JP4071456B2 - Magnetic circuit of speaker - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a magnetic circuit of an electrodynamic loudspeaker, and in particular, a pair of convex portions provided on the same yoke is opposed to a pole piece, and a pair formed between the pair of convex portions and the pole piece. The present invention relates to a magnetic circuit for a speaker in which a linear amplitude region is expanded by arranging a voice coil so as to straddle the magnetic gap.
[0002]
[Prior art]
An electrodynamic motor configured to drive a diaphragm by placing a voice coil in a magnetic gap formed between the pole piece and the yoke and energizing the voice coil with a signal current (sound current). In the type speaker, sound distortion occurs unless the voice coil amplitude is changed linearly with respect to the signal current level. Therefore, the amount of magnetic flux in the magnetic gap acting on the vibrating voice coil is kept constant. It is necessary to keep. However, as shown in FIG. 5, the outer peripheral surface of the pole piece 1 and the inner peripheral surface 2a of the yoke 2 are opposed to each other through the magnetic gap G, and the winding width is smaller than the width dimension W of the inner peripheral surface 2a. In the case of a speaker in which the voice coil 3 is arranged in the magnetic gap G, if the voice coil 3 is displaced to the upper side or lower side of the magnetic gap G in the drawing, the amount of magnetic flux acting on the voice coil 3 is rapidly reduced. In order to prevent sound distortion, the amplitude region of the voice coil 3 must be set small. If the winding width of the voice coil 3 is made larger than the width dimension W of the inner peripheral surface 2a, the linear amplitude region can be expanded. In this case, however, the weight of the voice coil 3 increases. As a result, the electroacoustic conversion efficiency deteriorates.
[0003]
Therefore, conventionally, as shown in FIG. 6, the first convex portion 4a and the second convex portion 4a having the same width dimension w are formed on the inner peripheral portion of the yoke 4 facing the outer peripheral surface of the pole piece 1 through the magnetic gaps G1 and G2. A voice coil 3 having a winding width L is arranged in the magnetic gaps G1 and G2 so as to be provided with a convex portion 4b and to face the lower half of the first convex portion 4a and the upper half of the second convex portion 4b. A proposed speaker has been proposed. The magnetic circuit of this speaker includes an integrated pole piece 1 and bottom plate 5, an annular magnet 6 magnetized in the axial direction of the pole piece 1 and disposed on the bottom plate 5, a pair of convex portions 4a, 4b and an annular yoke 4 disposed on the magnet 6. The first convex portion 4a of the yoke 4 is opposed to the pole piece 1 through the magnetic gap G1, and the second convex portion. The part 4b is opposed to the pole piece 1 through the magnetic gap G2. The gap lengths of the magnetic gap G1 and the magnetic gap G2 are equal, and the voice coil 3 wound around the cylindrical bobbin 7 is disposed in the magnetic gaps G1 and G2. The upper end portion of the bobbin 7 shown in the figure is joined to the inner peripheral portion of the diaphragm 8 made of conical cone paper or the like. Further, a frame 9 is fixed on the yoke 4, and this frame 9 supports the outer peripheral portion of the diaphragm 8 via the deformation joint portion 10 and allows the bobbin 7 to vibrate via the damper 11. I support it.
[0004]
In the speaker configured in this way, the magnetic flux supplied from the magnet 6 to the yoke 4 is distributed to the first convex portion 4a and the second convex portion 4b and heads toward the outer peripheral surface of the pole piece 1. Assuming that the same amount of magnetic flux is distributed to the convex portions 4a and 4b, the magnetic flux acting on the voice coil 3 has a height position at which the upper end of the voice coil 3 shown in FIG. Even in a state in which the lower end of the voice coil 3 is lowered to the height position Q in the state where it has been raised to P, all are equivalent. Therefore, even if the weight of the voice coil 3 is not increased undesirably, the linear amplitude region can be expanded, and the performance of the speaker can be improved. Such prior art is disclosed in, for example, Japanese Utility Model Laid-Open No. 1-65592.
[0005]
[Problems to be solved by the invention]
The speaker employing the magnetic circuit as shown in FIG. 6 can efficiently expand the linear amplitude region as compared with the speaker employing the magnetic circuit as shown in FIG. Since the distance between 4b and the magnet 6 is different, the amount of magnetic flux supplied from the magnet 6 to the second convex portion 4b is larger than the amount of magnetic flux supplied to the first convex portion 4a. It was. As a result, as indicated by a broken line in FIG. 4, the amount of magnetic flux in the magnetic gap G2 becomes larger than the amount of magnetic flux in the magnetic gap G1, so that the amplitude of the voice coil 3 is caused by the imbalance of the magnetic flux density distribution. There was a risk that it would not change linearly with the level of the signal current. That is, when the magnetic circuit as shown in FIG. 6 is employed to expand the amplitude region of the voice coil 3, the linearity with respect to the level of the signal current is likely to be lost, so that there is a problem that sound distortion is likely to occur.
[0006]
The present invention has been made in view of the actual situation of the prior art, and an object of the present invention is to obtain an unbalanced magnetic flux density distribution in a pair of magnetic gaps existing between a pair of convex portions provided on a yoke and a pole piece. It is an object of the present invention to provide a magnetic circuit for a speaker that is not balanced and can expand an amplitude region without impairing linearity with respect to a signal current level.
[0007]
[Means for Solving the Problems]
As a means for achieving the above-described object, the present invention provides a magnet having a pair of convex portions provided on the yoke, the magnet being disposed closer to the base side than the surface facing the pole piece of the second convex portion closer to the magnet. either providing a notch to reduce the magnetic flux directed to the second convex portion, or a first convex shape of the second protrusions is equal, the second convex portion, of and a yoke of magnetic material The material is made of a material having lower magnetic permeability than other parts. Thereby, since the magnetic flux amount supplied to the second convex portion on the side close to the magnet and the magnetic flux amount supplied to the first convex portion on the side far from the magnet can be set to be approximately equal, It is possible to avoid unbalance of the magnetic flux density distribution in the pair of magnetic gaps existing between the convex portion and the pole piece.
[0008]
DETAILED DESCRIPTION OF THE INVENTION
In the magnetic circuit of the speaker according to the present invention, a magnet magnetized in the axial direction of the pole piece is arranged on the bottom plate integral with the pole piece, and the yoke arranged on the magnet has a first A first convex portion opposed to the pole piece via a magnetic gap, and a second convex portion opposed to the pole piece via a second magnetic gap closer to the magnet than the first convex portion. In the magnetic circuit of the speaker in which the voice coil arranged in the first and second magnetic gaps drives the diaphragm when energized, the first convex portion and the second convex portion are provided. The shape of the surface facing the pole piece is the same, and the gap lengths of the first magnetic gap and the second magnetic gap are the same, and the pole piece of the second convex portion By providing a notch that reduces the magnetic flux from the magnet into the second convex portion on the base side of the opposing surface, the amount of magnetic flux in the first magnetic gap and the magnetic flux in the second magnetic gap are provided. or not the amount set to be substantially equal, or the first projection and the shape of the second convex portions is equal, another one of the second convex portion, and the yoke of a magnetic material The magnetic flux amount in the first magnetic gap is set to be substantially equal to the magnetic flux amount in the second magnetic gap by forming the material with a lower magnetic permeability than the portion.
[0009]
The first protrusion and the second protrusion is lever is the gap length is equal to the formation of the first magnetic gap and a second magnetic gap shape with equal opposing surfaces of the pole piece provided on the yoke, the magnet The amount of the magnetic flux supplied from the second convex portion closer to the magnet is larger than the first convex portion, but is closer to the base side than the surface of the second convex portion facing the pole piece. If the notch is provided to reduce the magnetic flux from the magnet into the second convex portion, the magnetic flux toward the first convex portion is increased accordingly, so the amount of magnetic flux supplied to each convex portion is substantially reduced. Can be set equally. That is, since the amount of magnetic flux in the first magnetic gap and the amount of magnetic flux in the second magnetic gap can be set substantially equal, the sound caused by the imbalance of the magnetic flux density distribution in both magnetic gaps can be set. Distortion can be eliminated, and therefore the amplitude region of a lightweight voice coil with a reduced winding width can be expanded without impairing linearity with respect to the signal current level.
[0010]
Even if the magnetic path of the second convex portion is not narrowed by the notch, the shapes of the first convex portion and the second convex portion are the same, and the second convex portion is made of a magnetic material and the yoke. By forming it with a material having a lower magnetic permeability than other parts, the amount of magnetic flux supplied from the magnet to the convex part can be reduced. Therefore, by appropriately selecting the material, it is possible to set the amount of magnetic flux supplied to the first convex portion and the amount of magnetic flux supplied to the second convex portion to be approximately equal, and the first and second The imbalance of the magnetic flux density distribution in the magnetic gap can be eliminated.
[0011]
【Example】
An embodiment will be described with reference to the drawings. FIG. 1 is a cross-sectional view of a speaker according to a first embodiment of the present invention, and portions corresponding to those in FIG.
[0012]
The speaker magnetic circuit shown in FIG. 1 includes an integral pole piece 1 and a bottom plate 5, an annular magnet 6 magnetized in the axial direction of the pole piece 1 and disposed on the bottom plate 5, The convex portion 4a and the second convex portion 4b are configured by an annular yoke 4 disposed on the magnet 6, and the shape of both convex portions 4a and 4b is the surface facing the pole piece 1 and the like. However, only the second convex portion 4b close to the magnet 6 has a notch 4c on the base side. This notch 4c reduces the magnetic flux from the magnet 6 into the second convex portion 4b, and accordingly, the magnetic flux toward the first convex portion 4a increases, and the magnetic flux supplied from the magnet 6 to the yoke 4 is increased. The projections 4a and 4b are equally distributed. The 1st convex part 4a is facing the pole piece 1 via the magnetic gap G1, and the 2nd convex part 4b is facing the pole piece 1 via the magnetic gap G2. The gap lengths of the magnetic gap G1 and the magnetic gap G2 are equal, and the voice coil 3 wound around the cylindrical bobbin 7 is disposed in the magnetic gaps G1 and G2. The upper end portion of the bobbin 7 shown in the figure is joined to the inner peripheral portion of the diaphragm 8 made of conical cone paper or the like. Further, a frame 9 is fixed on the yoke 4, and this frame 9 supports the outer peripheral portion of the diaphragm 8 via the deformation joint portion 10 and allows the bobbin 7 to vibrate via the damper 11. I support it.
[0013]
As described above, when the notch 4c is provided on the base side of the second convex portion 4b of the yoke 4, the magnetic flux supplied from the magnet 6 to the second convex portion 4b does not exist in the notch 4c. Therefore, the magnetic flux toward the first convex portion 4a is increased accordingly, so that the same amount of magnetic flux is supplied to the convex portions 4a and 4b having different distances to the magnet 6. it can. In the present embodiment, almost the same amount of magnetic flux is supplied to the convex portions 4a and 4b in this way, so that the magnetic flux amount in the magnetic gap G1 and the magnetic gap as shown by the solid line in FIG. The amount of magnetic flux in G2 is almost the same value, and the imbalance of the magnetic flux density distribution in both magnetic gaps G1 and G2 is eliminated.
[0014]
In the speaker configured as described above, when a signal current is supplied to the voice coil 3 to vibrate, the voice coil 3 drives the diaphragm 8 to generate a sound corresponding to the signal current. At this time, even if the voice coil 3 is vibrated in a wide amplitude region from the upper side of the magnetic gap G1 to the lower side of the magnetic gap G2, the magnetic flux density distribution in the magnetic gaps G1 and G2 is balanced. This strain is less likely to occur. That is, the voice coil 3 can be vibrated in a wide amplitude region without impairing the linearity with respect to the signal current level, and the performance of the speaker is enhanced. An inclusion made of a material having a lower magnetic permeability than the yoke 4 is disposed in the notch 4c of the convex portion 4b so as to adjust the amount of magnetic flux supplied to each convex portion 4a, 4b. Also good.
[0015]
FIG. 2 is a cross-sectional view of an essential part of a magnetic circuit according to a second embodiment of the present invention. In the magnetic circuit shown in the figure, an annular magnet 12 and an annular upper plate 13 are installed on a yoke 4 having a pair of convex portions 4a and 4b to increase the magnetic flux density in the magnetic gaps G1 and G2. It is. The direction of the magnetic pole of the magnet 12 on the yoke 4 is opposite to that of the magnet 6 on the bottom plate 5, and the magnetic flux supplied from the magnet 12 to the yoke 4 passes through the magnetic gaps G 1 and G 2 and the pole piece 1. Then, the magnet 12 is returned to the magnet 12 via the upper plate 13. Accordingly, the magnetic gaps G1 and G2 are supplied with the magnetic flux by the magnet 6 on the bottom plate 5 and the magnetic flux by the magnet 12 on the yoke 4, thereby increasing the magnetic flux density. However, since the pole piece 1 and the upper plate 13 are not an integrated product and a relatively large magnetic resistance is generated between the both poles 1 and 13, most of the magnetic flux in the magnetic gaps G1 and G2 is due to the magnet 6. is there.
[0016]
In the case of the magnetic circuit shown in FIG. 2, the notch 4d provided in the second convex portion 4b of the yoke 4 is relatively small. Therefore, when compared with the first embodiment described above, the second convex portion 4b The magnetic flux going is not reduced so much. That is, the amount of magnetic flux supplied from the magnet 6 on the bottom plate 5 is larger in the second convex portion 4b than in the first convex portion 4a, but the amount of magnetic flux supplied from the magnet 12 on the yoke 4 is reversed. In order to realize a configuration in which substantially the same amount of magnetic flux is supplied to both convex portions 4a and 4b, it is necessary to make the notch 4d small to some extent.
[0017]
FIG. 3 is a cross-sectional view of an essential part of a magnetic circuit according to a third embodiment of the present invention. In the magnetic circuit shown in the figure, the shapes of the first and second convex portions 4a and 4b of the yoke 4 are the same, and the notches described in the first and second embodiments are omitted. Only the convex part 4 b is formed of a material having a lower magnetic permeability than the other part of the yoke 4. That is, by setting the magnetic permeability of the second convex portion 4b close to the magnet 6 to be relatively low, the magnetic flux directed to the first convex portion 4a far from the magnet 6 can be increased. By appropriately selecting the material of the portion 4b, the magnetic flux supplied from the magnet 6 to the yoke 4 is equally distributed to the convex portions 4a and 4b, thereby eliminating the imbalance in the magnetic flux density distribution in the magnetic gaps G1 and G2. be able to.
[0018]
【The invention's effect】
The present invention is implemented in the form as described above, and has the following effects.
[0019]
Of the pair of convex portions provided on the yoke and opposed to the pole piece through the magnetic gap, the second convex portion from the magnet is closer to the base side than the surface facing the pole piece of the second convex portion closer to the magnet. A notch for reducing the magnetic flux toward the inside of the convex portion is provided, or the shapes of the first convex portion and the second convex portion are the same, and the second convex portion is made of a magnetic material and the other part of the yoke. By using a material with low magnetic permeability, the amount of magnetic flux in the magnetic gap between one convex portion and the pole piece is almost equal to the amount of magnetic flux in the magnetic gap between the other convex portion and the pole piece. Therefore, the distortion of sound caused by the imbalance of the magnetic flux density distribution in both magnetic gaps can be eliminated, and therefore the amplitude region of the voice coil can be expanded without impairing the linearity with respect to the signal current level. Hakare, it is possible to improve the performance of the speaker.
[Brief description of the drawings]
FIG. 1 is a cross-sectional view of a speaker according to a first embodiment of the present invention.
FIG. 2 is a cross-sectional view of a main part of a magnetic circuit according to a second embodiment of the present invention.
FIG. 3 is a cross-sectional view of main parts of a magnetic circuit according to a third embodiment of the present invention.
FIG. 4 is a characteristic diagram showing the amount of magnetic flux in a pair of magnetic gaps in the present invention and the prior art.
FIG. 5 is a cross-sectional view of a main part showing an example of a magnetic circuit of a speaker.
FIG. 6 is a cross-sectional view of a speaker according to a conventional example.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Pole piece 3 Voice coil 4 Yoke 4a 1st convex part 4b 2nd convex part 4c, 4d Notch 5 Bottom plate 6 Magnet 7 Bobbin 8 Diaphragm 9 Frame 12 Magnet 13 Upper plate G1 (1st) Magnetic gap G2 (second) magnetic gap

Claims (2)

A magnet magnetized in the axial direction of the pole piece is arranged on a bottom plate integral with the pole piece, and a yoke arranged on the magnet is connected to the pole piece via a first magnetic gap. There are provided first opposing convex portions, and a second convex portion facing the pole piece via a second magnetic gap on the side closer to the magnet than the first convex portion, In the magnetic circuit of the speaker in which the voice coil disposed in the first and second magnetic gaps drives the diaphragm when energized,
The first convex portion and the second convex portion have the same shape of the facing surface to the pole piece, and the first magnetic gap and the second magnetic gap have the same gap length . the base side of the opposing surfaces of the pole piece of the convex portion of the, by providing a notch to reduce the magnetic flux directed from the magnet to the second convex portion, and the magnetic flux amount in the first magnetic gap A magnetic circuit of a speaker, wherein the magnetic circuit is set so that the amount of magnetic flux in the second magnetic gap is substantially equal. A magnet magnetized in the axial direction of the pole piece is arranged on a bottom plate integral with the pole piece, and a yoke arranged on the magnet is connected to the pole piece via a first magnetic gap. There are provided first opposing convex portions, and a second convex portion facing the pole piece via a second magnetic gap on the side closer to the magnet than the first convex portion, In the magnetic circuit of the speaker in which the voice coil disposed in the first and second magnetic gaps drives the diaphragm when energized,
By forming the first convex portion and the second convex portion in the same shape, the second convex portion is made of a magnetic material and a material having lower magnetic permeability than the other portion of the yoke. A magnetic circuit for a speaker, wherein the magnetic flux amount in the first magnetic gap and the magnetic flux amount in the second magnetic gap are set to be substantially equal.

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