 1 Filed Feb. 17, 1942 J J MOYNIHAN LOUD SPEAKER AND CIRCUIT THEREFOR BIAS FOE.

B. E, 05 7'5: TOE AND x4146. TUBES PMTE VOLTAGE Foe B. F. T0555 Sept. 7, 1943.

I: l I i {70 I I E l l I l i I I Patented Sept. 7, 1943 UNITED i STATES PATENT OFFICE LOUD-SPEAKER fi firtcm'r msnnron I .John J. Moynihan, Boston, Mass, assignor of one-half to Joseph B. Brennan, Euclid, Ohio Application February 17, 1942, Serial No. 431,258

, 11 Claims.

This invention relates to loud Speakers and circuits therefor, and more particularly to the type of loud speaker used in conjunction with 1 ordinary radio receivers or public addressamplifiers wherein the energy for the operation of the speakers is derived. from vacuum tube amplifier's and the like.

' According to the'usual practice in the art, such loud speakers ordinarily include a. diaphragm, usually in the form of a cone, for emitting the sound, the diaphragm having attached to it' a voice coil which ordinarily consists of a number of turnsof fine wire and which carries a voice current corresponding to the sound to be reproduced.- The. voice coil is located in a ma neticfield, the coil ordinarily being positioned in an air gap in an iron core. An exciting coil may be employed to provide a strong field at the region in which the voice coil'is located. The

alternating current flowing in the voice coil former. This eliminates the direct current component of the platewcurrent from the voicecoil of the speaker and makes it possible more effeccircuit therefor wherein the above mentioned difficulties are eliminated. Another object is to provide a loudspeaker and circuit therefor wherein the necessity of employing a separate output transformer is done away with. A further objectis to provide a simple loud speaker which requires no leads for the voice coil and by the loud speaker field coil can act as a filter in an impedance-coupled amplifier.

tively to match the impedance of the plate circuit of the output rt ube with the impedance of the voice coil of the; speaker. The system' has several disadvantages amongwhich may be listed the following: the magnetic circuit of the output transformer is bia'sed by the presence of direct current in-the primary=.winding, and if this primary current is sumciently large, core saturation and, consequently, distortion of the wave form of the voice currents will take place in the 'of the same type and may be variable from time to time in any individual speaker as the leads occupy different positions; the-field of the speaker is supplied with D. C. excitation which constitutes a power loadon the rectifier-filter circuit of the receiver.

choke-for the power supply or rectifier system of the receiver or amplifier. to provide a circuit and the loud speaker for use therein wherein the loud speaker is provided with field coils which may be used as impedances Another object is to provide loud speakers or sound tranducers in which the response characteristics can be readily varied to suit particular requirements. 1

Further objects and advantages of 'my'invention become apparent, from the following de-- 'scription of various preferred forms thereof,

A further object is reference being made to the accompanying drawings in which Figure 1 diagrammatically illustrates a loud speaker made according to my invention, in conjunction with a typical amplifier circuit modified in accordance with my invention; Figures 2, 3, 4, 5 and 6 diagrammatically illustrate modified forms of loud speakers suitable for use in circuits such as the circuit of Figure 1; Figure '7 diagrammatically illustrates an impedance-coupled amplifier embodying a It is'accordingly a general object of the pres-i ent'invention to provide a loud speaker and a loud speaker and Briefiy, according'to'in my invention, I elimihate the need fora separately excited voice coil by inducing the voice currents in a short circuited voice coil or other conductor, which does not have any leads connected thereto. With such an arrangement, the output of the amplifier or receiver,- instead of being connected to the speaker through an output transformer is connected directly to the field coil of the loud speaker. The direct current component of the output plate current furnishes the strong electromagnetic field for the speakerwhile the voice current component results in the inducing of a similar voice current in a conductor carried by the diaphragm and positioned in the field. The

voice current so induced causes the conductor to vibrate in the magneticfield produced by the di- -put tube'i'i consists of two components, one" a.

such a condition rect current component of the output current. This vibration is transmitted to the speaker diaphragm, resulting in the production of sound.

In Figure 1 of the drawings, I have illustrated my invention as applied to a typical radio receiver. In the drawings I have omitted the units of the receiver in advance of the audio frequency amplifier and output stages, which may be conventional. The portion of the circuit illustrated includes the rectifier and filter units indicatedgenerally at ID; the volume control network H; the audio frequency amplifier stage ii; the output stage M; the tone control network ..|5;.and the loudspeaker Hi. The wiring diagram illustrated is conventional except for specific features which will be described in detail below. The values of the various resistances, .inductances and capacitances may readily be determined by those skilled in-the radio art.

It will be noted that the conventional output transformer is absent from this diagram. In-

stead, the plate current-of the output tube H is conducted directly to the coil |8 of the loud speaker Hi. This coil is wound upon a core l9, preferably laminated in order to reduce the effect of eddy currents, and having an air gap 20 in which the voice coil 2| is positioned. The voice coil 2|, which may consist of a single turn, is mounted upon an extension 22 connected to the conical diaphragm 23. The diaphragm may besupported in conventional manner by flexible spiders or supports 24 and 25 mounted in a suitable framework (not shown). V As noted above, the plate current of the outdirect current component the value of which is determined by the design of the output tube and the voltage applied to its plate, and the other an alternating current signal or voice current which is afunction of the signal or sound being reproduced. The direct current component of the output flowing through the coil I8 excites the core or field structure |9, producing a magnetic field or fiux in the air gap 20. The alternating current component or voice current causes a voice 45 current to be induced in coil 2| proportional to the voice current flowing through the coil l8. In this respect coil 2| may be considered'as the secondary of a transformer of which coil I8 is 20 where the magnetic flux is relatively large, the induced currents flowing in coil 2| cause it to move at any given instant in a direction and with a force determined by the instantaneous direction and value of the current flowingirl the coil 2|. Thus, the motion of coil 2|}corresponds to the voice current comp0nent-of the plate circuit of the output tube i1, and. this motion is trans- ;mitted to diaphragm 23 and radiated into the air as sound as in an ordinary speaker.

In some instances and with some circuits the direct current component of the plate circuit of the output tube may be insufficient to provide the desired magnetic -fiux in the gap 20. When may be wound on the field structure Hi. This coil may be either connected across the direct current power supply or, as shown in the drawg, in series in the filter circuit where it acts as a choke, just as in conventional arrangements 70 shading coil 35, thus producing a non-symmetrithe speaker field may be used as a filter choke.

InFigure 2 I have illustrated a modified arrangement of a loud speaker adapted to be ineluded in a circuit such as that shown in Figure shown in Figure l.

exists,- an additional coil 26 6 is provided' with additional magnetic material the voice coil, the voic coil being connected to' the diaphragm by spaced struts or leg 29 disposed on either side of the pole piece of the core l9a. Except for these changes the structure shown may be identical with that described with reference to Figure l.

In Figure 3 another modified form of speaker is shown. Here the field structure |9b may be identical with that described with reference to Figure 1, but the voice coil 2|b is a short-circuited multi-turn coil instead of the single turn the field coil to provide the optimum number of ampere-turns. Also with this type of coil different response characteristics can be obtained. For

example, if rthecoil is wound with wire composed of a material having a high temperature coefii- The coil may be designed with reference to the output of the amplifier and cient of resistivity, such as iron, the resistance of" the coil will increase as it is heated by currents induced therein. Thus an increase in input to such a device does not result in an as great an increase in output, because of the effect of the increased resistance. Such a coil thus acts to contract the range of value of current fiowing in the coil and of volume of sound reproduced.

The response characteristics can also be varied in other ways. be provided in the voice coil circuit, the impedance preferably being carried. by the diaphragm or voice coil support. Thus if the coil current has a relatively large inductance, the response of the speaker to the higher frequencies will be lessened while the response to lower fre- Iquencies will be afiected to a smaller extent, if

For example, an impedance mayat all Likewise, if the coil is provided with a 1 nected in series with a condenser 30, the conthe primary. As coil 2| is located in the air gap the diaphragm 230 so as to avoid the necessity denser also being supported for movement with \to the coil N3 of Figure 1 and towhlch the output current of the output tube of the amplifier may be supplied. Here, however, instead of usplate 33 is employed. The flat plate being in the magnetic field created by the direct current and the alternating current signal components ing one or more turns as the voice coil, the fiat of the output current will have eddy currents induced in it in the directions shown by the arrows, corresponding to the signal currents supplied to the coil 32. The field in the neighbora hood of the pole 3A is distorted by means of a cal field in the path of th induced eddy currents in the plate. The eddy currents act in the nonsymmetrical field to reciprocate the plate $3 in 1. In this modification the field structure Mia directions parallel to its longitudinal axis and with the reciprocations or vibrations proportional to the signal current supplied to the coil 32. The

I made directly to the apex of the conical dia-.- phragm 36 which is supported in any suitable frame-work by supporting spiders 3'l and 33.

In order to create the non-symmetrical relatlonship necessary for the'motion of the plate, the arrangement shown; in Figure 6 may be alternately used. In this arrangement a hole 39 is cut in the plate 33a so that the currents induced in the plate in the neighborhood ofthe pole 34a will be at any giveninstant preponderantly in the same direction.

My speakers, in which both alternating and direct current components are applied to the speaker field may be used effectively with amplifiers of types different from that shown-in Figure 1. Thus, for some purposes impedancecoupled amplifiers are advantageous in that lower plate voltages and higher plate currents can be used in the various amplifying stages. However, heretofore the cost of such amplifiers has been considered practically prohibitive and they have not come into any-extensive use. ,By my inventionimpedance coupled amplifiers can be constructed at low cost'by utilizing coilswound on the field structure of the loud s aker as the impedances. Such an arrang ent is shown in Figure '7 in conjunction with a three stage, impedance-coupled amplifier; embodying a conventional circuit except. for the features noted below. The arrangement of the diaphragm and voice coil is substantially identical with that described in conjunction with Figure 1, the same reference characters being applied to corresponding parts, but the field structure .40 vnot only has a coil 4| carrying the output cur matically in the drawing so that the direct cur-" rent components of the currents flowing into the coils 43 and 44 aid in the production of the desired magnetic field in which the voice coil 2Id operates. The connections are also such that the impedances of coils 32 and 33 to alternating voice currents are not neutralized by the interaction of the coils on the common core. This type of arrangement is advantageous in that a.

relatively high impedance, can be provided in the plate circuitof each amplifier stage while the direct current resistance in the amplifier stages 4 is relatively low. Thus it is possible to impress a higher percentage of the direct current power supply on the plate circuit of each tube, and this direct current may also be utilized to assist in energizing the speaker field.

From the foregoing description of various forms of my invention it will be evident that I have provided a loud speaker and circuit therefor whereby a speaker of the electro-dynamic type may be employed without any leads for moving conductor for the voice currents, with the result that the structure is simplified and the cost is reduced. As the friction load on the speaker occasioned by the leads to the voice coil-is eliminated, the efilciency and response characteristicsjof the speaker may be improved. The response characteristics may be varied to produce the desired 'efiects. Further, by em- ,ploying circuits according to my invention the output transformer ordinarily employed in amplifiers may be eliminated, the field structure and coil of'the speaker' serving the function of the output transformer. Also, with my invention.the field structure may be wound with an additional coil constituting a filter-choke and if desired my speakers may be employed in imdance-coupled amplifiers using coils wound on the field structures of the speakers as the impedances for the coupling. 'In'all of these arrangements there is a net'saving in'the power required to operate the amplifier, for the direct current component of the output tube, which is ordinarily wasted as heat, is employed to create the field in which the voice coil operates. A

further important saving is. made-in the "elim ination of the output transformer and in conjunction with the impedance-coupled amplifiers,

the very material saving in eliminating the sep'-.

arate impedances ordinarily employed in am-. plifiers of this type.

Those skilled in the art. will appreciate that ,various changes and modifications 'may be made in my invention without departing from the spirit and scope thereof. Forexample, features structure, and a short-circuited cylindrical voice coil situated in said air gap, said exciting coil being energized by a current having an alter- 5 nating component superimposed on a direct component, said voice coil having an alternating V current induced therein functional of the alternating component of the exciting current, and said voice coil being mounted so as to vibrate in said air. gap due to the interaction of the fiux in said air gap and the current in said voice coil. 2. A loud speaker including'in combination a ferro-magnetic field structure having an air gap,

an exciting coil for magnetizing said field structure, and a short circuited voice coil situated in said air gap, said exciting coil being energized by a current having an alternating component superimposed on a direct component, said voice coil having an alternating current induced therein functional of the alternating component of the exciting current, said voice coil being mounted so as to vibrate in said air gappdue to the interaction of the direct current flux in said air gap and the current in said voice coil, and means for increasing the alternating current fluxthreading said voice coil comprising ferromagnetic material in said field structure extending in parallel to said air gap adjacent said voice-coil.

3. A loudspeaker including in combination a ferro-magnetic field structure having an air gap, an exciting coil for magnetizing said field struc- .ture, a sound reproducing diaphragm, a short circuited voice coil supported by said diaphragm the fiux in said air gap and the current in said voice coil.

4. A loud speaker including in combination a ferro magnetic field structure having an air gap, an exciting coil for magnetizing said field structure, a sound reproducing diaphragm, a short circuited voice coil supported by said diaphragm and situated in said air gap, said voice coil being composed of material having a high thermal coefiic'ient of resistivity, said exciting coil being energized joy a current having an alternating component superimposed a direct component, said voice coil having an alternating current induced therein functional of the alternating component of the exciting current, and said voice cell being. mounted so as to vibrate insaid airgap due to the interaction of the fiux in said air gap and the current in said voice coil.

5. An electro-acoustic transducer comprising a field structure having an air'gap, means for producing a magnetic field across said air gap, a diaphragm, a voice-coil mechanically connected to said diaphragm and disposed in said air gap,

said voice coil beingcomposed of mat'erial having a 'highthermal ,coefiicient of resistivity.

6. In combination with an electronic amplifier of the type producing an output currentcontaining a direct current component and an alternating signal current, a loud speaker including a ferro-magnetic field structure having anair gap, an exciting coil for magnetizing said field structure, and a short-circuited voice coil situated in said air gap, said exciting coil being energized by the output current of said amplifier, said voice coil having an alternating current induced therein functional :of the alternating component of said output current and said voice coil being mounted sofas to vibrate in said air gap due to the interaction of the fiux in said air gap and the current in said voice coil.

' ,7. In combinationwith an electronic amplifier of the type producing an output current containing a direct current .component and an alter- 'nating [signal 'current component, a sound reproducer comprising. a field coil connected in the output circuit of the amplifier, a soundreproducing diaphragm, a conductive member mechanically connected to said diaphragm and disposed in the magnetic field created by said coil,

rent is induced in said conductive member and said induced current flowing in said conductive member disposed in the said field created by the direct'current component of said output current causes said member to move in directions and with forces depending upon the direction and intensity of said signal current.

8. A loud speaker comprising a field structure having an air gap, means associated with said field structure for producing a magnetic 'field across said air gap having a direct current component and having a component varying in accordance with a sound to be reproduced, a shortcircuited voice coil positioned in said field where-- by voice currents corresponding to said varying component of said field are induced therein and the presence of such voice currents causes said voice coil to vibrate in accordance with the direction and magnitude thereof, and means for translating said vibrations into sound.

9. In combination with an electronic amplifier, a sound reproducer comprising a field coil cone nected in the output circuit of the amplifier, a nd reprod ing diaphragm, a conductive metallic plate mechanically connected to said dia phragm and disposed in the magnetic field created by said coil, whereby eddy currents proportional to said signal currents are induced in sai conductive member, and said member moves in directions and with forces depending upon the direction and intensity of saidsignal current. 10. In combination, an impedance coupled electronic amplifier and -a loud speaker, said loud speaker having a field structure and a voice current carrying member disposed in the field thereciting coil therefor constituting a coupling impedancefor said amplifier, a sound reproducing disposed in the magnetic field created by said coil, whereby a current proportional to said output current is induced in said conductive member, and said member moves in directions and with forces depending upon the direction and intensity of said output current. I

diaphragm, a closed circuit conductive member mechanically connected to said diaphragm and I JOHN J. MOYNIHAN.

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