US2524780A - Pole piece centering arrangement for permanent magnet electrodynamic loudspeakers - Google Patents

Description

Oct. l0, 1950 a. A. ENGHOLM 2,524,780

POLE vPIECE CENTERING ARRANGEMENT EoR PERMANENT MAGNET ELECTRODYNAMIC LouDsPEAm-:Rs

Filed July 7', 1945 l ii APatented Oct. 10, 1 950 UNITED STATES PAT sr cme-E Y POLE PIECE CENTERING ARRANGEMENT FOR `PERMANENT MAGNET :ELECTRODY- VNAMIC LOUDSBEAKERS Bernard A. Engholm, Cleveland, Ohio,v assignor, by mesne assignments, Lto The 'Rola Company, Inc., .Cleveland, Ohio, a corporation of Ohio Application J lily v7,1945, SjerialNo. v603,605

i3 Claims;

w `hin which theaforesaid coil is supported for operation. f Y

In prior magnetic assemblies lthe :pole tipfhas been held onto the back frame Vby a screw that would extend through the back of the frame and into the pole-tip, or the tip wouldbe soldered lto the frame, vbut either operationl is diiiicult to attain hand at vthe same time jte .maintain the desireddegree of eiiic'iency of operation.

One of the objects of 'the present invention is to make an assembly which includesl the magnetic' elements as .aforesaid Without the ...necessity `for using a-screw or solder 'for holding themagnet andpole tip'inplace. The invention contemplates resilient means for centering the magnet and pole tip in proper position and for exerting spring tension thereon to maintain Ithe desired relationship between the respective parts of` the assembly. Y An additional object of the present invention is to protect the air gap against the entry of foreign particles which would interfere with the accuracy of voice reproduction. Such additional object contemplates the construction of a magnetic assembly as aforesaid, and the prevention of access of foreign particles to the air gap from inside the magnet structure. The invention is thus well adapted for installations employing a permanent magnet.

My invention as hereinafter described provides at once the means for preventing access of particles to the air gap from the region within the magnetic frame, and the means for holding tl-ie`separate magnetic pole piece in place. The invention may be summarized as comprising the means by which I accomplish these objects, or either of them. A preferred form of such means is illustrated in the drawings hereof and hereinafter more fully explained.

In the drawings, Fig. 1 is a diametric section partly in elevation through a loud speaker embodying this invention; Figs. 2. 3 and 4 are sections taken on planes indicated by the correspondingly numbered lines in Fig. 1.

In each of the views, I have shown an open rectangular magnetic frame composed of two There is an channel-shaped members II and I2 with their edge flanges secured together as, for instance, by straps I3 spot-welded to the anges. The web 9-of the member l2- commonly known as a magnet frame Yhas a central opening Iliand into this extends a pole piece l5 abutting a permanent magnet I 6 which is suitably secured, as by cement Il, to the web of the member ll. There is thus provided a permanent magnet within an open frameand having a central pole piece extending into an opening in the frame with an annular air gap between them.

' In Fig. 1, 2U indicates the housing or frame of the cone 2l which is of suitable vibratory material to hdeliver sound. The housing 20 has a centralportion 22 which is shown as riveted to theweb of the channell member I2. The outer edge Vof the cone is' secured to thehousing 20 in the'usual manner. The cone 2l carries at its apex the voice coil form 25 Vabout which is placed a suitable coil 26 which operates within the air gap I4.

Within the frame of the magnet and surrounding the! air gap at some distance from it, I provide a hollow cylindrical member or thimble 3S of non-magnetic material which is suitably secured 'to the web l2 of the magnet frame. Bearing against the outer peripheral edge of this drum is an annular disc 35 having spring-like characteristics, the inner periphery of which bears against the pole piece I5 of the magnet. The disc 35 is flanged at its outer edge toward the adjacent wall of the frame so that it is retained in place by overhanging the thimble 3U. The pole piece I 5 is preferably made conical, as shown at I9 and the inner periphery of the d isc 35 bears against such conical surface, this disc being slightly flexed inwardly when the parts are assembled. Thus the disc exerts a constant pressure against the pole tip I5 to maintain it in central position with respect to the opening I4.

It will be seen that the simple arrangement of the drum and disc described provides at once the means for positioning the separate pole piece and the vmeans for preventing access from the region about it to the air gap.r

I have found it very satisfactory to make the non-magnetic thimble 30 of formed zinc and the resilient disc of Phosphor bronze and to secure the drum in place by cement, shown at 3|, but the invention is not limited to those particular materials. it may also be cemented to the part I6.

In Figs. 2 and 3, I have shown the voice coil spider as surrounded by a dust protector. Briefly,

After the pole tip has been centered,...`

such construction comprises an annular cup-like member 40 secured to the magnet frame 9 and having radially extending ange 4| to which the outer portion of an imperforate spider 42 is attached. The inner end of the spider is shown as having a rcylindrical flange l43 which is rigidly attached as by cement to the neck of the cone 2 I. A closure disc 45 is shown as being attached to the inner face of the cone for sealing the outer end of the voice coil form.

An advantage of the present invention is the fact that constant pressure is exerted against the pole tip to maintain it in centralized position with reference to the aperture in the front plate of the magnetic structure. A further advantage is the fact that the aforesaid means also operates to protect the air gap from the entrance of foreign particles.

I claim:

1. A permanent magnet loud speaker comprising an open frame having spaced walls, a central magnetic member secured at one end to the Wall of the frame, a separate pole piece laterally shiftable on the other end of the magnetic member and having a conical head, the larger end of which engages the magnetic member and the smaller end of which joins a cylindrical portion which extends into an opening in the opposite wall of the frame leaving a surrounding air gap, a protecting device surrounding the separate pole piece and secured at one edge to the Wall of thev frame having the opening and having a portion under constraint constantly pressing axially on the conical portion of the separate pole piece to maintain the same centered in the air gap.

2. A permanent magnetic loud speaker comprising an open frame having spaced walls, a central magnetic member secured at one end to the wall of the frame, a separate pole piece laterally shiftable on the other end of the magnetic member and having a conical head, the larger end of which engages the magnetic member and the smaller end of which joins a cylindrical portion which extends into an opening in the opposite wall of the frame leaving a surrounding air gap, a thimble surrounding the pole piece and secured at its outer edge to the wall of the frame having 4 the opening, and a flexible disc having a central opening surrounding the separate pole piece and bearing at its inner edge against the conical portion thereof, said disc bearing against the thimble and constrained thereby to press against the conical surface of the separate pole piece.

3. A permanent magnetic loud speaker comprising an open frame having spaced walls, a central magnetic member secured at one end to the wall of the frame, a pole piece on the other end of the magnetic member and having a conical head, thelarger end of which engages the magnetic member and the smaller end of which joins a cylindrical portion which extends into an opening in the opposite Wall of the frame leaving a surrounding air gap, a thimble surrounding the pole piece and secured at its outer edge to the Lwall of the frame having the opening, anda flexible disc having a central opening surrounding the pole piece and bearing at its inner edge against the conical portion thereof, said disc overlapping the inner end of the thimble and constrained thereby to press against the conical surfaceof the separate pole piece, the disc being flanged at its vouter edge in the direction toward the frame portion having the opening to prevent the shifting of the disc upon the thimble.

. BERNARD A. ENGHOLM.

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

UNITED STATES PATENTS Number .Y

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