Acoustic device

Abstract

An object of the present disclosure is to provide an acoustic device capable of easily and effectively suppressing current distortion in a magnetic circuit.SOLUTION: An acoustic device according to an aspect of the present disclosure includes an annular magnet 10, a bottom yoke 20 having a mounting surface 21 on which the magnet 10 is mounted, a pole piece 30 disposed on the mounting surface 21 inside the inner circumferential surface of the magnet 10, and a top plate 40 disposed on a surface of the magnet 10 facing the surface mounted on the bottom yoke 30, in which a resistivity of the top plate 40 is lower than a resistivity of the pole piece 30.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to audio equipment. [Background technology]

[0002] A widely known acoustic device that converts an electric signal into sound includes a magnetic circuit that includes a magnet, a bottom yoke, a pole piece, a ring yoke, etc. To convert an electric signal into high-quality sound, it is necessary to reduce the distortion of the electric signal current (current distortion) caused by the magnetic circuit. A speaker that can reduce current distortion has been proposed (Japanese Utility Model Laid-Open Publication No. 57-23095). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Utility Model Application Publication No. 57-23095 Summary of the Invention [Problem to be solved by the invention]

[0004] The speaker in Patent Document 1 is said to be able to reduce high-frequency components in the current flowing through the voice coil and obtain high-quality reproduced sound by forming the members that make up the magnetic circuit from ferromagnetic stainless steel and forming at least a portion of the members that form the magnetic gap from ferromagnetic stainless steel containing at least one of Ti, Mo, and Zr. There is a demand for more effective reduction of current distortion in order to obtain reproduced sound that is faithful to the original sound.

[0005] In view of the above circumstances, an object of the present disclosure is to provide an acoustic device that can easily and effectively suppress current distortion in a magnetic circuit. [Means for solving the problem]

[0006] (1) An acoustic device according to one aspect of the present disclosure comprises a ring-shaped magnet, a bottom yoke having a mounting surface on which the magnet is placed, a pole piece arranged within the inner peripheral surface of the magnet on the mounting surface, and a top plate arranged on a surface of the magnet opposite to the surface that is placed on the bottom yoke, wherein the resistivity of the top plate is lower than the resistivity of the pole piece.

[0007] (2) In the above (1), the resistivity of the bottom yoke may be lower than the resistivity of the top plate.

[0008] (3) In the above (1) or (2), the pole piece may include a compression-molded body obtained by compressing and molding soft magnetic powder.

[0009] (4) In the above (3), the pole piece may further contain a metal material having a lower resistivity than the compression-molded body.

[0010] (5) In the above (4), the resistivity of the top plate may be higher than the resistivity of the metal material.

[0011] (6) In any one of (1) to (5) above, a slit may be formed in the top plate. [Effects of the Invention]

[0012] An acoustic device according to one aspect of the present disclosure can easily and effectively suppress current distortion in a magnetic circuit. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is a schematic plan view showing a magnetic circuit of an earphone, which is an acoustic device according to an embodiment of the present disclosure. [Figure 2] FIG. 2 is an end view taken along line AA of FIG. [Figure 3] FIG. 3 is a schematic enlarged view of a part of a cross section of a compression-molded body obtained by compression-molding soft magnetic powder. [Figure 4]FIG. 4 is a schematic end view showing a magnetic circuit of a speaker, which is an acoustic device according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. Note that the drawings are schematic illustrations of the configuration of the present disclosure, and the shape and scale of each component (each member) in each drawing may differ from the actual configuration.

[0015] [First embodiment] As an embodiment of the acoustic device of the present disclosure, an earphone having a so-called external magnet type magnetic circuit will be described.

[0016] <Earphones> 1 and 2, the earphone 1 mainly comprises an annular magnet 10, a bottom yoke 20 having a mounting surface 21 on which the magnet 10 is mounted, a pole piece 30 arranged within the inner circumferential surface of the magnet 10 on the mounting surface 21, and a top plate 40 arranged on the surface of the magnet 10 opposite the surface on which it is mounted on the bottom yoke 20. The magnet 10, bottom yoke 20, pole piece 30, and top plate 40 form a magnetic circuit.

[0017] The earphone 1 includes an outer ring 50 positioned to surround the periphery of the top plate 40, a diaphragm 60 whose outer periphery is fixed to the upper edge of the outer ring 50, and a voice coil 70 connected to the diaphragm 60. Note that the diaphragm 60 and the voice coil 70 are omitted from FIG. 1.

[0018] In the earphone 1, the magnetic flux generated by passing a current through the voice coil 70 and the electromagnetic force generated between the magnetic flux of the magnetic circuit cause the diaphragm 60 to reciprocate at a desired amplitude. This reciprocating movement of the diaphragm 60 vibrates the air, generating sound. Note that, below, the direction in which sound is emitted may be referred to as "front," and the opposite direction as "rear."

[0019] In this embodiment, the bottom yoke 20 is a substantially disk-shaped member, and the pole piece 30 and magnet 10 are substantially cylindrical members, but the shape of each member is not particularly limited. The pole piece 30 is disposed in the center of the mounting surface 21 (front surface) of the bottom yoke 20. In a plan view, the bottom yoke 20 has a larger diameter than the pole piece 30.

[0020] The magnet 10 is arranged on the mounting surface 21 so as to surround the pole piece 30. In other words, the magnet 10 is mounted on the bottom yoke 20 so as to be spaced apart from the pole piece 30 located on the inner periphery. A gap 80 is formed between the magnet 10 and the pole piece 30, forming a magnetic gap. A voice coil 70 is movably disposed in the gap 80. The outer diameter of the magnet 10 and the outer diameter of the bottom yoke 20 may be approximately the same or different.

[0021] Top plate 40 is disposed on the surface (front surface) of magnet 10 that faces the surface (rear surface) that is mounted on bottom yoke 20. Top plate 40 is positioned so as to surround the upper part of the outer periphery of pole piece 30. Specifically, top plate 40 is a substantially annular plate-shaped member that is disposed on the front surface of magnet 10 and is mounted on magnet 10 so as to be spaced apart from pole piece 30 that is located on the inner periphery side.

[0022] An outer ring 50 is disposed on the outer periphery of the top plate 40. That is, the outer ring 50 is placed on the magnet 10 so as to be located on the outer periphery of the top plate 40. The outer ring 50 has a circular plate-shaped bottom portion 51 and a wall portion 52 that rises forward from the bottom portion 51 (in the direction away from the magnet 10). The outer ring 50 is disposed in front of the magnet 10 so that the inner periphery of the bottom portion 51 is in contact with or close to the outer periphery of the top plate 40. That is, the inner diameter of the bottom portion 51 is approximately the same as the outer diameter of the top plate 40. The magnet 10, bottom yoke 20, pole piece 30, top plate 40, and outer ring 50 are disposed concentrically and fixed together by known means such as adhesive.

[0023] A through hole 22 may be formed in the center of the bottom yoke 20. Providing the through hole 22 reduces the air spring that occurs when sound is generated, thereby suppressing deterioration in sound quality. The bottom yoke 20 of this embodiment has one through hole 22 formed with a diameter that is approximately the same as the inner diameter of the pole piece 30. The number, diameter, shape, etc. of the through holes 22 are not particularly limited and may be set as desired depending on the shape of the earphone, the configuration of the magnetic circuit, etc. Note that "air spring" refers to the change in air pressure (change in internal pressure in the magnetic circuit) that occurs when air vibrates due to the reciprocating movement of the diaphragm 60.

[0024] The magnetic circuit may be provided with a notch 53 for passing a conductive wire to the voice coil 70. Specifically, the notch 53 may be formed in the outer ring 50, and the conductive wire may be passed through this notch 53.

[0025] Magnet 10 is preferably a sintered neodymium magnet formed by sintering neodymium magnet powder. Magnet 10 may also be a sintered ferrite magnet, alnico magnet, or samarium-cobalt magnet, but by using a sintered neodymium magnet, it is possible to achieve a balance between cost, dimensional accuracy, and magnetic properties.

[0026] 3, the pole piece 30 preferably contains a compression-molded body P obtained by compressing and molding soft magnetic powder 31. By containing the compression-molded body P in at least a portion of the pole piece 30, the resistivity can be easily increased, and eddy currents generated near the magnetic gap (gap 80) can be reduced, suppressing current distortion in the voice coil 70, thereby effectively reducing distortion in the sound reproduced by the earphone 1.

[0027] The pole piece 30 may further include a metal material with a lower resistivity than the compression-molded body P. In other words, the pole piece 30 may include a portion of the compression-molded body P obtained by compressing soft magnetic powder 31, and a remaining portion of the pole piece 30 may include a metal material with a lower resistivity than the compression-molded body P. An example of the metal material is low-carbon steel. By including a metal material with a relatively low resistivity in the pole piece 30, the cost of the pole piece 30 can be reduced, which in turn makes it easier to reduce the cost of the earphone 1. The pole piece 30 may have the compression-molded body P located in the portion close to the voice coil 70, and the metal material with a low resistivity located in the remaining portion.

[0028] The material of the soft magnetic powder 31 is not particularly limited, and examples thereof include powdered iron-based alloys such as pure iron, Fe-Al alloys, Fe-Si alloys, permalloy, permendur, and sendust, with permalloy being preferred.

[0029] The average particle size of the soft magnetic powder 31 is preferably 5 μm or more and 300 μm or less. The upper limit of the average particle size of the soft magnetic powder 31 may be 200 μm, or may be 150 μm, 100 μm, 50 μm, or 15 μm. By setting the particle size in this range, it is possible to easily reduce the size of the compression-molded body P. Note that the "average particle size" refers to the particle size at which the cumulative particle size distribution is 50% in the particle size distribution evaluated by the sieving method.

[0030] The compression-molded body P is preferably obtained by mixing a phenolic resin with the soft magnetic powder 31 and then compression-molding the mixture. The lower limit of the amount of phenolic resin mixed is preferably 0.5 mass %, more preferably 0.7 mass %. The upper limit of the amount mixed is preferably 2.0 mass %, more preferably 1.5 mass %. By mixing the phenolic resin in the amount within the above range with the soft magnetic powder 31, the strength of the compression-molded body P can be improved.

[0031] The surface of the compression-molded body P is preferably coated with a protective layer 32. Because the surface of the compression-molded body P is relatively fragile, there is a risk that part of the surface may peel off, particularly due to the strong magnetic field generated in and around the magnetic gap. The protective layer 32 covers the surface and prevents peeling. Because the protective layer 32 penetrates into the gaps between the soft magnetic powder 31 on the surface, it improves the bonding strength of the soft magnetic powder 31 on the surface and prevents peeling of the surface.

[0032] It is preferable that the material of the protective layer 32 is a non-magnetic material. By forming the protective layer 32 from a non-magnetic material, peeling of the surface can be suppressed without affecting the magnetic field generated in the magnetic gap.

[0033] The material for the protective layer 32 is not particularly limited, but examples include silicone-based resins and non-magnetic metals. Among these, it is preferable to use a non-magnetic metal in order to effectively suppress eddy currents. As the non-magnetic metal, copper, silver, etc., which have a higher conductivity than that of the soft magnetic powder 31, are preferred, and copper is particularly preferred. By using copper as the material for the protective layer 32, the eddy currents can be further suppressed, and the current distortion can be further reduced. Furthermore, the impedance in the high-frequency range can be reduced, and the sound pressure in the high-frequency range can be improved.

[0034] The upper limit of the average thickness (the distance from the surface of the compression-molded soft magnetic powder 31 to the surface of the protective layer 32) of the surface portion of the protective layer 32 may be 30 μm or 20 μm. The lower limit of the average thickness of the protective layer 32 may be 5 μm or 10 μm. By setting the average thickness of the protective layer 32 within the above range, it is possible to prevent a decrease in the magnetic flux density in the magnetic gap and effectively prevent peeling of the surface of the compression-molded body P. It is also possible to ensure a sufficient magnetic flux density. The average thickness of the protective layer 32 means the average value of the thickness (depth) of the protective layer 32 measured at any ten points.

[0035] The thickness (external dimension in the front-to-rear direction) of each of the top plate 40 and the bottom yoke 20 is not particularly limited, but may be, for example, 0.1 mm or more and 0.6 mm or less. The lower limit of the thickness may be 0.2 mm. The upper limit of the thickness may be 0.5 mm.

[0036] The thickness of the magnet 10 is not particularly limited, but may be, for example, 0.5 mm to 1.0 mm. The thickness of the pole piece 30 is not particularly limited, but may be, for example, 0.8 mm to 1.6 mm. By keeping the thicknesses within the above ranges, the magnetic circuit can be easily miniaturized, achieving an appropriate size for earphones.

[0037] The outer diameter of magnet 10 is not particularly limited, but may be, for example, 8.0 mm or more and 12.0 mm or less. The lower limit of the outer diameter may be 9 mm. The upper limit of the outer diameter may be 10 mm. The inner diameter of magnet 10 is not particularly limited, but may be, for example, 5.0 mm or more and 6.5 mm or less.

[0038] The inner diameter of the wall portion 52 of the outer ring 50 is not particularly limited, but may be, for example, 8.5 mm or more and 12.5 mm or less. The outer diameter of the outer ring 50 and the diameter of the bottom yoke 20 are not particularly limited, but may be, for example, 9.0 mm or more and 13.0 mm or less. The outer diameter of the pole piece 30 is not particularly limited as long as it is smaller than the inner diameter of the magnet 10 and a gap 80 (magnetic gap) can be formed between the pole piece 30 and the inner circumference of the magnet 10, but may be, for example, 4.0 mm or more and 5.5 mm or less. By setting each diameter within the above range, the magnetic circuit can be miniaturized, resulting in a size appropriate for earphones.

[0039] The resistivity of the top plate 40 in the acoustic device (earphone 1) is lower than that of the pole piece 30. Specifically, the pole piece 30 is formed of a magnetic material with high resistivity, and the top plate 40 is formed of a magnetic material with lower resistivity than the pole piece 30. The material of the top plate 40 is not particularly limited, but magnetic stainless steel is an example. By forming both the top plate 40 and the pole piece 30 from a magnetic material with high resistivity, eddy currents caused by the current in the voice coil 70 can be reduced, resulting in low distortion in the reproduced sound; however, this may increase the cost of the earphone 1. Because the circumferential length (distance around the circumference) of the magnetic circuit of the earphone 1 is longer than that of the pole piece 30, even if the top plate 40 is formed of a magnetic material with lower resistivity than the pole piece 30, the resistance value can be increased, effectively reducing eddy currents. Therefore, even if the top plate 40 is formed of a magnetic material with lower resistivity than the pole piece 30, low distortion in the reproduced sound can be achieved, and costs can be reduced.

[0040] The resistivity of the bottom yoke 20 in the earphone 1 is preferably lower than that of the top plate 40. In other words, the bottom yoke 20 is preferably formed from a magnetic material with an even lower resistivity than the top plate 40. The material for the bottom yoke 20 is not particularly limited, but may be iron, for example. By forming the bottom yoke 20 from a magnetic material with low resistivity, it is possible to prevent a decrease in magnetic flux density in the magnetic gap, ensure sufficient sound pressure, and make it easier to reduce costs.

[0041] It is preferable that the resistivity of the top plate 40 is higher than that of the metal material. That is, it is preferable that the resistivity of the top plate 40 is lower than that of the pole piece 30, and that the resistivities decrease in the order of the compression-molded body P forming part of the pole piece 30, the top plate 40, and the metal material forming the remainder of the pole piece 30. By decreasing the resistivities in the order of the compression-molded body P, the top plate 40, and the metal material, it is possible to reduce eddy currents while suppressing a decrease in magnetic flux density, thereby achieving sufficient sound pressure and low distortion in the reproduced sound.

[0042] Slits (not shown) may be formed in the top plate 40. The slits (grooves that axially penetrate the top plate 40) may be grooves with a partial bottom (grooves that do not penetrate all the way through). The number, orientation, and length of the slits formed in the top plate 40 in a plan view are not particularly limited and may be set arbitrarily. By forming the slits in the top plate 40, the resistance value of the top plate 40 changes, so that the resistivity of the top plate 40 relative to the resistivity of the pole piece 30 can be easily optimized, and the effect of improving the low distortion characteristics can be easily obtained.

[0043] [Second embodiment] As another embodiment of the acoustic device of the present disclosure, a speaker having an outer magnet type magnetic circuit will be described.

[0044] <Speaker> 4, the speaker 2 mainly comprises an annular magnet 110, a bottom yoke 120 having a mounting surface 121 on which the magnet 110 is mounted, a pole piece 130 arranged within the inner circumferential surface of the magnet 110 on the mounting surface 121, and a top plate 140 arranged on the surface of the magnet 110 opposite the surface mounted on the bottom yoke 120. The magnet 110, bottom yoke 120, pole piece 130, and top plate 140 form a magnetic circuit.

[0045] The speaker 2 includes an outer ring (not shown) positioned to surround the periphery of the top plate 140, a diaphragm (not shown) whose outer periphery is fixed to the upper edge of the outer ring, and a voice coil 170 connected to the diaphragm.

[0046] The pole piece 130 is disposed in the center of the mounting surface 121 (front surface) of the bottom yoke 120. The magnet 110 is disposed on the mounting surface 121 so as to surround the pole piece 130. In other words, the magnet 110 is mounted on the bottom yoke 120 so as to be spaced apart from the pole piece 130 located on the inner periphery side. A gap 180 is formed between the magnet 110 and the pole piece 130 as a magnetic gap. A voice coil 170 is disposed in the gap 180 so as to be able to move freely.

[0047] Top plate 140 is disposed on the surface (front surface) of magnet 110 that faces the surface (rear surface) that is mounted on bottom yoke 120. Top plate 140 is positioned so as to surround the upper part of the outer periphery of pole piece 130. Specifically, top plate 140 is a substantially annular plate-shaped member that is disposed in front of magnet 110 and is mounted on magnet 110 so as to be spaced apart from pole piece 130, which is located on the inner periphery side. Magnet 110, bottom yoke 120, pole piece 130, and top plate 140 are disposed concentrically and fixed to each other by known means such as adhesive.

[0048] The magnet 110 may be a sintered ferrite magnet, alnico magnet, or samarium-cobalt magnet, but is preferably a sintered neodymium magnet. The pole piece 130 preferably includes a compression-molded body P obtained by compressing soft magnetic powder 31 (see FIG. 3). The pole piece 130 preferably further includes a metal material having a lower resistivity than the compression-molded body P. In this case, the pole piece 130 preferably has the compression-molded body P disposed in the portion adjacent to the voice coil 170, and the metal material with a lower resistivity disposed in the other portions. The surface of the compression-molded body P is preferably covered with a protective layer 32.

[0049] The resistivity of the top plate 140 of the speaker 2 is lower than the resistivity of the pole piece 130. Specifically, the pole piece 130 is formed of a magnetic material with high resistivity, and the top plate 140 is formed of a magnetic material with lower resistivity than the pole piece 130. The material of the top plate 140 is not particularly limited, but may be, for example, magnetic stainless steel.

[0050] The resistivity of the bottom yoke 120 in the speaker 2 is preferably lower than that of the top plate 140. In other words, the bottom yoke 120 is preferably formed of a magnetic material with an even lower resistivity than the top plate 140. The material of the bottom yoke 120 is not particularly limited, but may be iron, for example.

[0051] The resistivity of the top plate 140 is preferably higher than that of the metal material. That is, the resistivity of the top plate 140 is preferably lower than that of the pole piece 130, and the resistivities of the compression-molded body P forming a part of the pole piece 130, the top plate 140, and the metal material forming the remainder of the pole piece 130 are preferably lower in this order. A slit (not shown) may be formed in the top plate 40.

[0052] [Other embodiments] The above-described embodiments do not limit the configuration of the present invention. Therefore, the above-described embodiments may include omissions, substitutions, or additions of components based on the description in this specification and common general technical knowledge, and all of these should be construed as falling within the scope of the present invention.

[0053] In the above embodiment, the acoustic device has been described as an external magnetic type earphone, but it may also be an internal magnetic type earphone, or other acoustic device such as a speaker or headphones.

[0054] The pole piece may be entirely formed from the compression molded body, and the bottom yoke and top plate may partially include the compression molded body as long as the resistivity requirement of the present disclosure is not violated. [Industrial Applicability]

[0055] The acoustic device of the present disclosure can reduce distortion in reproduced sound, and is therefore suitable for use as earphones and the like with excellent acoustic characteristics. [Explanation of symbols]

[0056] 1 earphones 2 speakers 10,110 magnets 20,120 Bottom Yoke 21,121 Placement surface 22 through holes 30,130 pole pieces 31 Soft magnetic powder 32 Protective layer 40,140 Top Plate 50 outer ring 51 Bottom 52 Wall 53 Cutout 60 diaphragm 70,170 voice coil 80,180 Gap (magnetic gap) P compression molded body

Claims

1. A ring-shaped magnet; a bottom yoke having a mounting surface on which the magnet is mounted; a pole piece disposed on the mounting surface within the inner circumferential surface of the magnet; a top plate disposed on a surface of the magnet opposite to a surface of the magnet placed on the bottom yoke; Equipped with An acoustic device in which the resistivity of the top plate is lower than the resistivity of the pole piece.

2. 2. The acoustic device according to claim 1, wherein the resistivity of the bottom yoke is lower than the resistivity of the top plate.

3. 3. The acoustic device according to claim 1, wherein the pole piece includes a compression-molded body obtained by compressing and molding soft magnetic powder.

4. The acoustic device according to claim 3 , wherein the pole piece further comprises a metal material having a lower resistivity than the compression-molded body.

5. The acoustic device according to claim 4 , wherein the resistivity of the top plate is higher than the resistivity of the metal material.

6. 3. The acoustic device according to claim 1, wherein a slit is formed in the top plate.

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