Electroacoustic transducer and headphones

Abstract

To provide an electroacoustic transducer and headphones which output sound in a well-balanced manner. [Solution] The electro-acoustic transducer 10 has a planar diaphragm 12 with 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 a plurality of sound emission holes are formed in the first yoke 18 and the second yoke 20, and the sound emission holes formed in the center of the first yoke 18 and the second yoke 20 have a smaller opening area than the sound emission holes formed in the outer periphery thereof.

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, in the planar electroacoustic transducer described in Patent Document 1, yokes are arranged on both sides of the diaphragm, and multiple magnets are attached to the yokes. In addition, each yoke has the same shape, and multiple sound emission holes are formed at equal intervals. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2017-130704 A 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 end is fixed, the amplitude increases from the outer peripheral part to the center part. Therefore, in a structure in which sound emission holes are formed at equal intervals in a yoke as in Patent Document 1, the sound pressure differs between the center part 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 a headphone capable of outputting 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 and second yokes, and the sound emission holes formed in the center have a smaller opening area than the sound emission holes formed in the outer periphery of the first and second yokes.

[0007] In the above embodiment, a first yoke and a second yoke are provided on both sides of the diaphragm with a gap therebetween, a plurality of first magnets are provided on the first yoke, and a plurality of second magnets are provided on the second yoke. As a result, when a current is passed through the coil, the diaphragm vibrates and sound is output. Here, a plurality of sound output holes are formed in each of the first yoke and the second yoke, and the sound output holes formed in the center of the yoke are formed to have a smaller opening area than the sound output holes formed in the outer periphery of the yoke. As a result, the sound output from the center, where the amplitude of the diaphragm is large, can be suppressed, and the difference in sound pressure between the center and outer periphery of the diaphragm can be reduced.

[0008] The electro-acoustic transducer of the second aspect is the first aspect, in which the first magnet and the second magnet are formed in an elongated shape to follow the coil pattern, 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 emitting hole in a slit shape along the first magnet and the second magnet, it is possible to increase the opening area of ​​the sound emitting hole 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 is different from that in the second yoke.

[0011] In the above embodiment, since the arrangement of the sound emission holes differs between 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 a sound output direction side, and the second yoke has a smaller number of sound emission holes than the first yoke.

[0013] In the above aspect, the magnetic permeability can be increased by maintaining the number of sound emission holes in the first yoke arranged on the sound output direction side while reducing the number of sound emission holes in the second yoke on the opposite side.

[0014] In the electro-acoustic transducer of the fifth aspect, in the first aspect, 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 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 rib, while the sound pressure can be increased by forming the opening at the corner between the flat portion and the rib.

[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. Effect of the Invention

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

[0019] [Figure 1] 1 is an exploded perspective view showing an electroacoustic transducer according to an embodiment. [Diagram 2]FIG. 2 is a front view of a diaphragm according to the embodiment. [Diagram 3] FIG. 4 is an enlarged view of a main part of the diaphragm. [Figure 4] 1 is a cross-sectional view showing a state in which an electro-acoustic transducer according to an embodiment is cut. [Diagram 5] 5 is a cross-sectional view showing the direction of magnetic flux relative to the cross-sectional view of FIG. 4. [Figure 6] 6(A) is a front view of the first yoke, and (B) is a cross-sectional view taken along line 6B-6B in FIG. 6(A). [Figure 7] 7(A) is a front view of the second yoke, and (B) is a cross-sectional view taken along line 7B-7B in FIG. 7(A). [Figure 8] FIG. 11 is a front view of a second yoke according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] An electroacoustic transducer 10 according to an embodiment will be described with reference to the drawings. Fig. 1 is an exploded perspective view showing an electroacoustic transducer according to an embodiment. The electroacoustic transducer 10 of the present embodiment is mounted on headphones, which are an example of an audio device.

[0021] In the following description, the upper side of the paper in FIG. 1 is referred to as the upper side of the electroacoustic transducer 10, and the lower side of the paper is referred to as the lower side of the electroacoustic transducer 10. An arrow H shown as appropriate in each drawing indicates the up-down direction of the electroacoustic transducer 10. Also, the diagonally lower left side of the paper in FIG. 1 is referred to as the front side of the electroacoustic transducer 10, and the diagonally upper right side of the paper is referred to as the rear side of the electroacoustic transducer 10. An arrow L shown as appropriate in each drawing indicates the front-rear direction of the electroacoustic transducer 10. Furthermore, the left and right sides of the electroacoustic transducer 10 as viewed from the front side are referred to as the left side and the right side, respectively. An arrow W shown as appropriate in each drawing indicates the left-right direction (width direction) of the electroacoustic transducer 10. However, the up-down, front-rear, left-right, and right-left of the electroacoustic transducer 10 are set for the convenience of explanation, and do not necessarily coincide with the up-down, front-rear, left-right, and right-left in the usage state.

[0022] As shown in FIG. 1, the electroacoustic transducer 10 of this embodiment includes 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] The diaphragm 12 is a planar member in which the coil 13 is formed in a predetermined pattern on the surface of an insulating thin film. For example, the diaphragm 12 is formed by forming a metal such as aluminum on the surface of a polymer film and etching it while leaving a predetermined pattern. The coil 13 is composed of a collection of multiple linear patterns arranged in parallel, but for convenience of explanation, the collection of linear patterns is depicted as the coil 13 in Figs. 1 to 3.

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

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

[0026] 3, the straight line portions 13A of the coil 13 are formed in a generally wavy shape when enlarged. The gap between adjacent straight line portions 13A is very narrow, and the pattern is formed so that the wave shapes of adjacent straight line portions 13A are staggered. Therefore, the gap between adjacent straight line portions 13A is generally constant from the upper end to the lower end.

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

[0028] The first yoke 18 includes a flat first planar portion 18A and first ribs 18B extending from both left and right ends of the first planar portion 18A toward the diaphragm 12. The first magnets 14 are elongated bar magnets extending in the up-down direction along the pattern of the coil 13, and seven of them are provided spaced apart in the left-right direction. Details of the first yoke 18 and the 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 (other side) surface 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 up-down direction along the pattern of the coil 13, and seven of them are provided at intervals in the left-right 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 at 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 to which the first yoke 18 is attached.

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

[0033] A rear case 24 is disposed on the rear side of the second yoke 20. A rear filter 28 is disposed on the rear side of 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 rear bolt holes 24A are formed at positions corresponding to the insertion holes 30A of the frame member 30. A recess is formed on 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 shape, 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 arranged at equal intervals in the left-right direction. The seven first magnets 14 are arranged such that the magnetic poles of adjacent first magnets 14 are opposite to each other. For example, the leftmost first magnet 14 has a portion facing diaphragm 12 as an S pole, and the first magnet 14 to the right of this first magnet 14 has a portion facing diaphragm 12 as an N pole.

[0037] On the other hand, seven second magnets 16 are arranged on the rear side of the diaphragm 12 with a predetermined gap between them. The seven second magnets 16 are fixed to the front surface of the second yoke 20 at 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 adjacent first magnets 14 are in the same direction. For this reason, the leftmost second magnet 16 has a portion facing the diaphragm 12 as an S pole, and the second magnet 16 on the right of this second magnet 16 has a portion facing the diaphragm 12 as an N pole.

[0038] Fig. 5 is a cross-sectional view showing the direction of magnetic flux in the cross-sectional view of Fig. 4, and the direction of magnetic flux is 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] Moreover, the magnetic flux flowing on the diaphragm 12 side flows so as to interlink 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 the first magnets 14 and the second magnets 16 is not particularly limited, and may be six or less, or eight or more.

[0040] Next, the first yoke 18 and the second yoke 20, which are essential parts of the present invention, will be described. 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 Fig. 6(A) and Fig. 6(B), 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 portion 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 portion 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 portion 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 used without distinction, they are 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, the same as 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] In addition, of the four upper sound emission holes 34A, two upper sound emission holes 34A are positioned 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, an upper opening 36A is formed outside the left and right upper sound emission holes 34A. The upper opening 36A is formed at the corner portion between the first flat portion 18A and the left and right first ribs 18B at the upper portion of the first yoke 18, and the opening width of the upper opening 36A is wider than the upper sound emission holes 34A. The length of the upper opening 36A in the up-down direction is approximately the same as the length of the upper sound emission holes 34A, so the upper opening 36A has a larger opening area than 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 in a slit shape along 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 in the corner portion between the first flat portion 18A in the lower portion 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] The central sound emission hole 34C is formed in a slit shape along the vertical direction, and the vertical length of the central sound emission hole 34C is approximately half the length of the upper sound emission hole 34A and the lower sound emission hole 34B. Therefore, the central sound emission hole 34C is formed to have a smaller opening area than the upper sound emission hole 34A and the lower sound emission hole 34B. In other words, the central sound emission hole 34C formed in the central portion has a smaller opening area than the upper sound emission hole 34A and the lower sound emission hole 34B formed in the outer periphery of the first yoke 18.

[0049] In addition, 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 rows, upper and lower, so that a total of eight central sound emission holes 34C are formed.

[0050] A central opening 36C is formed outside the left and right central sound emission holes 34C. The central opening 36C is formed at the corner between the first flat portion 18A and the left and right first ribs 18B in the center of the first yoke 18, and is formed to have a length in the up-down direction that is about half that of the upper opening 36A and the lower opening 36B. Note that the upper opening 36A, the lower opening 36B, and the central opening 36C each output the sound generated by the diaphragm 12, and therefore have the same function as the 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 FIG. 7(A) and FIG. 7(B), the second yoke 20 is formed of a soft magnetic material such as a thin iron plate in a substantially rectangular shape in front view, similar to the first yoke 18. In addition, a plurality of sound emission holes 38 are formed in the second flat surface portion 20A of the second yoke 20. In the present embodiment, as an example, four upper sound emission holes 38A, four lower sound emission holes 38B, and four central sound emission holes 38C are formed in the second flat surface portion 20A. The upper sound emission holes 38A, the lower sound emission holes 38B, and the central sound emission holes 38C penetrate the second flat surface portion 20A in the plate thickness direction. In the following description, when the upper sound emission holes 38A, the lower sound emission holes 38B, and the central sound emission holes 38C are used without distinction, they are simply referred to as sound emission 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, the same as 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] Moreover, the positions at which the upper sound emission holes 38A and the lower sound emission holes 38B are formed are substantially the same as those of the first yoke 18. Therefore, when viewed from the front-rear direction with the electroacoustic transducer 10 assembled, the upper sound emission holes 34A of the first yoke 18 and the upper sound emission holes 38A of the second yoke 20 are arranged to overlap each other.

[0055] An upper opening 40A is formed outside the left and right upper sound emission holes 38A, and a lower opening 40B is formed outside 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 surface 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. In addition, the vertical length of the upper opening 40A and the lower opening 40B is approximately the same as the upper sound emission hole 38A, so the upper opening 40A and the lower opening 40B have a larger opening area 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] The central sound emission hole 38C is formed in a slit shape along the vertical direction, and the vertical length of the central sound emission hole 38C is approximately half the length of the upper sound emission hole 38A and the lower sound emission hole 38B. Therefore, the central sound emission hole 38C is formed to have a smaller opening area than the upper sound emission hole 38A and the lower sound emission hole 38B. In other words, the central sound emission hole 38C formed in the central portion has a smaller opening area than the upper sound emission hole 38A and the lower sound emission hole 38B formed in the outer periphery of the second yoke 20.

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

[0059] In this way, the arrangement of the sound emission holes is different between the first yoke 18 and the second yoke 20, and no sound emission hole 38 is 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 smaller than the number of sound emission holes 34 formed in the first yoke 18 arranged on the sound output direction side.

[0060] A central opening 40C is formed outside the left and right central sound emission holes 38C. The central opening 40C is formed at the corner between the second flat portion 20A and the left and right second ribs 20B in the center of the second yoke 20, and is formed to have a length in the up-down direction that is about half that of the upper opening 40A and the lower opening 40B. Note that the upper opening 40A, the lower opening 40B, and the central opening 40C each output the sound generated by the diaphragm 12, and therefore have the same function as the sound emission hole 38.

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

[0062] In the electroacoustic transducer 10 of this embodiment, as shown in Fig. 4, a first yoke 18 and a second yoke 20 are provided on both sides of a diaphragm 12 with a gap therebetween. A plurality (seven) of first magnets 14 are provided on the first yoke 18 to form a magnetic circuit, and a plurality (seven) of 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), a plurality of sound emission holes 34 are formed in the first yoke 18, and a plurality of sound emission holes 38 are formed in the second yoke 20. The opening area of ​​the central sound emission hole 34C in the central portion is smaller than that of the upper sound emission hole 34A and the lower sound emission hole 34B formed in the outer periphery of the first yoke 18, and the opening area of ​​the central sound emission hole 38C in the central portion is smaller than that of the upper sound emission hole 38A and the lower sound emission hole 38B formed in the outer periphery of the second yoke 20. This makes it possible to suppress the sound output from the central portion where the amplitude of the diaphragm 12 is large, and to reduce the difference in sound pressure between the central portion and the outer periphery of the diaphragm 12.

[0064] That is, since the diaphragm 12 has a structure in which the outer peripheral end is fixed, when the diaphragm 12 vibrates in the front-rear direction, the amplitude is the largest in the central portion far from the fixed outer peripheral end. Therefore, the sound pressure generated from the diaphragm 12 is large in the central portion and small in the outer peripheral portion. In the electroacoustic transducer 10 according to this embodiment, in both the first yoke 18 and the second yoke 20, the opening areas of the sound emission holes 34 and sound emission holes 38 in the outer peripheral portion are made larger than those in the central portion, so that sound is more easily output from the outer peripheral portion than the central portion, and as a result, the balance of the sound pressure output from the electroacoustic transducer 10 is improved. On the other hand, in the first yoke 18 and the second yoke 20, the opening areas of the sound emission holes 34 and sound emission holes 38 in the central portion are made smaller than those in the outer peripheral portion, so that the magnetic permeability of the central portion of the first yoke 18 and the second yoke 20 can be increased, and the driving force of the diaphragm 12 can be secured.

[0065] Furthermore, in the electroacoustic transducer 10 of this embodiment, the sound emission hole 34 of the first yoke 18 and the sound emission hole 38 of the second yoke 20 are formed in the shape of a slit 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 hole 34 and the sound emission hole 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 points in each yoke where the magnetic permeability is high 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 sound output direction, 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 electroacoustic transducer 10 of this embodiment, an opening 36 is formed at a corner between the first planar portion 18A and the first rib 18B of the first yoke 18, and an opening 40 is formed at a corner between the second planar 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 opening 36 and the opening 40, the sound pressure can be increased. In particular, by forming the opening 36 and the opening 40 at the corner, openings can 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 planar portion 18A and the second planar 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 thereto, and may be the same as the sound emission holes 34 of the first yoke 18, for example, as shown in Fig. 6(A). Also, a modified arrangement shown in Fig. 8 may be adopted.

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

[0071] In this modification, four upper sound emission holes 52A, four lower sound emission holes 52B, and two central sound emission holes 52C are formed in the second flat surface portion 50A. The upper sound emission holes 52A, the lower sound emission holes 52B, and the central sound emission holes 52C penetrate the second flat surface portion 50A in the plate thickness direction. In the following description, when the upper sound emission holes 52A, the lower sound emission holes 52B, and the central sound emission holes 52C are not distinguished from each other, they are simply referred to as sound emission 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 outside the left and right upper sound emission holes 52A, and a lower opening 54B is formed outside 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 surface 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 the left and right upper openings 54A and the left and right upper sound emission holes 52A. Also, a second magnet 16 is attached between the left and right upper sound emission holes 38A and the adjacent upper sound emission holes 38A. Three second magnets 16 are attached in the center in the left-right direction, and the lower sound emission holes 52B are similarly arranged. Thus, 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] The central sound emission hole 52C is formed in a slit shape along the vertical direction, and the vertical length of the central sound emission hole 52C is approximately half the length of the upper sound emission hole 52A and the lower sound emission hole 52B. A central opening 54C is formed outside the left and right central sound emission holes 52C, and the arrangement of the central sound emission holes 52C and the central opening 54C is the same as in the embodiment.

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

[0077] 〔supplementary explanation〕 Although the electroacoustic transducer 10 according to the embodiment and the modified example has been described above, it is needless to say that the present invention can be embodied in various forms without departing from the scope of the present invention. For example, in the above embodiment, the sound emission holes are formed in a slit shape, but the present invention is not limited to this, and other shapes may be used, and sound emission holes may be formed in a substantially circular shape. Even in this case, the same effect as the embodiment can be obtained 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] In the above embodiment, as shown in Fig. 2, eight straight portions 13A of the coil 13 are formed, and seven first magnets 14 and second magnets 16 are arranged to correspond to these straight portions 13A, but this is not limited to the above. For example, nine or more straight portions 13A of the coil 13 may be formed, or seven or less straight portions 13A may be formed. 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 electroacoustic transducer 10 is 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 supplementary 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; 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 yoke have a smaller opening area than the sound emission holes formed in the outer periphery of the yoke. (Appendix 2) The electro-acoustic transducer 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 an arrangement of the sound emission holes is different between the first yoke and the second yoke. (Appendix 4) 4. The electro-acoustic transducer according to claim 1, wherein the first yoke is disposed on a sound output direction side, and the second yoke has a smaller number of sound output holes than the first yoke. (Appendix 5) The electro-acoustic transducer according to any one of Appendix 1 to Appendix 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 electroacoustic transducer according to any one of claims 1 to 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 1st plane 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 opening

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 at a distance from the diaphragm so as to face one surface of 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; having 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 portions of the first yoke and the second yoke have smaller opening areas than the sound emission holes formed in the outer periphery portions of the first yoke and the second yoke; Each of the first yoke and the second yoke includes a planar portion and a rib that is integrally formed with the planar portion and extends from both ends of the planar portion toward the diaphragm, An opening is formed at a corner portion between the flat portion and the rib. Electroacoustic transducer.

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 electroacoustic transducer according to claim 2, wherein the sound emission holes are arranged in a different manner in the first yoke and the second yoke.

4. The first yoke is disposed on a 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. A headphone equipped with an electro-acoustic transducer described in any one of claims 1 to 4.

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