US1884327A

US1884327A - Electrical apparatus

Info

Publication number: US1884327A
Application number: US242309A
Authority: US
Inventors: Spencer Percy Le Baron
Original assignee: Individual
Current assignee: Individual
Priority date: 1927-12-24
Filing date: 1927-12-24
Publication date: 1932-10-25
Anticipated expiration: 1949-10-25

Description

Filed Dec. 24. 1927 2 Sheets-Sheet 1 Fay. Z

INVENTOR. dqgrcy 4e B 1' M 1932- P. LE B. SPENCER ELECTRICAL APPARATUS Filed Dec. 24, 1927 2 Sheets-Sheet 2 Fly 2 IN V EN TOR. @1213; Le a/w- Sher Patented Oct. 25, 1932 PERCY LE BARON SPENCER, OI MEDFOBD, MASS AGEU'SETTB ELECTRICAL APPARATUS Application filed December 24, 1827. Serial No. 242,309.

The present invention relates to electrodynamic loud speakers and in particular to loud speakers in which the diaphra m or radiating element is moved by the e ectric forces created in the electrodynamic mechanism in both forward and reverse directions without the intervention of restoring forces supplied by springs or the like.

Loud speakers having electrodynamic driv- .ing or operating mechanism are known in the art. One kind of loud speaker of this type has an electrodynamic drive comprising a ma etic field set up between two concentric cylmdrical magnets in which is situated a cylindrical coil carrying the alternating or speech current. When the current in the alternating coil is in one direction the coil moves one way and when the current is in the oppo site direction the coil moves in the reverse 2 direction. This device while successfully used has certain objections. The coil must furnish the mechanical force to move the sound radiating member and must therefore be strong enough to withstand the mechanical g vibrations and still keep together. It must also be stiff enough to have practically no frictional mechanical losses. In addition to this to allow sufficient room for the coil to move up and down without coming in contact with the cylindrical pole pieces, the air gap must be wider than the coil whichapprecia 1y builds up the field current necessary to energize the air gap.

Another type of electrodynamic drive which may be employed in loud speakers is somewhat similar to that described above. In this type of drive the speech or alternating current is not conducted directly to a moving coil but is induced therein by means of a transformer. In some drives of this type both primary and secondary of the transformer are in the magnetic field, the primary being stationary however, and the secondary moveable and operating the sound radiating member. Where the primary and secondary are in the magnetic field a larger air gap is required when both the primary and secondary are situated therein than in the type Just previously mentioned. The advantage of 50 placing both primary and secondary in the air gap of the magnetic field-is reatest where a magnetic circuit is employe having two coaxial cylindrical air gaps. In this case the primary can be wound upon the core in opposite directions in order to do away with induc tive effects in the electric circuit and the secondary will therefore have current induced in opposite directions in both halves thereof. As has been pointed out above however, this system has its disadvantages in that the air gap is large necessitating both greater excitation in the direct current field and in the movin coil than is uite often desirable.

n the present invention all these difliculties have been overcome by the construction of the secondary of the transformer or the moving element in such a manner that there is no need of placing the primary in the magnetic field of the electrodynamic system of the loud speaker, but on the other hand, it can be entirely removed therefrom. In addition to this the construction of the secondary is such that in itself it is practically noninductive and furnishes therefore no out of place component which cuts down the efficiency and capacity of the loud speaker in addition to causing distortion because of different reactances at different frequencies. These advantages and other features and objects of the present invention will be explained more fully in the description of the embodiment shown in the annexed drawings, in which:

Figure 1 shows a sectional view through the center of the speaker.

Figure 2 shows a detail of an element of the speaker.

Figure 3 shows the element shown in Figure 2 after construction. 7

Figure 4 shows an end view of Figure 3 and Figure 5 shows a further detail.

In Figure 1, 1 and 3 are cylindrical soft iron pieces machined or pressed to the shape indicated in the drawings so that any section through them in the manner indicated in Figure 1 form a U shaped magnet 26 with the

pole faces

22 and 23 as close together as the construction will ordinarily allow. The

pieces

1 and 3 have

broad flanges

24 and 25 to provide a large surface area in order that the reluctance of the magnetic path across it .100

will be as low as possible and also to provide a large clamping surface for the machine screws 4 to hold the two halves of the magnet securely together and to the frame or case 5.

The magnet 26 is constructed in this manner so that the coil 2 may be prewound and placed within the space between the two arms of the magnet which are then clamped together. JVithin the cylindrical opening, left open by the

poles

22 and 23 of the magnet 26, is situated a copper, silver, or other kind of conducting element 27, which will be accurately described later, and within this conducting element 27 is a soft iron core 28. The soft iron core 28 is held in place by a non magnetic and preferably non conductive plate 29 through the centre of which passes a stud or bolt 30, supporting the core 28 firmly in place.

The path of the direct current flux obtained by direct current excitation of the coil 2 is, let us say, from the north pole 22 across the air gap adjacent thereto across the conducting element 27 to the core 28 and back in reverse direction to the south pole 23. In the upper air gap 31 the flux flows towards the core and in the lower air gap 32 the flux away from the core. If therefore the current is made to move in the conducting element in the upper part in one direction and in the lower part in the opposite direction, the forces acting on the conducting element Wlll make it move in the same direction.

The conducting element is shown alone in Figure 3 and comprises a flat rectangular portion 33 connected to a neck conducting element 16 which is connected to a circular lower portion 34 divided into two parts by the opening 36. Through the opening 35 1s placed a laminated iron core shown as 18 in Figure 1. The current induced in the winding 33 which in the present case is a single turn but may be more in other cases, flows through one side of the neck 16 to the upper part of the circular ortion 34, artly around this portion an then to t e lower ortion, and around this when it returns bac to the rest of the upper portion and to the other side of the conducting neck 16. The direction of the current in one instance is shown b the arrows 37 from which it will be note that the current in the u per part of the circular portion 34 always ows in the opposite direction from the lower portion.

A development of the conducting element is shown in Figure 2 from which it will be noted that it is stamped out of a single piece of material in flat form and comprises simply the two

flat portions

33 and 34 joined by a fiat neck 16. It should also be noted that a. T shaped slot 38 is provided running from the open center 35. This T slot forms the opening between the opposite halves of the neck 16 and the opening 36 of Figure 3.

As will be noted from above, due to the half of the circularportion 34 provides withv out the need of a primary in the magnetic field, the necessary polarity of current in the oppositely flowing magnetic fields of the two air gaps to produce forces driving the conductor in the same direction.

At one end of the conducting element, are the fingers 39 to which is fastened firmly the sound radiating element 21 by shellac or other suitable means. The radiating element in the present case is a cone, at the edge of which is fastened a soft leather or chamois strip which lays over the edge or flange 19 of the case 5. Across and within the neck of the cone is a fiat disc 40 which is firmly attached at its edges to the Wall of the cone.

Through the center of this disc passes the stud or bolt 30 which has already been mentioned above. The cone 21 is freely supported by means of the flexible edge 20 and the bolt 30 through the paper disc 40, so that whatever position the cone is placed in by motion of the conducting element, no restoring force is exerted in opposition and therefore no resonance effect due to the period of such a restoring force as for instance from the use of springs is present in the device.

Instead of the present method of support, the cone may be suspended b cords at various points or the cone may be entirely free and the conducting element suspended by flexible cords from the fingers 39 and from the neck 16. Either or any method of suspension may be used which will not hamper the free motion of the moving element.

The transformer for the conducting element is contained entirely within the unit and is supported by the brace 41 held fast to the magnet 26 by the screws 42.

The primary of the transformer consists of a w1nding 17 having a great number of turns and the secondary element already discussed. Both of these windings have a common closed core 18- The speech current is conducted to the winding 17 by means of the

leads

12 and 15 which connect with the connecting

studs

8 and 11 on the plate 43 of the case 7, fastened in turn by screws 6 to the magnet 1. The excitation for the direct current field is supplied by means of the

leads

13 and 14 which connect to the conducting studs 9 and 10.

The operation of the device should be obvious from the explanation and description given above. The principle of the operation conductor to move it in a direction perpendicular to the direction of the flux, one way if the current is flowing one way in the wire and the opposite way if the current is flowing oppositely in the wire.

In the present case the speech current induced in the conducting element always flows in opposite directions in the opposite halves thereof, but the flux also always flows in opposite directions across the opposite halves of the element. The forces therefore at any instant always work together. When the current flows one way the conducting element is forced in one direction and when it flows the other way it is urged in the other direction.

The commercial advantages of the present construction over the prior art, are great not only in the production of a loud speaker which will reproduce without distortion because of the elimination of varying reactance to different frequencies, but also in the pro duction of a loud speaker at a very reasonable cost because of the elimination of the primary element from the magnetic field and the elimination of careful machining to obtain a small air gap. v

The fact that a small air gap can be obtained with little difliculty also means that a highly efiicient instrument can be obtained and that a maximum response will be given for the amount of energy supplied to the apparatus. Further due to the fact that the conducting element is substantially non inductive there will be no electrical resonance effect either in the primary or secondary of the transformer or in the speaker itself. The added advantage that eddy current losses are practically eliminated without the use of a laminated core or magnet is possible because oft-he fact that the oppositelyconducting parts of the conducting element always make the varying magnetic forces in the magnetic circuit zero. The magnetizing force in the core due to the upper half of the conducting element is always compensated completely and accurately by the magnetizing force due to the lower half of the conducting element. This is possible because of the noninductive character of the moving element.

The above description and drawings show one form of my invention. I do not wish to limit my invention however to this form only for the invention may take other embodiments substantially equivalent and operating in the same manner as the embodiment above described.

Having now described my invention, I claim 1. A loud speaker comprising a core of magnetizable material, outer surrounding pole pieces and means for setting up magnetic fields between said core and said pole pieces, the flux in adjacent fields flowing to and. from the core, a conductive member having elements substantially surrounding said core but not completing a conductive turn about the same, the elements being situated in adjacent fields and the current flowing in oppofields, current conductive means positioned in said magnetic field and having conductive elements substantially surrounding but turned back upon themselves in such a fashion that there is no inductive effect with said core itself, the current in said elements in adjacent fields flowing in opposite directions, a sound radiating member attached at one end of said conductive member and means for conducting speech current to said conducting member.

3. A loud speaker comprising a core of magnetizable material, a shell shaped magnet surrounding said core and forming a plurality of magnetic air gaps between said core and shell, current conductive means positioned in said air gaps and substantially surrounding but turned back upon itself in such a fashion that there is no inductive effect with said core, the current flowing in said conductive means being directed to produce additive mechanical forces, a sound radiating means attached to said conductive member and means for impressing speech current on said conductive member.

4. A loud speaker comprising electromag netic means forming circular magnetic air gaps,substantially aligned current conducting means positioned concentrically in said air gap, but not electrically linking the flux in the core which is substantially within the enclosure of the conductor, the current flowing in said conductor causing the mechanical forces to add a sound radiating member attached to said conductor and means for impressing speech current on said conductor.

5. In an electrodynamic loud speaker acurrent conducting element having at least one turn with its longer sides disposed parallel to each other and formed to have each side make substantially, but not completely, a closed loop.

6. An electrodynamic loud speaker, comprising clectromagnetic means having a central core, a plurality of magnetic members surrounding but spaced from said core, forming a plurality of air gaps therebetween, a current conducting member having at least one completed turn with longer sides disposed parallel to each other and formed to have each said si de make substantially,but not completely, a closed loop fitting in said air gaps, a sound radiatin element connected to said conducting mem er and means to impress current upon said conducting member.

7. An electrodynamic loud speaker com- 5 prising electrodynamic means forming a plurality of aligned circular air gaps, a current conducting member having at least one completed turn, including two long sides disposed parallel to each other and formed to have each side make substantially but not com-. pletely a circle, located in separate air gaps. a sound radiating element connected to said conducting member and means to impress current upon said conducting member. 8. In an electrodynamic loud speaker a cur rent conducting element formed of a flat piece of conducting material of substantially T shape and having stamped out from within a substantially similar T shaped figure form-- ing a continuous conducting loop about the margin of the inner T, the top of said T being formed to make a substantially, but not completely closed loop.

9. In an electrodynamic loud speaker, a current conducting element forming a closed turn having two substantially parallel long sides, said long sides being formed in a substantially but not completely closed circle.

10. In an electrodynamic loud speaker a current conducting element forming a closed turn having two substantially parallel long sides, said long sides being formed in a substantially but not completely closed circle, a plurality of fingers rovided on one of said "3 long sides, and a radiating element mounted against said fingers.

PERCY LE BARON SPENCER.