Vibration Generator

Abstract

To provide a vibration generator that can prevent the influence of a reverse magnetic field acting on a voice coil.SOLUTION: A vibration generator comprises: a first magnetic circuit 15A that includes a pole piece 25, a first magnet 23 provided on one end side in a thickness direction of the pole pieces, and yoke 16 arranged to separate from the pole piece and forming a magnetic gap 38 between the pole piece and the yoke; a second magnetic circuit 15B that includes a pole piece, a second magnet 34 provided on the other end side in the thickness direction of the pole piece and repelling the first magnet, and a yoke; a voice coil 47 that is arranged in the magnetic gap and vibrates while being affected by a magnetic field generated in the first magnetic circuit; and a reverse magnetic field keep away unit 26 that is provided on an outer peripheral edge on the other end side in the thickness direction of the pole piece, and keeps a reverse magnetic field RM away from the magnetic field, the reverse magnetic field formed by the second magnetic circuit and directed opposite to the magnetic field.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a vibration generating device. [Background technology]

[0002] Patent Documents 1 and 2 disclose vibration generators that include a yoke, a permanent magnet, a pole piece, and a voice coil. The yoke has a support portion that extends along a predetermined axis, and a cylindrical portion that is an annular body located on the outer periphery of the support portion and centered on the axis. A permanent magnet is fixed to an axial end face of the support portion, and a pole piece is fixed to an end face of the permanent magnet opposite to the support portion.

[0003] A magnetic field is generated between the pole piece and the cylindrical portion. Furthermore, a voice coil, which is an annular body, is disposed in the annular space between the pole piece and the cylindrical portion so as to interfere with the magnetic field. When a current flows through the voice coil, the voice coil moves back and forth along the axis. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2011-259190 [Patent Document 2] Japanese Patent Application Laid-Open No. 2013-201769 Summary of the Invention [Problem to be solved by the invention]

[0005] The vibration generators of Patent Documents 1 and 2 generate a magnetic field in a predetermined direction and an opposing magnetic field in the opposite direction to the magnetic field, and these two magnetic fields may act on the voice coil. However, the vibration generators of Patent Documents 1 and 2 have room for improvement in terms of suppressing the influence of the opposing magnetic field acting on the voice coil.

[0006] An object of the present invention is to provide a vibration generator that can suppress the influence of an opposing magnetic field acting on a voice coil. [Means for solving the problem]

[0007] The vibration generator according to claim 1 comprises a pole piece, Lower end side a first magnetic circuit including a first magnet provided in the first magnetic circuit and a yoke disposed away from the pole piece and forming a magnetic gap between the pole piece and the yoke; Upper end side a second magnetic circuit including a second magnet that repels the first magnet and the yoke, a voice coil that is disposed in the magnetic gap and vibrates under the influence of the magnetic field generated in the first magnetic circuit, and a pole piece The upper end side an opposite magnetic field distancing portion provided on the outer periphery of the rotor, which keeps away an opposite magnetic field formed by the second magnetic circuit and directed in the opposite direction to the magnetic field, from the magnetic field; The opposing magnetic field distancing portion is an annular recess formed on the upper end of the outer circumferential surface of the pole piece and centered on the axis of the pole piece. .

[0008] The vibration generator according to claim 2 comprises a pole piece, Lower end side a top pole disposed away from the pole piece and forming a magnetic gap between the pole piece and the yoke; a first magnetic circuit including a first magnet disposed on the lower end side of the top pole; and a yoke disposed on the pole piece. The upper end side a second magnetic circuit including a second magnet and the top pole, a voice coil disposed in the magnetic gap and vibrating under the influence of the magnetic field generated in the first magnetic circuit, and a pole piece The upper end side an opposite magnetic field distancing portion provided on the outer periphery of the rotor, which keeps away an opposite magnetic field formed by the second magnetic circuit and directed in the opposite direction to the magnetic field, from the magnetic field; The opposing magnetic field distancing portion is an annular recess formed on the upper end of the outer circumferential surface of the pole piece and centered on the axis of the pole piece. .

[0009] In the inventions described in claims 1 and 2, the voice coil vibrates when a current flows through it. If the voice coil is significantly affected by the opposing magnetic field generated by the second magnetic circuit, a large difference will occur between the strength of the magnetic field acting on the voice coil in a region on one side of the direction of movement and the strength of the magnetic field acting on the voice coil in a region on the other side of the direction of movement. In this case, a large difference will occur between the force generated in the region on one side of the voice coil and the force generated in the region on the other side of the voice coil. However, in the inventions described in claims 1 and 2, an opposing magnetic field distancing portion is formed on the outer edge of the other end of the pole piece in the thickness direction, which distances the opposing magnetic field formed by the second magnetic circuit, which is in the opposite direction to the magnetic field formed by the first magnetic circuit, from the magnetic field. This suppresses the influence of the opposing magnetic field acting on the voice coil. As a result, a large difference is unlikely to occur between the strength of the magnetic field acting on the voice coil in a region on one side of the direction of movement and the strength of the magnetic field acting on the voice coil in a region on the other side of the direction of movement. Therefore, a large difference is unlikely to occur between the force generated by the voice coil in one region and the force generated by the voice coil in the other region.

[0011] Claims 1 and 2 In the invention described in the above, the opposing magnetic field keeping portion is an annular recessed portion having the axis of the pole piece as the center, Upper end side A space is formed between the outer periphery of the second magnetic circuit and the voice coil. As a result, the opposing magnetic field generated by the second magnetic circuit is elongated in the vibration direction of the voice coil and is away from the magnetic field. This makes it difficult for an opposing magnetic field to be formed within the vibration range of the voice coil, thereby suppressing the influence of the opposing magnetic field on the voice coil.

[0012] Claim 3 The vibration generating device according to claim 1 or claim 2 wherein the yoke comprises a cylindrical portion located on the outer periphery of the annular recess, the inner surface of the annular recess has an orthogonal surface perpendicular to the axis, and the axial end face of the cylindrical portion and the axial position of the orthogonal surface are the same.

[0013] Claim 3In the invention described in (1), the axial position of the end face of the cylindrical portion and the axial position of the orthogonal face are aligned, so that the direction of the magnetic field in the magnetic gap is perpendicular to the vibration direction of the voice coil, and therefore, an inverse magnetic field can be formed at a desired position away from the magnetic gap, and the influence of the inverse magnetic field on the voice coil can be suppressed.

[0014] Claim 4 The vibration generating device described in Claim 1 or Claim 2 In the pole piece The upper end side The diameter of the pole piece at the end of the magnet, centered on the axis, is approximately the same as the diameter of the second magnet, centered on the axis. The vibration generator described in claim 5 is the same as claim 1 or claim 2, in which the pole piece has a large diameter portion that forms the lower part of the pole piece and a small diameter portion that forms the upper part of the pole piece, and the annular recess is formed by the outer surface of the small diameter portion.

[0015] Claims 4 and 5 In the invention described in (1), the outer diameter of the second magnet is approximately the same as the outer diameter of the annular recess, so that the direction of the magnetic field formed by the second magnetic circuit between the second magnet and the pole piece is aligned with the vibration direction of the voice coil, thereby forming an opposing magnetic field at a desired position away from the magnetic gap. [Effects of the Invention]

[0016] According to the vibration generator of the present invention, the influence of the opposing magnetic field acting on the voice coil can be suppressed. [Brief explanation of the drawings]

[0017] [Figure 1] 1 is a cross-sectional view of a speaker according to a first embodiment. [Figure 2] FIG. 2 is an enlarged view of a main part of FIG. [Figure 3] 4 is a graph showing a magnetic flux density distribution and a BL curve according to the first embodiment. [Figure 4] FIG. 3 is a cross-sectional view similar to FIG. 2 of a comparative example of the first embodiment. [Figure 5] 6 is a graph showing a magnetic flux density distribution and a BL curve of a comparative example of the first embodiment. [Figure 6] FIG. 3 is a cross-sectional view similar to FIG. 2 of a first modified example. [Figure 7]4 is a graph similar to FIG. 3 for the first modified example. [Figure 8] FIG. 10 is a cross-sectional view similar to FIG. 2 of a second modified example. [Figure 9] 4 is a graph similar to FIG. 3 for a second modified example. [Figure 10] FIG. 10 is a cross-sectional view similar to FIG. 2 of a third modified example. [Figure 11] 10 is a graph similar to FIG. 3 for a third modified example. [Figure 12] FIG. 10 is a cross-sectional view similar to FIG. 2 of a fourth modified example. [Figure 13] 10 is a graph similar to FIG. 3 for a fourth modified example. [Figure 14] FIG. 10 is a cross-sectional view similar to FIG. 2 of a fifth modified example. [Figure 15] 10 is a graph similar to FIG. 3 for a fifth modified example. [Figure 16] FIG. 10 is a cross-sectional view of a speaker according to a second embodiment. [Figure 17] FIG. 17 is an enlarged view of the main part of FIG. [Figure 18] 4 is a graph similar to FIG. 3 of the second embodiment. [Figure 19] FIG. 10 is a cross-sectional view similar to FIG. 2 of a comparative example of the second embodiment. [Figure 20] 10 is a graph showing a magnetic flux density distribution and a BL curve of a comparative example of the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0018] A speaker (vibration generator) 10 according to a first embodiment will be described below with reference to Figs. 1 to 15. For convenience, the central axis CA shown in Fig. 1 is assumed to be parallel to the vertical direction. When the speaker 10 is actually used, the central axis CA may be parallel to a direction different from the vertical direction.

[0019] As shown in FIG. 1, the speaker 10 includes a magnetic circuit 15, a frame 40, a voice coil 47, a damper 48, and a diaphragm 49.

[0020] The magnetic circuit 15 includes a yoke 16, a first magnet 23, a pole piece 25, a second magnet 34, and a top pole 36.

[0021] The yoke 16, which is a soft magnetic material, has a base 17, a central convex portion 18, and a cylindrical portion 19. The yoke 16 is rotationally symmetrical about a central axis CA. The base 17 is a disk. The central convex portion 18 is a columnar portion that protrudes upward from the center of the base 17 along the central axis CA. The cylindrical portion 19 protrudes upward from the outer periphery of the base 17. An annular flange 20 is formed at the upper end of the cylindrical portion 19. The upper end surface 21 of the cylindrical portion 19 is a plane that is perpendicular to the direction parallel to the central axis CA. The amount by which the cylindrical portion 19 protrudes upward from the base 17 is greater than that of the central convex portion 18.

[0022] The lower surface of first magnet 23, which is a cylindrical hard magnetic body (permanent magnet), is fixed to the upper end surface of central protrusion 18. In this embodiment, first magnet 23 is a Nd (neodymium) magnet. The upper side of first magnet 23 is the north pole, and the lower side is the south pole. Furthermore, in this embodiment, first magnet 23 has an outer diameter R23 (see FIG. 1) of 18.5 mm, and a vertical dimension H23 of first magnet 23 is 4.0 mm.

[0023] The lower surface of the pole piece 25, which is a cylindrical soft magnetic body and centered on the central axis CA, is fixed to the upper end surface of the first magnet 23. The pole piece 25 is a single-piece molded product. An annular recess (reverse magnetic field distancing portion) 26 centered on the central axis CA is formed on the upper outer surface of the pole piece 25. Therefore, the pole piece 25 has a large-diameter portion 27 that forms the lower part of the pole piece 25 and a small-diameter portion 28 that forms the upper part of the pole piece 25. As shown in Figures 1 and 2, the upper surface of the outer periphery of the large-diameter portion 27 is formed by an orthogonal surface 29, which is a plane perpendicular to the central axis CA. The outer periphery of the small-diameter portion 28 is formed by a cylindrical surface 30 centered on the central axis CA. The orthogonal surface 29 and the cylindrical surface 30 are approximately perpendicular to each other. The small-diameter portion 28 of the pole piece 25 forms a protrusion that protrudes upward from the large-diameter portion 27. Furthermore, a tapered surface 31 that is inclined relative to the orthogonal surface 29 and forms an annular shape is formed on the outer periphery of the orthogonal surface 29. Furthermore, the upper end surface 21 of the yoke 16 and the orthogonal surface 29 are located at the same position in the direction of the central axis CA. In this embodiment, the vertical dimension H27 (see FIG. 1) of the large diameter portion 27 is 6.0 mm, and the vertical dimension H28 (see FIG. 1) of the small diameter portion 28 is 1.6 mm. Furthermore, the radial dimension R29 of the orthogonal surface 29 is 5.0 mm, and the diameter R28 of the small diameter portion 28 is 15.0 mm.

[0024] The lower surface of the second magnet 34, which is a cylindrical hard magnetic body, is fixed to the upper end surface of the small diameter portion 28. In this embodiment, the second magnet 34 is a Nd magnet. The outer diameter of the second magnet 34 is approximately the same as that of the small diameter portion 28. The lower side of the second magnet 34 is the north pole and the upper side is the south pole. In other words, the second magnet 34 and the first magnet 23 repel each other. Furthermore, the vertical dimension H34 of the second magnet 34 in this embodiment (see Figure 1) is 4.0 mm.

[0025] The bottom surface of the top pole 36, which is a cylindrical soft magnetic body, is fixed to the top end surface of the second magnet 34. Furthermore, the vertical dimension H36 (see FIG. 1) of the top pole 36 in this embodiment is 1.6 mm. The outer diameter of the top pole 36 is approximately the same as that of the second magnet 34. In this way, the first magnet 23 and the second magnet 34 are arranged coaxially with the central protrusion 18. In other words, the magnetic circuit 15 is an internal magnet type magnetic circuit.

[0026] Between the cylindrical portion 19 of the yoke 16 and the large diameter portion 27 of the pole piece 25, a magnetic gap 38 is formed, which is an annular space centered on the central axis CA.

[0027] The frame 40 is rotationally symmetric about the central axis CA. A mounting hole 41 is provided at the lower end of the frame 40, and an annular mounting groove 42 is formed on the inner circumferential surface of the mounting hole 41. The upper end 43 of the frame 40 has a larger diameter than the lower end, and the entire upper end of the frame 40 is open. A tapered portion 44 is provided between the lower end and the upper end 43 of the frame 40, and a step portion 45 is connected to the lower end of the tapered portion 44. As shown in FIG. 1 , the flange 20 is fitted into the mounting groove 42. That is, the lower end of the frame 40 is supported by the flange 20.

[0028] A voice coil 47 is provided in the magnetic gap 38. The voice coil 47 has a bobbin 47A having a substantially cylindrical shape centered on a central axis CA, and a coil 47B having a substantially cylindrical shape centered on the central axis CA and wound around the outer peripheral surface of the bobbin 47A. The voice coil 47 is capable of linearly reciprocating motion along the central axis CA. Both ends of the electric wire constituting the coil 47B are connected to an AC power source (not shown) via a control device (not shown). Furthermore, the inner peripheral portion of a damper 48 is connected to the bobbin 47A, and the outer peripheral portion of the damper 48 is connected to the stepped portion 45 of the frame 40.

[0029] Furthermore, the inner periphery of diaphragm 49, which is an annular member centered on central axis CA, is connected to bobbin 47A, and the outer periphery of diaphragm 49 is connected to the inner periphery of upper end 43 of frame .

[0030] Next, the operation and effects of the first embodiment will be described.

[0031] In the speaker 10 according to the first embodiment, as shown in FIG. 2, the cylindrical portion 19, the base 17, the central convex portion 18, the first magnet 23, and the large-diameter portion 27 of the pole piece 25 form a first magnetic circuit 15A, and a first magnetic field (magnetic field) MF1 is generated in the first magnetic circuit 15A. The direction of the first magnetic field MF1 is indicated by the arrow in FIG. 2. Furthermore, the large-diameter portion 27 and the small-diameter portion 28 of the pole piece 25, the second magnet 34, the top pole 36, and the upper end of the cylindrical portion 19 form a second magnetic circuit 15B, and a second magnetic field (reverse magnetic field) MF2 is generated in the second magnetic circuit 15B. The direction of the second magnetic field MF2 is indicated by the arrow in FIG. 2. That is, the direction of the second magnetic field MF2 is opposite to the direction of the first magnetic field MF1. For example, the second magnetic field MF2 is counterclockwise in the figure, and the first magnetic field MF1 is clockwise in the figure. Therefore, the first magnetic field MF1 and the second magnetic field MF2 are oriented in the same direction in the magnetic gap 38 between the pole piece 25 and the cylindrical portion 19. This increases the magnetic field density in the magnetic gap 38, thereby improving the vibration force of the voice coil 47.

[0032] As is clear from Fig. 2, the coil 47B interferes with the first magnetic field MF1 and the second magnetic field MF2. The reference numeral 47B in Fig. 2 indicates the right side edge of the coil 47B and schematically indicates its movable range. When power from the AC power supply is applied to the coil 47B, the voice coil 47 reciprocates along the central axis CA relative to the magnetic circuit 15. Accordingly, the diaphragm 49 vibrates vertically, thereby generating sound.

[0033] FIG. 3 shows the magnetic flux density distribution and BL curve of the speaker 10. The horizontal axis of FIG. 3 indicates the position in the direction of the central axis CA. "0" on the horizontal axis indicates the position CP in the direction of the central axis CA (see FIGS. 1 and 2) of the point that approximately coincides with the center of the large diameter portion 27 in the direction of the central axis CA. The vertical axis indicates the magnetic flux density B and the magnitude of the BL curve. The unit of magnetic flux density B is T (tesla), and T=N×A -1 ×M -1The unit of the BL curve is T×M=N / A. In BL, B is the magnetic flux density, L is the number of turns of coil 47B, and BL is the force coefficient. Furthermore, A is the current in amperes, N is Newtons, and M is the length of coil 47B in the axial direction. In Figure 3, the center point of coil 47B in the direction of the central axis CA and the vertical position of position CP are approximately the same.

[0034] Graph Gr1 in FIG. 3 represents the magnitude of magnetic flux density B. Graph Gr2, represented by a solid line in FIG. 3, represents the force coefficient when a unidirectional current is supplied from the AC power supply to voice coil 47, and graph Gr2, represented by a dotted line, represents graph Gr2, represented by a solid line, mirrored with respect to the central axis. When the center point of coil 47B and position CP are approximately aligned in the vertical direction, magnetic flux density B of the magnetic field acting on coil 47B is large, causing voice coil 47 to generate a large driving force. On the other hand, when the center point is farther from position CP, magnetic flux density B of the magnetic field acting on coil 47B is small, causing the driving force generated by coil 47B to be small.

[0035] 4 shows a cross-sectional view similar to FIG. 2 of speaker 100 of the comparative example. Speaker 100 has the same structure as speaker 10 except for pole piece 125. Pole piece 125 has the same configuration as large diameter portion 27. Top end surface 126 of pole piece 125 is a plane perpendicular to central axis CA, and the position of top end surface 126 in the direction of central axis CA is the same as that of top end surface 21 of yoke 16.

[0036] In speaker 100, as shown in FIG. 4, first magnetic circuit 15A-X is formed by cylindrical portion 19, base 17, central convex portion 18, first magnet 23, and pole piece 125, and first magnetic field MF1-X is generated in first magnetic circuit 15A-X. The direction of first magnetic field MF1-X is indicated by the arrow in FIG. 4. Furthermore, second magnetic circuit 15B-X is formed by pole piece 125, second magnet 34, top pole 36, and the upper end of cylindrical portion 19, and second magnetic field MF2-X is generated in second magnetic circuit 15B-X. The direction of second magnetic field MF2-X is indicated by the arrow in FIG. 4. That is, the direction of second magnetic field MF2-X is opposite to the direction of first magnetic field MF1-X.

[0037] 2 and 4, the second magnetic field MF2 and the first magnetic field MF1 interfere (converge) in speaker 10, and the second magnetic field MF2-X and the first magnetic field MF1-X interfere (converge) in speaker 100. However, because the annular recess 26 is formed in the pole piece 25 of speaker 10 and the vertical dimension of pole piece 25 is larger than that of pole piece 125, the second magnetic field MF2 of speaker 10 is located generally above the second magnetic field MF2-X of speaker 100.

[0038] Therefore, in the graph Gr1-X of FIG. 5 representing the comparative example, due to the influence of the second magnetic field MF2-X, the magnitude of the magnetic flux density B becomes negative in an area 5.5 mm or more above the position CP in the direction of the central axis CA, which is approximately the center of the pole piece 125 in the direction of the central axis CA. That is, in an area 5.5 mm or more above the position CP, a portion of the second magnetic field MF2-X becomes a counter magnetic field RM-X (see FIG. 4) that is oriented opposite to the magnetic field (hereinafter referred to as the main magnetic field) of the first magnetic field MF1-X and the second magnetic field MF2-X, which has the same direction as the first magnetic field MF1-X. In contrast, in the graph Gr1 of FIG. 3 representing the first embodiment, although influenced by the second magnetic field MF2, the magnitude of the magnetic flux density B becomes negative in an area 6.7 mm or more above the position CP. That is, in an area 6.7 mm or more above the position CP, a portion of the second magnetic field MF2 becomes a counter magnetic field RM (see FIG. 2) that is oriented opposite to the main magnetic field of the first magnetic field MF1-X and the second magnetic field MF2. An annular recess 26 is formed in the pole piece 25, and the outer diameter of the second magnet 34 is approximately the same as the small diameter portion 28. Therefore, the opposing magnetic field RM generated by the second magnetic circuit 15B is formed vertically elongated and away from the main magnetic field. Therefore, the opposing magnetic field RM of this embodiment is formed higher than the opposing magnetic field RM-X of the comparative example. Furthermore, in graphs Gr1 and Gr1-X, the magnitude of the magnetic flux density B in the region below position CP is positive or approximately zero. Therefore, while graph Gr1 is approximately symmetrical, graph Gr1-X is not.

[0039] Because graph Gr1 is nearly symmetrical, graph Gr2 representing the BL curve in FIG. 3 is also nearly symmetrical. In other words, the generation region of the opposing magnetic field RM is limited to a region a certain distance above position CP. When the opposing magnetic field RM reaches the voice coil 47, which interferes with the main magnetic field, the moving force of the voice coil 47 is reduced due to the influence of the opposing magnetic field RM. However, in this embodiment, the generation region of the opposing magnetic field RM is limited to a region a certain distance above position CP. Furthermore, because the orthogonal surface 29 and the upper end surface 21 are at the same vertical position, the orientations of the first magnetic field MF1 and the second magnetic field MF2 in the magnetic gap 38 are substantially horizontal. Therefore, the opposing magnetic field RM can be formed at a desired position above the magnetic gap 38. Therefore, the moving force of the voice coil 47 in the region above position CP is unlikely to decrease. Therefore, the magnitude of the moving force of the voice coil 47 in the region above position CP is substantially the same as that in the region below position CP. Therefore, the performance of the speaker 10 is unlikely to deteriorate.

[0040] In contrast, graph Gr1-X is not symmetrical, and therefore graph Gr2-X, which represents the BL curve of the comparative example shown in Fig. 5, is also not symmetrical. That is, there is a large difference between the moving force of voice coil 47 in the region above position CP and the moving force of voice coil 47 in the region below position CP. This makes it easy for the performance of speaker 100 to deteriorate.

[0041] Next, modifications of the first embodiment will be described with reference to FIGS.

[0042] 6 and 7 show a first modified example. As shown in FIG. 6, the orthogonal surface 29 of the pole piece 25A of the speaker (vibration generator) 10A of the first modified example is located 0.8 mm below the upper end surface 21 of the yoke 16. As shown in FIG. 7, the graph Gr1 of the first modified example is also approximately bilaterally symmetrical. This is because the annular recess 26 is formed in the pole piece 25A and the amount of vertical positional deviation between the orthogonal surface 29 and the upper end surface 21 is small. Even when the amount of vertical positional deviation between the orthogonal surface 29 and the upper end surface 21 is small, the orientations of the first magnetic field MF1 and the second magnetic field MF2 in the magnetic gap 38 are approximately horizontal. Therefore, as shown in FIG. 7, the graph Gr2 representing the BL curve is also approximately bilaterally symmetrical.

[0043] 8 and 9 show a second modified example. As shown in FIG. 8, the orthogonal surface 29 of the pole piece 25B of the speaker (vibration generator) 10B of the second modified example is located 0.8 mm above the upper end surface 21 of the yoke 16. As shown in FIG. 9, the graph Gr1 of the second modified example is also approximately bilaterally symmetrical. This is because the annular recess 26 is formed in the pole piece 25B, and the amount of deviation in the vertical position between the orthogonal surface 29 and the upper end surface 21 is small. Therefore, as shown in FIG. 9, the graph Gr2 representing the BL curve is also approximately bilaterally symmetrical.

[0044] 10 and 11 show a third modified example. As shown in FIG. 10, the cross-sectional shape of the inner surface of the annular recess (reverse magnetic field distancing portion) 26C of the pole piece 25C of the speaker (vibration generator) 10C of the third modified example is a substantially arcuate surface. The radius of curvature R of this arcuate surface is 1.6 mm. As shown in FIG. 11, the graph Gr1 of the third modified example is also substantially symmetrical. This is because the annular recess 26C is formed in the pole piece 25B, and the lower end of the annular recess 26C and the upper end surface 21 are located at the same vertical position. Therefore, as shown in FIG. 11, the graph Gr2 representing the BL curve is also substantially symmetrical. The third modified example may be applied to the first and second modified examples described above.

[0045] 12 and 13 show a fourth modified example. As shown in FIG. 12, part of the inner surface of the annular recess (reverse magnetic field distancing portion) 26D of the pole piece 25D of the speaker (vibration generator) 10D of the fourth modified example is a tapered surface 30D centered on the central axis CA. Furthermore, another part of the inner surface of the annular recess 26D is an orthogonal surface 29. As shown in FIG. 13, the graph Gr1 of the fourth modified example is also approximately bilaterally symmetrical. This is because the annular recess 26D is formed in the pole piece 25D and the orthogonal surface 29 and the upper end surface 21 are positioned at the same vertical position. Therefore, as shown in FIG. 13, the graph Gr2 representing the BL curve is also approximately bilaterally symmetrical. The fourth modified example may be applied to the first and second modified examples described above.

[0046] 14 and 15 show a fifth modified example. As shown in FIG. 14, the entire inner surface of the annular recess (reverse magnetic field distancing portion) 26E of the pole piece 25E of the speaker 10E of the fifth modified example is formed by a tapered surface 30E centered on the central axis CA. As shown in FIG. 15, the graph Gr1 of the fifth modified example is also approximately bilaterally symmetrical. This is because the annular recess 26E is formed in the pole piece 25E, and the lower end of the tapered surface 30E and the upper end surface 21 are positioned at the same vertical position. Therefore, as shown in FIG. 15, the graph Gr2 representing the BL curve is also approximately bilaterally symmetrical. The fifth modified example may be applied to the first and second modified examples described above.

[0047] Next, a speaker (vibration generator) 50 according to a second embodiment will be described with reference to Figures 16 to 20. The speaker 50 differs from the speaker 10 in the configuration of the magnetic circuit 51. In the following description, the same components as those in the first embodiment and components that are slightly different in structure but can be considered substantially the same will be denoted by the same reference numerals as those in the first embodiment.

[0048] The magnetic circuit 51 of the second embodiment includes a pole piece 25, a yoke 52, a second magnet 54, a first top pole 56, a second magnet 60, and a second top pole 62.

[0049] The yoke 52, which is made of a soft magnetic material, includes a base 17, a central protrusion 18, and a cylindrical portion 53. The vertical dimension of the cylindrical portion 53 is shorter than that of the cylindrical portion 19.

[0050] The lower surface of a pole piece 25 is fixed to the upper end surface of the central protrusion 18.

[0051] The lower surface of a second magnet 54, which is a cylindrical hard magnetic body (permanent magnet), is fixed to the upper end surface of the pole piece 25. In this embodiment, the second magnet 54 is a Nd magnet. The outer diameter of the second magnet 54 is approximately the same as that of the small diameter portion 28. The upper side of the second magnet 54 is the south pole, and the lower side is the north pole.

[0052] The lower surface of a first top pole 56, which is a cylindrical soft magnetic body, is fixed to the upper end surface of the second magnet 54. The outer diameter of the first top pole 56 is approximately the same as that of the second magnet 54. In this manner, the pole piece 25, the second magnet 54, and the first top pole 56 are arranged coaxially with the central protrusion 18.

[0053] The lower surface of a first magnet 60, which is an annular hard magnetic body (permanent magnet), is fixed to the upper surface of the cylindrical portion 53. In this embodiment, the first magnet 60 is a Nd magnet. The upper side of the first magnet 60 is the south pole, and the lower side is the north pole.

[0054] The lower surface of the second top pole 62, which is an annular soft magnetic body, is fixed to the upper end surface of the first magnet 60. An annular flange 63 is formed on the upper end of the second top pole 62. The upper end surface 64 of the second top pole 62 is a plane that is perpendicular to the direction parallel to the central axis CA. In this way, the first magnet 60 and the second top pole 62 are provided on the outer periphery of the central protrusion 18. In other words, the magnetic circuit 51 is an external magnet type magnetic circuit.

[0055] 16, a flange 63 is fitted into the mounting groove 42. That is, the lower end of the frame 40 is supported by the flange 63.

[0056] Next, the operation and effects of the second embodiment will be described.

[0057] In the speaker 50 according to the second embodiment, as shown in FIG. 17 , the cylindrical portion 53, the base 17, the central convex portion 18, the large-diameter portion 27 of the pole piece 25, the first magnet 60, and the second top pole 62 form a first magnetic circuit 15A, and a first magnetic field MF1 is generated in the first magnetic circuit 15A. The direction of the first magnetic field MF1 is indicated by the arrow in FIG. 17 . Furthermore, the large-diameter portion 27 and the small-diameter portion 28 of the pole piece 25, the second magnet 54, and the first top pole 56 form a second magnetic circuit 15B, and a second magnetic field MF2 is generated in the second magnetic circuit 15B. The direction of the second magnetic field MF2 is indicated by the arrow in FIG. 17 , which is opposite to the direction of the first magnetic field MF1. For example, the second magnetic field MF2 is counterclockwise in the figure, and the first magnetic field MF1 is clockwise in the figure. Therefore, the first magnetic field MF1 and the second magnetic field MF2 are oriented in the same direction in the magnetic gap 38 between the pole piece 25 and the second top pole 62. This increases the magnetic field density in the magnetic gap 38, thereby improving the vibration force of the voice coil 47.

[0058] When the AC power supply is applied to the coil 47B, the voice coil 47 reciprocates along the central axis CA relative to the magnetic circuit 51, causing the diaphragm 49 to vibrate in the vertical direction, thereby generating sound.

[0059] Fig. 19 shows a cross-sectional view similar to Fig. 17 of a speaker 130 that is a comparative example of the second embodiment. Speaker 130 has the same structure as speaker 50 except for pole piece 125. The position of upper end surface 64 of second top pole 62 and upper end surface 126 of pole piece 125 in the direction of central axis CA are the same.

[0060] In speaker 130 of the comparative example, as shown in Fig. 19, first magnetic circuit 15A-X is formed by cylindrical portion 53, base 17, central convex portion 18, pole piece 125, first magnet 60, and second top pole 62, and first magnetic field MF1-X is generated in first magnetic circuit 15A-X. The direction of first magnetic field MF1-X is indicated by the arrow in Fig. 19. Furthermore, second magnetic circuit 15B-X is formed by pole piece 125, second magnet 54, and first top pole 56, and second magnetic field MF2-X is generated in second magnetic circuit 15B-X. The direction of second magnetic field MF2-X is indicated by the arrow in Fig. 19, which is opposite to the direction of first magnetic field MF1-X.

[0061] 17 and 19, the second magnetic field MF2 and the first magnetic field MF1 interfere with (converge) in speaker 50, and the second magnetic field MF2-X and the first magnetic field MF1-X interfere with (converge) in speaker 130. However, because the annular recess 26 is formed in the pole piece 25 of speaker 50 and the vertical dimension of pole piece 25 is larger than that of pole piece 125, the second magnetic field MF2 of speaker 50 is located generally above the second magnetic field MF2-X of speaker 130.

[0062] Therefore, in graph Gr1-X of FIG. 20 representing the comparative example, due to the influence of second magnetic field MF2-X, the magnitude of magnetic flux density B becomes negative in the region 5.5 mm or more above position CP. That is, in the region 5.5 mm or more above position CP, a portion of second magnetic field MF2-X becomes a counter magnetic field RM-X (see FIG. 19) in the opposite direction to the main magnetic field. In contrast, in graph Gr1 of FIG. 18 representing the second embodiment, although influenced by second magnetic field MF2, the magnitude of magnetic flux density B becomes negative in the region 6.0 mm or more above position CP. That is, in the region 6.0 mm or more above position CP, a portion of second magnetic field MF2 becomes a counter magnetic field RM (see FIG. 17) in the opposite direction to the main magnetic field. An annular recess 26 is formed in pole piece 25, and the outer diameter of second magnet 54 is approximately the same as that of small diameter portion 28. Therefore, the opposing magnetic field RM generated by the second magnetic circuit 15B is formed vertically elongated and away from the main magnetic field. Therefore, the opposing magnetic field RM in this embodiment is formed higher than the opposing magnetic field RM-X in the comparative example. Furthermore, in graphs Gr1 and Gr1-X, the magnitude of the magnetic flux density B in the region below position CP is positive or almost zero. Therefore, while graph Gr1 is almost symmetrical, graph Gr1-X is not.

[0063] Because graph Gr1 is nearly symmetrical, graph Gr2 in FIG. 18, which represents the BL curve of the second embodiment, is also nearly symmetrical. In other words, the generation region of the reverse magnetic field RM is limited to a region that is a certain distance above position CP. Furthermore, because the orthogonal surface 29 and the upper end surface 64 are at the same vertical position, the orientations of the first magnetic field MF1 and the second magnetic field MF2 in the magnetic gap 38 are nearly horizontal. Therefore, the reverse magnetic field RM can be generated at a desired position above the magnetic gap 38. Therefore, the moving force of the voice coil 47 in the region above position CP is unlikely to decrease. Therefore, the magnitude of the moving force of the voice coil 47 in the region above position CP is nearly the same as that in the region below position CP. Therefore, the performance of the speaker 50 is unlikely to decrease.

[0064] In contrast, graph Gr1-X is not symmetrical, and therefore graph Gr2-X, which represents the BL curve of the comparative example shown in Fig. 20, is not symmetrical either. That is, there is a large difference between the moving force of voice coil 47 in the region above position CP and the moving force of voice coil 47 in the region below position CP. This makes it easy for the performance of speaker 130 to deteriorate.

[0065] Although the present invention has been described above based on the first and second embodiments, the present invention can be modified in design as appropriate within the scope of the gist thereof.

[0066] For example, the technical ideas of the first to fifth modifications may be applied to the second embodiment.

[0067] Each of the permanent magnets mentioned above may be a ferrite magnet.

[0068] The magnetic circuits 15, 51 and the voice coil 47 may be used as components of a vibration generating device other than a speaker. For example, the magnetic circuit 15 and the voice coil 47 may be used as components of a vibration actuator.

[0069] The pole piece 25 may be manufactured by manufacturing the large diameter portion 27 and the small diameter portion 28 separately and then joining the large diameter portion 27 and the small diameter portion 28 together.

[0070] The reverse magnetic field distancing portion may be configured with a structure different from the annular recess. [Explanation of symbols]

[0071] 10 10A 10B 10C 10D 100 Speaker (vibration generator) 16 York 18 Central convex part 19 Cylindrical section 23 First Magnet 25 25A 25B 25C 25D 25E Pole piece 26 26C 26D 26E Annular recess (reverse magnetic field prevention part) 29 Orthogonal Planes 34 Second magnet 38 Magnetic Gap 47 voice coil 50 Speaker (vibration generator) 52 York 53 Cylindrical section 60 Second Magnet 62 2nd Top Pole CA center axis RM Reverse magnetic field

Claims

1. a first magnetic circuit including a pole piece, a first magnet provided on a lower end side of the pole piece, and a yoke disposed apart from the pole piece and forming a magnetic gap between the pole piece and the yoke; a second magnetic circuit including the pole piece, a second magnet provided on an upper end side of the pole piece and repelling the first magnet, and the yoke; a voice coil disposed in the magnetic gap and vibrating under the influence of the magnetic field generated by the first magnetic circuit; an opposite magnetic field distancing portion provided on the outer circumferential edge of the upper end side of the pole piece, which keeps away an opposite magnetic field formed by the second magnetic circuit and directed in the opposite direction to the magnetic field, from the magnetic field; Equipped with A vibration generator in which the reverse magnetic field distancing portion is an annular recess formed on the upper end of the outer peripheral surface of the pole piece and centered on the axis of the pole piece.

2. a first magnetic circuit including a pole piece, a yoke provided on a lower end side of the pole piece, a top pole arranged apart from the pole piece and forming a magnetic gap between itself and the pole piece, and a first magnet provided on the lower end side of the top pole; a second magnetic circuit including the pole piece, a second magnet provided on an upper end side of the pole piece, and the top pole; a voice coil disposed in the magnetic gap and vibrating under the influence of the magnetic field generated by the first magnetic circuit; an opposite magnetic field distancing portion provided on the outer circumferential edge of the upper end side of the pole piece, which keeps away an opposite magnetic field formed by the second magnetic circuit and directed in the opposite direction to the magnetic field, from the magnetic field; Equipped with A vibration generator in which the reverse magnetic field distancing portion is an annular recess formed on the upper end of the outer peripheral surface of the pole piece and centered on the axis of the pole piece.

3. the yoke includes a cylindrical portion located on an outer circumferential side of the annular recess, an inner surface of the annular recess has an orthogonal surface perpendicular to the axis; 3. The vibration generator according to claim 1, wherein the axial end face of the cylindrical portion and the orthogonal face are positioned at the same axial position.

4. 3. The vibration generator according to claim 1, wherein the diameter of the upper end of the pole piece centered on the axis of the pole piece and the diameter of the second magnet centered on the axis of the pole piece are approximately the same.

5. The pole piece has a large diameter portion constituting a lower portion of the pole piece and a small diameter portion constituting an upper portion of the pole piece, 3. The vibration generator according to claim 1, wherein the annular recess is formed by an outer peripheral surface of the small diameter portion.

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