US2524836A - Permanent magnet electrodynamic loud-speaker - Google Patents

Description

Oct. 0,

E. L. RUHSSELL 2,524,836

. PERMANENT MAGNET ELECTRODYNAMIC LOUD-SPEAKER Filed April 2, 1947 2 Sheets-Sheet 1 uvvmroa Enm. L. RUSSELL Arman 21 Oct.v 10,1950 E. L. RUSSELL 2,

' PERMANENT MAGNET ELECTRODYNAMIC LOUD-SPEAKER Filed April 2,1947 2 Sheets-Sheet 2 INVENTOR. EARL L. RvssELL r v BY i 1" I 601mm, 9* 777 61407,

i z Fh'ToRNEY-s Patented Oct. 10, 1950 PERMANENT MAGNET ELECTRODYNAIWIC LOUD SPEAKER Earl L. Russell, Cleveland, Ohio, assignor to The Rola Company, Ina, Cleveland, Ohio, at corporation of Ohio Application April 2, 1947, Serial No. 738,894

This invention relates to loud speakers, and particularly to loud speakers of the permanent magnet type.

Loud speakers utilizing a permanent magnet for the field structure are subject to the accumulation of foreign particles in the confined space between the voice coil forms and the opening therefor in the front plate of the magnetic structure. Great care must be exercised in the manufacture of the loud speaker to avoid the possibility of magnetic particles being attracted to and held by the magnetic structure, as otherwise their presence would interfere with the normal reciprocating movement of the voice coil within the air gap and cause a scratching noise in the reproduction. The centering of the voice coil form within the air gap is also important. The con struction utilized, however, must be sufficient not only to maintain the proper spacing between the component parts, but must enable the speaker to withstand rough handling incident to the packing and shipment of the loud speakers from the manufacturer to the set manufacturer, and then to the ultimate user.

An effort heretofore has been made to overcome the aforementioned difficulty by permanently fastening the cone and housing assembly to thefield assembly after the voice coil form has been centered by means of a gauge with respect to the Claims. (Cl. 179-4155) an end view of the field structure as viewed in the direction indicated by the arrows 3-3 in Fig. 2; Fig. i is a rear view of the assembled loud speaker with a portion thereof broken away; Fig. 5 is a section taken on a plane indicated by the line 5-5 in Fig. i, and Fig. 6 is a section taken on a plane indicated by the line 6- 6 in Fig. 4.

The loud speaker with which the present invention is shown has a permanent magnetic field which includes a shell type core, indicated in general at H], and preferably comprises a strip of metal that is bent to form an open frame having a front plate H, a back plate It, a top plate [3 and a bottom plate It. The front plate has an opening l5 therein and the back plate has a pole piece [6 extending into the shell and substantially parallel to the top and bottom plates thereof. The pole piece terminates in a pole tip H which is concentrically disposed within the opening l5 and cooperates therewith to provide the air gap in which the voice coil is adapted to operate in the usual way. The pole piece It is held within central position within the shell by means of a resilient cup-shaped member that is so1-,

dered or otherwise securely fixed to the back of the front plate and is adapted to engage a tapered surface 2i on the pole piece to exert tension thereagain'st, so as to hold it firmly in central .p-osition with respect to the shell.

' is attached. The form carries the usual voice in order to get at the space in the region of the 7 air gap for the purpose of freeing the gap of foreign particles or in order to re-center the voice coil. In loud speakers utilizing a permanent magnet, such occurrence is apt to be sufficiently frequent to consitute a major item in the servicing and repairing of loud speakers.

An object of the present invention is to provide a loud speaker wherein the cone or diaphragm and its associated housing assembly can be removed from the field assembly without destroying or disturbing the relationship of the parts forming the diaphragm assembly, thereby enabling the field structure, in the region of the air gap, to be effectively cleaned or centered and the parts re assembled in an expeditious manner.

Referring now to the drawings, Fig. l is-a side elevation of a loud speaker embodying the present invention; Fig. Z'is an exploded view in side'elevation of the assembly shown in Fig. 1; Fig. 3 is threaded engagement with registering openings in the base of the cone housing. As is shown in Fig. 2, the openings 3% are larger than the diameter of the threaded shank of the fastener 35, as a result of which adjustment may be made between ,the field structure and the cone assembly whenever the screws are loosened.

The foregoing describes the component parts of the loud speaker, the assembly ofwhich may be made in accordance with that disclosed and described in my copending application Serial No. 127,961, filed November 17, 1949,- and assigned to The Rola Company, Inc. Briefly in carrying out the method of assembly, the plate 31 is staked or otherwise securely fastened to the front plate H, as by bosses 4!] which are extruded from the front plate and are adapted to enter correspondingly shaped openings in the plate 31'. Additionally, the attachment is made by threaded fastening members 4!, as is shown in Fig. 3. The plate and shell as a unit are then fastened to the cone housing 32 by means of the securingmembers 35, these being accessible from the rear of the housing as is shown in Fig. 4, inasmuch as the plate 31 is wider than the material of which the shell IE] is made.

After the shell has been assembled to the housing, then the pole piece i6 is centrally located therein by means of a suitable gauge placed between the pole tip and the wall of the Opening l5, and is locked in place by the resilient center ing member 29, after which solder is applied to hold the pole piece to the back wall of the shell and to hold the centering member to the front plate of the shell.

After the assembly of the magnetic structure, the centering member is cemented at its outer periphery to the base 3| of the cone housing, while being centered with respect to the axis of the pole tip by means of a gauge that is inserted within the air gap. The assembly of the cone and its associated voice coil form to the centering member 30 is made by applying cement to the neck of the cone on the outer portion thereof and then inserting the voice coil form into the air gap, using a customary centering gauge to space it with respect to the pole piece. The form is inserted until the centering member fits snugly against the neck of a cone, whereupon the cement operates effectively to join the two parts together. While the centering gauge is still in position, the base of the cone is cemented to the cone housing and sealed by means of the gasket 33 which is cemented thereto.

In the event of the voice coil form being inaccurately centered with respect to the pole piece, then it is only necessary to loosen the screws 35 and move the field assembly with respect to the cone assembly, using the customary centering gauge between the voice coil form and the pole tip, and then tightening the members 35.

In the event of metallic particles or other foreign particles being entrapped between the pole tip and the voice coil form, then upon removal of the fastening members 35, the field structure may be removed as a unit from the cone assembly, the air gap may be thoroughly cleaned and the parts reassembled by means of a centering gauge and replacement of the screws 35.

Heretofore it has been necessary to destroy the,

cone, together with its associated centering member, voice coil and voice coil form in order to relocate a form with respect to the walls of the air gap, or to make the air gap accessible for cleaning purposes. An advantage of the present invention, however, is that the adjustment and cleaning can be made without destroying any of the component parts, and without disturbing the connection between the cone, the centering member and the housing. Thus, a saving is made in parts and considerable reduction is effected in the time required to rebuild the loud speaker. Moreover, the invention is advantageous in that the cone assembly and field structure may be quickly adjusted merely by the insertion Of a centering gauge between the voice coil form and the pole tip at the time of tightening of the fastening members, which are readily accessible'from the exterior part of the unit.

I claim:

1. A loud speaker having a diaphragm, a voice coil form attached thereto, a centering member extending from the form radially thereof, a housing for the diaphragm, means for attaching the outer portion of the diaphragm to the housing, a field structure embodying a permanent magnet and including a shell-type core having an open ing for receiving the voice coil form, a pole piece disposed within said shell type core, a centering member secured within said shell type core and adapted to fixedly enclose the tip of said pole piece, thereby securing it firmly in central position with respect to said shell, a plate rigidly attached to the core and removable loose fitting fastening means for connecting the plate to the a housing.

2.. A loud speaker having a diaphragm, a voice coil form attached thereto, a centering member extending from the form radially thereon, a housing for the diaphragm, means for attaching the outer portion of the diaphragm to the housing, a field structure including a permanent magnetic type core having an opening for receiving a voice coil form, said core embodying an open frame of uniform width, a pole piece disposed within said core frame, a resilient centering member secured within said core frame and adapted to fixedly enclose the tip 0f said pole piece thereby retaining it firmly in central position with respect to said core frame, a plate rigidly attached to the frame and being wider than the frame, and loose fitting fastening means for detachably connecting the plate to the housing, said means being accessible from the exterior of said field structure.

3. A loud speaker having a permanent magnetic field structure including a core having a front plate with an opening therein, and a back; plate, a pole piece extending from the back plate and having a pole tip disposed within said open ing and disposed concentrically with respect thereto, a centering member secured to the front plate within said core structure and adapted to fixedly enclose said pole tip thereby retaining it firmly in central position with respect to said core structure, a diaphragm having a voice coil and a centering member attached thereto, the form being positioned between the pole tip and the wall of said opening, a housing, means for rigidly connecting the centering member and the diaphragm to the housing, a member rigidly fastened to the front plate and disposed between it and the housing and having an opening in registration with that in the front plate through which the voice coil form extends, said member having spaced openings therein, and said housing having openings in registration with the lastnamed openings, threaded fastening members extending through said last-mentioned registering openings for securing the magnetic field structure to the housing, the openings in the member being larger than the cross-sectional area of the associated fastening members, whereby the member and field structure as a unit may be adjusted radially with respect to the voice coil form.

4. A loud speaker having one unit comprising a permanent magnetic field structure, including a core, a pole piece, a resilient centering member secured within said field structure and adapted to fixedly enclose the tip of said pole piece thereby firmly retaining it in central position with respect to said field structure, and a plate connected together as a unit, and another unit comprising a diaphragm, a voice coil form, a center- 5. A loud speaker having a conical diaphragm,

a Voice coil form attached thereto, a flaring housing about the diaphragm, meansfor attaching the outer portion of the diaphragm to the outer portion of the housing, a centering member for the voice coil form extending radially outward therefrom and attached to the inner portion of the housing, a field structure of the shell type having a front with an opening for receiving the voice coil form, a pole piece disposed within said field structure, a resilient centering member secured within said field structure and adapted to fixedly enclose the tip of said pole piece thereby firmly retaining it in central position with respect to said field structure, a plate resting against said front and rigidly attached thereto and overhanging opposite sides of the field structure, and

'6 loose fitting fastening means at the overhanging portions of said plate for detachably connecting the plate to the inner portion of the housing, said means being accessible from the exterior of said field structure.

' EARL L. RUSSELL.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,721,023 Jensen July 16, 1929 1,859,518 Kingsford May 24, 1932 1,864,809 Dempster et a1. June 28, 1932 1,872,261 Engholm Aug. 16, 1932 1,881,324 Metoalf Oct. 4, 1932 1,886,816 Jensen Nov. 8, 1932 1,891,404 Engholm Dec. 20, 1932 1,897,294 Bernard -1 Feb. 14, 1933 1,905,702 Hardisty Apr. 25, 1933 1,906,196 Fisher Apr. 25, 1933 1,941,477 Jensen Jan. 2, 1934 1,948,361 Sollie Feb. 20, 1934 2,027,473 Creager Jan. 14, 1936 2,174,355 Sundstrom Sept. 26, 1939 2,200,490 Cornwell May 14, 1940

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