JPH0951597A - Magnetic circuit for speaker - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce the distortion due to the magnetic circuit of a speaker and improve the response by forming at least the part of a yoke, which faces a magnetic gap, of an iron powder bond. SOLUTION: A projection part 7 is formed at the bottom part of a frame 6 and the inner peripheral part 9 of a ring-shaped iron powder bond yoke 8 formed by binding iron powder with resin is fixed. Further, the outer peripheral surface part 12 of an NdFeB sintered magnet 11 having a nearly channel half- sectional shape is fixed to the inner peripheral part of a recessed part 10 formed on the outer peripheral side of the projection part 7 of the frame 6. Then magnetic gaps 15 and 16 are formed of the innermost peripheral surfaces 13 and 14 of the NdFeB sintered magnet 11 and the outer peripheral surface 19 of the ion powder bond yoke 8, and voice coils 17 and 18 are inserted into the magnetic gaps 17 and 18 and fed with electricity so that they are driven in the same direction. Consequently, a diaphragm vibrates to reproduce a sound. In this case, the NdFeB sintered magnet 11 is magnetized to have an N and an S pole.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an improvement in a speaker magnetic circuit, and more particularly to a speaker magnetic circuit for reducing harmonic distortion of speaker sound.

[0002]

2. Description of the Related Art A magnetic circuit is an important constituent member of a driving source of a speaker unit. However, the present speaker uses many metal parts and induces an eddy current in the metal parts when the voice coil is activated. The electric current causes the distortion of the voice, and also serves as an impediment to the high-speed response of the voice coil, which causes the deterioration of the sound quality. To improve this,
(1) A method of depositing a copper ring on the magnetic gap forming portion of the iron yoke that constitutes the magnetic circuit, and (2) a method of suppressing the generation of eddy current by using non-metallic components of the magnetic circuit.
In the case of (1), the cost is increased due to the increase in the number of parts, and the magnetic coil width in the magnetic circuit is increased, and the magnetic flux density of the gap is decreased, resulting in a decrease in the voice coil driving force. In the case of (2), a typical example of the non-metal yoke is soft ferrite, and this soft ferrite has a saturation magnetic flux density, which is one of the important characteristics of the yoke material, about 1/4 that of iron, The gap magnetic flux density of the magnetic circuit cannot be increased, sufficient voice coil driving force cannot be obtained, and there are drawbacks that are limited to low-output speakers.

[0003]

One example of a conventional magnetic circuit configuration of a speaker is as follows. As shown in FIG. 3, a sintered ferrite magnet 1 having anisotropy in the axial direction (Y direction) is used, and iron members (yokes) 2 and 3 are provided above and below the sintered ferrite magnet 1.
Are arranged to form the magnetic gap portion 4. Reference numeral 5 is a voice coil, which is located in the magnetic gap portion 4. This conventional speaker has the following disadvantages. The speaker operates by passing a voice current (alternating current) through the voice coil 5. At this time, the magnetic field generated from the voice coil 5 causes an eddy current in the iron members (yokes) 2 and 3, which causes distortion. . This is because the iron members 2 and 3 are soft iron and electrically conductive, and when an alternating magnetic field crosses the iron members, an eddy current is generated in a direction that prevents the change. Further, this eddy current also hinders the high-speed response of the voice coil 5, causing a delay in the actual movement of the voice coil 5 with respect to the signal applied to the voice coil, resulting in deterioration of sound quality. It is an object of the present invention to provide a speaker magnetic circuit in which distortion due to the speaker magnetic circuit is reduced and high-speed response is improved.

[0004]

SUMMARY OF THE INVENTION The present invention aims to solve the problems of the prior art by forming at least a portion of the yoke facing the magnetic gap with an iron powder bond in the magnetic circuit for a speaker. Is.

[0005]

The eddy current generated when the voice current flows in the voice coil of the speaker occurs in the surface layer (surface effect of eddy current) of the iron yoke around the voice coil of the magnetic circuit. Therefore, at least the portion of the yoke facing the magnetic gap is
By forming iron powder by resin-bonded iron powder bond instead of iron, the electric resistance in the peripheral portion of the magnetic gap is increased, and the generation of eddy current can be suppressed to a low level.

[0006]

Embodiments of the present invention will be described below in more detail with reference to the drawings. (Embodiment 1) FIG. 1 is a sectional view of a speaker incorporating the present invention. A ring-shaped iron powder bond yoke 8 is formed by forming a protrusion 7 on the bottom of the frame 6 and resin-bonding iron powder.
The inner peripheral portion 9 of is fixed. The outer peripheral portion 12 of the NdFeB sintered magnet 11 having a substantially U-shaped half cross section is fixed to the inner peripheral portion of the concave portion 10 formed on the outer peripheral side of the convex portion 7 of the frame 6. N
Magnetic gaps 15 and 16 are formed by the innermost peripheral surfaces 13 and 14 of the dFeB sintered magnet 11 and the outer peripheral surface 19 of the iron powder bond yoke 8, and voice coils 17 and 18 are inserted into the magnetic gaps 15 and 16, respectively. By energizing the voice coils 17 and 18 so that they are driven in the same direction, the diaphragm vibrates and the voice is reproduced. NdFeB
The sintered magnet 11 is N and S magnetized as shown. The iron powder bond yoke is made as follows. 92 wt% of iron powder having a particle size of 325 mesh under ground crushed by a ball mill, 2.5 wt% of epoxy resin, 0.5 wt% of curing agent, and the balance of organic solvent were kneaded, and after removing the organic solvent in a vacuum drying furnace, a predetermined shape was obtained. Compression molded into 1 and then 1
The epoxy resin is heated and cured at 20 ° C. for 3 hours. After that, as a surface rustproofing treatment, an epoxy resin is electrodeposited. The volume resistivity ρ of the iron powder bond yoke thus formed is about 10 ⁻³ Ω · cm, which is 10 ^{−5 of the} conventional iron yoke.
The electrical resistance is about 100 times larger than that of Ω · cm. Output sound pressure characteristics and step response characteristics (displacement of the diaphragm with respect to a step signal) of two types of speakers incorporating a magnetic circuit using the iron powder bond yoke and a conventional galvanized ring-shaped iron yoke. Was measured and shown in FIGS. 4, 5 and 6, respectively. Fig. 4 is the output sound pressure characteristic diagram of the speaker using the iron powder bond yoke,
FIG. 5 is an output sound pressure characteristic diagram of a speaker using a galvanized iron yoke, and FIG. 6 is a step response characteristic diagram of each speaker using an iron powder bond yoke and a galvanized yoke. As is clear from FIGS. 4 and 5, the speaker having the iron powder bond yoke has the third-order distortion reduced by about 15 dB at 1 KHZ or more. Further, as is clear from FIG. 6, the speaker having the iron powder bond yoke responds to the step signal in a shorter time than the one having the galvanized iron yoke, and the high-speed response of the voice coil to the signal. That is, the response of the diaphragm is improved. In this embodiment, the NdFeB sintered magnet is used for the magnetic circuit, but other permanent magnets (NdFeB bond magnet,
It can be easily inferred that the same effect can be obtained by using a ferrite magnet or the like). Further, in this embodiment, the yoke 8 is integrally formed only by the iron powder bond, but only the outer peripheral side of the yoke 8 facing the magnetic gaps 15 and 16 is formed by the iron powder bond, and the ring shape is formed on the inner peripheral side. It is also possible to sufficiently suppress the generation of eddy current distortion in the yoke 8 by inserting the iron yoke of 1 to form the yoke 8.

(Embodiment 2) FIG. 2 is a sectional view of a speaker incorporating the present invention. Convex portion 2 on the bottom of frame 21
2 is formed, and the inner peripheral portions of the ring-shaped iron powder bond yokes 24 and 25 formed by resin-bonding iron powder are bonded and fixed. The iron powder bond yokes 24, 25 are joined together via a ring-shaped NdFeB sintered magnet 26 having substantially the same diameter. A ring-shaped iron yoke 23 is fixed to the inner peripheral portion of the recess 27 of the frame 21. Magnetic gap portions 30 and 31 are formed at two upper and lower positions by the outer peripheral surfaces of the iron powder bond yokes 24 and 25 and the inner peripheral surface of the ring-shaped iron yoke 23, and the voice coil 28 and the magnetic gap portions 30 and 31 are formed in the magnetic gap portions 30 and 31. Audio is reproduced by inserting each of the voice coils 29 and energizing them so that the driving directions of the voice coils 28 and 29 are the same.
As shown in the figure, the ring-shaped NdFeB sintered magnet 26 has N
S-magnetized. Iron powder bond yoke 24 and 2
For No. 5, the one produced by the same production method as in Example 1 is used. The output sound pressure of two types of speakers, a magnetic circuit using the iron powder bond yoke prepared in this way and a speaker incorporating a magnetic circuit using an ordinary iron yoke as an alternative to the iron powder bond yoke The characteristics and the step response characteristics were measured, and the third-order distortion of the output sound pressure characteristics was smaller and the response was better in the speaker having the iron powder bond yoke as in Example 1. In this embodiment, the iron yoke 23 is provided on the outer peripheral side of the magnetic gap portions 30 and 31, but by providing an iron powder bond yoke in place of the iron yoke 23, it is possible to further suppress the generation of eddy currents. The sound quality can be improved.

[0008]

According to the present invention, distortion due to the magnetic circuit of the speaker can be reduced, and a speaker with improved sound quality can be provided at low cost.

[Brief description of drawings]

FIG. 1 is a vertical sectional view of a first embodiment of the present invention.

FIG. 2 is a vertical sectional view of a second embodiment of the present invention.

FIG. 3 is a vertical sectional view of a conventional speaker.

FIG. 4 is an output sound pressure characteristic diagram of a speaker using an iron powder bond yoke.

FIG. 5 is an output sound pressure characteristic diagram of a speaker using a galvanized iron yoke.

FIG. 6 is a step response characteristic diagram of a speaker using an iron powder bond yoke and a galvanized iron yoke.

[Explanation of symbols]

6 frame, 8 iron powder bond yoke, 11 Nd
FeB sintered magnet, 15, 16 magnetic gap, 17,
18 voice coils

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor, Kei Tanabe 1-1-8 Nishigotanda, Shinagawa-ku, Tokyo Inside Alpine Co., Ltd. (72) Inventor Naoki Shimamura 1-1-18 Nishigotanda, Shinagawa-ku, Tokyo Alpine Corporation

Claims (1)

[Claims] 1. In a speaker magnetic circuit having a yoke and a magnet, wherein a magnetic gap into which a voice coil is inserted is formed, at least a portion of the yoke facing the magnetic gap is formed of iron powder bond. A magnetic circuit characterized by that.