Magnetic circuit for speaker and speaker driver

Abstract

A speaker magnetic circuit (11) comprises: a yoke cover (12) formed of a tubular magnetic body and having a diaphragm (33) mounted to one end thereof on one side in an axial direction; a magnet (18) disposed on the inside of the yoke cover (12); a volume adjusting member (14) formed of a tubular non-magnetic body and provided between the yoke cover (12) and the magnet (18), the volume adjusting member (14) having a first groove portion (46A) extending in the axial direction formed therein; and a yoke base (20) formed of a magnetic body and provided on the other side of the magnet (18) in the axial direction, the yoke base (20) having a second groove portion (20A) formed in a position corresponding to the first groove portion (46A), the first groove portion (46A) and the second groove portion (20A) constituting a duct portion (D) communicating between a space on one side in the axial direction and a space on the other side in the axial direction inside the yoke cover (12).

Description

[Technical Field]

[0001] The present disclosure relates to a magnetic circuit for a speaker and a driver for a speaker. [Background technology]

[0002] International Publication No. 2020 / 218042 discloses an electroacoustic transducer including a diaphragm connected to a voice coil and a cylindrical magnet with a diameter larger than that of the voice coil. Meanwhile, Japanese Patent Application Laid-Open No. 2012-39353 discloses a microspeaker in which a magnet is disposed inside a cylindrical yoke. Summary of the Invention [Problem to be solved by the invention]

[0003] In an external magnet type structure in which a magnet is arranged on the outside, such as the electroacoustic transducer described in WO 2020 / 218042, a ring-shaped magnet is used, making it difficult to miniaturize the magnetic circuit. On the other hand, in an internal magnet type structure in which a magnet is arranged inside a yoke, such as the microspeaker described in JP 2012-39353 A, it is easy to miniaturize, but it is difficult to ensure magnetic flux density and adjust frequency characteristics.

[0004] An object of the present disclosure is to provide a speaker magnetic circuit and a speaker driver that are capable of ensuring magnetic flux density and adjusting frequency characteristics in an internal magnet type structure. [Means for solving the problem]

[0005] A magnetic circuit for a speaker according to a first aspect includes a yoke cover formed of a cylindrical magnetic material and having a diaphragm attached to one end on one axial side thereof; a magnet disposed inside the yoke cover; a volume adjustment member formed of a cylindrical non-magnetic material and disposed between the yoke cover and the magnet, the volume adjustment member having a first groove extending in the axial direction; and a yoke base formed of a magnetic material and disposed on the other axial side of the magnet, the second groove formed at a position corresponding to the first groove, the first groove and the second groove constituting a duct portion that communicates a space inside the yoke cover on one axial side with a space on the other axial side.

[0006] In the above aspect, the yoke cover is formed of a cylindrical magnetic material, and a diaphragm is attached to one axial end of the yoke cover. A magnet is disposed inside the yoke cover, and a magnetic circuit is formed between the magnet and the yoke cover. Furthermore, a yoke base made of a magnetic material is provided on the other axial side of the magnet. This improves the magnetic flux density of the magnetic circuit.

[0007] Here, a volume adjustment member is provided between the yoke cover and the magnet. The volume adjustment member is formed of a cylindrical non-magnetic material and has a first groove extending in the axial direction. A second groove is formed in the yoke base at a position corresponding to the first groove, and these first and second grooves form a duct. The duct connects the space on one axial side of the magnet to the space on the other axial side, allowing air around the diaphragm to move to the outside of the yoke base through the duct when the diaphragm vibrates, thereby adjusting the damping of the frequency characteristics. Note that the "first groove" here is not limited to a concave portion formed by recessing a part of the volume adjustment member, but is a concept that broadly includes a slit-like portion.

[0008] The magnetic circuit for a speaker according to the second aspect is the same as that according to the first aspect, in which the volume adjustment member extends axially from one axial end of the yoke cover to the yoke base so as to fill the gap between the magnet and the yoke cover.

[0009] In the above embodiment, because the volume adjustment member extends axially to the yoke base, the internal volume of the yoke cover can be adjusted simply by changing the shape and size of the first groove, making it easy to adjust the minimum resonance frequency (F0). For example, by adjusting the size of the first groove of the volume adjustment member, the internal volume of the yoke cover can be reduced. As a result, a decrease in the minimum resonance frequency (F0) can be prevented.

[0010] The magnetic circuit for a speaker according to the third aspect is the first or second aspect, wherein the volume adjustment member is provided with a protrusion that protrudes from the other axial end toward the yoke base, and the yoke base is formed with an engaging recess that engages with the protrusion.

[0011] In the above aspect, the protrusion formed on the volume adjustment member engages with the engaging recess formed on the yoke base, thereby preventing the volume adjustment member and the yoke base from moving relative to each other without fixing them by adhesive or other means, thereby maintaining the first groove formed on the volume adjustment member and the second groove formed on the yoke base in a state where their positions are aligned.

[0012] A magnetic circuit for a speaker according to a fourth aspect is any one of the first to third aspects, in which a yoke top made of a magnetic material and having a smaller diameter than the magnet is provided on one axial side of the magnet, and the volume adjustment member is configured to include an annular portion formed in an annular shape and capable of supporting the yoke top from the radial outside, and a side wall portion extending from the peripheral end of the annular portion to the other axial side and capable of supporting the magnet from the radial outside.

[0013] In the above aspect, the annular portion of the volume adjustment member supports the yoke top, and the side wall portion of the volume adjustment member supports the magnet, thereby preventing the central axes of the yoke top and the magnet from misaligning. In other words, the yoke top and the magnet can be positioned by the volume adjustment member for adjusting the volume, without the need for a separate positioning member.

[0014] A fifth aspect of the magnetic circuit for a speaker is the fourth aspect, wherein the yoke cover includes a top surface portion against which the annular portion of the volume adjustment member abuts, and a side wall portion extending axially from the peripheral end of the top surface portion to cover the volume adjustment member from the radially outer side, and the top surface portion is formed with an opening through which the yoke top is inserted, and a rising portion that protrudes from the opening edge of the opening toward one axial side beyond the yoke top.

[0015] In the above aspect, the volume adjustment member can be positioned by abutting the annular portion of the volume adjustment member against the top surface of the yoke cover. The yoke top is inserted through the opening in the top surface, and the raised portion formed on the edge of the opening protrudes toward one axial side beyond the yoke top. This allows magnetic field lines to pass obliquely from the yoke top toward the raised portion, improving the magnetic flux density of the magnetic circuit at the position of the coil disposed between the yoke top and the yoke cover. Since the yoke top and the yoke cover can be positioned axially by the volume adjustment member, the magnetic field lines can flow in the desired direction.

[0016] A speaker driver according to a sixth aspect includes a speaker magnetic circuit according to any one of the first to fifth aspects, a diaphragm provided at one axial end of the yoke cover, and a coil attached to the diaphragm and vibrating the diaphragm when current is applied thereto.

[0017] In the above embodiment, when the diaphragm vibrates, the air inside the yoke base moves through the duct, making it possible to easily adjust the frequency characteristics. [Effects of the Invention]

[0018] According to the speaker magnetic circuit and speaker driver of the present disclosure, it is possible to ensure magnetic flux density and adjust frequency characteristics in an internal magnet type structure. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is an exploded perspective view of a speaker driver according to an embodiment. [Figure 2] 2 is a cross-sectional view showing the speaker driver taken along line 2-2 in FIG. 1. FIG. [Figure 3] 3 is a cross-sectional view showing the speaker driver taken along line 3-3 in FIG. 1. [Figure 4] 10A to 10C are diagrams for explaining a method of assembling the speaker driver according to the embodiment, showing a procedure for fitting the yoke top into a jig. [Figure 5] 10A to 10C are diagrams for explaining a method of assembling the speaker driver according to the embodiment, showing a procedure for attaching a yoke base. [Figure 6] FIG. 10 is a cross-sectional view showing a first modified example of the volume adjusting member as viewed from the axial direction. [Figure 7] FIG. 10 is a cross-sectional view showing a second modified example of the volume adjusting member as viewed from the axial direction. DETAILED DESCRIPTION OF THE INVENTION

[0020] A speaker driver 10 according to an embodiment will be described with reference to the drawings. Note that Z in Fig. 1 indicates one axial direction of the speaker driver 10. In the following description, the Z direction side will be referred to as one axial side. Also, the side opposite to the Z direction will be referred to as the other axial side.

[0021] (Overall configuration of speaker driver 10) As shown in FIG. 1, a speaker driver 10 of this embodiment (hereinafter referred to as "driver 10") includes a yoke cover 12, a volume adjustment member 14, a yoke top 16, a magnet 18, a yoke base 20, a screen 22, a metal plate 24, a terminal 26, a coil 28, a diaphragm unit 30, and a cover member 32. In this embodiment, as shown in FIG. 2, the yoke cover 12, the volume adjustment member 14, the yoke top 16, the magnet 18, and the yoke base 20 form a speaker magnetic circuit 11 (hereinafter referred to as "magnetic circuit 11") The driver 10 of this embodiment is used in speakers mounted in, for example, earphones and headphones. The driver 10 of this embodiment is, for example, a small driver with a diameter of about 4 mm.

[0022] 1, the yoke cover 12 is made of a magnetic material and has a generally cylindrical shape with both axial ends open. Details of the yoke cover 12 will be described later.

[0023] The volume adjustment member 14 is a cylindrical member disposed inside the yoke cover 12 and is made of a non-magnetic material. In one example, the volume adjustment member 14 of this embodiment is made of a metal member containing aluminum as a main component. The volume adjustment member 14 includes an annular portion 44 formed in a substantially annular shape, and a side wall portion 46 extending from the peripheral end of the annular portion 44 to the other axial side (the opposite side to the Z direction). Details of the volume adjustment member 14 will be described later.

[0024] The yoke top 16 and the magnet 18 are disposed inside the volume adjustment member 14. As shown in Fig. 2, the magnet 18 is formed in a substantially cylindrical shape, and in this embodiment, the magnet 18 is, as an example, made of a neodymium magnet with an axial length of about 2 mm.

[0025] A yoke top 16 is disposed on one axial side of the magnet 18. The yoke top 16 is made of a magnetic material and is formed in a shape that combines a truncated cone and a cylinder, with the truncated cone-shaped portion abutting against one axial side surface of the magnet 18. The axial length of the yoke top 16 is shorter than that of the magnet 18, and the outer diameter of the yoke top 16 is smaller than that of the magnet 18. In other words, the magnet 18 is longer in the axial direction than the yoke top 16, and is formed with a larger diameter than the yoke top 16. Furthermore, a chamfered portion 16A is formed at one axial end of the yoke top 16.

[0026] As shown in Fig. 1, a yoke base 20 is disposed on the other axial side of the magnet 18. The yoke base 20 is made of a magnetic material and is formed into a flat, generally cylindrical shape, with an axial length of about 0.6 mm. The yoke base 20 is also formed with a larger diameter than the magnet 18, and has an outer diameter that is approximately the same as that of the volume adjustment member 14. Details of the yoke base 20 will be described later.

[0027] A screen 22 is disposed on the other axial side of the yoke base 20. As shown in FIG. 2, the screen 22 has a smaller diameter than the yoke base 20 and includes a substantially circular mesh member 22A and an annular support member 22B that supports the mesh member 22A. The mesh member 22A is a member having a plurality of ventilation holes that allow air to pass between the front and back sides, and is formed, for example, from a film having a large number of through-holes. Alternatively, the mesh member 22A may be formed from a material such as knitted fabric, nonwoven fabric, or urethane foam. The support member 22B of the screen 22 is formed, for example, from double-sided tape and is attached to a metal plate 24.

[0028] As shown in FIG. 1, metal plate 24 is made of a non-magnetic material such as stainless steel and has a generally flat plate shape with a larger diameter than screen 22. A peripheral wall portion 24A extends from the outer peripheral end of metal plate 24 to one axial direction side. As shown in FIG. 2, peripheral wall portion 24A is fitted onto the inner surface of side wall portion 42 of yoke cover 12 and abuts against yoke base 20, and the height of peripheral wall portion 24A is greater than the thickness of screen 22. This ensures a space between metal plate 24 and yoke base 20 for disposing screen 22. Furthermore, a vent hole 24B is formed in the center of metal plate 24, and this vent hole 24B provides communication between the inside and outside of driver 10.

[0029] A terminal 26 is attached to the other axial surface of the metal plate 24. The terminal 26 is formed in a substantially circular plate shape, and a communication hole 26A that communicates with the air vent 24B of the metal plate 24 is formed in the center of the terminal 26. An electrode 27 is provided on the other axial surface of the terminal 26, and a lead wire (not shown) extending from the coil 28 is connected to the electrode 27.

[0030] Meanwhile, a coil 28 and a diaphragm unit 30 are disposed on one axial side of the yoke cover 12. As shown in Fig. 1, the coil 28 is formed by winding an electric wire into a cylindrical shape, and the outer diameter of the coil 28 is smaller than that of the magnet 18. The coil 28 is also attached to the diaphragm unit 30.

[0031] 2, the diaphragm unit 30 includes a support ring 31 and a diaphragm 33. The support ring 31 is formed in a substantially circular ring shape and is sandwiched between a lid member 32 and a yoke cover 12. The diaphragm 33 is attached to one axial side of the support ring 31, and the coil 28 is fixed to the surface of the diaphragm 33 on the other axial side.

[0032] Diaphragm 33 has a generally flat central portion, and an edge portion 33A that bulges out toward one axial side is formed on the outer periphery of diaphragm 33. When current is applied to coil 28, coil 28 moves in the axial direction, and diaphragm 33 vibrates in accordance with this movement.

[0033] A cover member 32 is disposed on one axial side of the diaphragm unit 30. The cover member 32 is formed in a substantially cylindrical shape from a non-magnetic material such as stainless steel or aluminum. An opening 32A is formed in the center of the cover member 32, and sound generated by vibration of the diaphragm 33 is output from the opening 32A to the outside of the driver 10.

[0034] The lid member 32 is formed with a larger diameter on the other axial side than on one axial side, and a step portion 32B between the small diameter portion and the large diameter portion sandwiches the diaphragm unit 30 between the lid member 32 and the yoke cover 12. Furthermore, the other axial end portion of the lid member 32 is attached to the yoke cover 12.

[0035] (Configuration of magnetic circuit 11) Next, a detailed description will be given of the configuration of the magnetic circuit 11, which is a main part of this disclosure. The magnetic circuit 11 includes a yoke cover 12, a volume adjusting member 14, a yoke top 16, a magnet 18, and a yoke base 20.

[0036] 2, the yoke cover 12 includes a top surface portion 40 against which the annular portion 44 of the volume adjustment member 14 abuts, and a side wall portion 42 that extends from the peripheral end of the top surface portion 40 to the other axial side and covers the volume adjustment member 14 from the radially outer side. An opening 40A is formed in the center of the top surface portion 40, and the tip end of the yoke top 16 and the coil 28 are inserted into this opening 40A.

[0037] The side wall portion 42 extends in the axial direction up to the position of the terminal 26, and the other axial end face of the side wall portion 42 substantially coincides with the other axial end face of the terminal 26. An opening 42A is formed at the other axial end of the side wall portion 42, and parts such as the volume adjustment member 14, magnet 18, yoke base 20, metal plate 24, and terminal 26 are arranged inside the yoke cover 12 through this opening 42A.

[0038] 1 and 3, a notch 42B is formed in the side wall 42, and is cut out in the axial direction from one axial end to the other axial end of the yoke cover 12. The notch 42B is formed continuously up to the top surface 40, and a lead wire (not shown) that connects the terminal 26 and the coil 28 is passed through the notch 42B.

[0039] A rising portion 40B that protrudes toward one axial side is formed at the opening edge of the opening 40A in the top surface portion 40. The rising portion 40B is formed in a generally arc shape when viewed in the axial direction, and extends to just before the notch 42B formed in the side wall portion 42. As shown in FIG. 2, the rising portion 40B protrudes toward one axial side beyond the yoke top 16, so that magnetic field lines are directed obliquely from the vicinity of the chamfered portion 16A, which is the tip of the yoke top 16, toward the rising portion 40B.

[0040] As described above, the volume adjustment member 14 includes the annular portion 44 and the side wall portion 46, and one axial side of the annular portion 44 abuts against the top surface 40 of the yoke cover 12. An opening 44A with a diameter slightly larger than the opening 40A of the yoke cover 12 is formed in the center of the annular portion 44, and this opening 44A communicates with the opening 40A of the yoke cover 12. Furthermore, a protrusion 44B protrudes radially inward from the inner circumferential surface of the annular portion 44, and this protrusion 44B makes the inner diameter of the other axial end of the opening 44A smaller than the inner diameter of one axial end. The protrusion 44B is configured to support the yoke top 16 from the radially outer side.

[0041] The side wall portion 46 extends from the peripheral end of the annular portion 44 to the other axial side and is configured to be able to support the magnet 18 from the radially outer side. In the present embodiment, as an example, the other axial end of the side wall portion 46 extends to the same position as the other axial end of the magnet 18. In this manner, the volume adjustment member 14 extends in the axial direction from one axial end of the yoke cover 12 to the yoke base 20 so as to fill the gap between the magnet 18 and the yoke cover 12.

[0042] 1 and 3, a first groove 46A extending in the axial direction is formed in the side wall 46. The first groove 46A is formed at a position on the opposite side around the axis from the notch 42B of the yoke cover 12. In other words, the first groove 46A is formed at a position rotated 180 degrees around the axis from the notch 42B of the yoke cover 12.

[0043] Additionally, a protrusion 46B is provided on the side wall 46, protruding from the other axial end of the volume adjustment member 14 toward the yoke base 20. The protrusion 46B is formed at a position on the opposite side of the axis from the first groove 46A. In other words, the protrusion 46B is formed at a position rotated 180 degrees around the axis from the first groove 46A.

[0044] As shown in Fig. 1, a second groove 20A is formed in the yoke base 20 disposed on the other axial side of the magnet 18. The second groove 20A is formed in the outer peripheral surface of the yoke base 20 and is formed as a circular groove recessed radially inward, at a position corresponding to the first groove 46A. That is, as shown in Fig. 3, the first groove 46A and the second groove 20A are formed continuously in the axial direction, and the first groove 46A and the second groove 20A form a duct portion D extending in the axial direction.

[0045] Duct portion D connects the space on one axial side of yoke cover 12 to the space on the other axial side. That is, when the space around coil 28 (the space on one axial side) expands during vibration of diaphragm 33, air is introduced from the outside to the inside of driver 10 through communication hole 26A, vent hole 24B, and duct portion D. At this time, the pressure is adjusted by mesh member 22A of screen 22. Conversely, when the space around coil 28 narrows during vibration of diaphragm 33, air inside driver 10 is pushed out to the outside through duct portion D, vent hole 24B, and communication hole 26A, thereby adjusting the pressure.

[0046] As shown in Fig. 1, an engagement recess 20B is formed in the yoke base 20 by cutting out a substantially rectangular shape. The engagement recess 20B is formed at a position opposite (180 degrees) from the second groove 20A around the axis and is sized to allow engagement with the protrusion 46B of the volume adjustment member 14. As shown in Fig. 3, when the driver 10 is assembled, the protrusion 46B of the volume adjustment member 14 fits into and engages with the engagement recess 20B of the yoke base 20, preventing the yoke base 20 from moving circumferentially relative to the volume adjustment member 14.

[0047] (Method of assembling magnetic circuit 11) Next, a method for assembling the magnetic circuit 11 will be described. Note that in the following description, only a part of the procedure for assembling the magnetic circuit 11 will be illustrated and described. In the following description, the upper side of the drawing will be referred to as the upward direction, and the lower side of the drawing will be referred to as the downward direction.

[0048] As shown in Fig. 4, first, the yoke top 16 is fitted into the jig 100. The jig 100 includes a base portion 100A formed in a substantially disk shape and a cylindrical portion 100B erected in the center of the base portion 100A. For ease of explanation, only half of the jig 100 is shown in Figs. 4 and 5. Similarly, only half of the components constituting the driver 10 are shown, with cross sections shown.

[0049] The yoke top 16 is fitted into the cylindrical portion 100B of the jig 100 with the small diameter portion facing downward. At this time, for example, the inner surface of the upper end portion of the cylindrical portion 100B is formed in a tapered shape, and the truncated cone-shaped portion of the yoke top 16 is supported.

[0050] 5, after fitting the yoke top 16 into the jig 100, the yoke cover 12 is fitted into the jig 100. Then, the volume adjustment member 14 is placed inside the yoke cover 12, and the annular portion 44 of the volume adjustment member 14 is brought into contact with the top surface 40 of the yoke cover 12. At this time, the position of the protrusion 46B of the volume adjustment member 14 is aligned with the position of the notch 42B of the yoke cover 12.

[0051] Next, the magnet 18 is inserted inside the volume adjustment member 14, resulting in the state shown in FIG. 5. From this state, the yoke base 20 is inserted inside the yoke cover 12. At this time, if the positions of the engagement recess 20B of the yoke base 20 and the protrusion 46B of the volume adjustment member 14 are not aligned, the yoke base 20 cannot be attached. Furthermore, by aligning the positions of the engagement recess 20B of the yoke base 20 and the protrusion 46B of the volume adjustment member 14, the positions of the second groove 20A formed on the opposite side of the engagement recess 20B and the first groove 46A of the volume adjustment member 14 will match (see FIG. 1).

[0052] After the yoke base 20 is placed inside the yoke cover 12, the metal plate 24 to which the screen 22 is attached is fitted into the yoke cover 12, as shown in Figure 2. This results in the other axial side of the yoke cover 12 being blocked by the metal plate 24.

[0053] After fitting the metal plate 24 and assembling the magnetic circuit 11, a terminal 26 is adhered to the other axial side of the magnetic circuit 11, and a diaphragm unit 30 with a coil 28 attached and a cover member 32 are attached to one axial side of the magnetic circuit 11.

[0054] (action) Next, the operation of this embodiment will be described.

[0055] In the speaker driver 10 according to this embodiment, the yoke base 20 is provided on the other axial side of the magnet 18, thereby improving the magnetic flux density of the magnetic circuit. That is, even with a small driver 10, the magnetic flux density can be ensured.

[0056] 3, a volume adjustment member 14 is provided between the yoke cover 12 and the magnet 18. This allows the internal volume of the driver 10 to be freely adjusted while maintaining an appropriate gap between the yoke cover 12 and the magnet 18.

[0057] Here, a first groove 46A extending in the axial direction is formed in the side wall 46 of the volume adjustment member 14. Meanwhile, a second groove 20A is formed in the yoke base 20 at a position corresponding to the first groove 46A, and the first groove 46A and the second groove 20A together form a duct D. This allows air around the diaphragm 33 to move to the outside of the yoke base 20 through the duct D when the diaphragm 33 vibrates, thereby adjusting the frequency characteristics. For example, the duct D can be used to adjust the acoustics by increasing or decreasing the sound pressure at a predetermined frequency. At this time, the mesh member 22A of the screen 22 can prevent foreign matter from entering the inside of the driver 10.

[0058] In particular, in this embodiment, the protrusion 46B formed on the volume adjustment member 14 engages with the engagement recess 20B formed in the yoke base 20. This makes it possible to prevent the volume adjustment member 14 and the yoke base 20 from moving relative to each other in the circumferential direction without mechanically joining them, thereby maintaining good function of the duct portion D. In addition, in the yoke base 20 of this embodiment, the second groove portion 20A and the engagement recess 20B have different shapes, so the yoke base 20 cannot be installed in the wrong orientation when assembling the magnetic circuit 11.

[0059] Furthermore, in this embodiment, because the volume adjustment member 14 extends axially to the yoke base 20, the internal volume of the yoke cover 12 can be adjusted simply by changing the shape and size of the first groove, making it easy to adjust the minimum resonance frequency (F0). For example, by adjusting the first groove of the volume adjustment member 14, the internal volume of the yoke cover 12 can be reduced. As a result, a decrease in the minimum resonance frequency (F0) can be prevented. Furthermore, simply by changing the shape of the volume adjustment member 14, the internal volume of the yoke cover 12 can be fine-tuned, making it possible to obtain the desired minimum resonance frequency (F0).

[0060] Furthermore, in this embodiment, the annular portion 44 of the volume adjustment member 14 supports the yoke top 16, and the side wall portion 46 of the volume adjustment member 14 supports the magnet 18. This makes it possible to prevent the central axes of the yoke top 16 and the magnet 18 from being significantly misaligned. In other words, the yoke top 16 and the magnet 18 can be positioned without providing a separate positioning member.

[0061] In this embodiment, as shown in FIG. 2 , the rising portion 40B formed on the top surface 40 of the yoke cover 12 protrudes toward one axial side beyond the yoke top 16. This allows magnetic field lines to pass obliquely from the yoke top 16 toward the rising portion 40B, improving the magnetic flux density of the magnetic circuit 11. Furthermore, the volume adjustment member 14 allows the yoke top 16 and the yoke cover 12 to be positioned axially, allowing the magnetic field lines to flow in the desired direction. Furthermore, the yoke top 16 is positioned on the other axial side relative to the yoke cover 12, ensuring a wide gap between the yoke top 16 and the diaphragm 33. This effectively prevents the diaphragm 33 from interfering with the yoke top 16. In this embodiment, the chamfered portion 16A formed at the tip of the yoke top 16 prevents the adhesive used to bond the coil 28 to the diaphragm 33 from interfering with the yoke top 16.

[0062] In this embodiment, the first groove portion 46A is formed in only one location on the volume adjustment member 14, but the present invention is not limited to this. For example, the modified structures shown in Figures 6 and 7 may be employed.

[0063] (First Modification) 6, in the first modified example, two first grooves 46A are formed in the side wall 46 of the volume adjustment member 14. The first grooves 46A are formed at opposite positions (180 degrees) around the axis. In other words, the two first grooves 46A are formed at equal intervals in the circumferential direction.

[0064] Although not shown, second grooves 20A are formed in the yoke base 20 at positions corresponding to the two first grooves 46A, respectively. Therefore, in this modification, two duct portions D are formed.

[0065] (Second Modification) 7, in the second modified example, three first grooves 46A are formed in the side wall 46 of the volume adjustment member 14. The first grooves 46A are formed at positions spaced 120 degrees apart around the axis. In other words, the three first grooves 46A are formed at equal intervals in the circumferential direction.

[0066] Although not shown, second grooves 20A are formed in the yoke base 20 at positions corresponding to the three first grooves 46A, respectively. Therefore, in this modified example, three duct portions D are formed.

[0067] As described above, in the first and second modified examples, the number of first groove portions 46A is increased compared to the embodiment, and by forming the first groove portions 46A at equal intervals in the circumferential direction, the air flow becomes uniform and the diaphragm 33 can vibrate stably.

[0068] 〔supplementary explanation〕 The driver 10 and magnetic circuit 11 according to the embodiment have been described above, but it goes without saying that they can be embodied in various forms without departing from the spirit and scope of the present disclosure. For example, in the above embodiment, as shown in FIG. 2, the chamfered portion 16A is formed on the yoke top 16, but this is not limiting. If the diaphragm 33 and the adhesive for the diaphragm 33 do not interfere with the yoke top 16, the chamfered portion 16A may not be formed on the yoke top 16.

[0069] In the above embodiment, the rising portion 40B of the yoke cover 12 protrudes further toward one axial direction than the yoke top 16, and magnetic field lines are directed obliquely from the vicinity of the chamfered portion 16A of the yoke top 16 toward the rising portion 40B, but this is not limiting. For example, one axial end of the rising portion 40B and one axial end of the yoke top 16 may be located at the same position. In this case, magnetic field lines are directed radially from the yoke top 16 toward the rising portion 40B.

[0070] Furthermore, in the above embodiment, the length of the side wall portion 46 of the volume adjustment member 14 is set to a length that covers the entire magnet 18, but this is not limiting. For example, the side wall portion 46 may be formed to be shorter in the axial direction than the configuration shown in FIG. 2. In this case, it is possible to prevent the other axial end of the side wall portion 46 from protruding further axially than the magnet 18 due to design errors or the like, and it is possible to maintain good contact between the magnet 18 and the yoke base 20.

[0071] Furthermore, in the above embodiment, the first groove portion 46A is formed in a generally slit-like shape in the side wall portion 46 of the volume adjustment member 14, but this is not limited thereto and other shapes may be used. For example, the first groove portion 46A may be formed by recessing the side wall portion 46 radially outward. Even in this case, the duct portion D can be configured by the first groove portion 46A and the second groove portion 20A. The disclosure of Japanese Patent Application No. 2021-030902 is incorporated herein by reference in its entirety. All publications, patent applications, and technical standards mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent application, or technical standard was specifically and individually indicated to be incorporated by reference.

Claims

1. a yoke cover formed of a cylindrical magnetic material and having a diaphragm attached to one end on one axial side; a magnet disposed inside the yoke cover; a volume adjustment member formed of a cylindrical non-magnetic material and disposed between the yoke cover and the magnet, the volume adjustment member having a first groove portion extending in the axial direction; a yoke base made of a magnetic material, provided on the other axial side of the magnet, having a second groove formed at a position corresponding to the first groove, the first groove and the second groove constituting a duct portion that communicates a space on one axial side of the inside of the yoke cover with a space on the other axial side; and The volume adjustment member extends in the axial direction from one axial end of the yoke cover to the yoke base so as to fill a gap between the magnet and the yoke cover.

2. A yoke cover formed of a cylindrical magnetic material, with a diaphragm attached to one end on one axial side; a magnet disposed inside the yoke cover; a volume adjustment member formed of a cylindrical non-magnetic material and disposed between the yoke cover and the magnet, the volume adjustment member having a first groove portion extending in the axial direction; a yoke base made of a magnetic material, provided on the other axial side of the magnet, having a second groove formed at a position corresponding to the first groove, the first groove and the second groove constituting a duct portion that communicates a space on one axial side of the inside of the yoke cover with a space on the other axial side; and the volume adjustment member is provided with a protrusion that protrudes from the other axial end toward the yoke base, The yoke base has an engaging recess formed therein that engages with the protrusion.

3. a yoke top made of a magnetic material and having a smaller diameter than the magnet is provided on one axial side of the magnet, 3. The magnetic circuit for a speaker according to claim 1, wherein the volume adjustment member includes an annular portion formed in an annular shape and capable of supporting the yoke top from the radially outer side, and a side wall portion extending from a peripheral end of the annular portion to the other axial side and capable of supporting the magnet from the radially outer side.

4. the yoke cover includes a top surface portion against which the annular portion of the volume adjustment member abuts, and a side wall portion extending in the axial direction from a peripheral end portion of the top surface portion to cover the volume adjustment member from the radially outer side, 4. The magnetic circuit for a speaker according to claim 3, wherein the top surface portion is formed with an opening through which the yoke top is inserted and a rising portion that protrudes from an edge of the opening toward one axial side beyond the yoke top.

5. A magnetic circuit for a speaker according to any one of claims 1 to 4; a diaphragm provided at one axial end of the yoke cover; a coil attached to the diaphragm and vibrating the diaphragm when energized; A speaker driver having:

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