Speaker comprising ring magnet

Details Speaker comprising ring magnet Speaker comprising ring magnet

2000-12-15

2003-03-04

Barrera, Ramon M. (Department: 2832)

Electricity: magnetically operated switches, magnets, and electr

Magnets and electromagnets

Magnet structure or material

C381S412000, C381S420000

Reexamination Certificate

active

06529107

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a radially anisotropic ring magnet with improved linearity and/or peak value in a space magnetic flux density distribution than those of conventional ring magnets, and a speaker comprising such a radially anisotropic ring magnet for having improved linearity and/or peak value in thrust of a voice coil.
BACKGROUND OF THE INVENTION
Speakers of moving coil type have conventionally been used widely. A moving coil-type speaker is a speaker comprising a magnet and a yoke for generating a thrust for moving a voice coil in a magnetic gap, the voice coil coupled with a vibration system being movably disposed in the magnetic gap, and a driving current is caused to flow through the voice coil to generate sound.
FIG. 6
is a cross-sectional view showing an important part of a conventional moving coil-type speaker. In
FIG. 6
, a frame
1
formed by die-cast aluminum, etc. comprises a substantially conical upper frame
1
a
and a substantially arm-shaped lower frame
1
b
coupled with each other by screws
1
c.
The lower frame
1
b
is integrally provided with a cylindrical projection
1
d
at center, and a cylindrical inner yoke
7
made of a ferromagnetic material such as iron is fixed to an outer surface of a small-diameter portion
1
e
at a tip end of the projection
1
d.
Two voice coils
6
a,
6
b
wound in opposite directions are closely fixed to an outer surface of the inner yoke
7
with a gap therebetween in a vertical direction. Disposed around the outer surfaces of the voice coils
6
a
,
6
b
with a slight magnetic gap are radially magnetized ring magnets
5
a,
5
b.
The ring magnet
5
a
is magnetized such that its inner surface has an N pole and its outer surface has an S pole. The ring magnet
5
b
is magnetized such that its inner surface has an S pole and its outer surface has an N pole. The outer surfaces of the ring magnets
5
a,
5
b
are adhered to the inner surface of the cylindrical outer yoke
4
.
The ring magnets
5
a,
5
b
used in the speaker shown in
FIG. 6
are magnetized radially, and this speaker can avoid damage to its vibration system due to excess vibration generated when excess current flows through the voice coil, without needing a special safety gear. In the moving coil-type speaker, a driving current is enhanced to increase a stroke of the vibration system, to obtain a sound pressure in a low sound region on the same level as those in middle and high sound regions. To increase the stroke of the vibration system, increase in the linearity and/or peak value of the thrust of the voice coil is effective, desirable for satisfying the recent demand for miniaturization and increase in performance of speakers.
However, when a driving current is increased to enlarge the thrust of the voice coil, heat generated from the voice coil increases in proportion to the driving current. Thus, the temperature elevation (burning) of the voice coil should be prevented by limiting electric power supplied to the speaker and improving the heat dissipation of the speaker. Therefore, it is actually difficult to increase the thrust of the voice coil. It has also been found that when a moving coil-type speaker is constituted by conventional ring magnets
5
a
,
5
b
, linearity and/or peak value cannot fully be increased in an effective space magnetic flux density distribution crossing the voice coil movably disposed in the magnetic gap.
OBJECT OF THE INVENTION
Accordingly, an object of the present invention is to provide a speaker comprising a radially anisotropic ring magnet for providing improved linearity and/or peak value in the thrust of a voice coil as compared to conventional ones.
SUMMARY OF THE INVENTION
As a result of intense research in view of the above objects, the inventors have found that a radially anisotropic ring magnet with improved linearity and/or peak value in a space magnetic flux density distribution is obtained by providing a plurality of radially anisotropic regions along a center axis of the ring magnet, and by making a radial anisotropy direction in each region different from each other, and thus achieving the present invention.
The radially anisotropic ring magnet according to one embodiment of the present invention comprises at least one first radially anisotropic region having a radial anisotropy direction of 89° or more relative to a center axis thereof; and at least one second radially anisotropic region having a radial anisotropy direction of 40° or more and less than 89° relative to a center axis thereof, the first and second radially anisotropic regions being arranged along the center axis such that a space magnetic flux density distribution on an inner or outer surface of the ring magnet has increased linearity and/or peak value.
The radially anisotropic ring magnet according to another embodiment of the present invention comprises a plurality of radially anisotropic regions having radial anisotropy directions of 40° or more and less than 89° relative to a center axis thereof, the plurality of radially anisotropic regions being arranged along the center axis such that a space magnetic flux density distribution on an inner or outer surface of the ring magnet has increased linearity and/or peak value.
From the practical point of view, the above ring magnet is preferably made of an R—T—B permanent magnet having as a main phase an R
2
T
14
B intermetallic compound, wherein R is at least one rare earth element including Y, at least one of Nd, Dy and Pr being indispensable, and T is Fe or Fe and Co.
The present invention also provides a speaker comprising the above ring magnet.


REFERENCES:
patent: 4536230 (1985-08-01), Landa et al.
patent: 04023410 (1992-01-01), None
patent: 05176509 (1993-07-01), None
patent: 10177928 (1998-06-01), None
patent: 10304634 (1998-11-01), None

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