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DESCRIPTION JPH11341594

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DESCRIPTION JPH11341594
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
moving coil type speaker incorporating a movable voice coil, and more particularly to a magnetic
circuit structure thereof.
[0002]
2. Description of the Related Art FIG. 4 is a cross-sectional view of a magnetic circuit generally
employed in a moving coil type speaker. As shown in the figure, the magnetic circuit is joined to
a yoke 1 made of a magnetic material and having a center pole 1a erected at a central portion,
and a plate portion 1b of the yoke 1 to surround the center pole 1a. It is mainly composed of the
ring-shaped magnet 2 and the top plate 3 made of a magnetic material and joined on the magnet
2 to define the magnetic gap G between the center pole 1a, and the axial direction The direct
current magnetic flux from the magnet 2 which is magnetized is converged in the magnetic gap
G. Although not shown, a voice coil is wound around the outer peripheral surface of a cylindrical
bobbin bonded to a diaphragm made of cone paper or the like, and this voice coil is disposed in
the magnetic gap G. Therefore, by energizing the audio current, an electromagnetic force acts on
the voice coil, and the voice coil is driven to vibrate the diaphragm.
[0003]
However, in the magnetic circuit configured in this manner, a magnetic flux is generated when a
current flows in the voice coil, and this magnetic flux changes the magnetic flux density in the
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magnetic gap G, so the magnetic circuit is disposed in the magnetic gap G. The voice coil has a
problem that the inductance is increased particularly in a high frequency band, and the
reproduced sound of the speaker has a distortion called current distortion.
[0004]
Therefore, conventionally, as shown in FIG. 5, a cap 4 made of a nonmagnetic material having a
low electric resistance such as copper or aluminum is externally fitted to the center pole 1 a of
the yoke 1 and a voice coil is generated by the eddy current generated in the cap 4. There has
been proposed a technique of reducing the magnetic flux generated by the magnetic flux, thereby
reducing the change of the magnetic flux density in the magnetic gap G.
If such a cap 4 is attached to the magnetic circuit of the speaker, the impedance curve in the high
frequency band can be leveled as shown in FIG. 6, and the frequency characteristic of the
acoustic output is also improved as shown in FIG.
[0005]
As disclosed in Japanese Patent Application Laid-Open No. 63-215295, a metal film such as
copper or aluminum thinner than the cap 4 is clad on the center pole 1a or the top plate 3, and
the same effect is expected. Technology has also been proposed.
[0006]
As described above, in the former prior art, the cap 4 made of copper, aluminum or the like is
disposed in the magnetic gap G as a measure for suppressing current distortion of the speaker.
However, when the cap 4 is further disposed in the magnetic gap G in which the voice coil is
loosely inserted, the gap length of the magnetic gap G must be increased by the thickness of the
cap 4 and the magnetic flux in the magnetic gap G There is a problem that the density decreases.
In addition, in order to compensate for such a decrease in magnetic flux density, a larger magnet
2 is required, and there is also a problem that the magnetic circuit must be upsized.
[0007]
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On the other hand, in the latter prior art, since the metal film of copper or aluminum thinner than
the cap 4 is clad on the center pole 1a and the top plate 3, it is not necessary to increase the gap
length of the magnetic gap G so much. With a weak eddy current generated in a thin metal film,
the magnetic flux generated by the voice coil can not be sufficiently reduced, and the effect of
suppressing current distortion of the speaker is low.
[0008]
SUMMARY OF THE INVENTION According to the present invention, a ring-shaped two magnets,
which are magnetized in opposite radial directions, are arranged opposite to each other on the
outside of two voice coils, respectively, to form a cylindrical space inside a bobbin. By placing a
member with a small electric resistance in this empty space, it is possible to sufficiently suppress
the current distortion of the speaker without sacrificing the magnetic flux density or increasing
the size of the magnetic circuit. did.
[0009]
BEST MODE FOR CARRYING OUT THE INVENTION In a loudspeaker according to the present
invention, of the outer peripheral surface of a cylindrical bobbin, two voice coils wound around
two places spaced apart in the axial direction by a predetermined amount, and a material having
a lower electrical resistance than iron. A current distortion suppressing member which is
disposed on the inner side of the bobbin via an air gap, and two ring-shaped magnets magnetized
in opposite radial directions with respect to each other and disposed on the outer side of the two
voice coils via an air gap. And a yoke made of a magnetic material and joined to the outer
peripheral surface of the two magnets.
[0010]
The magnetic circuit of the speaker configured in this way utilizes the convergence of the DC flux
from the inner circumferential surface of one magnet across the two voice coils to the inner
circumferential surface of the other magnet. Even if a current distortion suppressing member
made of aluminum or the like is installed in the inner empty space to enhance the current
distortion suppressing effect of the speaker, there is no concern that the magnetic flux density
acting on the voice coil is lowered.
Therefore, the distortion of the reproduced sound in the high frequency band can be suppressed
and the sound quality can be improved without increasing the size of the magnetic circuit.
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[0011]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Referring to the drawings, FIG. 1 is
a sectional view of a loudspeaker according to a first embodiment of the present invention, and
FIG. 2 is a sectional view of a loudspeaker according to a second embodiment of the present
invention. 3 is a cross-sectional view of a loudspeaker according to a third embodiment of the
present invention.
[0012]
First, the first embodiment shown in FIG. 1 will be described. In this speaker, a cylindrical bobbin
10 made of nonmagnetic material and two portions of the outer peripheral surface of this bobbin
10 that are separated by a predetermined amount in the axial direction Are wound, two current
distortion suppressing members 13 made of substantially cylindrical aluminum disposed inside
the bobbin 10 with an air gap, and two ring-shaped magnets 14, 15 And a magnetic circuit
consisting of a cylindrical yoke 16, a magnetic circuit cover 17 accommodating and holding the
magnetic circuit and the current distortion suppressing member 13, a cone paper etc. And a
frame 21 supporting the diaphragm 18 via the elastic edge 19 and the damper 20. As shown in
FIG.
However, the two magnets 14 and 15 are magnetized in the direction opposite to each other in
the radial direction, and the inner peripheral surfaces of the magnets 14 and 15 are opposed to
the outside of the two voice coils 11 and 12 with an air gap therebetween. The inner
circumferential surface of the yoke 16 made of a magnetic material is joined to the outer
circumferential surface of each of the magnets 14 and 15.
[0013]
That is, in the magnetic circuit of this speaker, the magnetic flux crosses the voice coil 11 from
the inner circumferential surface of one of the magnets 14 to the inside and further crosses the
voice coil 12 outward to converge on the inner circumferential surface of the other magnet 15.
The magnetic circuit hardly uses a cylindrical space inside the bobbin 10.
Therefore, even if the current distortion suppressing member 13 made of aluminum which is
much thicker than the above-described cap 4 (see FIG. 5) is installed in this empty space to
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enhance the current distortion suppressing effect of the speaker, the voice coils 11, 12 There is
no concern to reduce the magnetic flux density acting on the
Therefore, this speaker has a high effect of suppressing distortion of reproduced sound in a high
frequency band without increasing the size of the magnetic circuit, and good sound quality can
be expected. In fact, when this loudspeaker is compared with the conventional loudspeaker
shown in FIGS. 4 and 5, the impedance curve in the high frequency band is largely leveled as
shown by the solid line in FIG. It is improved as shown by a solid line in FIG.
[0014]
In this speaker, when a voice current is supplied to the voice coils 11 and 12, a driving force in
the same direction is given to both 11 and 12 by the action of the electromagnetic force. Because
the vibration plate 18 is transmitted to the vibration plate 18, the vibration plate 18 vibrates
according to the audio current.
[0015]
In addition, although a relatively inexpensive and lightweight aluminum is preferable as a
material of the current distortion suppressing member 13, another material having a lower
electrical resistance than iron and which easily generates an eddy current, such as copper, may
be used.
[0016]
In the second embodiment shown in FIG. 2, the cylindrical current distortion suppressing
member 13 located inside the bobbin 10 and the magnetic circuit cover 17 are integrally made
of aluminum or the like, and the number of parts is smaller than that of the first embodiment.
Can reduce the number of assembly steps.
[0017]
In the third embodiment shown in FIG. 3, the current strain suppressing member 13, the
magnetic circuit cover 17 and the frame 21 are integrally made of aluminum or the like, and the
number of parts is further reduced and the number of assembling steps is reduced compared to
the second embodiment. be able to.
[0018]
The present invention is carried out in the mode as described above, and exhibits the effects as
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described below.
[0019]
Two ring-shaped magnets magnetized in opposite radial directions are disposed opposite to each
other on the outside of the two voice coils, and a magnetic circuit that hardly uses a cylindrical
space on the inner side of the bobbin, and the inner side of this bobbin The current distortion
suppressing member made of aluminum, copper, etc. is installed in the empty space of the
speaker, so the current distortion of the speaker using the current distortion suppressing
member much thicker than the cap etc. used in the conventional product. Even if the suppression
effect is enhanced, there is no concern to reduce the magnetic flux density acting on the voice
coil.
Therefore, the distortion of the reproduced sound in the high frequency band can be suppressed
and the sound quality can be improved without increasing the size of the magnetic circuit.
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