JP3631389B2 - Magnetic circuit for speaker and manufacturing method thereof - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to an electrodynamic loudspeaker magnetic circuit for converting an electric signal into an acoustic output and a method for manufacturing the same.
[0002]
[Prior art]
Conventionally, an electrodynamic speaker 1 as shown in FIG. 4 has been widely used in various acoustic products. As the most basic form of the speaker 1, a cylindrical bobbin 3 is joined to the center of a substantially conical diaphragm 2, and a voice coil 4 is wound around the outer peripheral surface of the bobbin 3. A center cap 5 is attached to the center of the diaphragm 2, and the peripheral edge of the diaphragm 2 is joined to the frame 6 via the edge 7. The middle part of the bobbin 3 is joined to the frame 6 by the damper 8. The edge 7 and the damper 8 are configured to elastically support the diaphragm 2 and the bobbin 3 so as to vibrate in the axial direction, and to have a damping action for damping the vibration.
[0003]
The voice coil 4 wound around the bobbin 3 is held in a strong magnetic field by a magnetic gap 11 formed in the magnetic circuit 10. The magnetic air gap 11 is formed between the outer peripheral surface 14 of the center pole 13 of the bottom yoke 12 and the inner peripheral surface 17 of the through hole 16 of the plate 15, and the magnetic flux generated from the permanent magnet 18 concentrates at high density.
[0004]
In the speaker 1, the ratio of the sound output generated with respect to the electrical input is evaluated as efficiency. The efficiency of the speaker 1 increases as the magnetic flux density of the magnetic gap 11 increases. When the voice coil 4 of the speaker 1 is electromagnetically acted in the magnetic gap 11, an axial electromagnetic force acts on the voice coil 4, and the bobbin 3 and the diaphragm 2 are displaced in the axial direction. Since the voice coil 4 is also displaced in the axial direction in the magnetic gap 11, it is desirable that the density of the magnetic flux interlinking with the voice coil 4 is uniform even when the voice coil 4 is displaced. This is because if the interlinkage magnetic flux density changes due to the displacement of the voice coil 4, the linearity of the acoustic output with respect to the electrical input is lost, and the sound quality deteriorates.
[0005]
FIG. 5A shows the configuration of the magnetic gap 11 portion of the magnetic circuit 10 of FIG. 4, and FIG. 5B shows the change in magnetic flux density along the axial direction in the magnetic gap 11. The magnetic flux density in the magnetic gap 11 generally increases in a range shorter than the thickness of the plate 15 and decreases near both ends of the thickness. This is because leakage to the outside increases. In particular, on the distal end side, the distal end of the outer peripheral surface 14 of the center pole 13 of the bottom yoke 12 is rounded, and the distance from the inner peripheral surface 17 of the through hole 16 of the plate 15 is increased. The tendency of
[0006]
[Problems to be solved by the invention]
In the magnetic circuit 10 as shown in FIG. 5, the shape of the center pole 13 of the bottom yoke 12 is a columnar shape, the tip surface has no irregularities, and the upper surface of the center pole 13 and the upper surface of the plate 15 are substantially the same. It is common to be. Further, the bottom yoke 12 is often manufactured by forging an iron material. For this reason, the tip of the outer peripheral surface 14 of the center pole 13 is rounded to some extent, and the tip side of the magnetic gap 11 is such that the tip surface of the center pole 13 and the surface of the plate 15 are substantially equal in height. The distance between the outer peripheral surface 14 of the center pole 13 and the inner peripheral surface 17 of the through-hole 16 of the plate 15 is considerably larger than the central portion. The magnetic flux density shown in FIG. 5 (b) also drops greatly on the tip side due to such roundness on the tip side of the center pole 13.
[0007]
The lack of symmetry and non-uniformity of the magnetic flux distribution in the magnetic gap 11 as shown in FIG. 5B can sufficiently reduce the amplitude linearity as a speaker and fully demonstrate the ability of the permanent magnet 18. Therefore, the efficiency is reduced and the sound pressure level is lowered.
[0008]
An object of the present invention is to provide a magnetic circuit for a speaker and a method for manufacturing the same, which can improve the uniformity of magnetic flux distribution in the magnetic gap, and improve the efficiency and linearity of sound quality as a speaker. is there.
[0009]
[Means for Solving the Problems]
The present invention provides a magnetic circuit for a speaker that forms a magnetic gap between an outer peripheral surface of a center pole and an inner peripheral surface of a through hole formed in a plate in order to apply an electromagnetic force to a voice coil.
In the center part of the center pole tip surface, a cylindrical recess is formed,
A value obtained by subtracting the radius of the recess from the radius of the center pole and the depth of the recess have a 5: 4 relationship.
[0010]
According to the present invention, a cylindrical recess is formed at the center portion of the center pole tip surface, and the value of the difference between the radius of the recess and the radius of the center pole and the depth of the recess have a 5: 4 relationship. The magnetic flux passing near the tip of the center pole has a higher density at the peripheral part than at the central part. The magnetic flux density at the peripheral edge of the center pole tip is increased, and the magnetic gap formed between the outer peripheral surface of the center pole and the inner peripheral surface of the through hole of the plate also increases the magnetic flux density at the front end side in the axial direction of the center pole. It is possible to improve the efficiency and the deterioration of linearity on the sound quality on the tip side of the center pole.
[0011]
Furthermore, the present invention provides a speaker magnetic circuit in which a magnetic gap is formed between an outer peripheral surface of a center pole and an inner peripheral surface of a through hole formed in a plate in order to apply an electromagnetic force to a voice coil.
The peripheral edge of the center pole tip surface is formed in a curved surface such that the shape in a cross section including the axis is an arc shape,
The radius of curvature of the curved surface is equal to the amount of protrusion of the center pole tip from the plate surface,
In the center part of the center pole tip surface, a cylindrical recess is formed,
A value obtained by subtracting the radius of the recess from the radius of the center pole and the depth of the recess have a 5: 4 relationship.
[0012]
According to the present invention, the tip of the center pole protrudes from the surface of the plate, the protruding amount is equal to the radius of curvature of the curved surface of the peripheral edge of the center pole, and a recess is formed on the center side of the tip surface of the center pole. Since the depth of the recess has a 5: 4 relationship with the difference between the radius of the pole and the radius of the recess, the magnetic flux density in the magnetic gap is increased to improve the efficiency as a speaker, and the uniformity along the axial direction To improve the linearity of the sound quality.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
FIG. 1A shows a schematic configuration of a portion of a magnetic gap 21 of a magnetic circuit 20 as an embodiment of the present invention. The magnetic gap 21 is formed between the outer peripheral surface 24 of the center pole 23 of the bottom yoke 22 and the inner peripheral surface 27 of the through hole 26 of the plate 25. The bottom yoke 22 extends in the central axis direction and has a substantially columnar center pole 23, and a flange-shaped bottom portion 22a extending from the base end of the center pole 23 in the radial direction perpendicular to the central axis 20a. Consists of. The flange portion 22 a of the bottom yoke 22 sandwiches the permanent magnet 28 with the plate 25. The permanent magnet 28 has an annular shape and is magnetized in the thickness direction. As a result, the upper surface of the permanent magnet 28 passes through the plate 25, passes through the magnetic gap 21 from the inner peripheral surface 27 of the through hole 26 of the plate 25, and enters the center pole 23 from the outer peripheral surface 24 of the center pole 23 of the bottom yoke 22. Then, a magnetic path from the upper surface of the flange portion 22a of the bottom yoke 22 to the lower surface of the permanent magnet 28 is formed. Of the magnetic path, the portion that passes through the plate 25 and the bottom yoke 22 is formed of an iron material or the like in which the plate 25 or the bottom yoke 22 is a ferromagnetic material. Unless this is done, a large amount of magnetic flux can pass through well. In the magnetic gap 21, the magnetic flux is less likely to pass than in the bottom yoke 22 or the plate 25. Since the magnetic resistance increases as the interval between the magnetic gaps 21 increases, the magnetic flux density also decreases at a portion where the interval between the magnetic gaps 21 is too large.
[0016]
In the present embodiment, as shown in FIG. 1A, the tip of the center pole 23 is projected from the surface of the plate 25, and the projection amount h is equal to the radius of curvature R of the tip of the center pole 23 (h = R), an increase in the distance of the magnetic gap 22 on the tip side of the center pole 23 is prevented, and the outer peripheral surface of the center pole 23 in the magnetic gap 21 and the inner peripheral face 27 of the through hole 26 of the plate 25 are Can be made uniform. As a result, as shown in FIG. 1B, the uniformity and symmetry of the magnetic flux distribution in the magnetic gap 21 in the axial direction are increased, so that the efficiency as a speaker can be improved and the sound quality can be improved. Such an effect has been confirmed by experiments and simulations using the finite element method.
[0017]
FIG. 2 (a) shows a schematic configuration of a magnetic gap 31 portion of a magnetic circuit 30 according to another embodiment of the present invention. In this embodiment, parts corresponding to those of the embodiment of FIG. 1 are denoted by the same reference numerals, and redundant description is omitted. In the magnetic circuit 30 shown in FIG. 2A, a substantially cylindrical recess 35 is formed at the center portion of the tip surface of the center pole 33 of the bottom yoke 32. The relationship between the difference A between the radius of the recess 35 and the radius of the center pole 33 and the depth B of the recess 35 is determined so that A: B = 5: 4. Since the center portion of the center pole 33 is recessed, the magnetic flux is concentrated in the peripheral portion within the center pole 33, and the magnetic flux density on the surface facing the magnetic gap 32 can be increased. In the magnetic gap 31, the magnetic flux density is high on the outer peripheral surface 34 of the center pole 33, so that the magnetic flux density can be increased in the magnetic gap 31 as shown in FIG. Such an effect has been confirmed by experiments and experimental results using the finite element method. Thereby, the magnet performance of the permanent magnet 28 can be used efficiently, the electromagnetic conversion efficiency in the magnetic gap 31 can be improved, and the efficiency as a speaker can be improved.
[0018]
FIG. 3 shows a schematic configuration of a magnetic air gap 41 portion of a magnetic circuit 40 as still another embodiment of the present invention. In the present embodiment, portions corresponding to the embodiment of FIG. 1 or FIG. 2 are given the same reference numerals, and redundant description is omitted. In the embodiment of FIGS. 1 and 2, the magnetic circuits 20 and 30 are of the outer magnet type, but in the present embodiment, they are of the inner magnet type. In the inner magnetic circuit 40, the pole piece 42 has a center pole 43 at the tip side, and a magnetic gap 41 is formed between the outer peripheral surface 44 of the center pole 43 and the inner peripheral surface 47 of the through hole 46 on the surface of the yoke plate 45. It is formed. The permanent magnet 48 is sandwiched between the lower surface of the pole piece 42 and the upper surface of the central portion of the yoke plate 45. In the pole piece 42 of this embodiment, the tip of the center pole 43 protrudes from the surface of the yoke plate 45, the protrusion amount h is equal to the radius of curvature R of the round edge of the center pole 43, and is the same as that of the embodiment of FIG. Produces an effect. Moreover, a concave portion 49 similar to the concave portion 35 of the embodiment of FIG. 2 is formed on the center side of the tip of the pole piece 42, and the same effect as that of the embodiment of FIG. In this way, as shown in FIG. 3B, in this embodiment, the uniformity of the magnetic flux distribution in the axial direction in the magnetic gap 41 and the improvement of the magnetic flux density can be achieved.
[0019]
1 and 2 use the outer magnetic type magnetic circuits 20 and 30, but the inner magnetic type magnetic circuit similar to the embodiment of FIG. The magnetic flux distribution can be made uniform and the magnetic flux density can be increased. In the embodiment of FIG. 3, an inner magnetic type magnetic circuit 30 is configured, but the outer magnetic type similar to the embodiment of FIGS. 1 and 2 is also combined with the embodiment of FIG. 1 and FIG. 2. An effect can be produced.
[0020]
【The invention's effect】
As described above, according to the present invention, a cylindrical concave portion is formed at the center portion of the tip surface of the pole piece, and the depth of the concave portion is 5: 5 with respect to the difference between the radius of the pole piece and the radius of the concave portion. Thus, the magnetic flux density on the peripheral side inside the center pole can be increased, and the magnetic flux on the tip side can be increased even in the magnetic gap, thereby increasing the magnetic flux density in the magnetic gap.
[0021]
Furthermore, according to the present invention, the curvature radius of the curved surface at the peripheral edge of the center pole is made equal to the protruding amount of the center pole protruding from the plate surface, and a cylindrical recess is formed in the center portion on the tip surface of the center pole. In addition, since the depth value of the recess has a 5: 4 relationship with respect to the difference between the radius of the recess and the radius of the pole piece, the magnetic flux can increase the magnetic flux density and improve the uniformity.
[Brief description of the drawings]
FIG. 1 is a partial cross-sectional view showing a configuration in the vicinity of a magnetic gap 21 of a magnetic circuit 20 according to an embodiment of the present invention, and a graph showing a magnetic flux distribution in the magnetic gap 21. FIG.
2 is a partial cross-sectional view showing a configuration in the vicinity of a magnetic gap 31 of a magnetic circuit 30 according to another embodiment of the present invention, and a graph showing a magnetic flux distribution in the magnetic gap 31. FIG.
3 is a partial cross-sectional view showing a configuration in the vicinity of a magnetic gap 41 of a magnetic circuit 40 according to still another embodiment of the present invention, and a graph showing a magnetic flux distribution in the magnetic gap 41. FIG.
4 is a cross-sectional view showing a schematic configuration of a conventional general electrodynamic speaker 1; FIG.
5 is a partial cross-sectional view showing a configuration in the vicinity of the magnetic gap 11 of the magnetic circuit 10 of the speaker 1 of FIG. 4 and a graph showing a magnetic flux distribution in the magnetic gap 11. FIG.
[Explanation of symbols]
20, 30, 40 Magnetic circuits 21, 31, 41 Magnetic gaps 22, 32 Bottom yokes 23, 33, 43 Center poles 24, 34, 44 Outer surface 25 Plates 26, 46 Through holes 27, 47 Inner surfaces 28, 48 Permanent Magnet 35, 49 Recess 42 Pole piece 45 Yoke plate

Claims (2)

In the magnetic circuit for a speaker that forms a magnetic gap between the outer peripheral surface of the center pole and the inner peripheral surface of the through hole formed in the plate in order to apply an electromagnetic force to the voice coil,
In the center part of the center pole tip surface, a cylindrical recess is formed,
A speaker magnetic circuit, wherein a value obtained by subtracting the radius of the recess from the radius of the center pole and the depth of the recess have a relationship of 5: 4. In the magnetic circuit for a speaker that forms a magnetic gap between the outer peripheral surface of the center pole and the inner peripheral surface of the through hole formed in the plate in order to apply an electromagnetic force to the voice coil,
The peripheral edge of the center pole tip surface is formed in a curved surface such that the shape in a cross section including the axis is an arc shape,
The radius of curvature of the curved surface is equal to the amount of protrusion of the center pole tip from the plate surface,
In the center part of the center pole tip surface, a cylindrical recess is formed,
A speaker magnetic circuit, wherein a value obtained by subtracting the radius of the recess from the radius of the center pole and the depth of the recess have a relationship of 5: 4.

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