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DESCRIPTION JPH04363999

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DESCRIPTION JPH04363999
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
electrodynamic speaker.
[0002]
2. Description of the Related Art In recent years, as digital signal processing technology has
dramatically progressed, the quality of the electric signal supplied to the speaker is greatly
improved, and a speaker capable of high-quality sound reproduction corresponding to this is
realized. It is being sought. On the other hand, with the fusion of sound and video, it has become
common for the speaker to take measures against magnetic shielding in the magnetic circuit in
order to prevent the influence of the color shift of the cathode ray tube and the like. For high
sound quality reproduction, it is desirable that the driving force distortion of the speaker itself be
extremely small. Currently, as a measure to reduce the driving force distortion of the speaker
itself, a long voice coil type in which the winding width of the voice coil is made larger than the
thickness of the plate forming a magnetic gap with the center pole or vice versa. The short voice
coil type which makes width small is used. In addition, a short ring is provided in the magnetic
gap in order to remove the influence of the eddy current that causes the driving force distortion
during high-pitched sound reproduction. On the other hand, the magnetic shielding measure is
performed by making a yoke cover covering the outer peripheral portion of the magnetic circuit
magnetically the same polarity with a magnet dedicated to magnetic shielding that does not form
a magnetic gap and a magnetic path.
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[0003]
A conventional speaker will be described below. FIG. 4 shows a cross-sectional view of a
conventional speaker. In the figure, 1 is a bottom plate, 2 is a center pole, 3 is a top plate forming
a magnetic gap with the center pole 2, 4 is a magnet, 5 is a short ring, 6 is a magnet for
demagnetizing, and 7 is a yoke cover.
[0004]
In the conventional loudspeaker, a magnet 6 for exclusive use of the magnetic shield is
magnetized in the direction opposite to the magnet 4 to be magnetic-shielded and provided on
the lower surface of the bottom plate 1 and in contact with the magnet 6 and the top plate 3 A
cover 7 is provided. As a result, since the top plate 3 and the yoke cover 7 have the same
magnetic polarity, magnetic leakage to the outside of the speaker is extremely reduced. Further,
the short ring 5 is in the magnetic path in the magnetic gap.
[0005]
SUMMARY OF THE INVENTION In such a conventional technique, in order to reduce the driving
force distortion which increases with the large amplitude in the low frequency range at the time
of large input, the voice coil is formed even in the large amplitude. As a structure that does not
protrude from the inside of the magnetic gap, a long voice coil type in which the winding width
of the voice coil is larger than the thickness of the top plate 3 or conversely, the winding width of
the voice coil is smaller than the thickness of the top plate 3 The short voice coil form has been
used.
[0006]
That is, the volume of the voice coil present in the magnetic gap is designed to be constant in the
desired amplitude range of the voice coil, and the driving force is also designed to have a
constant value regardless of the magnitude of the amplitude.
However, in the case of the long voice coil type, in order to obtain a constant driving force in a
desired amplitude range, the winding width of the voice coil must be taken very long, as a result,
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the weight of the voice coil becomes large. Moreover, the voice coil portion present outside the
magnetic gap does not contribute to the driving force at all, so that the electrical energy can not
be effectively converted to mechanical energy, and the efficiency as a speaker is lowered.
[0007]
On the other hand, in the case of the short voice coil type, in order to obtain a constant driving
force in a desired amplitude range, it is necessary to take a very thick top plate 3 which forms
the center pole 2 and the magnetic gap. As a result, the volume occupied by the voice coil in the
magnetic gap becomes very small, and from the viewpoint of conversion efficiency, magnetic
energy can not be used effectively. Moreover, in order to obtain a desired magnetic flux density
in the magnetic gap, a very large magnet is required, and the magnetic circuit becomes huge,
which causes a practical problem in terms of shape, weight, and cost.
[0008]
Next, in the middle to high frequency range, an alternating current magnetic field generated in
the voice coil distorts the current flowing in the voice coil due to the eddy current, and as a
result, distortion occurs in the driving force. In order to improve this current distortion, a
material with high electrical conductivity, such as copper, is provided as a short ring 5 in the
magnetic gap. However, since the short ring 5 is present in the magnetic gap between the center
pole 2 and the top plate 3, the center pole 2 is designed to be smaller by the thickness of the
short ring 5, and the short ring 5 is a nonmagnetic material. Because of this, the magnetic path of
the magnetic gap becomes wide, and a sufficient magnetic flux density can not be obtained in the
magnetic gap, which causes the efficiency of the speaker to be lowered.
[0009]
As a countermeasure against magnetic shielding, by using the magnetic shielding magnet 6 to
make the yoke cover 7 covering the outer peripheral portion of the magnetic circuit and the top
plate 3 magnetically the same pole, the magnetic leakage to the outside of the speaker is slight.
There is. However, in such a structure, the volume and weight of the speaker become large due to
the presence of the magnetic shield magnet 6 and the yoke cover 7, which is not preferable in
practical use.
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[0010]
In the present invention, the driving force is constant even at the time of large amplitude, and the
presence of the short ring 5 does not reduce the magnetic flux density in the magnetic gap, and
the driving weight is extremely small. The purpose is to provide.
[0011]
SUMMARY OF THE INVENTION In order to achieve the above object, according to the present
invention, two annular magnets magnetized in the circumferential direction have a gap
corresponding to the thickness of the annular magnet in the vertical direction. A magnetic gap is
provided between the center pole and the yoke, the outer circumferential surface of the annular
magnet and the inner circumferential surface of the yoke, or the inner circumferential surface of
the annular magnet and the outer circumferential surface of the center pole, and the winding
width of the voice coil is A short ring is provided in the gap between the two annular magnets,
the sum of the gap between the two annular magnets and the thickness of one annular magnet.
[0012]
The present invention provides a speaker with extremely low magnetic leakage which does not
require a magnet for exclusive use of the magnetic shielding, and has a constant driving force
even at the time of large amplitude, and at the time of high frequency input to the speaker.
Driving force distortion due to eddy currents can be suppressed to a very low level, and a
sufficient magnetic flux density can be obtained in the magnetic gap while having a short ring.
[0013]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A structural cross-sectional view
of a first embodiment of the present invention and a detailed view of a voice coil portion are
shown in FIG. 1 and FIG. 2 respectively.
Here, (Fig. 1 (a)) shows an outer peripheral surface of the two annular magnets and (Fig. 1 (b))
shows that the outer peripheral surface of the two annular magnets and (Fig. 1 (b)) constitute a
magnetic gap. This is the case where the magnetic gap is formed by the inner circumferential
surface of the yoke.
In the figure, 8 is a plate, 9 is a center pole, 10 is a yoke, 11 and 12 are annular magnets
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magnetized in the circumferential direction, and 13 is a voice coil.
[0014]
The operation in the above configuration will be described.
Tmag in FIG. 2 is the thickness of the annular magnets 11 and 12, Tdis is the gap between the
annular magnets 11 and 12, and Tvc is the winding width of the voice coil 13. When the voice
coil 11 moves upward from the neutral point of the vertical amplitude ((a) of FIG. 2), the upward
moving distance is up to Tdis + Tmag / 2 as shown in (FIG. 2 (b)) The driving force is constant
because the volume of the voice coil 11 present in the magnetic gap is constant. Further, when
moving downward from the state of (FIG. 2A), the driving force becomes constant similarly until
the downward moving distance is Tdis + Tmag / 2 as shown in (FIG. 2C). Further, since the
annular magnets 11 and 12 are magnetized in the circumferential direction, the plate 8 and the
yoke 10 have the same magnetic polarity, and the magnetic leakage to the outside of the speaker
is extremely reduced.
[0015]
Next, a structural cross-sectional view of the second embodiment is shown in FIG. FIG. 3 (a)
shows the case where the magnetic gap is constituted by the inner circumferential surface of the
two annular magnets and the outer circumferential surface of the center pole, and FIG. 3 (b)
shows the outer circumferential surface of the two annular magnets and the yoke. The magnetic
gap is formed with the inner circumferential surface of The major difference from the first
embodiment is that the short ring 14 is provided in the gap between the annular magnets 11 and
12, and the other configuration is the same. As in the prior art, the short ring 14 is made of a
material having a high electrical conductivity, such as copper. Since the short ring 14 is provided
in the gap between the annular magnets 11 and 12, the magnetic circuit can be configured
without widening the magnetic path of the magnetic gap by the amount of the short ring as in
the prior art. Flows through the short ring 14.
[0016]
As described above, the present invention provides a speaker which has a constant driving force
even at large amplitude, does not have a short ring in the magnetic path, and does not require a
magnet for exclusive use of a magnetic shield. In the long voice coil type and the short voice coil
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type, which are means for making the driving force constant so far, including the problem that
electric energy and magnetic energy can not be effectively used, to release the eddy current. Was
short in the magnetic path, so the magnetic path of the magnetic gap became wider and
sufficient magnetic flux density could not be obtained in the magnetic gap, and the reduction in
size and weight could not be achieved due to the presence of the dedicated magnet Since it is
possible to solve the problem, it is possible to realize a highly efficient, compact and lightweight
speaker with extremely low driving force distortion that could not be obtained with conventional
speakers. That.
[0017]
Brief description of the drawings
[0018]
1 is a structural cross-sectional view of a speaker according to a first embodiment of the present
invention.
[0019]
2 is a detailed view of the voice coil portion of the speaker of the first embodiment of the present
invention.
[0020]
3 is a structural cross-sectional view of the speaker of the second embodiment of the present
invention.
[0021]
4 is a structural cross-sectional view of a conventional speaker.
[0022]
Explanation of sign
[0023]
8 plate 9 center pole 10 yoke 11, 12 annular magnet 13 voice coil 14 short ring
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