Electroacoustic transducer and headphones

Abstract

To provide an electroacoustic transducer and headphones that output balanced sound.SOLUTION: An electro-acoustic transducer 10 includes a planar diaphragm 12 having a coil 13 formed in a predetermined pattern on the surface of an insulating thin film, a first yoke 18 arranged at a distance from the diaphragm so as to face one side of the diaphragm, a plurality of first magnets 14 provided on the first yoke 18, a second yoke 20 arranged at a distance from the diaphragm so as to face the other side of the diaphragm, and a plurality of second magnets 16 provided on the second yoke, and the first yoke 18 and the second yoke 20 each have a plurality of sound emission holes formed therein, and the sound emission holes formed in the center of the first yoke 18 and the second yoke 20 have smaller opening areas than the sound emission holes formed in the outer periphery thereof.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an electro-acoustic transducer and a headphone. [Background technology]

[0002] Patent Document 1 discloses a planar electroacoustic transducer equipped with a planar diaphragm. Specifically, the planar electroacoustic transducer described in Patent Document 1 has yokes arranged on both sides of the diaphragm, and a plurality of magnets attached to the yokes. Furthermore, each yoke has the same shape, and has a structure in which a plurality of sound emission holes are formed at equal intervals. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2017-130704 Summary of the Invention [Problem to be solved by the invention]

[0004] However, since the diaphragm of an electroacoustic transducer has a structure in which the outer peripheral edge is fixed, the amplitude increases from the outer peripheral part toward the center. Therefore, in a structure in which sound emission holes are formed at equal intervals in the yoke, as in Patent Document 1, the sound pressure differs between the center and the outer peripheral part, and there is room for improvement in terms of balanced sound output.

[0005] An object of the present invention is to provide an electro-acoustic transducer and headphones that can output sound in a well-balanced manner. [Means for solving the problem]

[0006] The electro-acoustic transducer of the first aspect comprises a planar diaphragm having a coil formed in a predetermined pattern on the surface of an insulating thin film, a first yoke arranged at a distance from the diaphragm so as to face one side of the diaphragm, a plurality of first magnets provided on the first yoke, a second yoke arranged at a distance from the diaphragm so as to face the other side of the diaphragm, and a plurality of second magnets provided on the second yoke, wherein a plurality of sound emission holes are formed in each of the first yoke and the second yoke, and the sound emission holes formed in the center of the first yoke and the second yoke have smaller opening areas than the sound emission holes formed in the outer periphery thereof.

[0007] In the above-described embodiment, a first yoke and a second yoke are provided on both sides of the diaphragm with a gap therebetween, with a plurality of first magnets provided in the first yoke and a plurality of second magnets provided in the second yoke. By passing a current through the coil, the diaphragm vibrates and outputs sound. Here, a plurality of sound emission holes are formed in each of the first yoke and the second yoke, with the sound emission holes formed in the central portion of the yoke having a smaller opening area than the sound emission holes formed in the outer periphery. This suppresses sound emitted from the central portion, where the amplitude of the diaphragm is large, and reduces the difference in sound pressure between the central portion and the outer periphery of the diaphragm.

[0008] The electro-acoustic transducer of the second aspect is the same as that of the first aspect, except that the first magnet and the second magnet are formed in an elongated shape to follow the pattern of the coil, and the sound emission hole is formed in a slit shape along the first magnet and the second magnet.

[0009] In the above aspect, by forming the sound release hole in a slit shape along the first magnet and the second magnet, the opening area of ​​the sound release hole can be increased while ensuring the mounting area of ​​the first magnet and the second magnet.

[0010] An electroacoustic transducer according to a third aspect is the second aspect, wherein the arrangement of the sound emission holes in the first yoke and the second yoke is different.

[0011] In the above embodiment, since the sound emission holes are arranged differently in the first yoke and the second yoke, the locations where the magnetic permeability is high in each yoke can be set arbitrarily, and the behavior of the diaphragm can be adjusted.

[0012] An electro-acoustic transducer according to a fourth aspect is the third aspect, wherein the first yoke is disposed on the sound output side, and the second yoke has fewer sound emission holes than the first yoke.

[0013] In the above aspect, the number of sound emission holes in the first yoke arranged in the sound output direction can be maintained while the number of sound emission holes in the second yoke on the opposite side can be reduced, thereby increasing the magnetic permeability.

[0014] In the electro-acoustic transducer of the fifth aspect, in the first aspect, the first yoke and the second yoke are each configured to include a planar portion and ribs extending from both ends of the planar portion toward the diaphragm, and openings are formed at the corners between the planar portion and the ribs.

[0015] In the above aspect, the rigidity of the first yoke and the second yoke can be increased by forming the ribs, and sound pressure can be increased by forming openings at the corners between the flat portion and the ribs.

[0016] A headphone according to a sixth aspect includes the electro-acoustic transducer according to any one of the first to fifth aspects.

[0017] The above embodiment has the effects described in the first to fifth embodiments. [Effects of the Invention]

[0018] The electro-acoustic transducer and headphones according to the present invention can output sound in a well-balanced manner. [Brief explanation of the drawings]

[0019] [Figure 1] 1 is an exploded perspective view showing an electroacoustic transducer according to an embodiment. [Figure 2]FIG. 2 is a front view of a diaphragm according to the embodiment. [Figure 3] FIG. 2 is an enlarged view of a main part of the diaphragm. [Figure 4] 1 is a cross-sectional view showing a cut state of an electro-acoustic transducer according to an embodiment. [Figure 5] 5 is a cross-sectional view showing the direction of magnetic flux in relation to the cross-sectional view of FIG. 4. [Figure 6] 6A is a front view of the first yoke, and FIG. 6B is a cross-sectional view taken along line 6B-6B in FIG. 6A. [Figure 7] 7A is a front view of the second yoke, and FIG. 7B is a cross-sectional view taken along line 7B-7B in FIG. 7A. [Figure 8] FIG. 10 is a front view of a second yoke according to a modified example. DETAILED DESCRIPTION OF THE INVENTION

[0020] An electro-acoustic transducer 10 according to an embodiment will be described with reference to the drawings. Fig. 1 is an exploded perspective view showing an electro-acoustic transducer according to an embodiment. The electro-acoustic transducer 10 according to this embodiment is mounted in headphones, which are an example of an acoustic device.

[0021] In the following description, the upper side of the paper in FIG. 1 will be referred to as the upper side of the electro-acoustic transducer 10, and the lower side of the paper will be referred to as the lower side of the electro-acoustic transducer 10. Arrow H, as appropriate, shown in each drawing indicates the up-down direction of the electro-acoustic transducer 10. Furthermore, the diagonally lower left side of the paper in FIG. 1 will be referred to as the front side of the electro-acoustic transducer 10, and the diagonally upper right side of the paper will be referred to as the rear side of the electro-acoustic transducer 10. Arrow L, as appropriate, shown in each drawing indicates the front-to-rear direction of the electro-acoustic transducer 10. Furthermore, the left and right sides of the electro-acoustic transducer 10 as viewed from the front side will be referred to as the left and right sides, respectively. Arrow W, as appropriate, shown in each drawing indicates the left-to-right direction (width direction) of the electro-acoustic transducer 10. However, the up-down, front-to-rear, and left-to-right directions of the electro-acoustic transducer 10 are set for the convenience of explanation and do not necessarily coincide with the up-down, front-to-rear, and left-to-right directions when in use.

[0022] As shown in FIG. 1, the electroacoustic transducer 10 of this embodiment is composed of a diaphragm 12, a first magnet 14, a second magnet 16, a first yoke 18, a second yoke 20, a front case 22, a rear case 24, a front filter 26, and a rear filter 28.

[0023] Diaphragm 12 is a planar component in which coil 13 is formed in a predetermined pattern on the surface of an insulating thin film. For example, diaphragm 12 is formed by forming a metal film such as aluminum on the surface of a polymer film and then etching it to leave the predetermined pattern. Coil 13 is composed of a collection of multiple linear patterns arranged in parallel, but for ease of explanation, in Figures 1 to 3, the collection of linear patterns is depicted as coil 13.

[0024] Fig. 2 is a front view of diaphragm 12 in this embodiment, and Fig. 3 is an enlarged view of a main portion of diaphragm 12. As shown in Fig. 2, a substantially rectangular frame member 30 is attached to the outer peripheral edge of diaphragm 12. A plurality of insertion holes 30A are formed in the outer peripheral portion of frame member 30, and bolts (not shown) for assembling electroacoustic transducer 10 are inserted into insertion holes 30A.

[0025] The coil 13 includes linear portions 13A extending substantially linearly in the vertical direction and arc portions 13B folded back at the upper and lower ends of the linear portions 13A. The linear portions 13A are formed at equal intervals in the left-right direction. In the present embodiment, eight linear portions 13A are arranged in the left-right direction, for example. Seven arc portions 13B are formed to connect adjacent linear portions 13A. Therefore, the pattern of the coil 13 on the diaphragm 12 is formed into a meandering pattern as a whole. The linear portions 13A are formed over the entire diaphragm 12, and these linear portions 13A form regions that interlink with magnetic flux from a first magnet 14 and a second magnet 16, which will be described later.

[0026] 3, the straight line portions 13A of the coil 13 are formed in a generally wavy shape when enlarged. The gaps between adjacent straight line portions 13A are very narrow, and the wave shapes of adjacent straight line portions 13A are formed in a pattern such that they alternate. Therefore, the gaps between adjacent straight line portions 13A are generally constant from the top to the bottom.

[0027] As shown in Figure 1, a first yoke 18 is arranged at a distance from the diaphragm 12 so as to face the front side (one side) of the diaphragm 12, and a first magnet 14 is arranged between the first yoke 18 and the diaphragm 12.

[0028] First yoke 18 includes a planar first flat portion 18A and first ribs 18B extending from both left and right ends of first flat portion 18A toward diaphragm 12. Seven first magnets 14 are elongated bar magnets extending in the vertical direction along the pattern of coil 13, and are provided spaced apart in the horizontal direction. Details of first yoke 18 and first magnets 14 will be described later.

[0029] A second yoke 20 is arranged at a distance from the diaphragm 12 so as to face the rear side (other side) of the diaphragm 12, and a second magnet 16 is arranged between the second yoke 20 and the diaphragm 12.

[0030] The second yoke 20 includes a flat second planar portion 20A and second ribs 20B extending from both left and right ends of the second planar portion 20A toward the diaphragm 12. The second magnets 16 are elongated bar magnets extending in the vertical direction along the pattern of the coil 13, and seven of them are provided spaced apart in the horizontal direction. Details of the second yoke 20 and the second magnets 16 will be described later.

[0031] A front case 22 is disposed in front of the first yoke 18. A front filter 26 is disposed in front of the front case 22. The front case 22 is formed in a shape that covers the diaphragm 12 and the frame member 30 from the front side, and has front bolt holes 22A formed in positions corresponding to the insertion holes 30A of the frame member 30. A recess is formed in the rear surface of the front case 22, into which the first yoke 18 is attached.

[0032] The portion of front case 22 facing diaphragm 12 is formed in a generally lattice pattern, with nine openings formed therein. Front filter 26 is attached to front case 22 so as to cover the openings formed in front case 22. Front filter 26 is formed in a generally rectangular shape from nonwoven fabric such as felt.

[0033] A rear case 24 is disposed behind the second yoke 20. A rear filter 28 is disposed behind the rear case 24. The rear case 24 is formed in a shape that covers the diaphragm 12 and the frame member 30 from the rear side, and has rear bolt holes 24A formed at positions corresponding to the insertion holes 30A of the frame member 30. A recess is formed in the front surface of the rear case 24 to which the second yoke 20 is attached.

[0034] The portion of the rear case 24 facing the diaphragm 12 is formed in a generally lattice pattern, with nine openings formed therein. The rear filter 28 is attached to the rear case 24 so as to cover the openings formed in the rear case 24. The rear filter 28 is formed in a generally rectangular shape from a nonwoven fabric such as felt. The front filter 26 and the rear filter 28 are formed in different shapes, and adjust the sound pressure output from the electro-acoustic transducer 10.

[0035] 4 is a cross-sectional view of the electroacoustic transducer 10 according to the embodiment, seen from above. As shown in FIG. 4, the diaphragm 12 is sandwiched between a front case 22 and a rear case 24.

[0036] Seven first magnets 14 are arranged on the front side of diaphragm 12 with a predetermined gap between them. The seven first magnets 14 are fixed to the rear surface of first yoke 18 and are arranged at equal intervals in the left-right direction. The seven first magnets 14 are arranged so that the magnetic poles of adjacent first magnets 14 are opposite to each other; for example, the leftmost first magnet 14 has a south pole at the part facing diaphragm 12, and the first magnet 14 to the right of this first magnet 14 has a north pole at the part facing diaphragm 12.

[0037] Meanwhile, seven second magnets 16 are arranged on the rear side of diaphragm 12 with a predetermined gap between them. The seven second magnets 16 are fixed to the front surface of second yoke 20 in positions facing the first magnets 14, and are arranged at equal intervals in the left-right direction. The seven second magnets 16 are arranged so that the magnetic poles of adjacent second magnets 16 are opposite to each other, and so that the magnetic poles of the opposing first magnets 14 are in the same direction. For this reason, the part of the leftmost second magnet 16 facing diaphragm 12 is an S pole, and the part of the second magnet 16 to the right of this second magnet 16 facing diaphragm 12 is an N pole.

[0038] Fig. 5 is a cross-sectional view showing the direction of magnetic flux relative to the cross-sectional view of Fig. 4, with the direction of magnetic flux indicated by arrows. As shown in Fig. 5, a magnetic circuit is formed by the first yoke 18 and the first magnet 14, and a magnetic circuit is formed by the second yoke 20 and the second magnet 16. In particular, in this embodiment, the first magnet 14 and the second magnet 16 are configured so that magnetic flux flows toward the adjacent magnets.

[0039] Furthermore, the magnetic flux flowing on the diaphragm 12 side interlinks with the straight portion 13A of the coil 13 of the diaphragm 12. Note that a permanent magnet such as a neodymium magnet is used for the first magnet 14 and the second magnet 16. The number of first magnets 14 and second magnets 16 is not particularly limited, and may be six or less, or eight or more.

[0040] Next, we will explain the first yoke 18 and the second yoke 20, which are essential parts of the present invention. Fig. 6(A) is a front view of the first yoke 18, and Fig. 6(B) is a cross-sectional view taken along line 6B-6B in Fig. 6(A).

[0041] As shown in FIGS. 6A and 6B, the first yoke 18 is made of a soft magnetic material such as a thin iron plate and has a substantially rectangular shape in front view. A plurality of sound emission holes 34 are formed in the first flat surface 18A of the first yoke 18. In the present embodiment, as an example, four upper sound emission holes 34A, four lower sound emission holes 34B, and eight central sound emission holes 34C are formed in the first flat surface 18A. The upper sound emission holes 34A, the lower sound emission holes 34B, and the central sound emission holes 34C penetrate the first flat surface 18A in the plate thickness direction. In the following description, when the upper sound emission holes 34A, the lower sound emission holes 34B, and the central sound emission holes 34C are not to be distinguished from one another, they will be simply referred to as sound emission holes 34.

[0042] The upper sound emission hole 34A is formed in the shape of a slit along the vertical direction, similar to the longitudinal direction of the first magnet 14, and the vertical length of the upper sound emission hole 34A is approximately one-fifth of the vertical length of the first planar portion 18A.

[0043] Furthermore, of the four upper sound emission holes 34A, two upper sound emission holes 34A are arranged close to each other in the center in the left-right direction, and the other two upper sound emission holes 34A are formed at twice the pitch of the central upper sound emission hole 34A.

[0044] Furthermore, upper openings 36A are formed outward of the left and right upper sound emission holes 34A. The upper openings 36A are formed at the corners between the first flat portion 18A and the left and right first ribs 18B at the top of the first yoke 18, and the opening width of the upper openings 36A is wider than the upper sound emission holes 34A. Furthermore, the length of the upper openings 36A in the up-down direction is approximately the same as the length of the upper sound emission holes 34A, so the opening area of ​​the upper openings 36A is larger than that of the upper sound emission holes 34A.

[0045] One first magnet 14 is attached between the left and right upper openings 36A and the left and right upper sound emission holes 34A. Furthermore, two first magnets 14 are attached at equal intervals between the left and right upper sound emission holes 34A and the central upper sound emission hole 34A. Furthermore, one first magnet 14 is attached between the central upper sound emission holes 34A.

[0046] The lower sound emission holes 34B are formed as slits extending in the up-down direction and are formed in approximately the same shape as the upper sound emission holes 34A. Four lower sound emission holes 34B are formed in the left-right direction at approximately the same pitch as the upper sound emission holes 34A, and lower openings 36B are formed outside the left and right lower sound emission holes 34B.

[0047] The lower opening 36B is formed at the corner between the first flat portion 18A at the bottom of the first yoke 18 and the left and right first ribs 18B, and is formed in substantially the same shape as the upper opening 36A.

[0048] Central sound emission hole 34C is formed in the shape of a slit extending in the vertical direction, and the vertical length of central sound emission hole 34C is approximately half the lengths of upper sound emission hole 34A and lower sound emission hole 34B. Therefore, central sound emission hole 34C is formed to have a smaller opening area than upper sound emission hole 34A and lower sound emission hole 34B. In other words, central sound emission hole 34C formed in the central portion has a smaller opening area than upper sound emission hole 34A and lower sound emission hole 34B formed in the outer periphery of first yoke 18.

[0049] Furthermore, the central sound emission holes 34C are formed in four in the left-right direction at approximately the same pitch as the upper sound emission holes 34A and the lower sound emission holes 34B, and are formed in two tiers, upper and lower, so that there are a total of eight central sound emission holes 34C.

[0050] Center openings 36C are formed outside the left and right center sound emission holes 34C. Center openings 36C are formed at the corners between first flat portion 18A and left and right first ribs 18B in the center of first yoke 18, and are formed with lengths in the up-down direction that are approximately half those of upper openings 36A and lower openings 36B. Note that upper openings 36A, lower openings 36B, and center openings 36C each output sound generated by diaphragm 12, and therefore have the same function as sound emission holes 34.

[0051] Next, a description will be given of the second yoke 20. Fig. 7(A) is a front view of the second yoke 20, and Fig. 7(B) is a cross-sectional view taken along line 7B-7B in Fig. 7(A).

[0052] As shown in FIGS. 7A and 7B, the second yoke 20, like the first yoke 18, is made of a soft magnetic material such as a thin iron plate and has a generally rectangular shape in front view. A plurality of sound output holes 38 are formed in the second flat surface 20A of the second yoke 20. In this embodiment, as an example, four upper sound output holes 38A, four lower sound output holes 38B, and four central sound output holes 38C are formed in the second flat surface 20A. The upper sound output holes 38A, the lower sound output holes 38B, and the central sound output holes 38C penetrate the second flat surface 20A in the plate thickness direction. In the following description, when the upper sound output holes 38A, the lower sound output holes 38B, and the central sound output holes 38C are not to be distinguished from one another, they will simply be referred to as sound output holes 38.

[0053] The upper sound emission hole 38A and the lower sound emission hole 38B are formed in the shape of slits along the vertical direction, similar to the longitudinal direction of the second magnet 16, and the vertical length of the upper sound emission hole 38A and the lower sound emission hole 38B is approximately one-fifth of the vertical length of the second planar portion 20A.

[0054] Additionally, the positions at which the upper sound output holes 38A and the lower sound output holes 38B are formed are substantially the same as those of the first yoke 18. Therefore, when viewed from the front-to-rear direction with the electroacoustic transducer 10 assembled, the upper sound output holes 34A of the first yoke 18 and the upper sound output holes 38A of the second yoke 20 are arranged to overlap.

[0055] An upper opening 40A is formed outward from the left and right upper sound emission holes 38A, and a lower opening 40B is formed outward from the left and right lower sound emission holes 38B. The upper opening 40A and the lower opening 40B are formed at the corners between the second flat portion 20A of the second yoke 20 and the left and right second ribs 20B, and the opening widths of the upper opening 40A and the lower opening 40B are wider than the upper sound emission hole 38A. Furthermore, the vertical lengths of the upper opening 40A and the lower opening 40B are approximately the same as the upper sound emission hole 38A, so the upper opening 40A and the lower opening 40B have larger opening areas than the upper sound emission hole 38A.

[0056] One second magnet 16 is attached between the left and right upper openings 40A and the left and right upper sound emission holes 38A. Furthermore, two second magnets 16 are attached at equal intervals between the left and right upper sound emission holes 38A and the central upper sound emission hole 38A. Furthermore, one second magnet 16 is attached between the central upper sound emission holes 38A.

[0057] Central sound emission hole 38C is formed in the shape of a slit extending in the vertical direction, and the vertical length of central sound emission hole 38C is approximately half the lengths of upper sound emission hole 38A and lower sound emission hole 38B. Therefore, central sound emission hole 38C is formed to have a smaller opening area than upper sound emission hole 38A and lower sound emission hole 38B. In other words, central sound emission hole 38C formed in the central portion has a smaller opening area than upper sound emission hole 38A and lower sound emission hole 38B formed in the outer periphery of second yoke 20.

[0058] Here, central sound emission holes 38C are formed only on the outer periphery of second yoke 20. Specifically, two central sound emission holes 38C are formed vertically between leftmost upper sound emission hole 38A and leftmost lower sound emission hole 38B. Two central sound emission holes 38C are also formed vertically between rightmost upper sound emission hole 38A and rightmost lower sound emission hole 38B. However, no sound emission holes are formed between left central sound emission hole 38C and right central sound emission hole 38C.

[0059] In this way, the arrangement of the sound emission holes differs between the first yoke 18 and the second yoke 20, and no sound emission holes 38 are formed in the central portion of the second flat surface portion 20A of the second yoke 20. For this reason, the number of sound emission holes 38 formed in the second yoke 20 is fewer than the number of sound emission holes 34 formed in the first yoke 18, which is arranged on the sound output direction side.

[0060] Center openings 40C are formed outside the left and right center sound emission holes 38C. Center openings 40C are formed at the corners between second flat portion 20A and left and right second ribs 20B in the center of second yoke 20, and are formed with lengths in the up-down direction that are approximately half those of upper openings 40A and lower openings 40B. Note that upper openings 40A, lower openings 40B, and center openings 40C each output sound generated by diaphragm 12, and therefore have the same function as sound emission holes 38.

[0061] (action) Next, the operation of this embodiment will be described.

[0062] 4, in the electro-acoustic transducer 10 of this embodiment, a first yoke 18 and a second yoke 20 are provided on both sides of the diaphragm 12 with a gap therebetween. A plurality of (seven) first magnets 14 are provided on the first yoke 18 to form a magnetic circuit, and a plurality of (seven) second magnets 16 are provided on the second yoke 20 to form a magnetic circuit. As a result, when a current is passed through the coil 13 of the diaphragm 12, the diaphragm 12 vibrates and sound is output.

[0063] 6(A) and 7(A), first yoke 18 has a plurality of sound emission holes 34 formed therein, and second yoke 20 has a plurality of sound emission holes 38 formed therein. Central sound emission hole 34C at the center has a smaller opening area than upper sound emission holes 34A and lower sound emission holes 34B formed at the outer periphery of first yoke 18, and central sound emission hole 38C at the center has a smaller opening area than upper sound emission holes 38A and lower sound emission holes 38B formed at the outer periphery of second yoke 20. This makes it possible to suppress sound output from the center, where the amplitude of diaphragm 12 is large, and to reduce the difference in sound pressure between the center and outer periphery of diaphragm 12.

[0064] That is, because the diaphragm 12 has a fixed outer peripheral edge, when it vibrates in the front-to-rear direction, the amplitude is greatest in the central portion, farthest from the fixed outer peripheral edge. Therefore, the sound pressure generated by the diaphragm 12 is greater in the central portion and smaller in the peripheral portion. In the electroacoustic transducer 10 according to this embodiment, the opening areas of the sound output holes 34 and 38 in the peripheral portions are larger than those in the central portions in both the first yoke 18 and the second yoke 20. This makes it easier for sound to be output from the peripheral portions than from the central portions, resulting in a better balance of the sound pressure output from the electroacoustic transducer 10. Meanwhile, the opening areas of the sound output holes 34 and 38 in the central portions of the first yoke 18 and the second yoke 20 are smaller than those in the peripheral portions. This increases the magnetic permeability in the central portions of the first yoke 18 and the second yoke 20, thereby ensuring the driving force of the diaphragm 12.

[0065] Furthermore, in the electroacoustic transducer 10 of this embodiment, the sound emission holes 34 of the first yoke 18 and the sound emission holes 38 of the second yoke 20 are formed in the shape of slits along the first magnet 14 and the second magnet 16, so that the mounting area of ​​the first magnet 14 and the second magnet 16 can be secured while the opening area of ​​the sound emission holes 34 and the sound emission holes 38 can be increased.

[0066] Furthermore, in the electroacoustic transducer 10 of this embodiment, the sound emission holes 34 of the first yoke 18 and the sound emission holes 38 of the second yoke 20 are arranged differently, so that the locations of high magnetic permeability in each yoke can be set arbitrarily, and the behavior of the diaphragm 12 can be adjusted.

[0067] In particular, in this embodiment, the number of sound emission holes 38 in the second yoke 20 is made smaller than the number of sound emission holes 34 in the first yoke 18, so that the number of sound emission holes 34 in the first yoke 18 arranged on the forward side, which is the direction in which sound is output, is maintained while the number of sound emission holes 38 in the second yoke 20 on the opposite side is reduced, thereby increasing magnetic permeability.

[0068] Furthermore, in the electro-acoustic transducer 10 of this embodiment, an opening 36 is formed at the corner between the first flat portion 18A and the first rib 18B of the first yoke 18, and an opening 40 is formed at the corner between the second flat portion 20A and the second rib 20B of the second yoke 20. By forming the first rib 18B and the second rib 20B in this manner, the rigidity of the first yoke 18 and the second yoke 20 can be increased. Furthermore, by forming the openings 36 and the openings 40 at the corners, openings can also be secured in the first rib 18B and the second rib 20B, and the sound pressure can be increased while maintaining the rigidity of the first flat portion 18A and the second flat portion 20A.

[0069] In the above embodiment, the sound emission holes 38 of the second yoke 20 are arranged as shown in Fig. 7(A), but the arrangement is not limited to this and may be the same as the arrangement of the sound emission holes 34 of the first yoke 18, as shown in Fig. 6(A). Also, a modified arrangement shown in Fig. 8 may be adopted.

[0070] (Variation) Fig. 8 is a front view of a second yoke 50 according to a modified example. As shown in Fig. 8, the second yoke 50, like the second yoke 20 of the embodiment, is formed of a soft magnetic material such as a thin iron plate and has a substantially rectangular shape when viewed from the front. The second yoke 50 includes a planar second flat portion 50A and second ribs 50B extending from both left and right ends of the second flat portion 50A toward the diaphragm 12, and a plurality of sound emission holes 52 are formed in the second flat portion 50A.

[0071] In this modification, four upper sound output holes 52A, four lower sound output holes 52B, and two central sound output holes 52C are formed in the second flat surface portion 50A. The upper sound output holes 52A, the lower sound output holes 52B, and the central sound output holes 52C penetrate the second flat surface portion 50A in the plate thickness direction. In the following description, when the upper sound output holes 52A, the lower sound output holes 52B, and the central sound output holes 52C are not to be distinguished from one another, they will be simply referred to as sound output holes 52.

[0072] The upper sound emission hole 52A and the lower sound emission hole 52B are formed in the shape of slits along the vertical direction, similar to the longitudinal direction of the second magnet 16, and the vertical length of the upper sound emission hole 52A and the lower sound emission hole 52B is approximately one-fifth of the vertical length of the second planar portion 50A.

[0073] An upper opening 54A is formed outward from the left and right upper sound emission holes 52A, and a lower opening 54B is formed outward from the left and right lower sound emission holes 52B. The upper opening 54A and the lower opening 54B are formed at the corners between the second flat portion 50A of the second yoke 50 and the left and right second ribs 50B, and the opening widths of the upper opening 54A and the lower opening 54B are wider than the upper sound emission holes 52A.

[0074] A second magnet 16 is attached between each of the left and right upper openings 54A and each of the left and right upper sound emission holes 52A. In addition, a second magnet 16 is attached between each of the left and right upper sound emission holes 38A and an adjacent upper sound emission hole 38A. Three second magnets 16 are attached in the center in the left-right direction, and a similar arrangement is also formed for the lower sound emission hole 52B. In this manner, in this modified example, the sound emission holes in the center in the left-right direction are moved outward compared to the second yoke 20 of the embodiment.

[0075] Central sound emission hole 52C is formed in the shape of a slit extending in the vertical direction, and the vertical length of central sound emission hole 52C is approximately half the length of upper sound emission hole 52A and lower sound emission hole 52B. Central openings 54C are formed outside left and right central sound emission holes 52C, and the arrangement of central sound emission holes 52C and central openings 54C is the same as in the embodiment.

[0076] According to this modification, similar to second yoke 20 of the embodiment, the difference in sound pressure between the center and outer periphery of diaphragm 12 can be reduced while suppressing the sound output from the center of diaphragm 12, where the amplitude of the sound is large.

[0077] 〔supplementary explanation〕 The electroacoustic transducer 10 according to the embodiment and the modified examples has been described above, but it goes without saying that it can be embodied in various forms without departing from the spirit of the present invention. For example, in the above embodiment, the sound emission holes are formed in a slit shape, but this is not limited thereto and other shapes are also possible, such as substantially circular sound emission holes. Even in this case, the same effect as the embodiment can be achieved by making the opening area of ​​the sound emission holes formed in the center of the yoke smaller than that of the sound emission holes formed in the outer periphery.

[0078] 2, eight straight portions 13A of the coil 13 are formed, and seven first magnets 14 and seven second magnets 16 are arranged to correspond to these straight portions 13A, but this is not limited to this. For example, nine or more straight portions 13A of the coil 13 may be formed, or seven or fewer. Furthermore, the number and arrangement of the first magnets 14 and second magnets 16 may be changed as appropriate depending on the shape of the coil.

[0079] Furthermore, in the above embodiment, the electro-acoustic transducer 10 is described as being mounted on headphones, which are an acoustic device, but the present invention is not limited to this and may be mounted on acoustic devices other than headphones.

[0080] The following additional notes are further disclosed regarding the above embodiment.

[0081] (Appendix 1) an electro-acoustic transducer comprising: a planar diaphragm having a coil formed in a predetermined pattern on the surface of an insulating thin film; a first yoke arranged at a distance from the diaphragm so as to face one side of the diaphragm; first magnets arranged at a distance from the first yoke and forming a magnetic circuit with the first yoke; a second yoke arranged at a distance from the diaphragm so as to face the other side of the diaphragm; and second magnets arranged at a distance from the second yoke and forming a magnetic circuit with the second yoke; wherein the first yoke and the second yoke each have a plurality of sound emission holes, and the sound emission holes formed in the center of the yoke have a smaller opening area than the sound emission holes formed in the outer periphery. (Appendix 2) An electro-acoustic transducer as described in Appendix 1, wherein the first magnet and the second magnet are formed in an elongated shape to follow the pattern of the coil, and the sound emission hole is formed in a slit shape along the first magnet and the second magnet. (Appendix 3) 3. The electro-acoustic transducer according to claim 1, wherein the first yoke and the second yoke have sound emission holes arranged in different positions. (Appendix 4) 4. The electro-acoustic transducer according to claim 1, wherein the first yoke is disposed on the sound output side, and the second yoke has a smaller number of sound emission holes than the first yoke. (Appendix 5) The electro-acoustic transducer according to any one of Supplementary Note 1 to Supplementary Note 4, wherein the first yoke and the second yoke each include a planar portion and ribs extending from both ends of the planar portion toward the diaphragm, and openings are formed at corners between the planar portion and the ribs. (Appendix 6) A headphone comprising the electro-acoustic transducer according to any one of Supplementary Note 1 to Supplementary Note 5. [Explanation of symbols]

[0082] 10 Electroacoustic Transducer 12 Diaphragm 13 Coil 14 First magnet 16 No. 2 Magnet 18 No. 1 ヨーク 18A First flat surface 18B No. 1 20 No. 2 ヨーク 20A Second flat surface 20B 2nd リブ 34, 38, 52 sound holes 36, 40, 54 openings

Claims

1. a flat diaphragm having a coil formed in a predetermined pattern on the surface of an insulating thin film; a first yoke disposed opposite one surface of the diaphragm at a distance from the diaphragm; a plurality of first magnets provided on the first yoke; a second yoke disposed at a distance from the diaphragm so as to face the other surface of the diaphragm; a plurality of second magnets provided on the second yoke; and an electro-acoustic transducer, wherein a plurality of sound emission holes are formed in each of the first yoke and the second yoke, and the sound emission holes formed in the central portion of the first yoke and the second yoke have smaller opening areas than the sound emission holes formed in the outer periphery thereof.

2. The first magnet and the second magnet are formed in an elongated shape so as to follow the pattern of the coil, The electro-acoustic transducer according to claim 1 , wherein the sound emission hole is formed in a slit shape along the first magnet and the second magnet.

3. 3. The electro-acoustic transducer according to claim 2, wherein the sound emission holes of the first yoke and the second yoke are arranged differently.

4. The first yoke is disposed on the sound output side, The electro-acoustic transducer according to claim 3 , wherein the second yoke has a smaller number of sound emission holes than the first yoke.

5. the first yoke and the second yoke each include a planar portion and ribs extending from both ends of the planar portion toward the diaphragm, The electro-acoustic transducer according to claim 1 , wherein an opening is formed at a corner between the flat portion and the rib.

6. A headphone comprising the electro-acoustic transducer according to any one of claims 1 to 5.

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