JPH02239800A - Magnetic circuit for acoustic transducer - Google Patents

Abstract

PURPOSE:To suppress the adverse effect of AC magnetic flux modulating DC magnetic flux and to make the circuit stable by adopting the constitution such that the reluctance of an outer peripheral part of a top plate or that in the vicinity of a joint between the top plate and a shield cover is increased in the component of the magnetic circuit. CONSTITUTION:A DC magnetic flux is formed to a magnetic gap 6 with a 1st magnet 2 and a 2nd magnet 4. A taper 3a is formed to an outer peripheral part of the top plate 3 and the reluctance of the magnetic circuit is increased, then the AC magnetic flux is reduced thereby suppressing the modulation of the DC magnetic flux at the magnetic gap 6. Moreover, the DC magnetic flux is reduced and the DC magnetic flux of a loop invalidating the magnetic gap 6 is decreased and the DC magnetic flux of a valid loop is easily passed; and the magnetic gap 6 has a high magnetic flux density, resulting that the stable magnetic circuit with high performance is obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention is applied to a magnetic circuit of an acoustic transducer.

[Prior art] Fig. 2 is a sectional view showing half of a magnetic circuit of a conventional acoustic transducer. In the figure, l is a bottom plate having a center pole la, 2 is a first magnet, 3 is a top plate, 4 is a second magnet, 5 is a shield cover 6
is a magnetic gap formed by the center pole la and the inner circumference of the top plate 3.

FIGS. 3(a) and 3(b) are explanatory diagrams showing the flows of DC magnetic flux and AC magnetic flux in the magnetic circuit of FIG. 2. FIG. In the conventional magnetic circuit as shown in FIG. 2, the first magnet 2 or the first magnet 2 and the second magnet 4
A DC magnetic flux is formed in the magnetic gap 6 by this. The flow of DC magnetic flux in the magnetic circuit is shown in FIG. 3(a). This DC magnetic flux flow consists of four loops of DC magnetic flux. In Fig. 3(a), φd1 is the center pole 1a,
The DC magnetic flux of the loop that revolves around the bottom plate l, the first magnet 2, and the top plate 3, φd2 is the center pole 1
a, DC magnetic flux of the loop that revolves around the bottom plate l, the second magnet 4, the shield cover 5, the bottom plate 1, the first magnet 2, and the top brakes l and 3, φd3 is the first magnet 2, the bottom plate 1, and the shield cover 5
．． The DC magnetic flux of the loop around the top plate 3 and Φd4 are the DC magnetic flux of the loop around the bottom plate l, the shield cover 5, and the second magnet 4.

Furthermore, in the magnetic circuit described above, when an audio signal flows through a voice coil (not shown) inserted into the magnetic gap 6, an alternating current magnetic flux is generated. The AC magnetic flux generated in this way consists of four loops of AC magnetic flux, which are shown in FIG. 3(b). In FIG. 3(b), φ. 1 is the AC magnetic flux of the loop that revolves around the magnetic gap 6, φ, 2 is the AC magnetic flux of the loop that rotates around the center pole 1a, the bottom plate l, the first magnet 2, and the top plate 3, φ
83 is the AC magnetic flux of the loop that revolves around the center pole 1a, bottom plate 1, shield cover 5, and top plate 3, and φd4 is the loop that goes around the center pole 1a, bottom plate 1, second magnet 4, shield cover 5, and top plate 3. is the alternating magnetic flux of the loop. By the way, these AC magnetic flux Φ. 1 to φ, 4 modulated the DC magnetic fluxes φd1 and φd2 in the magnetic gap 6, making the operation of the magnetic circuit unstable.

[Problems to be Solved by the Invention] Since the conventional magnetic circuit is configured as described above, the AC magnetic flux φa1 forms an asymmetrical AC magnetic flux in the vicinity of the magnetic gap 6, and the AC magnetic fluxes φ81, φa21 Φ
83 and φ34 modulate the DC magnetic fluxes φdl and φd2 in the magnetic gap 6 portion. That is, AC magnetic flux φ8
2 modulates the magnetic flux density at the operating point of the first magnet 2, and the AC magnetic flux Φa4 modulates the magnetic flux density at the operating point of the second magnet 4, which makes the operation of the magnetic circuit unstable. Ta.

This invention was made to solve the above-mentioned problems, and aims to suppress the adverse effects of alternating current magnetic flux that modulates direct current magnetic flux, and to obtain a stable magnetic circuit for an acoustic transducer.

[Means for Solving the Problems] The magnetic circuit of the acoustic transducer according to the present invention comprises a bottom plate having a center pole, a first magnet, a top plate, a second magnet, and a shield cover. The structure is such that the magnetic resistance is increased near the outer periphery of the top plate or the joint between the top plate and the shielding force part.

[Function] The magnetic circuit of the acoustic transducer in this invention includes a bottom plate having a center pole. Among the components of the magnetic circuit consisting of the first magnet, top plate, second magnet, and shield cover, increase the '6I1 air resistance near the outer periphery of the top plate or the joint between the top plate and the shield cover. This structure suppresses the modulation of the DC magnetic flux that is effective against the magnetic gap, and also reduces the AC magnetic flux that modulates the magnetic flux density at the operating points of the first and second magnets, stabilizing the operation of the magnetic circuit. can be converted into

Embodiment FIG. 1 is a sectional view showing a half portion of a magnetic circuit of an acoustic transducer according to an embodiment of the present invention. In the figure, 1 is a bottom plate with a center pole 1a, 2 is a first magnet, 3 is a top plate with a tapered portion 3a formed on the outer periphery, 4 is a second magnet, 5 is a shield cover, 6 is a center pole 1a and the top This is a magnetic gap formed by the inner circumference of the plate 3.

Next, the operation of the magnetic circuit of the acoustic transducer according to the embodiment of the present invention will be described. In the magnetic circuit shown in FIG. 1, a first magnet 2 and a second magnet 4 form a DC magnetic flux in a magnetic gap 6. A tapered portion 3a is formed on the outer periphery of the top plate 3, which increases the magnetic resistance as a magnetic circuit, so that the alternating current magnetic fluxes φ63 and φ84 are reduced as shown in FIG. 3(b). Therefore, the DC magnetic flux φdl. in the magnetic gap 6 shown in FIG. 3(a). Modulation of φd2 can be suppressed. In addition, since the DC magnetic flux φd3 is also reduced, the DC magnetic flux φd3 of the loop that was ineffective with respect to the magnetic gap 6 is reduced, and the effective DC magnetic flux φd2 of the loop becomes easier to flow, that is, the DC magnetic flux φd2 increases. Therefore, the magnetic gap 6 has a high magnetic flux density, and as a result, a high-performance and stable magnetic circuit can be obtained.

In the above embodiment, the tapered portion 3a is formed on the outer circumference of the top plate 3 to increase the magnetic resistance.
The DC magnetic flux φd3 shown in FIG. 3(a) and the AC magnetic flux φ83, φ shown in FIG. 3(b). The structure is such that the magnetic resistance is increased in a common part through which the three loops 4 pass, that is, a part near the outer periphery of the top plate 3 through which the DC magnetic flux φd3 passes, and a part in the shield cover 5 where the DC magnetic flux φd3 passes. In this case, the same effect as in the above embodiment can be obtained.

[Effects of the Invention] As described above, according to the magnetic circuit of the acoustic transducer of the present invention, the magnetic circuit structure includes a bottom plate having a center pole, a first magnet, a top plate, a second magnet, and a shield cover. Among them, the magnetic resistance is increased near the outer periphery of the top plate or the joint between the top plate and the shield cover, so the magnetic resistance as a magnetic circuit is large, so the alternating current magnetic flux is reduced. can reduce its influence and suppress the modulation of DC magnetic flux in the part of the magnetic gap, and at the same time can reduce the reactive magnetic flux and increase the effective magnetic flux, thereby obtaining a high-performance and stable magnetic circuit. It has the excellent effect of being able to

[Brief explanation of drawings]

FIG. 1 is a sectional view showing a half of the magnetic circuit of an acoustic transducer according to an embodiment of the present invention. ) and (b)
2 is an explanatory diagram showing the flow of DC magnetic flux and AC magnetic flux in the magnetic circuit of FIG. 2. FIG. In the figure, 1... Bottom plate, 1a... Center pole, 2... First magnet, 3... Top plate, 3a... Taper part, 4... Second magnet, 5...・Shield cover 6...magnetic gap. In addition, the same symbols in the figures indicate the same or equivalent parts. Figure 1

Claims (1)

[Claims] A bottom plate having a center pole at the center, a first magnet fixed on the bottom plate, and a voice coil fixed on the first magnet and between the center pole. A top plate forming a magnetic gap to be inserted, a second magnet fixed to the lower surface of the bottom plate with the magnetization direction opposite to the first magnet, and a bowl-shaped magnet fixed to the lower surface of the second magnet. and a shield cover whose upper edge opening faces the outer periphery of the top plate or the lower surface of the top plate, the outer periphery of the top plate or the top plate A magnetic circuit for an acoustic transducer, characterized in that the magnetic circuit is configured to increase magnetic resistance near the joint with the shield cover.