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DESCRIPTION JPH06141397

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DESCRIPTION JPH06141397
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
electrodynamic speaker having a magnetic circuit in which a magnet is magnetically repelled.
[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 has been
significantly improved, and a speaker capable of high-quality sound reproduction has been
required correspondingly. ing. On the other hand, along with the integration 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 color shift of the Braun tube and the like.
Moreover, with the spread of high energy product rare earth magnets, the magnetic circuit is
required to be compact and lightweight while taking measures against magnetic shielding. Here,
for high-quality sound reproduction, it is desirable that the driving force distortion of the speaker
itself be extremely small. At present, as a measure to reduce driving force distortion of the
speaker itself, a short voice coil system is used in which the winding width of the voice coil is
made smaller than the thickness of the plate forming the center pole and the magnetic gap. On
the other hand, as a measure against magnetic shielding, on the upper and lower surfaces of a
plate that forms a magnetic gap with the center pole, two magnets magnetized in opposite
directions are joined, and provided between the upper magnet and the outer periphery of the
underplate. This is done by making the obtained yoke magnetically copolar with the underplate.
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[0003]
The conventional speaker will be described below. FIG. 4 shows a cross-sectional view of a
conventional speaker. In FIG. 4, 1 is a center pole, 2 is an under plate having the center pole 1
joined to the center, 3 is a plate disposed to form a magnetic gap with the side of the center pole
1, 4 is an upper surface (plate 3 side ) Is a magnet magnetized in the N pole and the lower
surface (under plate 2 side) in the S pole, 5 is the S pole in the upper surface (yoke 6 side) and N
pole in the lower surface (plate 3 side) Two magnets, 6 is a yoke forming a magnetic circuit
between the magnet 5 and the under plate 2, 7 is a voice coil which moves up and down in the
magnetic gap according to the electric signal, 8 is a voice coil 7 and supports voice Voice coil
bobbin moving with the coil 7, 9 is a damper with one end fixed to the frame 12 and the other
end attached to the voice coil bobbin 8, 10 the voice coil bobbin 8 mounted on the center side It
is a diaphragm attached to the frame 12 periphery via the edge 11.
[0004]
In the conventional speaker, in order to reduce driving force distortion, a short voice coil system
in which the thickness of the plate 3 is made large relative to the winding width of the voice coil
7 is adopted, and in order to achieve magnetic shielding type, A magnetized magnet 5 is provided
on the upper surface of the plate 3, and a yoke 6 in contact with the magnet 5 and the under
plate 2 is provided. As a result, since the under plate 2 and the yoke 6 have the same magnetic
polarity, magnetic leakage to the outside of the speaker is reduced.
[0005]
SUMMARY OF THE INVENTION In the prior art as described above, the center pole is fixed in
order to make the driving force constant by reducing the driving force distortion which increases
with the large amplitude in the low frequency range at the time of large input. The plate 3
forming a magnetic gap with 1 had to be thick enough for the voice coil 7 to be present in the
magnetic gap in the desired amplitude range. However, in order to obtain a desired magnetic flux
density in the magnetic gap, extremely large magnets 4 and 5 are required, and even if a high
energy product rare earth magnet is used, the size of the magnets 4 and 5 becomes quite large.
As a result, the magnetic circuit becomes huge and the weight becomes very large, which causes
a problem in practical use.
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[0006]
In addition, as a measure against magnetic shielding, by joining the magnet 5 and the under plate
2 with the yoke 6, the yoke 6 and the under plate 2 that widely cover the outer peripheral
portion of the magnetic circuit are magnetically polarized to the outside of the speaker. Leaks are
small. However, in such a structure, magnetic leakage increases between the inner peripheral
surface of the yoke 6 and the outer peripheral surfaces of the plate 3 and the magnets 4 and 5,
and the utilization efficiency of the magnets 4 and 5 is low. Further, if the distance between the
inner peripheral surface of the yoke 6 and the outer peripheral surfaces of the plate 3 and the
magnets 4 and 5 is increased in order to reduce the magnetic leakage, the volume and weight of
the magnetic circuit become large, which is not preferable for practical use. Furthermore, in such
a magnetic circuit in which the two magnets 4 and 5 are magnetically repelled, the distance
between the voice coil 7 and the damper 9 inevitably increases due to the presence of the
magnet 5 and the yoke 6. . If this distance becomes long, the voice coil bobbin 8 becomes long,
and not only the weight of the voice coil bobbin 8 increases, but also rolling easily occurs at the
time of driving, and the magnetic gap and the voice coil 7 or voice coil bobbin 8 contact and
abnormality There is a problem of generating a sound. Also, in general, when the voice coil
bobbin 8 is long, the circular shape of the voice coil bobbin 8 itself is hard to be held and easily
deformed, so that it is easy to contact at the magnetic gap portion.
[0007]
An object of the present invention is to provide a small and lightweight speaker which has high
utilization of magnets, can reduce the occurrence of rolling, and is small in consideration of the
conventional problems.
[0008]
The present invention according to claim 1 comprises two magnets arranged in a magnetically
repulsive direction, a center pole, an under plate, and a magnetic circuit formed by the two
magnets. The yoke has one end fixed to the frame and the other end mounted to the voice coil
bobbin moving up and down, and the upper end face of the yoke is along the lower surface of the
damper when the voice coil bobbin moves the lowermost. It is a speaker which has a shape which
becomes like.
[0009]
According to a third aspect of the present invention, there is provided a center pole, two magnets
disposed in a magnetic repulsion direction on each surface of both end faces of the center pole,
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and a top plate disposed on the surface of one magnet. And an under plate disposed on the
surface of the other magnet, and a yoke disposed on the outer peripheral portion of the under
plate and provided so as to form a magnetic gap between the side surfaces of the center pole,
and A convex portion is formed at the central portion of the surface on the center pole side of the
magnet, and a concave portion fitted to the convex portion is formed at the central portion of the
surface of the center pole facing the surface.
[0010]
According to the present invention of claim 1, since the upper end face of the yoke is shaped to
be along the lower surface of the damper when the voice coil bobbin moves the lowermost, the
length of the voice coil bobbin can be shortened, The utilization of magnets can be increased.
[0011]
According to the third aspect of the present invention, the convex portion at the central portion
of the surface on the center pole side of the magnet on the top plate side and the concave portion
at the central portion of the surface of the center pole facing the surface are engaged with each
other Therefore, the height to the top plate can be reduced, the utilization of magnets can be
increased, and the size and weight can be reduced.
[0012]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be
described below based on the drawings showing the embodiments.
[0013]
FIG. 1 is a structural sectional view of a loudspeaker according to a first embodiment of the
present invention.
That is, an under plate 17 is provided at the bottom of a cup-shaped frame 24 forming the outer
case of the speaker, and a cylindrical magnet 15 is provided at the center of the under plate 17.
A cylindrical center pole 13 is provided on the upper surface, a cylindrical magnet 14 is provided
on the upper surface of the center pole 13, and a top plate 16 is further provided on the upper
surface of the magnet 14.
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Also, a cylindrical yoke 18 is provided around the under plate 17 so as to form a magnetic gap
with the side surface of the center pole 13.
The upper end surface of the yoke 18 is formed by an inclined surface which is low on the side of
the center pole 13 and high on the outer side so as to be substantially parallel to the lower
surface of the damper 21 when the voice coil bobbin 20 moves downward most.
[0014]
The above-mentioned magnetic gap is provided with a voice coil 19 which generates a driving
force in response to an electric signal, and the voice coil 19 is attached to an end of the voice coil
bobbin 20 and is moved up and down by the driving force of the voice coil 19 It is configured to
be able to.
A damper 21 for supporting the voice coil bobbin 20 is provided between the midway portion of
the voice coil bobbin 20 and the frame 24, the diaphragm 22 is attached to the upper end of the
voice coil bobbin 20, and the outer periphery of the diaphragm 22 has an edge 23. Are attached
to the frame 24.
[0015]
Next, the operation of the first embodiment will be described.
[0016]
Tmu and Tmd in FIG. 1 are the thicknesses of magnets 14 and 15, Tc is the thickness of center
pole 13, Tp is the thickness of top plate 16, Tu is the thickness of under plate 17, Tv is the
winding width of voice coil 19, Tvd is The distance from the center of the voice coil 19 to the
damper 21.
When the voice coil 19 moves upward from the neutral point of the amplitude, the moving
distance (with the neutral point as the origin and the upper direction on the drawing as positive
and the lower direction as negative) is (Tc−Tv) / When the volume of the voice coil 19 present
in the magnetic gap is constant up to 2 and the movement distance moves downward, on the
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other hand, the voice present in the magnetic gap until the movement distance is-(Tc-Tv) / 2.
Since the volume of the coil 19 is constant, the driving force is constant.
[0017]
Further, since the magnets 14 and 15 are magnetized in a magnetically repelling direction, the
magnet 14 forms a magnetic path by the center pole 13, the yoke 18 and the top plate 16, and
the magnet 15 forms a magnetic path together with the center pole 13. The yoke 18 and the
under plate 17 form a magnetic path.
Therefore, the top plate 16, the under plate 17 and the yoke 18 have the same magnetic polarity
and the magnetic leakage to the outside of the magnetic circuit is extremely reduced.
Further, as described above, since there are two magnetic paths, all the magnetic flux supplied
from the magnets 14 and 15 does not pass through the lower surface of the center pole 13 and
the under plate 17 as in the prior art. The under plate 17 is less likely to be magnetically
saturated, and the diameter of the center pole 13 and the thickness Tu of the under plate 17 can
be reduced. When the magnetic circuit has the above structure, almost no space exists inside the
magnetic circuit except for the magnetic gap, so the magnetic leakage excluding the magnetic
gap is extremely small inside, and the magnetic utilization efficiency of the magnet is high.
Become. The small space inside the magnetic circuit and the high utilization efficiency of the
magnet make it possible to reduce the size and weight of the magnetic circuit.
[0018]
Here, in order to enhance the utilization efficiency of the magnet and reduce the magnetic
leakage to the outside of the magnetic circuit, it is preferable to set the height of the yoke 18 to
Tc + Tmu + Tmd + Tp, but when the distance Tvd between the voice coil 19 and the damper 21
becomes long Not only the weight of the voice coil bobbin 20 is increased, but also rolling tends
to occur, and the yoke 18 or the center pole 13 etc. collides with the voice coil 19 or the voice
coil bobbin 20 in the magnetic gap to generate an abnormal sound. Cause problems such as
disconnection of the voice coil 19. Moreover, as a result of the voice coil bobbin 20 becoming
very long, the circular shape of the voice coil bobbin 20 becomes difficult to hold, and further, a
collision at the magnetic gap portion with respect to rolling tends to occur. Therefore, in order to
prevent this problem, the distance Tvd between the voice coil 19 and the damper 21 should be as
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short as possible. That is, rolling can be prevented as the height of the yoke 18 approaches Tc +
Tmd. However, if the height of the yoke 18 is shortened, the distance between the top plate 16
and the yoke 18 increases and the utilization efficiency of the magnet 14 decreases and the
magnet Leakage will increase. Therefore, by making the position of the upper end of the outer
peripheral portion of the yoke 18 higher than the position of the upper end of the inner
peripheral portion, the distance between the top plate 16 and the yoke 18 can be reduced to
improve the utilization efficiency of the magnet. Leakage can be reduced.
[0019]
Here, the position of the upper end of the outer peripheral portion of the yoke 18 is just the
outer peripheral surface of the yoke 18 when the vibration system moves downward to the
maximum and the damper 21 collides with the upper end of the inner peripheral portion of the
yoke 18. It is most effective if the height at which the upper end of the vibration system also
collides (that is, an inclination substantially parallel to the lower surface of the damper 21 when
the vibration system moves downward to the maximum) is provided. At this time, if the position
of the upper end of the outer peripheral portion of the yoke 18 is lower than the height
described above, the distance between the top plate 16 and the yoke 18 becomes large, the
utilization efficiency of the magnet 14 becomes small, and the magnetic leakage increases.
Conversely, if the position of the upper end of the outer peripheral portion of the yoke 18 is
higher than the height described above, the distance between the voice coil 19 and the damper
21 becomes large, and the voice coil bobbin 20 becomes long and rolling easily occurs.
[0020]
Next, FIG. 2 shows a structural cross-sectional view of the speaker of the second embodiment. A
major difference from the first embodiment is that in order to enhance the utilization efficiency
of the magnet 14 and to reduce the magnetic leakage, the central portion on the lower surface
side of the magnet 14 has a convex structure and the thickness of the outer peripheral portion of
the magnet 14 is a central portion The area of the exposed portion of the outer periphery of the
magnet 14 is reduced without changing the volume of the magnet 14 by making the convex
portion of the magnet 14 fit with the concave portion provided on the upper surface of the
center pole 13 The structure is The other configuration is the same, and the operation of this
embodiment is completely the same as that of the first embodiment, but the distance between the
top plate 16 and the yoke 18 becomes close by adopting the above-mentioned structure, The
magnetic resistance in the magnetic path formed by the magnet 14, the center pole 13, the yoke
18, and the top plate 16 is reduced, the utilization efficiency of the magnet 14 is increased, and
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the magnetic leakage to the outside of the magnetic circuit is reduced. . Further, since the
distance from the center of the center pole 13 to the top surface of the top plate 16 is shortened,
the voice coil bobbin 20 can also be shortened. As a result, since the circular deformation of the
voice coil bobbin 20 can be made very small, when rolling occurs, a collision with the magnetic
gap hardly occurs.
[0021]
In the above embodiment, the upper end face of the yoke 18 is formed by the inclined flat
surface, but the invention is not limited thereto. For example, as shown in FIG. 3A, when the voice
coil bobbin 20 is moved to the lowermost side A plane P1 substantially parallel to the plane Pd
passing through the lower surface of the damper 21 may be considered, and the step shape may
be configured such that each end passes through the plane P1. In this case, as shown in FIG. 3B,
it may have a step shape of one step. Alternatively, as shown in FIG. 3C, the shape of the upper
end face of the yoke 18 is formed in a wave shape centered on the plane P3 substantially parallel
to the plane Pd so as to conform to the shape of the lower surface of the damper 21. It is also
good.
[0022]
In the above embodiment, the present invention is applied to a speaker having a configuration in
which a magnet is provided on the center pole 13 side, but instead is applied to a speaker having
a configuration in which a magnet is disposed outside the conventional voice coil bobbin of FIG.
Of course it is good.
[0023]
As is apparent from the foregoing, according to the present invention, since the upper end
surface of the yoke has a shape that follows the lower surface of the damper when the voice coil
bobbin is moved to the lowermost position, It has the advantages of being able to increase
utilization and reducing the occurrence of rolling.
[0024]
In addition, when the convex part of the central part of the surface on the center pole side of the
magnet on the top plate side and the concave part of the central part of the surface of the center
pole opposite to the surface are fitted and arranged, use of the magnet There is an advantage
that the rate can be increased and the size and weight can be reduced.
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