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JPH0290896

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DESCRIPTION JPH0290896
[0001]
FIELD OF THE INVENTION The present invention relates to a magnetic circuit of a speaker, and
more particularly to a magnetic shield type magnetic circuit provided with a shield cover. [Prior
Art] FIG. 4 is a side view showing a partial cross section of a magnetic shield type magnetic
circuit of a conventional speaker disclosed in, for example, Japanese Utility Model Laid-Open
Publication No. 61-72993. In the figure, (1) is a bottom plate having a center pole (1a), (2) is a
first magnet fixed on the bottom plate (1), and (3) is fixed on the first magnet (2) The plate (4)
has a magnetization direction opposite to that of the first magnet (2) and the second magnet is
fixed to the lower surface of the bottom plate (1). Shield cover fixed so that the upper edge
opening faces the outer periphery of the top plate (3), and (6) the center pole (1a) and the top
plate (3) of the bottom plate (1) The magnetic gap (7) is a voice coil inserted in the magnetic gap
(6). In the above configuration, DC magnetic flux is created in the magnetic gap (6) by the first
magnet (2) and the second magnet (4). However, when an audio signal flows through the voice
coil (7) inserted in the magnetic gap (6), an alternating magnetic flux is generated, and this
alternating magnetic flux modulates the above-mentioned direct current magnetic flux. As a
result of analyzing this flow of alternating current magnetic flux using the finite element method,
it was found that the flow of alternating current magnetic flux has four loops. FIG. 5 is an
operation explanatory view showing the flow of this AC magnetic flux. In the figure, Φ is a first
alternating current flux loop around the magnetic gap, Φ2 is a second alternating current flux
loop around the center pole (1a), the bottom plate (1), the first magnet (2) and the top plate (3) ,
Φ3 is a third AC flux loop that turns around the center pole (1a), bottom plate (1), shield cover
(5), top plate (3), Φ 4 is center pole (1a), bottom plate (1), second It is a 4th alternating current
magnetic flux loop which turns around a magnet (4), a shield cover (5) top plate (3). [Problems to
be Solved by the Invention] Since the magnetic circuit of the conventional speaker is configured
as described above, the total AC flux loop Φ2, 33, Φ generated by the voice signal flowing in the
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voice coil is used in the magnetic gap. The DC magnetic flux density is modulated, the magnetic
flux density at the operating point of the first magnet is modulated by the second AC magnetic
flux loop Φ2, and the magnetic flux density at the operating point of the second magnet is
modulated by the fourth AC magnetic flux loop 、. There is a problem that the operation of is
unstable.
The present invention has been made to solve the above-mentioned problems, and can suppress
the influence of the AC magnetic flux generated by the sound No. 48 and stabilize the magnetic
circuit of the speaker? The purpose is U. [Means for Solving the Problems] In the magnetic circuit
of the speaker according to the present invention, the shield cover is vertically divided into two,
and a strip member made of electroconductive material is inserted between the two divided
shield covers. is there. Further, in a magnetic circuit of a speaker according to another invention
of the present invention, a large number of extraction holes are provided on the outer peripheral
portion of the shield cover, and rivets made of a conductive material are punched into these
extraction holes. Furthermore, the magnetic circuit of the speaker according to the invention
outside the present invention divides the top plate into the inner peripheral portion and the outer
peripheral portion, and winds the magnetic material thin film on which the conductive plating is
applied to the outer peripheral portion top plate. It is what was constructed. [The magnetic
circuit of the speaker according to the first aspect of the invention is a part of the AC magnetic
flux generated by the audio signal in a strip member made of a conductive material inserted in
the shield cover 1jil, which has been two minutes under -L. The eddy current is consumed, and in
particular, the modulation of the magnetic flux density at the operating point of the second
magnet is suppressed, and a more stable magnetic circuit is obtained. In the magnetic circuit of
the speaker in the second invention, a part of AC magnetic flux generated by an audio signal is
eddy current in a rivet made of electroconductive material which is driven into a large number of
punched holes provided on an outer peripheral portion of a shield cover. Consumed as. In the
magnetic circuit of the speaker according to the third aspect of the present invention, a part of
the AC magnetic flux generated by the audio signal is consumed as eddy current in the
conductive plated thin film of the magnetic material forming the outer peripheral top plate. An
embodiment of the present invention will be described below with reference to the drawings. FIG.
1 is a side view showing a partial cross section of one embodiment of the present invention, in
which (1) is a bottom plate, (1a) is a center pole, (2) is a first magnet, and (3) is a top Plate, (4)
the second magnet, (5) the shield cover, (5a) the upper part of the shield cover (5) divided up and
down, (sb) the lower part divided into two, (6 Is a magnetic gap, (7) is a voice coil, and (8) is a
strip made of a conductive material inserted between the shield cover upper portion (5a) and the
lower portion (5b). Thus, by dividing the shield cover (5) into upper and lower parts and
inserting a strip member (8) made of a conductive material between them, the fourth of the four
loops of the flow of the AC magnetic flux shown in FIG. 3, 4th alternating current magnetic flux
loop 3.3.
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Φ is consumed as an eddy current in the conductive strip (8) to suppress its generation. For
example, comparing the case where the conductive strip (8) is inserted and the case where it is
not inserted, the input of 100 Hz, 1 w is given to the voice coil (7), the magnetic flux density
change ΔBg in the magnetic gap (6) is 5 The magnetic flux density change ΔBm in the%
reduction cylinder first magnet 2) was also reduced by 5%, and the magnetic flux density change
ΔBm2 in the second magnet (4) was reduced by 25%. From this result, the modulation
(.DELTA.B.sub.m,) of the magnetic flux density especially at the operating point of the second
magnet (4) is considerably suppressed, which contributes to the stabilization of the magnetic flux
density in the magnetic gap (6). Although copper was used as the conductive strip member (8) in
the above analysis, the conductivity is larger than that of the magnetic member constituting the
magnetic circuit, and another conductive material such as aluminum or silver may be used. It
plays the same effect. In addition, the conductive magnet (F-shaped member (8) can be used as a
bonding member for the shield covers (5a) and (5b), for example, by making the cross-sectional
shape as shown in the figure, It can be assembled without any change, and 5 problems in the
assembly process will not occur. In addition, the lower part (5b) of the shield cover is shallower
than the conventional shield cover, so that the yield of the manufacturing process is improved,
and the upper part (5a) can be easily obtained simply by cutting the pipe material. is there. The
conductive strip (8) may be manufactured, for example, at low cost by curling the extrusion and
shorting the ends. FIG. 2 is a side view showing a partial cross section of another embodiment of
the present invention, in which (1) is a bottom plate, (1a) is a center pole, (2) is a first magnet, (3)
'. Top plate, (4): second magnet, (5): seal 1 to cover, (6): magnetic gear knob, (7): Heuss coil, (9):
many provided on outer periphery of shield cover (5) The drilled hole (10) is a rivet made of a
conductive material such as copper which is driven into the drilled hole (9). Also in the above
configuration, the conductive rivets (10) are punched into the multiple holes (9) provided in the
outer peripheral portion of the shield cover (5), whereby the four loops of the flow of AC
magnetic flux shown in FIG. Among them, the third and fourth alternating current magnetic flux
loops 33 and Φ4 are consumed as eddy currents in the conductive rivet (10), and the same
effect as the embodiment shown in FIG. 1 can be obtained. The third time is a side view showing
a partial cross section of still another embodiment of the present invention, in which (1) is a
bottom plate, (la) is a center pole, (2) is a first magnet, (3) Is the top plate, and (3a) is the inner
circumference divided by the diameter of the boundary between the DC flux rotating to the
magnetic gap (6) determined by DC flux analysis and the DC flux rotating to the shield cover (5)
side The top plate, (3b) was placed outside the inner peripheral top plate (3a).
An outer peripheral top plate formed by spirally winding a thin film of a magnetic material
subjected to copper plating, (4) is a second magnet, (5) is a shield cover, (6) is a magnetic gap,
and (7) is It is a voice coil. Thus, the top plate (3) is divided into the inner peripheral portion (3a)
and the outer peripheral portion (3b), and the outer peripheral top plate (3b) is formed by
winding a magnetic material thin film subjected to copper plating. Of the four loops of the flow of
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alternating magnetic flux shown in FIG. The fourth AC flux loop Φ 1, Φ is consumed as an eddy
current in the copper plating applied to the surface of the magnetic thin film of the outer
peripheral top plate 3 b, and the generation thereof is suppressed. For example, comparing the
case of the present embodiment in which the top plate (3) is divided with the case of the
conventional example in which the top plate (3) is not divided, the magnetic gap (6) is obtained
when the voice coil (7) is given an input of 100 Hz, IW. The magnetic flux density change Δ in
work is reduced by 11%, the magnetic flux density change ΔBm1 in the first magnet (2) is also
reduced by 11%, and the magnetic flux density change ΔBm □ in the second magnet (4) is
reduced by 51%. From this result, the modulation (68 m 2) of the magnetic flux density
especially at the operating point of the second magnet (4) was largely suppressed, and it was
possible to sufficiently contribute to the stabilization of the magnetic flux density in the magnetic
gap (6). Although copper is used as the conductive plated member of the magnetic thin film, the
same effect can be obtained by using another conductive material such as silver if the
conductivity is larger than that of the magnetic member constituting the magnetic circuit. Since
the diameter of the inner peripheral top plate (3a) can be smaller than that of the conventional
top plate (3), the material yield is improved and the manufacturing can be performed at low cost.
Also, the outer peripheral top plate (3b) is manufactured by winding a copper-plated steel plate
around a guide a-laser and slicing it to a required width, and it is very stable without a significant
increase in cost A magnetic circuit is obtained. In one or more embodiments, the upper edge
opening of the shield cover is configured to face the top plate outer peripheral surface, but the
upper edge opening may be configured to face the lower surface of the top plate. As described
above, according to the present invention, the shield cover is vertically divided into two, and a
strip member made of a conductive material is inserted between the two divided shield covers, or
the outer periphery of the shield cover A large number of holes are provided in the part, and
rivets made of a conductive material are inserted into these holes, or the top plate is divided into
an inner peripheral part and an outer peripheral part, and the outer peripheral top plate is
subjected to conductive plating. Since the magnetic material thin film is wound, the modulation
of the magnetic flux density by the audio signal of the operating point of the second magnet is
suppressed to a low level, and the stable magnetic circuit of the speaker in which the modulation
of the magnetic flux density in the magnetic gap is minimized. There is an effect that can be
obtained without the cost increase.
[0002]
Brief description of the drawings
[0003]
FIG. 1 is a side view showing a partial section of one embodiment of the present invention, FIG. 2
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is a side view showing a partial section of another embodiment of the present invention, and FIG.
3 is a further embodiment of the present invention. FIG. 4 is a side view showing a partial cross
section of a conventional magnetic shield type magnetic circuit of a speaker, and FIG. 5 is an
operation explanatory view showing the flow of alternating magnetic flux in the magnetic circuit.
.
In the figure, (1) is a bottom plate, (Ia) is a center pole, (2) is a first magnet, (3) is a top plate, (3a)
is an inner peripheral top plate, and (3b) is an outer peripheral top plate , (4) is the second
magnet, (5) is the shield cover -1 (5a) the shield cover upper part, (5b) is the shield cover lower
part, (6) is the magnetic gap, (7) is the voice coil, (8) is a strip-like member, (9) is a drilled hole,
and (10) is a membrane vent. The same reference numerals in the drawings denote the same or
corresponding parts.
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