US3466405A

US3466405A - Permanent magnet basket assembly for a speaker

Info

Publication number: US3466405A
Application number: US515322A
Authority: US
Inventors: Rollin J Parker
Original assignee: General Electric Co
Current assignee: General Electric Co
Priority date: 1965-12-21
Filing date: 1965-12-21
Publication date: 1969-09-09
Anticipated expiration: 1986-09-09
Also published as: NL6616887A; DE1300146B; FR1505287A; GB1164306A; BE691587A

Description

PERMANENT MAGNET BASKET ASSEMBLY FOR A SPEAKER R. J. PARKER Sept. 9, 1969 2 Sheets-Sheet 1 Filed Dec. 21,

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lNl ENTOR ROLLIN J. PARKER A T TO/PNE V Sept. 9, 1969 J. PARKER 3,466,405

PERMANENT MAGNET BASKET ASSEMBLY FOR A SPEAKER Filed Dec. 21', 1965 2 Sheets-Sheet 2 15 FIGJO FIG. [2

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lNVENTOR 22 ROLLIN J. PARKER A TTORNE Y United States Patent 3,466,405 PERMANENT MAGNET BASKET ASSEMBLY FOR A SPEAKER Rollin J. Parker, Greenville, Mich., assignor to General Electric Company, a corporation of New York Filed Dec. 21, 1965, Ser. No. 515,322 Int. Cl. H04r 9/02, 11/06, 13/02 US. Cl. 179117 Claims ABSTRACT OF THE DISCLOSURE This invention relates to a speaker magnet assembly and more specifically to a permanent magnet and basket assembly for a speaker and to a process for its manufacture.

Typical permanent magnet speakers contain a basket to which are attached a permanent magnet, a pole piece and return path elements, the latter making up the yoke structure of the magnetic circuit. The return path elements in a conventional speaker will comprise one or more components which together form a cup-shaped structure surrounding the usually cylindrical speaker magnet. The return path elements must have sufficient cross-sectional area so that the flux density does not exceed the saturation point of the metal. The return path elements are therefore generally of more substantial gauge than the metal which makes up the speaker basket. This factor plus the shape of the path of magnetic flux in the return path circuit has resulted in the two components-basket and return pathbeing hitherto comprised of at least two separate units.

The present invention has as its principal object a simplified permanent magnet-basket assembly for a speaker made up of an integral return path-basket unit. It is an additional object to provide such an assembly which permits greater speaker magnet efficiency and performance. A still further object of the invention is to provide a process for manufacturing permanent magnet-speaker assemblies more simply and economically than has heretofore been possible by manufacturing the speaker baskets and return path element as an integral unit.

In my co-pending application S.N. 515,401, assigned to the same assignee as the present application and filed of even date herewith, I have disclosed a new way of orienting speaker magnets along a curved path disposed about the axis of the magnet which permits more eificient concentration of magnetic flux at the air gap. The present invention is directed to speaker magnet assemblies of markedly improved and simplified design, to a large extent made possible by orienting the magnets as set forth in my above-identified co-pending application.

The speaker magnet assembly of the present invention comprises a basket having a central aperture therein, a return path element depending from said central aperture which is formed from and integral with said basket, and a permanent magnet disposed within said return path element. The magnetic circuit of the speaker assembly is made up only of the permanent magnet itself and the return path element formed from the basket. No pole 3,466,405 Patented Sept. 9, 1969 ice piece or bottom return path elements are necessary. In its preferred form, the return path element of the speaker assembly is tubular, i.e., a hollow tube open at both the bottom and the top. The speaker magnet assemblies of the invention are manufactured by shaping that portion of the basket, from which one or more of the apertures in the basket are formed, into the return path element. A permanent magnet is then fitted within the thus shaped return path element such that the magnet contacts the return path element at a lower axial extremity of the return path element and is separated from the return path element at an upward axial extremity of the return path element, the separation serving to form an air gap adapted to receive the coil of the speaker.

The invention will be more clearly understood from the following description taken in connection with the accompanying drawing in which:

FIGURES 1 through 8 illustrate schematically the successive steps of manufacture of a speaker magnet assembly of the invention; and

FIGURES 9 through 13 illustrate schematically the successive steps of manufacture of a second embodiment of a speaker magnet assembly of the invention.

In manufacturing the speaker assemblies of the invention, a sheet 1 of relatively light-gauge, low-carbon steel is first drawn to form a central depression 2, as shown in FIG. 1. This central depression is then elongated as shown in FIG. 2. Such elongation also acts to thin out somewhat the gauge of the steel forming the depression. The depression 2 is now reverse-drawn as shown in FIG. 3, to approximately double the gauge of the walls of the depression, at the same time, of course, reducing the length of the depression approximately in half. The depression 2 is now pierced as shown in FIG. 4 to form an opening 3.

The reverse-drawn and pierced depression 2 must now be accurately sized and crimped at a die station to form the precise shape and tolerances required for optimum performance in a speaker circuit. As illustrated at FIG. 5, the depression is now shaped to form a tubular return path element 4. Specifically, tube 4 is crimped at a lower axial extremity thereof to form an annular collar 5 of reduced diameter. The inner surface of the collar 5 is flat to form continuous and close contact with the speaker magnet between the inner surface of the collar and the lower axial extremity of the magnet. The remainder of the tube is also accurately sized in order to form at 6 the precise air gap distance required upon insertion of the permanent magnet.

A typical sheet, such as 1 in FIG. 1, is about 0.040" gauge in thickness. The thickness of the reverse-drawn tube in FIG. 3 will be approximately 0.070" gauge, or somewhat less than twice the original gauge, the difference resulting from the elongation that has occurred in the tube.

The basket is then shaped and cut as illustrated in cross section in FIGS. 6 and 7 and in plan in FIG. 8. After shaping basket 7 in conical form, four Windows 8 are blanked out. A cylindrical permanent magnet 9 is press-fit within integral return path element 4 as shown in FIGS. 7 and 8. Four holes 10 at each corner of the basket are also pierced to provide apertures for attachment of the speaker to a radio receiver housing or other amplification .device. The complete permanent magnet circuit and basket thus consist of but two elements-the integral basketreturn path element and a permanent magnet.

The process of manufacturing a speaker magnet assembly in accordance with a second embodiment of the invention is illustrated in FIGS. 9 through 13. A sheet of steel 15 is drawn as illustrated in FIG. 9 to form a depression 16 and is then pierced to form an opening 17. The pierced depression is partially reverse-drawn as shown in FIG. to form an annular collar 18 of reduced diameter.

The sheet is now shaped and cut as illustrated in FIGS. 11 and 12 to form the conical portion of the speaker basket. This is accomplished by first shaping the sheet 15 in conical form to form the basket 19 and then piercing four holes, two of which are in the form of

windows

20 and 20', as illustrated in FIG. 11. The remaining two holes 21 and 21' are pierced so as to leave T-

shaped tabs

22 and 22 integral with the basket. Each of the T-shaped tabs is then bent downward and away from the basket and shaped into the form of a half of a hollow cylinder or tube, as illustrated in FIG. 12. Upon further bending down and back, tabs 22 and 22 form intimate contact with depression 16. The tabs 22 and 22' and depression 16 now together form double-gauge walls of the completed return path element 23, as illustrated in FIG. 13. After accurately sizing the return path element, a permanent magnet may be press-fit within the shaped return path element to form the speaker magnet assembly as shown in connection with the first embodiment.

The invention is, to a considerable extent, made possible by the utilization of a permanent magnet oriented in a manner set forth in my above-referred-to co-pending application S.N. 515,401. As there set forth, the permanent magnet is oriented along an axially disposed curve. Such orientation is shown at 11 in FIG. 7 of the drawing of the present application. This permits a number of significant advantages in the construction of the permanent magnet speaker. Measurements indicate that 90% of the total magnetomotive force is made available at the air gap as opposed to 65-75% in conventional magnet structures. Additionally, virtually 100% of the total magnetic flux may by made to enter the general region of the voice coil vs. a loss of as much as 20% of such flux to regions outside the voice coil regions in conventional magnet structures. Because of the greater efiiciency of the magnetic circuit, it is possible to use lower flux densities to achieve equipment air gap .densities, and thus equivalent speaker performance. This permits a smaller cross-sectional area in the return path element because the flux density per unit of return path is smaller. This enables efiicient speaker magnet structures to be built, utilizing thin-gauge, softsteel return paths, thus enabling the return path element itself to be made of the same material as the basket. This, in effect, permits utilization as a return path element of a portion of the basket structure previously discarded. Additionally, because of the manner in which the permanent magnet is oriented, a conventional bottom return path element is unnecessary.

Aother advantage of the invention is also illustrated in FIG. 7. The width of the air gap 12 is the same as the width of the throat 13 formed between the remainder of the return path element and the lateral sides of the permanent magnet. While this structure is not unknown in the speaker art, it has almost always been avoided because greatest efficiency in speaker structures is obtained by maintaining a large degree of separation between the axialfiow of magnetic flux in the magnet and return axial flow in the lateral portion of the return path. This discourages radiation of flux from the sides of the magnet to the return path element at areas other than the air gap. In conventional speaker assemblies the flux flows in an axial direction through the permanent magnet-any radial flow of flux other than at the extremities of the magnet must be discouraged. In the speaker magnet construction shown in FIG. 7, there is already a radial component 4 (toward the sides of the magnet) in the flow of flux in the magnet so that radial flow is not discouraged except for a very small area at the axial center of the magnet. The invention thus makes it possible to reduce considerably the dimensions of the throat area of the permanant magnet return path system and thus to miniaturize the construction of the speaker. While the air gap 12 and throat 13 need not be the same dimension as a FIG. 7, the throat section may nevertheless be narrower in the present speakers than in conventional speaker structures.

What I claim as new and desire to secure by Letters Patent of the United States is:

1. A permanent magnet-basket assembly for a speaker comprising:

a basket having a central aperture therein,

a return path element extending from said central aperture which is formed from and integral with said basket,

and a permanent magnet disposed within said return path element, said return path element surrounding said permanent magnet laterally only and open at the bottom thereof, the magnetic circuit of said assembly consisting essentially only of said permanent magnet and integral return path element.

2. The permanent magnet-basket assembly of claim 1 in which the return path element is in the shape of a tube, the lower axial extremity of which contacts the speaker magnet and the upper axial extremity of which is spaced from the speaker magnet to form an air gap.

3. The permanent magnet-basket assembly of claim 1 in 'which the return path element consists of a doublegauge thickness of the sheet material from which the basket is formed.

4. The permanent magnet-basket assembly of claim 1 in which the return path element consists of a multiplegauge thickness of the sheet material from which the basket is formed.

5. A permanent magnet-basket assembly for a speaker comprising:

a basket having a central aperture therein,

and a permanent magnet disposed within said return path element, said return path element surrounding said permanent magnet laterally only and open at the bottom thereof, the magnetic circuit of said assembly consisting essentially only of said permanent magnet and integral return path element, the lower axial extremity of the return path element contacting the speaker magnet, the upper axial extremity of the return path element being spaced from the speaker magnet to form an air gap, and the intermediate portions of the return path element being spaced from the speaker magnet by a distance substantially equal to the width of the air gap.

References Cited UNITED STATES PATENTS 3,133,162 5/1964 Coen 179-119 2,320,402 6/1943 Blessing 179117 2,260,063 10/1941 Stone 179115.5

KATHLEEN H. CLAFFY, Primary Examiner A. A. MCGILL, Assistant Examiner