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JPH0243897

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DESCRIPTION JPH0243897
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates mainly
to a magnetic circuit in an electrodynamic speaker that radiates sound waves from a diaphragm
directly or through a horn. <Prior Art> Magnetic circuits generally used in such an
electrodynamic speaker include an external magnet type and an internal magnet type, and
among these, the external magnet type is shown in FIG. As described above, the magnet 1 formed
of a permanent magnet and the yoke 3 with a center ball 2 and a plate 4 formed of a magnetic
material with high magnetic permeability attached respectively to both poles of the magnet 1
form a substantially annular shape. An air gap (magnetic gap) 5 is formed between the center
ball 2 and the inner circumferential surface of the plate 4. An electromagnet may be used as the
magnet 1 in addition to the permanent magnet, and the magnetic flux generated from the magnet
1 passes through the yoke 3 with the center pole 2 and the plate 4 and is concentrated in the air
gap 5. A strong cylindrical magnetic field is generated in the air gap 5. When a voice current is
supplied to a movable voice coil (not shown) disposed in the air gap 5, the voice coil vibrates in
the vertical direction by the electromagnetic induction action based on Fleming's left-hand rule. A
compression wave is created by a diaphragm (not shown) directly connected to the voice coil,
and is emitted as an acoustic wave into the acoustic space. <Problems to be Solved by the
Invention> However, the magnetic flux M in the air gap 5 is not only distributed between the
center ball 2 and the inner peripheral surface of the plate 4, but also a large loop above and
below the air gap 5. As a result, the magnetic flux density of the air gap portion 5 is lowered to
decrease the speaker sound pressure level, and the non-uniform distribution of the magnetic flux
M increases nonlinear distortion. Therefore, there is a problem that it is difficult to perform
accurate and efficient electroacoustic conversion. The present invention has been made in view
of such conventional problems, and it is an object of the present invention to provide a speaker
magnetic circuit having a configuration in which uniform and high-density magnetic flux
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distribution can be obtained in air gaps. It is <Means for Solving the Problems> In the present
invention, a magnetic circuit of a speaker is configured as follows as a technical means for
achieving the problems described above. That is, in the magnetic circuit of a speaker which is
substantially annularly formed by the magnet and the magnetic member and in which the air gap
where the magnetic flux is concentrated is formed in a part of the annular, the air gap in the
magnetic member It is characterized by the configuration in which the surface facing the gap is
removed (the surface in the vicinity of the air gap is covered with the magnetic shield layer made
of a superconducting material).
<Operation> On the surface provided with a magnetic material member through which a high
density magnetic flux passes, for example, a magnetic center such as a center ball, a plate or a
yoke, the magnetic flux can not pass because of the Meissner effect of the superconducting
material, that is, the perfect diamagnetic property. . Since this magnetic shielding layer is
provided on the surface of the vicinity of the air gap except for the surface facing the air gap
where the magnetic flux should be concentrated, unnecessary leakage of magnetic flux does not
occur, and the target magnetic flux The magnetic flux is led without loss to the air gap where it
should be concentrated. Therefore, a uniform magnetic flux distribution with a high density can
be obtained in the air gap, and therefore, it functions as a magnetic circuit of a speaker having a
small non-linear distortion with respect to an audio current flowing in the voice coil and a high
efficiency of excitation. Preferred embodiments of the present invention will be described in
detail with reference to the drawings. FIG. 1 shows a longitudinal cross-sectional view of a
magnetic circuit according to an embodiment of the present invention applied to the external
magnet type, and in the figure, the same reference numerals as in FIG. And omit the description.
Then, the surface of the center ball 2 facing the air gap 5 is removed (the surface and the surface
of the plate 4 other than the air gap surface 5 and the side end surface are covered with the
magnetic shield layer 6 made of a superconducting material) Only the ones in Figure 3 differ.
Therefore, leakage of the magnetic flux to the outside is prevented by the Meissner effect of the
superconducting material of the magnetic shield N6 in the center ball 2 and the plate 4 through
which high density magnetic flux passes by having high permeability per se. Since the highdensity magnetic flux without leakage loss passes only from the surface without the magnetic
shield layer 6 facing the air gap 5, a very high density magnetic flux M can be obtained in the air
gap 5. Further, the distribution of the magnetic flux M in the air gap portion 5 becomes uniform
by not drawing a large loop which spreads in the vertical direction due to the leakage magnetic
flux as shown in FIG. As described above, the magnetic flux M having a high density and uniform
distribution in the air gap 5 produces a non-linear distortion to the voice current flowing through
the voice coil located in the air gap 5 and a highly efficient excitation force is obtained. FIG. 2
shows a longitudinal sectional view of a magnetic circuit according to another embodiment of the
present invention applied to the internal magnet type, which is formed substantially annularly by
the magnet 7, the center ball 8 and the yoke 9, An air gap 10 is formed between the ball 9 and
the center ball 8. The surface of the yoke 9 near the space 10 except for both end surfaces facing
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the space 10 and the surface of the center ball 8 excluding the space 10 facing the surface are
covered with the magnetic shield N6 made of a superconducting material. The configuration is
the same as that of the first embodiment, and the same effect can be obtained.
<Effects of the Invention> As described in detail above, according to the magnetic circuit of the
speaker of the present invention, the magnetic shielding layer made of a superconducting
material is used as the surface excluding the inner surface facing the air gap in the vicinity of the
air gap of the magnetic member. Since it is provided so as to cover, it is possible to prevent the
leakage of the magnetic flux outside the air gap, to obtain a magnetic flux of high density and
uniform distribution in the air gap, and less non-linear distortion to the voice current flowing in
the voice coil And, a highly efficient excitation force can be obtained, and a speaker capable of
performing high-quality sound reproduction can be provided.
[0002]
Brief description of the drawings
[0003]
FIG. 1 is a longitudinal sectional view of an embodiment of the present invention, FIG. 2 is a
longitudinal sectional view of another embodiment of the present invention, and FIG. 3 is a
longitudinal sectional view of a conventional external magnetic circuit.
1, 7, 2, 8, 3, 3, 9, 4, 3, 4, 5,. Magnetic barrier layer
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