JPH02237393A - Magnetic circuit for acoustic device - Google Patents

Abstract

PURPOSE:To reduce a change in the magnetic flux density in a magnetic air gap by mounting a conductive ring to an outer circumferential part of a projection prolonged part of a center pole, between an outer circumferential face of the center pole and an inner circumferential face of a 1st magnet and between the outer circumferential part of the 1st magnet and the inner circumferential part of a shield cover. CONSTITUTION:A top of a center pole 1a is prolonged from the upper face of a top plate 4 and a conductive ring 10b is fitted to the outer circumferential face of the projection prolonged part. Then conductive rings 2a, 10a are fitted in a tense state between the outer circumferential face of the center pole 1a and the inner circumferential face of the 1st magnet 3, and between the outer circumferential face of the 1st magnet 3 and the inner circumferential face of the shield cover 6. Thus, the change in the magnetic flux density in a magnetic gap 8 is suppressed.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a magnetic circuit for an audio device, and particularly relates to measures against changes in the magnetic flux density of a magnetic air gap and changes in the magnetic flux density of a first magnet and a second magnet. It is something.

[Conventional technology]

Figure 4 is a vertical sectional view of the right half of the conventional magnetically shielded magnetic circuit disclosed in Japanese Utility Model Application Publication No. 1-7-29-9-3. In the figure, fi+ is the center pole (1a).
bottom play}, (21 is a conductive ring fitted on the outer peripheral surface of the center pole (1a), (3
) is the first magnet fixed on the bottom plate {1}}, (41 is the monkey-shaped top plate fixed on top of it}, +5) is the first magnet (3) whose magnetization direction is different from that of the first magnet (3). The second magnet is reversely fixed to the lower surface of the bottom plate (1), (6) is the shield cover that houses these parts, and (7) is the center pole (1).
This is a voice coil inserted into the magnetic nitrogen gap (8) formed between the top plate (4) and the top plate (4).

The conventional magnetic circuit is constructed as described above, and a magnetic field is formed in the air gap (8) by the first magnet (5) and the second magnet (5). (
When an audio signal flows through the voice coil (7) inserted in the voice coil (7), AC magnetic flux is generated, and this AC magnetic flux changes the DC magnetic field. FIG. 6 shows the result of analyzing the flow of AC magnetic flux in the magnetic circuit shown in FIG. 4 using the finite element method. The flow of AC magnetic flux has four loops as shown below.

That is, Φ in the figure is a loop that goes around the vicinity of the magnetic gap (8), Φ2 is a loop that goes around the center pole (1a), bottom play} +1+, first magnetic pole 3) and top plate (4), and Φ3 is a loop that goes around the center pole (1a), bottom play} Paul (Ia)
, the loop that goes around the bottom plate {1}, the shield cover (6) and the top plate (4), Φ4 is the center pole (1a), the bottom plate (1), the second magnet (5j, the shield cover (6) and the top plate) } (4) A loop that turns e, and then Figure 5 (a
) and (b) show typical examples of analysis results of AC magnetic flux of a conventional magnetic circuit.

By the way, the above figure 5(a) shows the center pole (1a)
A conductive ring (2) is inserted into the outer circumferential surface of the coil, and an input equivalent to 100 Hz, IW is applied to the voice coil (7).The magnetic field line diagram for the case of 'f7C' is shown in Fig. 5 at the center pole (1a). It is a line of magnetic force diagram when an input equivalent to 50Hz, IW is applied to the voice coil (7) into which the above conductive ring (2) is inserted.

In this analysis, the outer diameter of the center pole (1a) is 36w
n, the outer diameter of the first magnet (3) is 99 mm, and the inner diameter is 50 mm.
The first angle is ±15 degrees, and the outer diameter of the second magnet (5) is 8Qmt.
n, the inner diameter is 32 ± 12 gates, and the length of the magnetic gap (8) is 1. 2 arts, 4 The conductive ring (2) is made of copper.

In Fig. 3, ΔB is the amount of change in the magnetic flux density of the magnetic air gap g (8) at each frequency, ΔBrn is the change in the magnetic flux density of the first magnet (3), and ΔB m2 is the amount of change in the magnetic flux density of the second magnet (5). ) shows the change in magnetic flux density of Q − in the figure.
Q is when the center pole (1a) does not have a 4-conductor ring (2+), and low opening is when the 4-conductor ring (2) is inserted into the center pole (1a).

In other words, the amount of change ΔB in magnetic flux density in the magnetic gap (8)
is dominated by the above-mentioned Φ, Φ2, Φ3, Φ4, and Φ1, which has a particularly large influence on g, is dominated by the center pole (1a
) to the top plate (4) side, the center of Φ1 is below the vertical center of the magnetic gap (8), so there is vertical asymmetry, and this greatly affects the size of ΔB. giving.

g Also, the amount of change in magnetic flux density of the first magnet (3) ΔBm1
is dominated by Φ2, which is the center pole (1a) l
c By inserting the conductive ring (2), it is improved compared to the case without the conductive ring. In addition, the amount of change ΔB m 2 in the magnetic flux density of the second magnet (5) is controlled by Φ4, which also depends on the center pole (1a) and the conductive ring (2).
) is improved compared to the case without a conductive ring.

[Problem to be solved by the invention]

Since the conventional magnetic circuit is configured as described above, Φ
, forms an asymmetric AC magnetic flux in the magnetic gap (8),
Φ1, Φ2, Φ3, Φ4 modulate the DC magnetic flux density of the magnetic air gap ΔB, and Φ2 modulates the magnetic flux density Bm at the operating point of the first magnet 3)g.
This modulated the magnetic flux density Bm2 at the operating point of the second magnet (5), making the operation of the ΔB m 2 L y magnetic circuit unstable.

Furthermore, in the prior art, as shown in Fig. 4, conductive rings (2
) has been used to solve the above problems, but its effectiveness is insufficient, especially for the above-mentioned Φ1 and Φ
2 was insufficient.

This invention was made in order to solve the above-mentioned problems, and particularly aims to suppress the influence of the above-mentioned Φ, , Φ2.

[Failure to solve the problem]

In the magnetic circuit according to this invention, the center pole (1a)
The top of the top plate (4) protrudes from the upper surface of the top plate (4), and a conductive ring (1 ob
), and also between the outer circumferential surface of the center pole (1a) and the inner circumferential surface of the first magnet (3), and between the outer circumferential surface of the first magnet (3) and the inner circumferential surface of the shield force bar (6). The conductive rings (2a) and (10a) are fitted in a stretched state.

[Effect]

In the magnetic circuit of this invention, the vertically asymmetric AC magnetic flux caused by Ri Φ1 is made symmetrical by the extended protrusion of the center pole.
1j The AC magnetic fluxes of Φ2, Φ3, Φ4 induce a back electromotive force in each of the above conductive rings, and current flows through the conductive ring due to this back electromotive force, and the magnetic flux generated by this current causes the original Φ1, Φ2, The alternating current magnetic fluxes of Φ3 and Φ4 are canceled. Furthermore, since the center pole, first magnet, and shield cover are fixed at fixed positions, the magnetic flux density B is also stabilized.

g [Example] An example of the present invention will be described below. That is, in FIGS. 1 and 2, the same parts as those in FIGS. )
(11) a) is a conductive ring attached in a stretched state between the outer circumferential surface of the first magnet (3) and the inner circumferential surface of the first magnet (3); A conductive ring is installed in tension between the circumferential surfaces, and (1 o
b) is a conductive ring fitted to the outer peripheral surface of the protruding extension of the center pole (1a) that protrudes from the upper surface of the top plate (4); the presence of these is a feature of the present invention. .

As described above, in the present invention shown in FIG. 1(a), the top of the center pole (1a) is connected to the top plate (4).
A conductive ring (10b) is fitted onto the outer circumferential surface of this protruding extension, and the outer circumferential surface of the center pole (1a) is connected to the inner circumferential surface of the first magnet (3). A conductive ring (2a) is fitted in between, and a conductive ring (10a) is fitted in tension between the outer peripheral surface of the first magnet (3) and the inner peripheral surface of the shield cover (6), respectively. By making the center of the above Φ become the center of the magnetic gap (8) in the vertical direction, and by consuming the AC magnetic flux of Φ1, Φ2, Φ3, and Φ4 as eddy current by each of the conductive rings, the magnetic gap is The change in magnetic flux density ΔB in (8) is suppressed.

The results of this analysis are shown in Figure 2. FIG. 2 is an AC magnetic flux line diagram analyzed using the finite element method, and shows the case where an input corresponding to a frequency of 100 Hz and ly is given to the voice coil (7). In this case, the outer diameter of the center pole (1a) is 36 m, and the outer diameter of the center pole (1a) is 36 m.
) has an outer diameter of 90mm, an inner diameter of 50mm-±15mm, an outer diameter of the second magnet (5) of 80mm, and an inner diameter of 32mm-±12mm.
The protrusion amount of the gate and center pole (1a) is 1Qmm, the thickness of each conductive ring (2a) (10a) (10b) is 1mm, the thickness of the top plate (4) is 8Tnm, and the conductive The sex ring was made of copper.

In addition, Figure 3 shows the results of AC magnetic flux analysis in which the values of △B, △Bm1, and g ∆Bm2 are plotted at each frequency.
The case of FIG. 1(a) of this invention is indicated by △1△ in the figure. As is clear from this figure, the change in magnetic flux density ΔB
is much smaller than the conventional example. Furthermore, the change ΔBm in the magnetic flux density at the operating point of the g1-th magnet and the change ΔBm2 in the magnetic flux density at the operating point of the second magnet (as in the prior example) have also been improved.

Furthermore, in another embodiment of the present invention shown in FIG. 1(b), (1
0a) is a conductive ring attached between the outer peripheral surface of the first magnet 3) and the inner peripheral surface of the shield cover (6),
This is to suppress Φ2, Φ3, and Φ4 among the four loops of the flow of AC magnetic flux shown in Fig. 6. The AC magnetic flux of 02, Φ3, and Φ4 is
a) is consumed as eddy current. For example, comparing the case with and without the conductive ring (10a), when inputting 100 Hz and lW to the voice coil (7), ΔB decreased by 10%, g ΔBm was the same, and ΔBm 2 decreased by 95%. .

In addition, the first magnet (3) can be easily fixed in place by using the conductive ring (2a) described above.

Similarly, by using the conductive ring (10a), the shield cover {6} can also be easily fixed in a fixed position, so that the variation in the magnetic flux density B due to positional deviation by 1 degree is suppressed, and the resonance level is also reduced.

In the embodiment shown in FIG. 1(b) above, the conductive ring (2)
Although the case where the conductive ring (10a) is used in combination has been described, the conductive ring (10a) may be used alone, and the same effect as the tenon can be expected in that case as well.

〔Effect of the invention〕

Since the magnetic circuit for an acoustic device according to the present invention is configured as described above, it is possible to extremely reduce the change in magnetic flux density in the magnetic air gap, and also to suppress the single resonance of the center pole and magnet and the natural resonance of the shield cover. This has the effect of providing a stable magnetic circuit with no deterioration in sound quality.

[Brief explanation of drawings]

Fig. 1(-)(b) is a sectional view of a magnetic circuit in each embodiment of this invention, Fig. 2 is an AC magnetic field line diagram in an embodiment of this invention, and Fig. 3 is a diagram of an embodiment of this invention and a conventional one. Figure 4 is a cross-sectional view of a conventional magnetic circuit, and Figure 5 (a) is a comparison diagram with an example.
)(b) is the AC magnetic field line diagram in the conventional magnetic circuit, No. 6
The figure is a basic flow chart of alternating current magnetic flux in this type of magnetic circuit. Note that (1) in the figure is the bottom plate. (1a) is the center pole, (2a), (10a), and (10b) are the conductive rings, (3) is the first magnet, (4) is the top plate, (5) is the second magnet, and (6) is the shield cover. , (7) is a voice coil, and (8) is a magnetic air gap. In other figures, the same reference numerals indicate the same parts.

Claims (1)

[Claims] a bottom plate having a center pole in the center; a first magnet fixed on the bottom plate;
A top plate fixed on the magnet and forming a magnetic gap between which the voice coil is inserted and the center pole; and a second magnet fixed to the lower surface of the bottom plate with the direction of magnetization opposite to that of the first magnet. and a bowl-shaped shield cover fixed to the lower surface of the second magnet, the upper edge opening of which abuts against the outer peripheral edge of the top plate, the top of the center pole protruding from the upper surface of the top plate. A conductive ring is fitted to the outer circumference of the protruding extension, and between the outer circumferential surface of the center pole and the inner circumferential surface of the first magnet, and between the outer circumferential surface of the first magnet and the inner circumferential surface of the shield cover. A magnetic circuit for an audio device, characterized in that a conductive ring is mounted in a stretched state on both sides or on the latter side.