US3867587A

US3867587A - Magnetic circuit for an electro-acoustic converter

Info

Publication number: US3867587A
Application number: US315970A
Authority: US
Inventors: Isao Yamamuro
Original assignee: Pioneer Electronic Corp
Current assignee: Pioneer Corp
Priority date: 1971-12-17
Filing date: 1972-12-18
Publication date: 1975-02-18
Anticipated expiration: 1992-02-18
Also published as: DE2261499A1; JPS5234212B2; DE2261499B2; JPS4868218A

Abstract

An improvement in an electro-acoustic converter having a magnetic anisotropic circuit with air gap therein, the improvement including an air gap formed of a magnetic material laminated with an insulating layer having a comparatively higher magnetic resistance in the magnetic circuit, thereby increasing a magnetic resistance against a magnetic flux caused by a voice coil and acting so as to reduce eddy current losses, and thus eliminating the reproduction distortion caused by the magnetic non-linearity of the magnetic circuit.

Description

United States Patent H91 Yamamuro Feb. 18, 1975 1 1 MAGNETIC CIRCUIT FOR AN 3,665,352 5/1972 Dietrich a a1 179/119 ELECTRO ACOUSTIC CONVERTER 3,783,311 l/l974 Sato et a1. 179/115.5 R

Isao Yamamuro, Tokorozawa, Japan Inventor:

Pioneer Electronic Corporation, Tokyo, Japan Filed: Dec. 18, 1972 Appl. No.: 315,970

Assignee:

Foreign Application Priority Data Dec. 17, 1971 Japan 46-102518 US. Cl. 179/115.5 R, 179/119 R Int. Cl H041 9/02 Field of Search l79/1l5.5 R, 115.5 VC, 179/117,119 R; 335/231, 236, 296, 301,

References Cited UNITED STATES PATENTS 10/1934 Brzeski 179/1 15.5 R 6/1943 Blessing 179/1 15.5 R l/l972 Mauz 179/1 15.5 R

INSULATING LAYERS OTHER PUBLICATIONS Brailsford, Magnetic Materials, 1960, Methuen and Co., Chaps. 4 and 5, pp. 84-136.

Primary ExaminerWilliam C. Cooper Assistant Examiner-George G. Stellar Attorney, Agent, or FirmSughrue, Rothwell, Mion, Zinn & Macpeak [57] ABSTRACT coil and acting so as to reduce eddy current losses,

and thus eliminating the reproduction distortion caused by the magnetic non-linearity of the magnetic circuit.

2 Claims, 6 Drawing Figures MAGNETICALLY ANISOTROPIC MATERIAL Pmmsum 3,867. 587

FIG. la FIG. lb

PRIOR ART PRIOR ART I FIG. Ic PRIOR ART FIG. 2' PIC-5.3 M NETICMY 7 9 5 7 INSULATING IIIA TL IIZE I086 8 I0 I? s 579 '1 4\ W4 4 I 3 2 I 2 I FIG; 4

MAGNETIC CIRCUIT FOR AN ELECTRO-ACOUSTIC CONVERTER CROSS-REFERENCE TO RELATED APPLICATIONS This application is related in subject matter to copending applications Ser. No. 315,962 and 315,963 filed Dec. 18, 1972, by Isao Yamamuro and assigned to a common assignee with the present application. Application Ser. No. 315,963 has issued as U.S. Pat. No. 3,830,986.

BACKGROUND OF THE INVENTION 1. Field of the Invention This invention relates to a magnetic circuit for an electro-acoustic converter such as a speaker or a microphone.

2. Description of the Prior Art Normal magnetic material has a magnetic hysteresis loop characteristic and the relation of magnetizing force and magnetic flux density is non-linear. Therefore, when magnetic flux of a voice coil passes through a center pole and a plate near an air gap, the magnetic reaction in the voice coil results in a distorted output signal from the electro-acoustic converter such as a speaker or a microphone.

Accordingly, various methods eliminating the distortion have been attempted, such as methods of covering a center pole a with a copper cap b as shown in FIG. la, putting in a copper ring c as shown in FIG. lb, or making a depression on an upper surface of a center pole a and plating the depression with copper d as shown in FIG. 10. The above-mentioned methods shown in FIGS. la and lb, however, not only require a higher level of manufacturing technique than a conventional normal magnetic circuit for making the air gap a predetermined size, but also results in decreasing the magnetic flux density within the air gap due to the substantial increase of the air gap width. When using copper ring c, the copper ring disturbs the magnetic flux distribution in the air gap thus disturbing the output signal. In the last case shown in FIG. lc, it is difficult to uniformly plate with sufficient thickness.

SUMMARY OF THE INVENTION The present invention has taken notice of the aforementioned problems and eliminates the distortion caused bythe magnetic circuit. The primary object of the present invention is to provide a magnetic circuit for an electro-acoustic coverting device characterized in that a portion or all of the magnetic circuit elements defining the air gap have magnetically anisotropic characteristics, thereby increasing the magnetic resistance against magnetic flux caused by a voice coil and eliminating the reproduction of distortion caused by the magnetic non-linearity in the magnetic circuit.

Another object of the present invention is to provide a magnetic circuit for an electro-acoustic converter which includes an air gap defined by magnetic parts of magnetic material laminated with an insulating layer so as to have the magnetic anisotropy whereby the reproduction distortion caused by the inductance of the coil is sharply reduced.

Another object of the present invention is to provide a magnetic circuit for an electro-acoustic converter whereby an electro-acoustic converter having a high conversion efficiency may be manufactured without difficulty because the eddy current power loss is decreased and most of the magnetic flux is used effeciently.

BRIEF DESCRIPTION OF THE DRAWINGS FIGS. la-lc are vertical sections of conventional magnetic circuit portions for an electro-acoustic converter.

FIGS. 2 and3are vertical sections of embodiments of a magnetic circuit in accordance with the present invention.

FIG. 4 is an enlarged fragmentary sectional view schematically illustrating directions of magnetic flux of a voice coil.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Explaining one embodiment of the present invention in accordance with the drawings, 1 is a yoke, 2 is a center pole fixed in the center of the yoke l, 3 is a ringshaped magnet, 4 is a plate fixed on the

magnet

3, 5 is a voice coil cylinder, and 6 is a voice coil.

In the embodiments shown in FIGS. 2 and 3, the upper outside portion of the pole 2 and the inside portion of the plate 4 are respectively constructed with

magnetic parts

7 and 8, made of a stack of layers of magnetically anisotropic material such as two directional silicon steel 9 interleaved with insulating layers 10 having comparatively higher magnetic resistance so as to have characteristics of magnetic anisotropy. The easy magnetizing axis and hard magnetizing axis of the

parts

7 and 8 are consequently directed at right angles and parallel to the voice coil 6.

Therefore, the magnetic flux out of the magnet 3 returns to the same magnet 3 by way of the plate 4, the easy magnetizing axis of the magnetically anisotropic part 8, the air gap, the easy magnetizing axis of the magnetically anisotropic part 7, the center pole 2 and the yoke l. Namely, the magnetic flux for driving the speaker passes the air gap through the same path as in the conventional magnetic circuit. The total magnetic resistance of the magnetic circuit is slightly greater as compared with that of the conventional magnetic circuit, because the magnetic flux for driving the voice coil passes through the easy magnetizing axis of the magnetic

anisotropic parts

7 and 8.

The magnetic flux caused by the voice coil 6 follows the path shown by dotted lines in FIG. 4, that is, the magnetic flux completes closed loops which pass along both of the hard magnetizing axes of the magnetically

anisotropic parts

7 and 8. However, the magnetic flux passing the magnetically anisotropic parts is limited because of the high magnetic resistance and the magnetic saturation brought about with the small magnetic flux. Consequently, the reproduction distortion due to the magnetic non-linearity of the magnetic circuit elements decreases greatly because of the weak mutual relation of the magnetic flux of the voice coil 6 and the magnetic circuit parts. Further, since the resistance of the two directional silicon steel is higher than that of normal iron, silicon steel is useful for diminishing eddy current power loss caused by the magnetic flux of the voice coil in the magnetic circuit elements. Further, the insulating layers 10 not only act as magnetic resistance members, but are useful to decrease the eddy current power loss, and thus a speaker or a microphone having a high conversion efficiency may be produced without difficulty because the magnetic flux acts to good advantage. Further, the sheets of magnetically anisotropic material or normal magnetic material act as short rings, and thus the distortion is reduced even more.

In addition, the functions and advantages such as mentioned above are achieved by laminating the sheets of the-magnetically anisotropic material or the normal magnetic material using adhesive paste layers or insulating paint layers.

As described above, the magnetic circuit of the present invention is composed of laminated magnetic parts which increase the magnetic resistance against the magnetic flux caused by a voice coil. The sheets of the magnetically anisotropic material are oriented such that the direction of the easy magnetizing axis is the same as the magnetic flux for driving the speaker or the microphone within the air gap. Consequently, the reproduction distortion is drastically reduced. Since the insulating layers are between the sheets of the magnetic material, the eddy current power loss decreased, consequently a speaker or a microphone having high conversion efficiency may be manufactured.

While the invention has been particularly shown and described with reference to preferred embodiments thereof, it will be understood by those skilled in the art that various changes in form and details may be made therein without departing'from the spirit and scope of the invention.

What is claimed is:

1. An electro-acoustic converter comprising:

a. a center pole;

b. voice coil means surrounding said center pole;

c. magnetic means surrounding said center pole and said voice coil means; and

d. plate means fixed to said magnetic means; the improvement comprising e. wherein at least a portion of said center pole is a stack of layers of a magnetically anisotropic material interleaved with insulating layers;

f. wherein at least a portion of said plate means is a stack of layers of a magnetically anisotropic material interleaved with insulating layers.

2. The apparatus of claim 1 wherein said at least a portion of said plate means is all of said plate means. =l

Claims

1. An electro-acoustic converter comprising: a. a center pole; b. voice coil means surrounding said center pole; c. magnetic means surrounding said center pole and said voice coil means; and d. plate means fixed to said magnetic means; the improvement comprising e. wherein at least a portion of said center pole is a stack of layers of a magnetically anisotropic material interleaved with insulating layers; f. wherein at least a portion of said plate means is a stack of layers of a magnetically anisotropic material interleaved with insulating layers.

2. The apparatus of claim 1 wherein said at least a portion of said plate means is all of said plate means.