US2123640A - Sound translating device - Google Patents

Description

[July 12, 1938. wARNKE 2,123,640 v I scum) TRANSLATINGVDEVICE Filed April 28, 1934 I: n C r r Patented July 12,- 1938 UNITED STATES SOUND TRANSLATING DEVICE Herbert R. Warnke, Camden, N. J., assignor to Radio Corporation of America, a corporation of Delaware Application April 28, 1934, Serial No. 722,821

4 Claims.

My'invention relates to sound translating devices, and more particularly to loudspeakers of the movable coil or dynamic type having a permanent magnet field and a conical diaphragm.

In permanent'magnet dynamic speaker design with which I amfamiliar, large permanent magnet field yokes usually comprising a multiplicity of bars have often been employed. The yokes and other parts of the speaker including the center and outer pole pieces are usually held together by bolts or rivets, and these structures have lacked desirable compactness and magnetic efiiciency relative to bulk. Furthermore, as it is necessary that certain parts of the speaker be critically positioned relative to each other, it has been necessary that the holes for the bolts 01' rivets which hold the speaker together be very accurately located. This, of course, is objectionable from a manufacturing standpoint as it adds to the cost of and retards speed of production.

Also, welding has been used in assembling certain of the speaker parts. However, there are certain disadvantages in this method, namely, the structures must be subjected to heat which often causes warping and the misalignment of the parts, and forms must be employed to hold the various parts in position during the operations.

It is, accordingly, the primary object of my in-v vention to provide a permanent magnet dynamic type loudspeaker and method of assembly therefor which will be free from the defects and disadvantages of the prior art as noted in the foregoing.

A further object of my invention is to provide a permanent magnet dynamic type loudspeaker of high magnetic efliciency relative to bulk and of a substantially small dimension from front to back and,

A still'further object of my invention is to provide for a permanent magnet dynamic type loud speaker, a method of assembly for the sev' eral parts which is adaptable to speedy production yet which insures extreme accuracy in locating the parts relative to each other.

In accordance with my invention, I provide a dynamic type loudspeaker having permanent magnet field structure comprising one or more permanent U -shaped magnets.

In the structure. including one magnet, the ends or poles of the magnet are held in contact respectively with the top end of a soft iron plate constituting an outer pole piece substantially the width of the magnet and the top end of a second soft iron plate which is disposed to the 'rear of the first plate and is spaced therefrom by a nonmagnetic spacing member. Fixed to the rear plate is a soft ironcylindrical center pole piece which extends'for'ward and into a circular open.- ing in the front plate to provide an air gap for 5 the movable coil of a cone type diaphragm. To insure accurate location-of the center pole piece in the opening in the front plate, I have devised a method of assembly whereby such accuracy is obtained although liberal tolerances may be allowedin the location of holes and studs therefor which hold the partstogether.

In the embodiment of my invention which includes a plurality of U-shaped permanent magnets, the front and back plates are modified to provide contacting surfaces for the respective poles of the magnets.

Welded to the front plate is a forwardly extending housingorrframe including a flange to which the rim of a cone diaphragm is attached. An opening substantially the width and thickness of a pole of the L l-shaped magnet is provided in'the housing through which the pole extends. The opening serves to prevent horizontal displacement of the magnet relatlveto the ends of the front and back plates. and a single screw passes through the top of the magnet, extends'downward and is threaded into the spacing member to prevent vertical displacement.

The novel features which I consider character- 30 istic of my invention are set forth with particularity'in the appended claims. The invention itself, however, both as to its organization and its method of operation, together with additional objects and advantages thereof, will best be un- 35 derstood from the following description of specific embodiments, when read in connection with the accompanying drawing, in which,

Figure l is a view in perspective of a permanent magnet dynamic type loudspeaker con- 40 structed in accordance with my invention and employing a single U-shaped permanent magnet.

Fig.2 is a vertical sectional View of a loudspeaker wherein the structure shown in Figure 1 has been modified to employ a plurality of permanent U-shaped magnets.

Fig. 3 is a view partly in section and looking in the direction of the arrows on the line'33 of Fig. 2. V 50 Fig. 4 is a rear view of the back plate employed in the structure shown in Fig. 2.

Fig. 5 is a view in section illustrating a method of assembly for certain parts of my improved loudspeaker.

Fig. 6 is a sectional view taken on the line B6 of Fig. 5.

Fig. '7 is a fragmentary sectional View further illustrating the method of assembly; and.

Fig. 8 is an end view of a spacing member.

Referring, now, to the drawing wherein like numerals refer to like parts throughout, there is shown in Fig. l a dynamic type loudspeaker including permanent magnet field structure constructed in accordance with one embodiment of my invention.

A frustro-conical diaphragm I is mounted within a housing 3 and integral with the housing is a circular flange 5 to which the rim of the diaphragm is secured in any suitable manner. The housing 3, which is constructed of a light nonmagnetic metal such as aluminum, is constituted by an open frame-work in order to further reduce weight and includes top and bottom portions 1 and 9, respectively, extending rearwardly of the flange. Back strips II and I2 are integral with the top and bottom portions I and 9, respectively, and serve as places of attachment for an assembly of the speaker parts which will now be described. I

The above notedassembly comprises a plate l3 which functions as an outer pole piece, a back plate I5, a center pole piece I'I fixed to the back plate I5, and a non-magnetic spacing member I9 interposed between the two plates. upon the assembly with its two poles held in contact respectively with the top ends of the front and back plates I3 and I5 is a permanent 'U-shaped magnet 2I.' The magnet 2| may be made of cobalt steel to provide a maximum degree'of magnetic efiiciency. However, as cobalt steel is relatively expensive, in order to reduce manufacturing cost, I prefer to use chrmium steel, which is comparatively inexpensive and entirely satisfactory. The front plate I3, the back plate I5, and the center pole piece I! are preferably constructed of soft iron to provide maximum magnetic permeability. As heretofore noted, the spacing member I9 is made of a nonmagnetic material, such as a zinc alloy, for example. Thus, the magnetic flux is confined as nearly as possible to the proper path which is, of course, between the outer and center pole pieces. I

"The front plate I3, which is substantially rectangular in shape and the width of the permanent U-shaped magnet'ZI, has its top end bent over to the front at right angles to provide a surface of sufiicient area. for overall contact with an end or pole; of the U-shaped magnet 2|. Formed in the front plate I3 is a circular opening 23 of sufiicient size to allow the entrance of a voice coil 25.

Extending into and centered in the opening 23 in the front plate I3 isthe center pole piece I! which is of a smaller diameter than the opening. The space thus provided betwenthe center pole piece I1 and the Walls of the opening in the front plate I3 provides an air gap for the voice coil 25. It will be observed from the drawing that the center pole piece I? is of a reduced diameter at the rear of the air gap and that the opening in the front plate I3 is countersunk. This acts to confine the magnetic flux as nearly as possible across the air gap between the center and outer poles. A reduced cylindrical extension 21 terminates the center pole piece II at the rear and a hole is provided in the rear plate I into which the reduced extension 21 fits with its end flat- Mounted tened or riveted over to securely fix it to the plate.

The top of the back plate I5 is of substantially the same width and thickness as that of the pole of the U-shaped magnet 2| which is held in contact therewith. From the top downward, the plate I5 is of a gradually diminished width and is the shape of an inverted isosceles triangle, having its apex cut off even with the bottom edge of the center pole piece I1. The diminution in the width of the back plate I5 is such that its side edges are tangent with the periphery of the rear face of the center pole piece II. This reduces the amount ofsurface of the back plate which extends beyond the limits of the center pole piece, thus reducing flux loss between the front and back plates.

Referring now to Fig. 2, it will be seen that I may include a plurality of permanent magnets in my improved loudspeaker, thus increasing its magnetic efiiciency. In this arrangement, it will be seen that the front plate Hat and back plate I5a extend downward and terminate in ends similar to their upper ends and so provide faces against which the respective ends of a second U-shaped magnet 2 la are held in contact.

In Fig. 4, it will be noted that the back plate I5a is of a reduced width at the center where the center pole piece I I is secured and that it flares outwardly'toward the top and bottom to a width substantially that of the magnets.

From the above, it will be apparent that the plates I3 and I5 may be still further modified to accommodate more than two magnets. For example, extensions similar to those provided at the bottoms of the plates in Fig. 2 may be provided at their sides. No illustration of this is thought to be necessary, as it is apparent that the structures at the sides of the plates would be a duplication of those at the tops and bottoms.

Interposed between the front plate I3 and the back plate I5 and spaced from and located above the center pole piece I1, in the structure shown in Fig. 1, is the non-magnetic spacing member I9 which serves to hold the plates including the center pole piece in proper relationship. The ends of the spacing memberl9'abut the inside faces of the plates respectively and are accurately positioned and positively held in place in a novel manner to be presently described.

In order that the back and front plates I3 and. I5'may be securely maintained in their relative positions after assembly and the center pole piece thus centered in the opening in the front plate, it is desirable to locate the spacing member I9 as near to the center pole piece as possible. Also, the ends of the spacing member must have sufficient contact area with the inside faces of the plates. In order to accomplish this, the under side 29 of the spacing member I9 is substantially semi-cylindrical in shape, as shown in Fig. l, and is located so that it is spaced slightly away from and encircles substantially the upper half of the center pole piece I'I. 'At its bottom, the spacing member I9 extends laterally on either side of the center pole piece I1 to a width substantially that of the front plate I3, and at its top, it is substantially the width of the back plate I5. As will be seen from the drawing, this construction provides the spacing member with ample contact surface at the ends which abut the inside faces of the plates. Furthermore,it permits the member l9 to be located in a position Where it most easily maintains the front and back plates in their relative positions and thus the center pole piece properly centered in the opening in the front plate.

The method of assembling the front plate l3, back plate [5, center pole l1 and the spacing member l3 will now be described with reference to Figs. 5, 6, '7 and 8 of the drawing.

As previously noted, the rear extension 21 of the center pole piece IT is fitted into a hole in the'back plate l and its end riveted over to firmly afiix it theretc.- This is the first step in the assembly of the above mentioned parts. Studs 31 on one end and studs 33 on the opposite end are integral with the spacing member. The studs are fitted into, holes provided in the front and back plates respectively and are riveted over, thus securing and locating the plates and center pole piece in their proper relationship to each other. It will, of course, be understood that the end of the center pole piece I! must be very accurately located in the opening 23 in the front plate l3 to provide the air gap for the voice coil 25 which is located therein. It will be readily appreciated that if the studs 3i and 33 are positioned in their holes in the conveni tional manner, the holes, as well as the studs,

must be very accurately located. This is not adaptable to high speed production and entails expensive operations.

To avoidthe above noted disadvantages, I provide what I believe to be a novel method of assembly for the parts referred to, wherein liberal tolerances in drifting the holes and in locating the studs may be allowed.

The studs 35, located upon the end of the spacing member it which abuts the front plate l 3, are of conventional design as will be noted from an inspection of Fig. 6. The location of the studs in the holes in the front plate l3 and the riveting over of their ends constitutes the second step in my method of assembly and is performed in the usual manner.

In accordance with my invention, the location of the center pole piece ll, relative to the back plate l5, and the spacing member l9 relative to the front plate 53, need not be achieved with any great degree of accuracy. However, the third step in my method of assembly, which is constituted by the affixation of the back plate Hi to the spacing member l9. and consequently the positioning of the center pole piece ll in the opening in the front plate 53, must accurately locate the center pole piece as has been previously noted.

The third assembly step will now be described, reference being had to Fig. 8 of the drawing, which is a view of the end of the spacing member it which abuts the back plate l5. It will be seen that the studs 33 have base portions 35 which are hexagonal in shape and about the i height of a conventional nut of the same dimensions, as will be more clearly seen in Fig. 6. At the base of the studs and extending under the corners of the hexagonal portions are circular grooves 3'! in the spacing members 19.

The holes in the back plate [5 for the studs 33 are of a slightly larger diameter than the cylindrical portions of the studs but smaller than the hexagonal portions 35. Although I have found it convenient to make the base portions hexagonal, they may, of course, be made in other shapes.

In Fig. 5 is shown a form 39 with speaker parts which are to be assembled positioned thereon. The form 39 comprises a block 4i having integral therewith an upstanding cylindrical portion 43 and a cylindrical well 45 at the bottomthereof and extending within the block.

The cylinder 43 has an outer diameter that will permit the front plate I3 tobe placed face downward upon the form with the cylinder fitting snugly within the opening 23 in the plate, as will be noted in Fig. 5. The inner diameter of the cylinder 43, as also will be noted, allows the center pole piece H to be fitted snugly therein. From the above, it will be seen that the thickness of the cylinder wall is substantially equal to the width of the air gap which is provided for the voice coil 25 in the assembled loudspeaker.

Considering the assembled front plate l3 and spacing member. I9 as a unit and the assembled back plate l5 and center pole piece I? as another unit, the assembly of these parts will now be described. I

The front plate. 13, with the spacing member l9 uppermost, is placed upon the form 39 with the cylindrical portion 43 of the form extending up-' wardly through the opening 23 in the front plate. Next the center pole piece I! is fitted within the cylinder 43, the cylindrical ends of the studs 33 on the spacing member l9 are allowed to enter the holes provided for them in the back plate l5, and the pole piece I! is extended into the well 45 provided in the form 39 therefor. As illustrated in Figs. 5 and 6, it will be seen that the center pole piece i! will only be allowed to enter the cylinder 43 to a point where the back plate will rest upon the hexagonal portions 35 of the studs 33 as the dimension of the hexagonal bases across their corners is greater than the diameter of the holes in the plate.

From an inspection of Figs. 6 and 7, it will be seen that application of suificient pressure upon the back plate I5 will cause the edges of the holes in the plate to cut or shave off the corners of the hexagonal basis 35 of the studs and thus form for themselves new tightly fitting studs constituted by the mutilated hexagonal bases. A conventional press or the like (not shown) is utilized to exert pressure upon the back plate until its under;

face is flush with the adjacent end of the spacing member, and in so doing, the holes in the plate are caused to act upon the hexagonal bases of the studs in the manner described above. It is, of course, obvious that the material from which the studs and spacing member are constructed is softer than the back plate.

In order to prevent the shaved off fragments of the hexagonal bases 35 of the studs 33 from becoming wedged between the plate l5 and the spacing member I9, and so preventing them from being completely pressed together, the circular wells 3! in the spacing member at the base of the studs are provided to receive the shavings.

In Fig. 6, it will .be noted that the studs 33 are not in exact alignment with the holes in the back plate 15. However, from the foregoing, it will be seen that, in spite of the misalignment of the parts, the center pole piece ll is accurately located within the opening 23 in the front plate I3 to provide an air gap for the voice coil 25.

At the completion of the above described operation, the ends of the studs 33 are flattened or riveted over, and removal of the assembly from the form 39 completes the operation.

In connection with the structure shown in Fig. 2, wherein two U-shaped magnets are employed, it will be noted that a second spacing member l9a is utilized to further strengthen the union between the back and front plates [3a and l5a, re-' spectively. The second spacing member [9a is located relatively in the same relationship below the center pole piece IT as the first spacing member I9 is located above, is substantially of. the same construction, and is secured to the front plate 13a and back plate Ia in the same manner. The same method of assembly as described in connection with the structure shown in Fig. 1 is followed throughout, and it will be obvious that the assembly form 39 need only be slightly modified to accommodate the bent over bottom end of the front plate l3a.

Upon the completion of the assembly operations described above, the surfaces of the back plate I5 and front plate l3 upon which the ends of the U-shaped magnet 2| are to be located are ground to insure uniform contact therewith. The assembly is then attached to the diaphragm cone housing 3 by welding the front plate [3 to the back strips H and I2 thereof,'as will be seen in Fig. 1.

Provided in the top of the cone housing 3 is the opening 41 which serves to locate the U- shaped magnet 2| in proper relation to the front and rear plates l3 and I5, as is clearly shown in Fig. 3. The magnet 2| is placed in position upon the front and back plates with a pole extending through the opening 41 and a screw 49, passed through a hole in its top, extends downward and is threaded into the spacing member I9. It will be observed that the opening in the cone housing prevents horizontal displacement of the magnet and the screw prevents vertical dislodgement.

It will be noted in Fig. 1 that I have utilized the bottom portion 9 of the cone housing for mounting an audio transformer or the like. However, in the construction shown in Fig. 2 the bottom 9a of the housing 3a is constructed substan tially like the top portion la thereof and the second U-shaped magnet Zia is located and retained in position by the opening 41a and the screw 49a threaded into the second spacing member [9a. From the foregoing, it will be seen that I have provided a permanent magnet dynamic type loudspeaker of exceptionally compact design. Furthermore, the permanent magnet structure has been positioned relative to the diaphragm so as to make the unit as shallow as possible without the sacrifice of magnetic efiiciency. Such characteristics in a loudspeaker make it particularly adaptable to use in an automobile radio, for example. 7

Although I have used both riveting and welding in assembling my loudspeaker, it will be noted that the riveting operations are adaptable to high speed production without the sacrifice of accuracy and are free from the disadvantages of the prior art. Furthermore, the points of the structure which are subjected to Welding are located where any warping caused by heat cannot affect the parts which must be accuratelypositioned.

Although I have shown and described specific embodiments of my invention, I am fully aware that many modifications thereof are possible. My invention, therefore, is not to be restricted except insofar as is necessitated by the prior art and by the spirit of the appended claims.

I claim as my invention:

1. In a loudspeaker including permanent magnet field structure and a voice coil, the combination of a plate comprising an outer pole piece and having an opening therein, a second plate of magnetic material spaced from said first named plate, a center pole piece attached to said second named plate and extending into said opening in said first named plate whereby an air ap for said voice coil is provided, and non-magnetic means spacing said plates from each other and maintaining ,said plates in such relation as to provide said air gap.

2. In a dynamic type loud speaker, the combination of a plate comprising an outer pole piece, a second plate spaced from said first named plate, non-magnetic means maintaining said plates in spaced relation, a center pole piece attached to said second named plate, and a permanent magnet having its poles respectively in contact with portions of said first and second named plates, said magnet being so disposed with respect to one of said plates as to have at least a portion thereof in the plane of said latter plate. 3. In a loudspeaker including a diaphragm and a voice coil, the combination of a housing for said diaphragm having a plurality of openings therein, a plate comprising an outer pole piece having an opening therein and attached to the back of said housing, said plate having an end thereof bent over and extending into said housing through one of said openings therein, a second plate disposed to the rear of said first named plate, a non-magnetic spacing member interposed between and having its ends respectively attached to the inner faces of said first and second named plates, a center pole piece attached to said second named plate and extending forward into said opening in said first named plate whereby an air gap is formed for said voice coil, and permanent magnet structure having a pole thereof extending through one of said openings in said housing and contacting With the bent over portion of said first named plate and having its other pole contacting with an end of said second named plate.

4. The invention as set forth in claim 3 characterized in that said magnet structure comprises a plurality of permanent magnets each having a pole thereof extending through one of said openings in said housing and contacting with an end portion of said first named plate and having the other pole thereof contacting with one end of said second named plate.

HERBERT R. WARNKE.

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