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DESCRIPTION JPH0272796

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DESCRIPTION JPH0272796
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the
improvement of the magnetic circuit of a speaker, and more particularly to the magnetic circuit
of a magnetically shielded speaker. [Prior Art] FIG. 5 is a cross-sectional view of a magnetic
circuit of a conventional magnetic shield type speaker, for example, the magnetic circuit
disclosed in Japanese Utility Model Laid-Open Publication No. 81-72993. In the figure, (1) has a
center pole (3) at the center, bottom plate 1-1 (4) has a first magnet, (5) has a top plate, and (6)
has a second magnet and the first magnet has magnetization. It is attached with the direction
reversed. (7) is a shield cover (8) is a magnetic gap (9) (this is a voice coil inserted). Next, the
operation will be described. Conventional magnetic circuit: It has the above-described
configuration, and a direct current magnetic flux is formed in the magnetic gap portion (9) by the
first magnet and the second magnet. However, when an audio | voice signal flows into the voice
coil (8) inserted in the magnetic gap part (9), alternating current magnetic flux generate | occur |
produced and this alternating current magnetic flux was modulating the said direct current
magnetic flux. As a result of AC flux analysis of this AC flux flow using the finite element method,
it was found that the AC flux flow has four loops as shown in FIG. In the figure, Φ1 is a loop
around the magnetic gap, 22 is a center pole, bottom brake 1 ·, the first magnet, a loop around
the top plate, Φ3 is a loop around the center pole, bottom plate, shield cover top plate, φ4 is a
center Paul, bottom play +-,! 2 Magnet, shield cover A loop around the top plate. In the analysis,
pole diameter 36 au +, first magnet outer diameter 901 × inner diameter 50 mm-thickness 151.
2nd magnet outer diameter 80 out X inner diameter 32 m closeness-thickness 12 ■. 1-Tub plate
thickness 81 pots, gap length 1.2 mm. As a result of analyzing the magnetic circuit composed of
copper in the conductive ring, as shown in FIG. 7, the change amount of the magnetic flux
density in the gap portion at each frequency (68 g) the change amount of the magnetic flux
density of the first magnet (ΔB ml), The amount of change (68 m 2) in the magnetic flux density
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of the second magnet l became the characteristics of the conventional example. In addition, the
amount of change in magnetic flux density in the magnetic gap portion (ΔBgl is Φl, Φ2. 3.3.
Since it is dominated by 44 and Φ1, which has a particularly large influence, if the flow direction
from the pole piece to the plate side is positive, the center of Φ1 is below the gap center, so it is
vertically asymmetric, which is 68g in size. Affect.
Further, the change amount ΔBml of the magnetic flux density of the first magnet is controlled
by Φ2. Further, the amount of change ΔB @ 2 of the magnetic flux density of the second magnet
is dominated by 44, and the conventional magnetic circuit is configured as described above, so
Φ1 constitutes an asymmetric magnetic flux of the magnetic gap. 3.3. Φ4 modulates the direct
current magnetic flux density (B3) of the magnetic gap portion (to ΔB), Φ2 modulates the
magnetic flux density at the operating point of the first magnet (B + m) (ΔBml), and 44 is the
operating point of the second magnet The magnetic flux density (B + m2) was modulated (68 m2)
L, which made the operation of the magnetic circuit unstable. The present invention has been
made to solve the above 1 gJ problem, suppresses the influence of alternating magnetic flux, and
the magnetic circuit of the magnetic speaker according to the present invention has the center
pole protruding from the top surface of the top plate. A ring of conductive material fitted to
either the extended outer periphery or the outer periphery of the lower surface of the top plate
of the center pole and the extended outer periphery, or a surface of the upper plate Of the first
magnet, the bottom plate, the second magnet, or a part or all of the space surrounded by the
shield cover, the conductive member is shaped like an annular two-disc, etc. It is a thing.
[Operation] The magnetic circuit in the present invention makes the upper and lower
asymmetrical alternating magnetic fluxes of Φ1 symmetrical by the above means, and Φ1 °
Φ2. 3.3. The AC magnetic flux of 44 is consumed as an eddy current by the conductive member,
and the conductive member ((12Φ2. 3.3. The back electromotive force is induced by the
alternating magnetic flux of Φ4, and the current flows through the conductive member by the
back electromotive force, and the magnetic flux generated by the current causes the original 11
° Φ2. 3.3. It acts to cancel the AC magnetic flux of Φ4. Embodiment of the Invention] An
embodiment shown in FIGS. 1 to 3 of the present invention will be described below with
reference to the drawings. In the figure, (1) is a bottom plate having a center pole (3), (4) is a first
magnet, (5) is a l · bubrayt, and the center pole (3) is extended beyond the top plate surface.
There is. (6) is the second magnet, (7) is the shield cover (8) is a voice coil inserted in the air gap
(9). (102) is a conductive ring fitted to the outer periphery of the lower portion of the center pole
and formed of copper or the like, and (104) is formed of copper or the like fitted to the outer
periphery of the projecting extension of the center pole (1) It is a conductive ring. Further, (21) is
a conductive member attached to the top plate 1- (5), (22) is a conductive member attached to
the outer periphery of the top plate 5, and (23) is a top plate 1 (5) A conductive member
mounted between the first magnet I and the first magnet I (4), a conductive member mounted
between the bottom plate (1) and the first magnet (4), and a bottom plate (25) 1) and a
conductive member mounted between the second magnet I- (6), (26) is a conductive member
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mounted between the second magnet (6) and the shield cover (7), (41) is a top It is a conductive
member attached to a part or all of the space enclosed by the play (5), the first magnet (4), the
bottom plate (1), the second magnet (6) and the shield cover (7). .
Next, the operation and action of the magnetic circuit of the magnetically shielded speaker
configured as described above will be described. When a direct current magnetic flux is formed
in the magnetic gap portion (9) by the first magnet (4) and the second magnet (6), and an audio
signal flows in the voice coil (8) inserted in the magnetic gap portion (9) Occurs. The AC
magnetic flux modulates the DC magnetic flux density (Bg) of the gap portion, the magnetic flux
density (B1) of the operating point of the first magnet, and the magnetic flux density (8 m 2) of
the operating point of the second magnet. In order to solve these problems, the center pole (1) is
protruded and extended from the top plate (5), and a conductive ring (104) is fitted to the outer
periphery of this protruding extension, and the lower part of the center pole (1) By fitting the
conductive nong (102) to the outer peripheral part, the center of Φ1 becomes the upper and
lower centers of the gap part as shown in FIG. Φ 2. 3.3. The modulation (68 g) of the magnetic
flux density in the gap portion can be suppressed as shown in FIG. 7 by keeping the alternating
current magnetic flux of Φ 4 consumed as an eddy current by the ring of the conductive
member. In addition, FIG. 4 which is an example of an analysis result is demonstrated in detail.
FIG. 4 shows an AC magnetic field diagram analyzed using the finite element method. Frequency
100 Hz for voice coil. This is a case where an input equivalent to IW is given. Pole diameter 36
vsi, first magnet outer diameter 90 maX inner diameter 5, Oam-thickness 15 mm, second magnet
outer diameter 801 × inner diameter 32 ■-thickness 12 votes-ball protrusion 1 10 mm,
thickness of conductive ring 2 mm, tube plate thickness 8 mm. Moreover, C steel was used as a
conductive ring. Also, ΔBg at each frequency, ΔB 1. FIG. 7 plots the value of ΔBa + 2. This FIG.
7 is drawn compared with a prior art example. As apparent from the figure, the modulation ΔBg
of the magnetic flux density is considerably smaller than that of the prior art. Compared with the
conventional example, at 200 Hz, the conventional ΔRg = 19 gavss is 68 mm and 4.2 g * vss,
which is about 174.5. The modulation (ΔBat) of the magnetic flux density at the operating point
of the first magnet and the modulation (ΔBm2) of the magnetic flux density at the operating
point of the second magnet are also greatly improved over the prior art. In addition, in the case
where the conductive member is attached in an annular or disc shape, of the four loops of the
flow of alternating magnetic flux, Φ2. 3.3. It is made to suppress Φ4 and Φ2. Reduce the
consumption of the alternating current flux of 33 ° Φ4 as an eddy current by the conductive
member.
For example, for the conductive member, the top plate (5), the first magnet! -(4), bottom plate (1),
second magnet I-(6), and shield cover (7) (3) When zlW input was given, ΔBglO% decreased,
ΔBml equivalent, ΔBgg 295% decreased. From this result, it is possible to considerably suppress
the modulation (ΔBm + 2) of the magnetic flux density at the operating point of the second
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magnet. Also, Φ2. Since .PHI.3.PHI.4 passes through the gap, it also contributes to the
modulation (68 g) of the magnetic flux density in the gap, but according to the above result, the
value of about 10% .DELTA.Bg can be suppressed at 100 Hz lW input. Although copper is used as
the conductive member in the above, the same effect can be obtained if the conductivity is larger
than that of the magnetic member constituting the magnetic circuit. As described above,
according to the present invention, the modulation (68 g) of the direct current magnetic flux
density of the magnetic gap portion? The modulation (.DELTA.B ml) of the magnetic flux density
at the operating point of the first magnet and the modulation (68 m @ 2) of the magnetic flux
density of the second magnet can be performed as much as possible, and there is an effect that a
stable magnetic circuit can be obtained.
[0002]
Brief description of the drawings
[0003]
1, 2 and 3 are sectional views of a magnetic circuit according to one embodiment of the present
invention, FIG. 4 is an AC magnetic field diagram of one embodiment of the present invention,
and FIG. 5 is a magnetic circuit showing a conventional example. 6 is an AC magnetic field
diagram of a conventional example, and FIG. 7 is ΔBg, ΔBml of an embodiment of the present
invention and the conventional example.
It is the figure which compared 68 m2. In the figure, (102), (1041 is a conductive ring, (21). (22),
(23), (24), (25), <26) and (41) are conductive members, and (103) is a pole piece attached to the
top of the center pole (1). In the drawings, the same reference numerals indicate the same or
corresponding parts. Agent Masao Oiwa (2 others) Fig. Fig. ぢ Fig. Fig. 第 Fig. Ψ
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