JPH077792

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DESCRIPTION JPH077792
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
speaker unit with reduced magnetic field leakage from a magnetic circuit and a method of
manufacturing the same.
[0002]
2. Description of the Related Art In recent years, the resolution of the display has been greatly
improved by the drastic improvement of the image technology, but in connection with this, the
leakage magnetic field from the speaker unit which adversely affects the image of the display
There is a need to further reduce the number, and there is a need to reduce the leak more than
ever.
[0003]
For example, a speaker unit as shown in FIG. 1 is known as a device that reduces the leakage
magnetic field.
[0004]
That is, on the lower plate 1 having the center pole 2, a ring-shaped main magnet 3 is attached.
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A ring-shaped upper plate 4 is attached to the top of the ring-shaped main magnet 3, and a
magnetic gap 5 is formed between the center pole 2 and the upper plate 4.
On the lower surface side of the lower plate 1, a ring-shaped auxiliary magnet 6 is attached
which is magnetized in the axial direction and whose magnetization direction is reversed to that
of the main magnet 3.
[0005]
Each component provided above and below around the upper plate 4 is covered by a shield cover
7, includes the shield cover 7, and the magnetic circuit 8 is covered by each component covered
by the shield cover 7. Is configured. A frame 9 which is expanded upward is attached to the
upper portion of the upper plate 4.
[0006]
In the speaker having such a configuration, the auxiliary magnet 6 is provided on the lower
surface side of the lower plate 1 and the shield cover 7 is additionally provided, thereby reducing
the magnetic potential difference between the magnetic circuit 8 and the frame 9. The incidence
decreases.
[0007]
However, in the speaker having such a configuration, although the leakage magnetic field from
the rear of the speaker can be reduced, there is a magnetic potential difference between the
frame 9 fixed on the upper plate 4 and the center pole 2 A stray magnetic field is generated in
the frame 9 as indicated by the broken line in FIG.
[0008]
As a solution to such a defect, for example, Japanese Utility Model Laid-Open No. 62-186592
discloses a speaker unit as shown in FIG.
[0009]
That is, in the upper part of the center pole 2 located inside the frame 9, the spacer 13 of
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nonmagnetic material is in a state that the cancel magnet 12 has the same pole (N pole) as the
center pole 2 facing the center pole 2 side. It is coaxially disposed via.
Here, in order to dispose the canceling magnet 12 in the voice coil 11, the diameter including the
spacer 13 is formed smaller than the outer diameter φA of the center pole 2. Therefore, a rare
earth magnet, an alnico magnet, etc. The ones that have a large energy product are used.
[0010]
In the speaker unit having such a configuration, the canceling magnet 12 provided inside the
frame 9 acts to cancel the stray magnetic field between the center pole 2 and the frame 9, so the
leakage magnetic field from the front of the speaker Since the magnetic field from the center
pole 2 is more concentrated on the upper plate 4 due to the repulsive action of the canceling
magnet 12, the magnetic flux density of the magnetic gap 5 is increased and the efficiency of the
speaker is improved. It has become.
[0011]
However, the conventional speaker unit described above has the following problems.
[0012]
That is, as shown in FIG. 3, when assembling the speaker unit, the main magnetic circuit 8 is
assembled, the vibration system is assembled, the main magnetic circuit 8 is magnetized, the
shield cover 7 and the canceling magnet 12 are assembled, and the cancel magnet assay is
performed. The procedure for assembling the magnetizing, main magnetic circuit 8 and canceling
magnet assay is taken.
[0013]
For this reason, the gap between the outer diameter of the upper plate 4 and the inner diameter
of the shield cover 7 is usually large (0.5 mm to 1.5 mm) for the reason that the cancel magnet
assay is attached last.
However, in such a case, the reluctance of the gap is increased, so that there is a disadvantage
that the leakage flux from the frame 9 to the shield cover 7 is increased.
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[0014]
Further, in order to improve the positional accuracy between the outer diameter of the upper
plate 4 and the inner diameter of the shield cover 7, advanced manufacturing techniques are
required, and it is extremely difficult to obtain dimensional accuracy.
[0015]
By the way, in the past, the resolution of the TV set was not too high, so even a large magnetic
leakage did not matter so much, but the resolution for the computer display and the monitor TV
for high vision became high. Therefore, even a slight magnetic leakage may cause color
unevenness and color deviation.
In addition, the distance between the CRT and the speaker also tends to shrink with the need for
downsizing and thinning of the TV set, and from this also, development of a speaker with lower
magnetic leakage is strongly desired.
[0016]
SUMMARY OF THE INVENTION The present invention has been made in view of such
circumstances, and an object thereof is to provide a speaker unit which can reduce the
generation of leakage flux significantly and to easily obtain dimensional accuracy, and a method
of manufacturing the same. Do.
[0017]
According to the first aspect of the present invention, a ring-shaped main magnet and an
auxiliary magnet are disposed at the upper and lower portions of a lower plate having a center
pole, and the center pole is provided with the above-mentioned center pole and the like. A
speaker comprising an upper plate forming a magnetic gap between them, the lower plate, the
main magnet, the auxiliary magnet and the upper plate covered by a shield cover, and a frame
expanded upward on the upper plate. In the unit, the gap between the bonding portion between
the outer peripheral edge of the upper plate and the shield cover is as small as possible.
[0018]
The invention according to claim 2 is characterized in that the upper plate or the shield cover is
provided with a bent portion, and the outer peripheral edge portion of the upper plate and the
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shield cover are joined via the bent portion. Do.
[0019]
The invention as set forth in claim 3 is characterized in that an offsetting magnet for offsetting a
leakage flux generated by the main magnet is attached to the upper portion of the center pole.
[0020]
The invention according to claim 4 is characterized in that a ring-shaped main magnet and an
auxiliary magnet are disposed at the upper and lower portions of a lower plate having a center
pole, and an upper plate forming a magnetic gap with the center pole above the main magnet. In
the method of manufacturing the speaker unit, the outer cover is disposed, the lower plate, the
main magnet, the auxiliary magnet and the upper plate are covered with the shield cover, and the
frame expanded upward is attached to the upper plate. The outer peripheral edge of the upper
plate is pressed into the peripheral edge.
[0021]
In the speaker unit and the method of manufacturing the same according to the present
invention, the gap between the outer peripheral edge of the upper plate and the joint portion
between the shield cover is made as small as possible, whereby the magnetic potential difference
between the frame and the shield cover is as small as possible. Because it is made smaller, the
occurrence of leakage flux from the frame to the shield cover is reduced.
[0022]
Further, by attaching a canceling magnet for canceling the magnetic potential difference
remaining at the top of the center pole, the leakage flux from the frame or the shield cover
toward the top of the center pole inside the frame is canceled.
[0023]
Furthermore, by press-fitting the outer peripheral edge of the upper plate to the outer peripheral
edge of the shield cover, not only it becomes easy to obtain dimensional accuracy, but also
dimensional variations can be absorbed by the press-in portion.
[0024]
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DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be
described in detail with reference to the drawings.
In the drawings described below, the same reference numerals as in FIG. 2 denote the same parts
in FIG.
[0025]
FIG. 4 shows an embodiment of the speaker unit according to the present invention. A ringshaped main magnet 3 is provided on the lower plate 1 having the center pole 2.
A ring-shaped upper plate 4 is provided above the ring-shaped main magnet 3.
A frame 9 which is expanded upward is attached to the upper portion of the upper plate 4.
A ring-shaped auxiliary magnet 6 is attached to the lower surface side of the lower plate 1.
[0026]
Each component provided above and below around the upper plate 4 is covered by a shield cover
7, includes the shield cover 7, and the magnetic circuit 8 is covered by each component covered
by the shield cover 7. Is configured.
Further, the gap between the outer peripheral edge of the upper plate 4 and the inner surface of
the shield cover 7 is made as small as, for example, 0.5 mm or less.
[0027]
In the speaker unit having such a configuration, the gap between the outer peripheral edge of the
upper plate 4 and the inner surface of the shield cover 7 is made as small as possible, whereby
the magnetic potential difference between the frame 9 and the shield cover 7 is made as small as
possible. As a result, the occurrence of leakage flux from the frame 9 to the shield cover 7 is
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reduced.
[0028]
In the test results, the leakage flux could be reduced by about 1/3 to 1/5 as compared with the
speaker unit having the configuration shown in FIG.
[0029]
FIG. 5 shows another embodiment in the case where the configuration of the speaker unit of FIG.
4 is changed. In this embodiment, a cancel magnet 15 which is a canceling magnet is disposed on
the center pole 2 of the lower plate 1. ing.
[0030]
Here, the cancel magnet 15 disposed on the center pole 2 needs to be set in such a size that the
average magnetic flux density inside the magnet becomes zero in order to cancel the magnetic
potential difference of the top face of the pole.
At this time, in order to ensure stable operation, it is necessary to use a material with high
coercivity.
Specifically, the coercivity (iHc) is 4.8 kOe or more, and as the material name, for example, TDK
FB5E, Sumikin SSR-330IH, and Hitachi YBM-2BF are preferable.
[0031]
In addition, although it is possible to use a rare earth magnet such as samarium cobalt or
neodymium iron, it tends to be generally expensive.
[0032]
In the speaker unit having such a configuration, since the cancel magnet 15 is disposed on the
center pole 2 of the lower plate 1, the leakage flux generated between the frame 9 or the shield
cover 7 and the center pole 2 is canceled by the cancel magnet 15. Be offset.
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[0033]
As a result of the test, it was possible to further reduce the leakage flux by about 1/2 to 1/3 as
compared with the above example.
[0034]
Incidentally, the material of the frame 9 may be a magnetic material such as an iron plate or a
nonmagnetic material such as a resin or aluminum.
However, when the frame 9 is made of a nonmagnetic material, the attenuation effect of the
leakage flux can be further enhanced.
That is, when an iron plate which is a magnetic body is used, a residual magnetic flux is
generated in the iron plate itself, so the reduction rate of the leakage magnetic flux is reduced.
[0035]
Therefore, in this embodiment, it is possible to prevent the leakage flux more reliably than in the
above embodiment.
[0036]
Subsequently, a method of reducing the gap between the outer peripheral edge of the upper
plate 4 and the inner surface of the shield cover 7 will be described.
[0037]
That is, as shown in FIGS. 6 and 7, the outer peripheral edge portion 7a of the shield cover 7 is
thinned by press processing, and the outer peripheral edge portion 7a of the upper plate 4 is
press-fit into this portion.
[0038]
In this case, since the thinned outer peripheral edge portion 7a of the shield cover 7 is easily
deformed, even when the outer peripheral edge portion 7a of the upper plate 4 is press-fit into
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this portion, dimensional accuracy can be easily obtained.
In addition, since the portion is easily deformed, dimensional variation can be absorbed.
[0039]
Further, as shown in FIG. 10, the outer peripheral edge 7a of the shield cover 7 and the outer
peripheral edge of the upper plate 4 are bent by bending the outer peripheral edge 7a of the
shield cover 7 to the upper peripheral edge of the upper plate 4. You may make it press-contact.
[0040]
Furthermore, as shown in FIG. 11, the outer peripheral edge 4 a of the upper plate 4 is bent
toward the outer peripheral edge 7 a of the shield cover 7 so that the outer peripheral edge 7 a
of the shield cover 7 and the outer peripheral edge of the upper plate 4 are And may be in
pressure contact with each other.
[0041]
When bending the outer peripheral edge portion 7a of the shield cover 7 and the outer
peripheral edge portion 4a of the upper plate 4 as described above, for example, it may be
performed by caulking as shown in FIG. it can.
[0042]
As described above, according to the speaker unit and the method of manufacturing the same of
the present invention, the gap between the bonding portion between the outer peripheral edge of
the upper plate and the shield cover is made as small as possible. Since the difference in
magnetic potential between the shield cover and the shield cover is minimized, the occurrence of
magnetic flux leakage from the frame to the shield cover is reduced.
[0043]
Further, by attaching a canceling magnet for canceling the magnetic potential difference
remaining at the top of the center pole, the leakage flux from the frame or the shield cover
toward the top of the center pole inside the frame is canceled.
[0044]
Furthermore, by press-fitting the outer peripheral edge of the upper plate to the outer peripheral
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edge of the shield cover, not only it becomes easy to obtain dimensional accuracy, but also
dimensional variations can be absorbed by the press-in portion.
[0045]
As a result, it is possible to greatly reduce the occurrence of the leakage flux and to easily obtain
dimensional accuracy.
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