JP2000224695A - Magnetic circuit for speaker - Google Patents

Abstract

PROBLEM TO BE SOLVED: To attain improvement in the symmetry or magnetic flux density of magnetic flux distribution in a magnetic gap. SOLUTION: As shown in (a), the top end side of a center pole 23 is protruded from the surface of a plate 25 in a magnetic gap 21 of a magnetic circuit 20 and a protrusion quantity (h) is equal to a radius of curvature R of roundness at the top end of the center pole 23. As shown in (b), the magnetic flux distribution in the magnetic gap 21 is lowered on the top end side and base end side of the magnetic gap 21 while since the center pole 23 is protruded on the top end side and the radius of curvature R at a peripheral edge is equal to the protrusion quantity (h), an interval between an outer peripheral surface 24 of the center pole 23 and an inner peripheral surface 27 of a hole 26 on the plate 25 in the magnetic gap 21 can be fixed. Thus, concerning the magnetic flux distribution in the magnetic gap 21, uniformity is improved and symmetry between top end side and base end side is improved as well.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dynamic speaker type magnetic circuit for converting an electric signal into an acoustic output.

[0002]

2. Description of the Related Art Conventionally, an electrodynamic loudspeaker 1 as shown in FIG. 4 has been widely used for various acoustic products.
In the most basic form of the speaker 1, a cylindrical bobbin 3 is joined to the center of a generally 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 periphery of the diaphragm 2 is joined to a frame 6 via an edge 7. An intermediate portion of the bobbin 3 is joined to the frame 6 by a damper 8. The edge 7 and the damper 8 are configured to elastically support the diaphragm 2 and the bobbin 3 so as to be able to vibrate in the axial direction, and to have a damping function of damping the vibration.

[0003] The voice coil 4 wound around the bobbin 3
It 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 is concentrated at high density.

In the speaker 1, a ratio of a sound output generated to an electric 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 receives an electromagnetic action in the magnetic gap 11, an electromagnetic force acts on the voice coil 4 in the axial direction, and the bobbin 3 and the diaphragm 2
Are displaced in the axial direction. Voice coil 4 also has magnetic gap 11
It is desirable that the density of the magnetic flux interlinking with the voice coil 4 be uniform even if the voice coil 4 is displaced because the displacement is performed in the axial direction. If the magnetic flux density linked by the displacement of the voice coil 4 changes, the linearity of the acoustic output with respect to the electrical input is impaired, and the sound quality is degraded.

FIG. 5 shows the magnetic air gap 1 of the magnetic circuit 10 shown in FIG.
(A) shows the configuration of the portion 1 and (b) shows the change in magnetic flux density along the axial direction in the magnetic gap 11. Magnetic gap 1
The magnetic flux density at 1 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 increases, so that it is lower than the proximal end side. The tendency becomes large.

[0006]

In the magnetic circuit 10 as shown in FIG. 5, the center pole 13 of the bottom yoke 12
Is generally cylindrical, the tip surface has no irregularities, and the height of the upper surface of the center pole 13 and the upper surface of the plate 15 are almost the same. 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 somewhat rounded, and the tip of the center pole 13 is
If the surface of the plate 1 is substantially equal in height, the outer peripheral surface 14 of the center pole 13 and the plate 1
The distance between the through hole 16 and the inner peripheral surface 17 of the hole 5 is considerably larger than that at the center. Due to the roundness of the tip of the center pole 13 as well, the magnetic flux density shown in FIG.

The lack of symmetry and non-uniformity of the magnetic flux distribution in the magnetic air gap 11 as shown in FIG. 5B lowers the amplitude linearity of the loudspeaker and makes full use of the permanent magnet 18. In this case, the efficiency is reduced and the sound pressure level is reduced.

An object of the present invention is to provide a magnetic circuit for a loudspeaker capable of improving the uniformity of the magnetic flux distribution in the magnetic air gap and improving the efficiency as a loudspeaker and the linearity in sound quality.

[0009]

According to the present invention, 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. In the magnetic circuit for the speaker, the peripheral portion of the center pole tip surface is formed into a curved surface such that the cross-section including the axis becomes an arc shape, and the radius of curvature of the curved surface is such that the center pole tip projects from the plate surface. A magnetic circuit for a loudspeaker characterized by being equal in quantity.

According to the present invention, the magnetic gap formed between the outer peripheral surface of the center pole and the inner peripheral surface of the through hole provided in the plate is such that the front end of the center pole protrudes from the surface of the plate, and the amount of protrusion and the center Since the value of the radius of curvature in the section including the axis of the periphery of the pole tip is equal, the gap between the magnetic gaps on both the tip side of the center pole and the base side of the center pole becomes equal within the range of the plate thickness, The magnetic flux distribution in the air gap is made uniform, and the symmetry between the distal end side and the proximal end side can be improved. Since the magnetic flux distribution of the magnetic air gap increases on the front end side of the center pole and the symmetry with the base end side improves, the efficiency as a speaker improves, the output sound pressure level increases, and the sound quality linearity increases. Be improved.

Further, the present invention relates to a speaker magnetic circuit for forming 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 for applying an electromagnetic force to a voice coil. A column-shaped recess is formed at the center of the tip of the center pole, and 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. Speaker magnetic circuit.

According to the present invention, a cylindrical concave portion is formed at the center of the front end face of the center pole, and the value of the difference between the radius of the concave portion and the radius of the center pole and the depth of the concave portion are 5: 4.
Therefore, the magnetic flux passing near the tip of the center pole has a higher density at the periphery than at the center. The magnetic flux density at the periphery of the tip of the center pole increases, and even in 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, the magnetic flux density at the tip of the center pole in the axial direction is reduced. It is possible to improve the efficiency and the linearity deterioration in the sound quality on the tip side of the center pole.

Further, the present invention relates to a speaker magnetic circuit for forming 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 for applying an electromagnetic force to a voice coil. The peripheral portion of the center pole tip end surface is formed into a curved surface such that the cross-section including the axis forms an arc shape, and the radius of curvature of the curved surface is equal to the projection amount of the center pole tip from the plate surface. A columnar recess is formed in the center of the pole tip surface,
A magnetic circuit for a speaker, characterized in that a value obtained by subtracting the radius of the concave portion from the radius of the center pole and the depth of the concave portion have a relationship of 5: 4.

According to the present invention, the tip of the center pole projects from the surface of the plate, the amount of projection is equal to the radius of curvature of the curved surface of the periphery of the center pole, and a recess is formed on the center side of the tip face of the center pole. And the depth of the recess is 5 for the difference between the radius of the center pole and the radius of the recess:
Because of the relationship 4, the magnetic flux density in the magnetic air gap can be increased to improve the efficiency as a speaker, and the uniformity along the axial direction can be improved, thereby improving the linearity of sound quality.

[0015]

FIG. 1 (a) shows a schematic configuration of a magnetic air gap 21 of a magnetic circuit 20 according to an embodiment of the present invention. The magnetic gap 21 is formed in the bottom yoke 2
The outer peripheral surface 24 of the center pole 23 and the plate 25
And the inner peripheral surface 27 of the through hole 26. The bottom yoke 22 extends in the center axis direction and has a substantially columnar shape.
And a flange-shaped bottom portion 22a extending in a radial direction perpendicular to the central axis 20a. The flange portion 22 a of the bottom yoke 22 sandwiches the permanent magnet 28 with the plate 25. The permanent magnet 28 is annular and magnetized in the thickness direction. As a result, the upper surface of the permanent magnet 28 passes through the plate 25, the inner peripheral surface 27 of the through hole 26 of the plate 25 passes through the magnetic gap 21,
A magnetic path from the upper surface of the flange portion 22 a of the bottom yoke 22 to the lower surface of the permanent magnet 28 is formed by entering the center pole 23 from the outer peripheral surface 24 of the center pole 23 of the bottom yoke 22. In the magnetic path, a portion passing through the plate 25 and the bottom yoke 22 has a relatively small magnetic resistance and is magnetically saturated because the plate 25 and the bottom yoke 22 are formed of a ferromagnetic iron material or the like. Unless otherwise, many magnetic fluxes can be transmitted well. In the magnetic gap 21, the magnetic flux is harder to pass than in the bottom yoke 22 and the plate 25. Since the magnetic resistance increases as the gap between the magnetic gaps 21 increases, the magnetic flux density decreases at a portion where the gap between the magnetic gaps 21 is too large.

In this embodiment, as shown in FIG. 1A, the tip of the center pole 23 is made to protrude from the surface of the plate 25, and the amount of projection h becomes equal to the radius of curvature R of the tip of the center pole 23. (H = R), it is possible to prevent the magnetic gap 22 from increasing on the tip side of the center pole 23, and to prevent the center pole 23 in the magnetic gap 21 from increasing.
Of the plate 25 and the inner peripheral surface 27 of the through hole 26 of the plate 25 can be made uniform. As a result, FIG.
As shown in (b), the uniformity and symmetry of the magnetic flux distribution in the magnetic gap 21 in the axial direction are increased, and the efficiency as a speaker and the sound quality can be improved. Such effects have been confirmed by experiments and simulations using the finite element method.

FIG. 2A shows a schematic configuration of a magnetic air gap 31 of a magnetic circuit 30 according to another embodiment of the present invention. In the present embodiment, portions corresponding to the embodiment of FIG. 1 are denoted by the same reference numerals, and redundant description will be omitted. FIG.
In the magnetic circuit 30 shown in (a), a substantially cylindrical concave portion 35 is formed at the center of the tip end 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 concave, the magnetic flux concentrates on the peripheral portion in the center pole 33, and the magnetic flux density on the surface facing the magnetic gap 32 can be increased.
Since the magnetic flux density is high on the outer peripheral surface 34 of the center pole 33 in the magnetic gap 31, even in the magnetic gap 31, FIG.
As shown in (b), the magnetic flux density can be increased.
Such an effect has been confirmed by experiments and experimental results using the finite element method. As a result, 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.

FIG. 3 shows a schematic configuration of a magnetic gap 41 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 denoted by the same reference numerals, and redundant description will be omitted. In the embodiment of FIGS. 1 and 2, the magnetic circuit 2
Although 0 and 30 are the outer magnet type, in the present embodiment, they are the inner magnet type. In the magnetic circuit 40 of the inner magnet type, the tip side of the pole piece 42 becomes the center pole 43 and the center pole 4
3 and a through hole 4 on the surface of the yoke plate 45.
The magnetic gap 41 is formed between the magnetic gap 41 and the inner peripheral surface 47. The permanent magnet 48 is sandwiched between the lower surface of the pole piece 42 and the upper surface of the center of the yoke plate 45. In the pole piece 42 of the present embodiment, the tip of the center pole 43 protrudes from the surface of the yoke plate 45, and the protrusion amount h is equal to the radius of curvature R of the rounded edge of the center pole 43,
The same effect as the embodiment of FIG. 1 is obtained. Moreover, the recess 3 of the embodiment of FIG.
A recess 49 similar to that of FIG. 5 is formed, and the same effect as in the embodiment of FIG. Thus, as shown in FIG. 3B, in the present 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.

Although the embodiment shown in FIGS. 1 and 2 uses the outer-magnet type magnetic circuits 20 and 30, the inner-magnet type magnetic circuit similar to the embodiment shown in FIG. , 31 and the magnetic flux density can be made uniform and the magnetic flux density can be increased. Although the embodiment shown in FIG. 3 constitutes the magnetic circuit 30 of the inner magnet type, the outer magnet type similar to the embodiment shown in FIGS. 1 and 2 can be obtained by combining the embodiments shown in FIGS. The effect can be achieved.

[0020]

As described above, according to the present invention, the tip of the center pole is projected from the surface of the plate, and the radius of curvature of the periphery of the tip of the center pole is made equal to the projection amount. Of the magnetic flux density at the distal end of the loudspeaker, and the magnetic flux distribution shows good symmetry between the distal end and the proximal end in the axial direction, improving the uniformity and improving the efficiency and sound quality as a speaker. Can be planned.

Further, according to the present invention, a cylindrical concave portion is formed at the center portion of the tip end surface of the pole piece, and the depth of the concave portion is smaller than the difference between the radius of the pole piece and the radius of the concave portion.
Because of the relationship of 5: 4, 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, so that the magnetic flux density in the magnetic gap can be increased.

Further, according to the present invention, the radius of curvature of the curved surface of the peripheral portion of the center pole is made equal to the amount of projection of the center pole from the plate surface, and the center of the center pole has a cylindrical shape at the center. A recess is formed,
Since the value of the depth of the concave portion has a relationship of 5: 4 with respect to the difference between the radius of the concave portion and the radius of the pole piece, it is possible to increase the magnetic flux density by the magnetic gap and improve the uniformity.

[Brief description of the drawings]

FIG. 1 is a partial cross-sectional view showing a configuration near a magnetic gap 21 of a magnetic circuit 20 according to an embodiment of the present invention, and FIG.
4 is a graph showing a magnetic flux distribution at 1.

FIG. 2 is a partial cross-sectional view showing a configuration near 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 shows a magnetic circuit 40 according to still another embodiment of the present invention.
3 is a partial cross-sectional view showing the configuration near the magnetic gap 41 and a graph showing the 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.

5 is a magnetic air gap 1 of a magnetic circuit 10 of the speaker 1 of FIG.
1 is a partial cross-sectional view showing a configuration near 1 and a graph showing a magnetic flux distribution in a magnetic gap 11.

[Explanation of symbols]

 20, 30, 40 Magnetic circuit 21, 31, 41 Magnetic gap 22, 32 Bottom yoke 23, 33, 43 Center pole 24, 34, 44 Outer surface 25 Plate 26, 46 Through hole 27, 47 Inner surface 28, 48 Permanent Magnet 35,49 recess 42 pole piece 45 yoke plate

Claims (3)

[Claims] 1. A magnetic circuit for a speaker, wherein 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 for applying an electromagnetic force to a voice coil. The peripheral edge of the tip surface is formed into a curved surface having a circular arc shape in a cross section including the axis, and the radius of curvature of the curved surface is equal to the amount of protrusion of the center pole tip from the plate surface. Magnetic circuit for speaker. 2. A speaker magnetic circuit which 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 for applying an electromagnetic force to a voice coil. A speaker having a columnar concave portion formed at a center portion of a front end surface thereof, wherein a value obtained by subtracting a radius of the concave portion from a radius of the center pole and a depth of the concave portion has a relationship of 5: 4. For magnetic circuit. 3. A speaker magnetic circuit for forming 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 for applying an electromagnetic force to a voice coil. The peripheral edge of the front end surface is formed into a curved surface such that the cross section including the axis forms an arc shape. The radius of curvature of the curved surface is equal to the amount of projection of the center pole tip from the plate surface. A column-shaped concave portion is formed at the center portion of the speaker magnet, and a value obtained by subtracting the radius of the concave portion from the radius of the center pole and the depth of the concave portion have a relationship of 5: 4. circuit.