US3632904A

US3632904A - Moving coil loudspeaker with eddy current suppression

Info

Publication number: US3632904A
Application number: US36761*A
Authority: US
Inventors: Paul Mauz
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-03-24
Filing date: 1970-03-24
Publication date: 1972-01-04
Anticipated expiration: 1989-01-04

Abstract

An improved structure for a dynamic vibration generator, such as a loudspeaker or a microphone, which includes stacked sheets of high permeability material in the area of the pole gaps to suppress eddy currents.

Description

United States Patent Inventor Appl. No. Filed Patented Priority Paul Mauz Badstrasse 1, 724 Horb, Germany Mar. 24, 1970 Jan. 4, 1972 Feb. 17, 1965 Germany Continuation of application Ser. No. 500,630, Oct.22, 1965, now abandoned. This application Mar. 24, 1970, Ser. No. 36,761

MOVING COIL LOUDSPEAKER WITH EDDY CURRENT SUPPRESSION 3 Claims, 1 Drawing Fig.

US. Cl 179/119 R, 179/115.5 R, 335/231 Int. Cl -H04r 9/02 [50] Field oISeareh 179/1 15.5

[56] References Cited UNITED STATES PATENTS 1,976,874 10/1934 Brzeski 179/1 l5.5 OTHER REFERENCES Brailsford, Magnetic Materials, 1960, Methuen & Co., Chaps. lV&V

Bardell, Magnetic Materials in the Electrical Industry, 1960, MacDonald & Co., Chap. 4

Primary Examiner-Kathleen H. Claffy Assistant Examiner-Thomas L. Kundert Atmrney--Shlesinger, Shlesinger & Arkwright ABSTRACT: An improved structure for a dynamic vibration generator, such as a loudspeaker or a microphone, which includes stacked sheets of high permeability material in the area of the pole gaps to suppress eddy currents.

PATENTEU JAN 4 I972 ATTORNEY MOVING COIL LOUDSPEAKER WITH EDDY CURRENT SUPPRESSION This application is a continuation of application Ser. No. 500,630, filed Oct. 22, 1965, and now abandoned.

This invention relates to dynamic vibration generators, and more particularly to dynamic loudspeakers having a permanent ring-shaped magnet and having a vibratory coil connected with a diaphragm centered in its cylindrical annular gap.

The application of the invention extends furthermore to dynamic microphones or dynamic sound systems of any kind. Such sound systems usually consist of a ringlike magnet of any construction where a cylindrical annular gap is provided between the central core and the annular plate surrounding the core. A vibratory coil with a conventional tensioned diaphragm is centered in the annular gap.

The flux of the permanent magnet acts crosswise to the longitudinal axis of the vibratory coil in the annular gap of the magnet. The vibratory coil connected for example to an output amplifier is fed with audiofrequency currents, which create in the coil a magnet field which extends perpendicularly to the field of the permanent magnet. The magnetic reproduction field, continuously varying as a function of the audiofrequency currents, pushes the coil alternately inward and outward in relation to the ring magnet. By the connection of the vibratory coil with a diaphragm, the audiofrequency electric vibrations are transformed into mechanical sound vibrations by such an arrangement.

The known dynamic vibration systems, as used at present for loudspeakers and dynamic microphones, cannot satisfy higher requirements. It is known that by amplification of the magnetic flux in the annular gap the quality of reproduction. of loudspeakers can be improved. This is attributable to the fact that with a stronger magnetic field the vibratory coil is deflected with greater force or the deflecting movement is delayed less. It has been observed, for example, that the reproduction volume increases proportionally with the increase in magnetic field strength. The known measures for accommodating as great as possible a magnetic field strength between the pole surfaces determined by the size of a magnet are limited by the saturation values of the iron.

For the improvement of the reproduction quality or frequency fidelity in dynamic sound systems the present invention proceeds from a hitherto neglected, but influential process. The magnetic field of the current-carrying vibratory coil, which moves in the field of the permanent magnet, leads to reactions in the massive iron of the permanent magnet. That is, the moving magnetic field of the vibratory coil produces eddy currents in the poles in the zone of the gap. The losses due to the eddy currents weaken the magnetic field of the vibratory coil, so that therefore also the movement or the deflection of the vibratory coil from the field of the permanent magnet is impaired or delayed, owing to which in turn the audiofrequency vibrations to be transformed are varied harmfully for the quality of reproduction.

It is known that electric vibrations of higher frequencies or the magnetic fields of the vibratory coil thus varying more rapidly produce greater eddy currents than the lower. This results in a vibration mixture in which the audio vibrations of different pitch are delayed or damped in different degree, so that a distortion of the acoustic pattern occurs.

The invention thus has the task of providing means whereby the eddy currents in the area of the magnet poles which are attributable to the current-carrying vibratory coil are eliminated or sufficiently reduced. The solution of this problem resides in that the poles on both sides of the annular gap consist of annular, low remanence dynamo sheets which are stacked on one another in the longitudinal direction of the gap. The sheets thus extend crosswise to the direction of movement of the coil and their outer or inner end faces are directed toward the coil. The width of the sheets is evident from the particular operating data or from the strength of the audiofrequency currents and from the frequency range to be transmitted. As the lower vibrations in the vibrator coil brin about a more widely expandrng magnetic field t an the hrg er vibrations, care must be taken-that also these low vibrations or the magnetic field produced by them remains unweakened in the poles of the magnet and that no eddy currents are produced.

Instead of dynamo sheets, the poles on both sides of the gap may consist of high-frequency iron, housed in corresponding annular cavities on both sides of the air gap. The following may be considered high-frequency iron: pulverized iron, iron chips, sintered iron, separately, pure or mixed, iron dust embedded in plastic, iron oxide compounds with other metals which combine good permeability with poor conductivity.

According to another proposal of the invention, the central core of the ring magnet contiguous to the pole region is recessed or reduced in its diameter. Thereby eddy current losses contiguous to the pole region are avoided, and at the same time the magnetic field is concentrated.

The figure illustrates the invention with respect to a few ex amples of embodiment The FIGURE shows diagrammatically a loudspeaker according to the invention.

According to the diagrammatic representation of a dynamic loudspeaker as set forth in the FIGURE, the magnetically energized circuit (cup-shaped magnet) consists of a circular iron disc 1, a ring 2 formed for example of sintered magnet iron, and an iron pole ring 3 fitted thereupon which surrounds a core portion 4 which is secured by threads or by adhesive means to the circular disc 1. The structural parts I, 2 and 3 can also be secured to one another by adhesive means. The air gap of the magnet, in which the oscillation coil 5 of the loudspeaker is centered, is forrned of transformer sheet metal rings punched out in the form of two concentric rings 6 and 7, whereby the outer ring 6 is fastened in a corresponding recess in pole ring 3 whereas the inner ring 7 is fastened in a corresponding recess in core portion 4. The oscillation coil 5 is connected with the aid of conventional fastening means to the diaphragm 8 of the loudspeaker, As a further embodiment, the iron core may be recessed, that is, its diameter may be recessed in relation to the part lying above or below.

The radial thickness or depth of the aforesaid means for suppressing eddy currents is smaller in the case of loudspeakers of smaller output than in the case of larger loudspeakers. As an average, the axial depth is about 5 millimeters.

I claim:

1. A dynamic vibration generator comprising:

a. a permanent magnet having a cylindrical annular air gap,

b. a vibratory coil in said annular gap,

c. a diaphragm connected to said vibratory coil,

d. poles on each side of said air gap having recesses therein,

e. means for suppressing eddy currents also positioned on each side of said air gap adjacent said coil in said recesses,

f. said suppressing means being in the form of a stacked plurality of flat rings of dynamo sheet material having axes parallel to the path of said vibratory coil and being positioned transversely to said vibratory coil path.

2. A dynamic vibration generator as set forth in claim I wherein said recesses are formed by shoulders on the inner and outer circumferences of respective poles for centering and supporting said dynamo sheets.

3. A dynamic vibration generator as defined in claim I wherein said suppressing means has a radial depth of approximately 5 millimeters.

Claims

1. A dynamic vibration generator comprising: a. a permanent magnet having a cylindrical annular air gap, b. a vibratory coil in said annular gap, c. a diaphragm connected to said vibratory coil, d. poles on each side of said air gap having recesses therein, e. means for suppressing eddy currents also positioned on each side of said air gap adjacent said coil in said recesses, f. said suppressing means being in the form of a staCked plurality of flat rings of dynamo sheet material having axes parallel to the path of said vibratory coil and being positioned transversely to said vibratory coil path.

2. A dynamic vibration generator as set forth in claim 1 wherein said recesses are formed by shoulders on the inner and outer circumferences of respective poles for centering and supporting said dynamo sheets.

3. A dynamic vibration generator as defined in claim 1 wherein said suppressing means has a radial depth of approximately 5 millimeters.