Electroacoustic transducer and headphones

Abstract

This electroacoustic transducer (10) has: a planar diaphragm (12) in which a coil is formed in a predetermined pattern on a surface of an insulating thin film; a first yoke (18) that is disposed at a distance from the diaphragm (12) in such a manner as to face one surface of the diaphragm (12), and that is provided with a first magnet (14) on the surface on the diaphragm (12) side; a second yoke (20) that is disposed at a distance from the diaphragm (12) in such a manner as to face the other surface of the diaphragm (12), and that is provided with a second magnet (16) on the surface on the diaphragm (12) side; a first case (22) that holds the first yoke (18); and a second case (24) that holds the second yoke (20) and is disposed on the opposite side of the diaphragm (12) from the first case (22). The diaphragm (12) is sandwiched between the first case (22) and the second case (24) via a plate member (50) outside of the first yoke (18) and the second yoke (20).

Description

Electroacoustic Transducer and Headphones

[0001] The present invention relates to an electroacoustic transducer and headphones.

[0002] Japanese Unexamined Patent Application Publication No. 2007-336293 discloses an electromagnetic transducer (electroacoustic transducer) that reproduces audible sound by supplying an audio signal to a coil pattern formed on a vibrating membrane, and has a structure in which sheet-shaped buffer members are respectively disposed between a lower permanent magnet plate and the vibrating membrane (diaphragm), and between an upper permanent magnet plate and the vibrating membrane.

[0003] In the structure described in Japanese Unexamined Patent Application Publication No. 2007-336293, contact between the vibrating membrane (diaphragm) and the magnet plates is suppressed by the buffer members. However, stress may act on the diaphragm depending on the fitting state of the outer shell case, which may affect sound quality in this case.

[0004] An object of the present invention is to provide an electroacoustic transducer that can maintain favorable sound quality regardless of the fitting state of a case.

[0005] The electroacoustic transducer according to a first aspect comprises: a planar diaphragm in which a coil is formed in a predetermined pattern on a surface of an insulating thin film; a first yoke disposed at an interval from the diaphragm so as to face one surface of the diaphragm, the first yoke including a first magnet on the surface facing the diaphragm; a second yoke disposed at an interval from the diaphragm so as to face the other surface of the diaphragm, the second yoke including a second magnet on the surface facing the diaphragm; a first case that holds the first yoke; and a second case disposed on an opposite side to the first case with the diaphragm interposed therebetween, the second case holding the second yoke, wherein the diaphragm is sandwiched between the first case and the second case via a plate member at a position outside the first yoke and the second yoke.

[0006] In the above embodiment, a first yoke is positioned opposite one side of the planar diaphragm, and the first yoke is equipped with a first magnet. A second yoke is positioned opposite the other side of the diaphragm, and the second yoke is equipped with a second magnet. As a result, when an electric current is passed through the coil of the diaphragm, the diaphragm vibrates due to the action of the magnetic circuit formed by the first yoke, the first magnet, the second yoke, and the second magnet, and sound is produced.

[0007] Furthermore, the first case and the second case are positioned with the diaphragm in between, with the first yoke held in the first case and the second yoke held in the second case. In addition, the diaphragm is sandwiched between the first case and the second case via a plate member on the outside of the first and second yokes. As a result, the stress generated at the fitting portion between the first case and the second case is relieved by the plate member, and the transmission of stress to the diaphragm can be suppressed.

[0008] In the second embodiment of the electroacoustic transducer, in the first embodiment, a plurality of diaphragm-side through holes are formed on the diaphragm outside the coil, the plate member is formed in a frame shape and has plate member-side through holes formed at positions corresponding to the diaphragm-side through holes, and one of the first case and the second case is provided with a projection that is inserted into the diaphragm-side through holes and the plate member-side through holes.

[0009] In the above embodiment, a projection is provided on one of the first case and the second case, and a through hole on the diaphragm side and a through hole on the plate member side are inserted through this projection. This allows the diaphragm and the plate member to be positioned together with a simple structure.

[0010] In the third embodiment of the electroacoustic transducer, in the second embodiment, the other of the first case and the second case has a recess into which the projection is inserted, and the projection and the recess are fastened together by a bolt.

[0011] In the above embodiment, the first case and the second case can be easily positioned simply by inserting the projection into the recess. Furthermore, by fastening the projection and the recess with a bolt, a screwing distance equal to the protruding length of the projection can be secured. As a result, even if the thickness of the first case and the second case is relatively thin, the first case and the second case can be firmly fastened together.

[0012] In the fourth embodiment of the electroacoustic transducer, in the third embodiment, the diameter of the through-hole on the plate member side is smaller than that of the through-hole on the diaphragm side, and the inner diameter of the recess is smaller than that of the through-hole on the plate member side.

[0013] In the above embodiment, since the diameter of the through-hole on the plate member side is smaller than the through-hole on the diaphragm side, the plate member can be brought into contact with the entire surface of the diaphragm, and the transmission of stress generated at the fitting portion between the first case and the second case to the diaphragm can be effectively suppressed. Furthermore, since the inner diameter of the recess is smaller than the through-hole on the plate member side, even if the plate member deforms in such a way that it is crushed between the first case and the second case, it can be prevented from getting stuck between the protrusion and the recess.

[0014] In the fifth embodiment of the electroacoustic transducer, in the third or fourth embodiment, the plate member is arranged on the side of the diaphragm in the direction of sound output, and the bolt is screwed into the projection from the side of the sound output.

[0015] In the above embodiment, since the bolt is screwed into the projection from the sound output direction side, the distortion of the case located on the sound output direction side of the first and second cases tends to be larger. Here, since the plate member is located on the sound output direction side of the diaphragm, the distortion generated in the case can be effectively suppressed. Note that "sound output direction side" here refers to the side facing the user's ear.

[0016] The electroacoustic transducer according to the sixth embodiment is provided in any one of the first to fifth embodiments with a claw portion that engages with the other in one of the first case and the second case, and the plate member has a notch formed at a position corresponding to the claw portion.

[0017] In the above embodiment, the first case and the second case can be engaged by the claw portion. Furthermore, since the plate member has a notch formed at a position corresponding to the claw portion, the plate member can be easily positioned during assembly by utilizing the notch.

[0018] In the seventh embodiment of the electroacoustic transducer, the plate member is formed of an elastic material in any one of the first to sixth embodiments.

[0019] In the above embodiment, the plate member undergoes elastic deformation, which can relieve the stress generated at the fitting portion between the first case and the second case.

[0020] In the eighth embodiment of the electroacoustic transducer, in any one embodiment of the first to sixth embodiments, the plate member is formed of a material with high rigidity.

[0021] In the above embodiment, by forming the plate member from a highly rigid material, it is possible to suppress the transmission of stress generated at the fitting portion between the first case and the second case to the diaphragm.

[0022] The headphones according to the ninth embodiment include an electroacoustic transducer as described in any one of the first to eighth embodiments.

[0023] The above embodiment has the effects described in the first to eighth embodiments.

[0024] According to the electroacoustic transducer and headphones of the present invention, good sound quality can be maintained regardless of the fit of the case.

[0025] This is an exploded perspective view showing an electroacoustic transducer according to the first embodiment. This is a front view of the diaphragm in the first embodiment. This is a front view of the plate member in the first embodiment. This is a cross-sectional view showing the electroacoustic transducer according to the first embodiment cut in the width direction and viewed from the top and bottom. This is an enlarged cross-sectional view showing an enlarged view of the main part of Figure 4. This is an enlarged cross-sectional view corresponding to Figure 5, showing an electroacoustic transducer according to a modified example.

[0026] <First Embodiment> The electroacoustic transducer 10 according to the first embodiment will be described with reference to the drawings. Figure 1 is an exploded perspective view showing the electroacoustic transducer according to the first embodiment. The electroacoustic transducer 10 of the first embodiment is mounted on headphones, which are an audio device, as an example.

[0027] The arrows H, L, and W shown in each figure as appropriate indicate the vertical, horizontal, and left-right directions of the electroacoustic transducer 10, respectively. However, the vertical, horizontal, and left-right directions of the electroacoustic transducer 10 are set for the sake of explanation and do not necessarily correspond to the vertical, horizontal, and left-right directions of the electroacoustic transducer 10 in actual use.

[0028] As shown in Figure 1, the electroacoustic transducer 10 of the first embodiment is composed of a diaphragm 12, a first magnet 14, a second magnet 16, a first yoke 18, a second yoke 20, a first case 22, a second case 24, a front filter 26, a rear filter 28, and a plate member 50.

[0029] The diaphragm 12 is a planar component in which a coil 13 is deposited on the surface of an insulating thin film in a predetermined pattern. For example, the diaphragm 12 is formed by depositing 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 an assembly of multiple linear patterns arranged in parallel, but in Figures 1 and 2, for the sake of explanation, the assembly of linear patterns is depicted as the coil 13.

[0030] Figure 2 is a front view of the diaphragm 12 in the first embodiment. As shown in Figure 2, a substantially rectangular frame member 30 is attached to the outer peripheral end of the diaphragm 12, which is outside the coil 13. Multiple diaphragm-side through holes 30A are formed in the outer peripheral portion of the frame member 30.

[0031] In the first embodiment, as an example, eight diaphragm-side through holes 30A are formed along the circumferential direction of the frame member 30. Below the coil 13, three diaphragm-side through holes 30A are formed in the left-right direction, and above the coil 13, three diaphragm-side through holes 30A are formed in the left-right direction. In addition, one diaphragm-side through hole 30A is formed on the right side of the coil 13, and one diaphragm-side through hole 30A is formed on the left side of the coil 13.

[0032] The coil 13 is composed of a straight section 13A extending substantially in a straight line in the vertical direction, and an arc-shaped section 13B formed by folding back the upper and lower ends of the straight section 13A. The straight sections 13A are formed at equal intervals in the left-right direction, and in the first embodiment, for example, eight straight sections 13A are arranged in the left-right direction. In addition, seven arc-shaped sections 13B are formed so as to connect adjacent straight sections 13A. As a result, the pattern of the coil 13 on the diaphragm 12 is formed in a meandering pattern as a whole. Furthermore, the straight sections 13A are formed over the entire surface of the diaphragm 12, and these straight sections 13A form a region that links with the magnetic flux from the first magnet 14 and the second magnet 16, which will be described later.

[0033] As shown in Figure 1, the first yoke 18 is positioned at a distance from the diaphragm 12 so as to face the front (one side) surface of the diaphragm 12, and the first magnet 14 is positioned between the first yoke 18 and the diaphragm 12.

[0034] The first yoke 18 is composed of a planar first flat portion 18A and first ribs 18B extending from both the left and right ends of the first flat portion 18A toward the diaphragm 12. The first yoke 18 is also provided with a first magnet 14 on the surface facing the diaphragm 12. The first magnet 14 is a long bar magnet that extends vertically along the pattern of the coil 13, and seven of them are provided spaced apart in the left-right direction.

[0035] Multiple sound-emitting holes are formed in the first yoke 18. The position and number of sound-emitting holes are not particularly limited, but it is preferable to reduce the opening area of ​​the sound-emitting holes formed in the central part of the first yoke 18. This makes it possible to reduce the sound pressure in the central part where the amplitude is large and to balance the sound pressure.

[0036] The second yoke 20 is positioned at a distance from the diaphragm 12 so as to face the rear (other) surface of the diaphragm 12, and the second magnet 16 is positioned between the second yoke 20 and the diaphragm 12.

[0037] The second yoke 20 is composed of a planar second flat portion 20A and second ribs 20B extending from both the left and right ends of the second flat portion 20A toward the diaphragm 12. The second yoke 20 is also provided with a second magnet 16 on the surface facing the diaphragm 12. The second magnet 16 is a long bar magnet that extends vertically along the pattern of the coil 13, and seven of them are provided spaced apart in the left-right direction. Details of the second yoke 20 and the second magnet 16 will be described later.

[0038] Multiple sound-emitting holes are formed in the second yoke 20. The position and number of sound-emitting holes are not particularly limited, and a different pattern of sound-emitting holes may be formed in the second yoke 20 than in the first yoke 18. Furthermore, it is preferable to reduce the opening area of ​​the sound-emitting holes formed in the central part of the second yoke 20. This reduces the sound pressure in the central part where the amplitude is large, and balances the sound pressure.

[0039] A first case 22, which holds the first yoke 18, is positioned on the front side of the first yoke 18. A front filter 26 is positioned on the front side of the first case 22. The first case 22 is shaped to cover the diaphragm 12 and the frame member 30 from the front, and front bolt holes 22A are formed at positions corresponding to the diaphragm-side through holes 30A of the frame member 30. A recess is formed on the rear surface of the first case 22 to which the first yoke 18 is attached.

[0040] In the first case 22, the portion facing the diaphragm 12 is formed in a roughly grid pattern, with nine openings. The front filter 26 is attached to the first case 22 so as to cover the openings formed in the first case 22. The front filter 26 is formed in a roughly rectangular shape from a nonwoven fabric such as felt.

[0041] A second case 24 that holds the second yoke 20 is disposed on the rear side of the second yoke 20. Further, a rear filter 28 is disposed on the rear side of the second case 24. The second case 24 is disposed on the opposite side to the first case 22 with the diaphragm 12 interposed therebetween, and is formed in a shape that covers the diaphragm 12 and the frame member 30 from the rear side. Further, in the second case 24, a rear bolt hole 24A is formed at a position corresponding to the diaphragm-side through hole 30A of the frame member 30. Furthermore, a recessed portion to which the second yoke 20 is attached is formed on the front surface of the second case 24.

[0042] A portion of the second case 24 facing the diaphragm 12 is formed in a substantially lattice shape, and nine openings are formed therein. The rear filter 28 is attached to the second case 24 so as to cover the opening formed in the second case 24. The rear filter 28 is formed into a substantially rectangular shape by, for example, a non-woven fabric such as felt. The front filter 26 and the rear filter 28 are formed in different shapes respectively, and adjust the sound pressure output from the electroacoustic transducer 10.

[0043] A plate member 50 is disposed between the diaphragm 12 and the second case 24. The plate member 50 is formed of an elastic material such as urethane foam, foam material, or rubber, and has a function of relieving stress. Further, as an example, the plate member 50 of the first embodiment is formed of a frame-shaped sheet member with a hollowed central portion.

[0044] Figure 3 is a front view of the plate member 50 according to the first embodiment. As shown in Figure 3, when viewed from the front, the plate member 50 has a substantially rectangular outer shape with rounded corners, and includes an opening 50A in the central portion. The opening 50A is formed larger than the region of the diaphragm 12 where the coil 13 is provided, so that when the plate member 50 is superimposed on the diaphragm 12, the coil 13 and the plate member 50 do not overlap each other.

[0045] A plurality of plate-member-side through holes 50B are formed in the outer peripheral portion of the plate member 50. As an example in the first embodiment, eight plate-member-side through holes 50B are formed along the circumferential direction of the plate member 50. Here, the eight plate-member-side through holes 50B are formed at positions corresponding to the diaphragm-side through holes 30A formed in the diaphragm 12.

[0046] Further, a notch 50C is formed at the vertically central portion of a vertically extending portion of the plate member 50. Two notches 50C are formed on each of the left and right sides, and have a shape obtained by notching the width direction end of the plate member 50 into a substantially rectangular shape. These notches 50C are formed at positions corresponding to claw portions 22C (see FIGS. 4 and 5) described later. In other words, the notches 50C are formed so as to avoid interference between the plate member 50 and the claw portions 22C.

[0047] Note that, as an example in the first embodiment, the thickness of the plate member 50 is set to 0.5 mm, but the present invention is not limited thereto. For example, the thickness of the plate member 50 may be formed to 0.6 mm or more, or may be formed to 0.4 mm or less. However, increasing the thickness of the plate member 50 will cause distortion in the plate member 50 itself. Further, reducing the thickness of the plate member 50 reduces the function of relieving stress, so it is preferable to form the plate member with a thickness between 0.3 mm and 0.7 mm, and more preferable to form it with a thickness between 0.4 mm and 0.6 mm.

[0048] FIG. 4 is a cross-sectional view showing the electroacoustic transducer according to the first embodiment cut in the width direction and viewed from the vertical direction. As shown in FIG. 4, in a state where the first case 22 and the second case 24 are assembled, the first yoke 18 and the second yoke 20 face each other with the diaphragm 12 interposed therebetween.

[0049] The first case 22 and the second case 24 are assembled by a bolt 40 and the claw portions 22C. The claw portions 22C protrude from the outer peripheral end of the first case 22 toward the second case 24, and engage with the rear surface of the second case 24.

[0050] Seven first magnets 14 are positioned in front of the diaphragm 12, with a predetermined gap between them and the diaphragm 12. The seven first magnets 14 are fixed to the rear surface of the first yoke 18 with adhesive or the like, and are arranged at equal intervals in the left-right direction. Furthermore, the seven first magnets 14 are arranged so that the magnetic poles of adjacent first magnets 14 are opposite. For example, the leftmost first magnet 14 has a south pole in the portion facing the diaphragm 12, and the first magnet 14 to its right has a north pole in the portion facing the diaphragm 12.

[0051] On the other hand, seven second magnets 16 are arranged on the rear side of the diaphragm 12, with a predetermined gap between them and the diaphragm 12. The seven second magnets 16 are fixed to the front surface of the second yoke 20 in a position opposite to the first magnet 14, and are arranged at equal intervals in the left-right direction. Furthermore, the seven second magnets 16 are arranged so that the magnetic poles of adjacent second magnets 16 are opposite in direction, and the magnetic poles of the opposing first magnet 14 are in the same direction. For this reason, the leftmost second magnet 16 has a south pole in the part facing the diaphragm 12, and the second magnet 16 to the right of this second magnet 16 has a north pole in the part facing the diaphragm 12.

[0052] 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 the first embodiment, the first magnet 14 and the second magnet 16 are configured so that magnetic flux flows toward adjacent magnets.

[0053] The magnetic flux flowing on the diaphragm 12 side flows in a manner that links with the linear portion 13A of the coil 13 of the diaphragm 12. The first magnet 14 and the second magnet 16 are permanent magnets such as neodymium magnets. The number of the first magnet 14 and the second magnet 16 is not particularly limited and may be six or fewer, or eight or more.

[0054] Next, the clamping state of the diaphragm 12 and the plate member 50, which are the main parts of the first embodiment, will be described with reference to Figure 5.

[0055] Figure 5 is an enlarged cross-sectional view showing an enlarged portion of the main part of Figure 4. As shown in Figure 5, the diaphragm 12 is sandwiched from both sides by the first case 22 and the second case 24. Specifically, the diaphragm 12 is sandwiched from both sides by the first case 22 and the second case 24 via the plate member 50, outside the region of the magnetic circuit where the first yoke 18 and the second yoke 20 are located.

[0056] A projection 22B is formed on the outer peripheral end of the first case 22, projecting toward the second case 24. The projection 22B is formed in a substantially tapered shape such that the tip has a smaller diameter than the base, and a through hole 30A formed in the diaphragm 12 and a through hole 50B formed in the plate member 50 are inserted through the projection 22B. In addition, a front bolt hole 22A is formed in the projection 22B, penetrating in the axial direction (front-to-back direction). For this reason, the projection 22B is formed in a substantially cylindrical shape.

[0057] The projection 22B formed on the first case 22 is inserted into the recess 24B formed on the second case 24. The recess 24B is formed in a shape corresponding to the projection 22B. Specifically, the recess 24B is formed in such a way that the hole diameter is smaller on the bottom side than on the first case 22 side, and is formed to such a size that a slight gap is created between the projection 22B and the recess 24B when the projection 22B is inserted into the recess 24B.

[0058] The second case 24 has a rear bolt hole 24A that communicates with the bottom of the recess 24B. The rear bolt hole 24A penetrates from the rear surface of the second case 24 to the bottom of the recess 24B, and a bolt 40 is screwed into the rear bolt hole 24A from the rear side. In other words, the bolt 40 is screwed into the projection 22B from the sound output direction side, and the projection 22B and the recess 24B are mechanically fastened together by the bolt 40.

[0059] The diaphragm 12 and the plate member 50 are sandwiched between the surrounding portion of the projection 22B in the first case 22 and the edge of the hole in the recess 24B in the second case 24. Specifically, the plate member 50 is positioned on the rear side of the diaphragm 12, which is the sound output direction side. The front surface of the diaphragm 12 is in contact with the first case 22, and the rear surface of the diaphragm 12 is in contact with the plate member 50. The front surface of the plate member 50 is in contact with the diaphragm 12, and the rear surface of the plate member 50 is in contact with the second case 24.

[0060] In the first embodiment, a plate member 50 is arranged on the rear side of the diaphragm 12, and the distance between the first yoke 18 and the diaphragm 12 is designed to be approximately the same as the distance between the second yoke 20 and the diaphragm 12.

[0061] The through-hole 50B formed in the plate member 50 has a smaller diameter than the through-hole 30A formed in the diaphragm 12. That is, the gap between the through-hole 50B and the projection 22B is smaller than the gap between the through-hole 30A and the projection 22B. Furthermore, the inner diameter of the recess 24B is smaller than the diameter of the through-hole 50B.

[0062] (Function) Next, the function of the first embodiment will be explained.

[0063] In the electroacoustic transducer 10 of the first embodiment, as shown in Figure 4, a first yoke 18 and a second yoke 20 are provided on both sides of the diaphragm 12 with a gap between them. The first yoke 18 is provided with a plurality (7) of first magnets 14 to form a magnetic circuit, and the second yoke 20 is provided with a plurality (7) of second magnets 16 to form a magnetic circuit. As a result, when an electric current is passed through the coil 13 of the diaphragm 12, the diaphragm 12 vibrates and sound is output.

[0064] In the electroacoustic transducer 10 of the first embodiment, a first case 22 and a second case 24 are arranged with a diaphragm 12 in between, with a first yoke 18 held in the first case 22 and a second yoke 20 held in the second case 24. Furthermore, the diaphragm 12 is sandwiched between the first case 22 and the second case 24 via a plate member 50 on the outside of the first yoke 18 and the second yoke 20. As a result, the stress generated at the fitting portion between the first case 22 and the second case 24 is relieved by the plate member 50, and the transmission of stress to the diaphragm 12 can be suppressed.

[0065] In the electroacoustic transducer 10 of the first embodiment, as shown in Figure 5, a projection 22B is provided on the first case 22, and the diaphragm-side through hole 30A and the plate member-side through hole 50B are inserted through this projection 22B. This allows the diaphragm 12 and the plate member 50 to be positioned together with a simple structure.

[0066] In the first embodiment, the first case 22 and the second case 24 can be easily positioned simply by inserting the projection 22B into the recess 24B of the second case 24. Furthermore, by fastening the projection 22B and the recess 24B with a bolt 40, a screwing distance equal to the protruding length of the projection 22B can be secured. As a result, the first case 22 and the second case 24 can be firmly fastened together even when the thickness of the first case 22 and the second case 24 are relatively thin.

[0067] In the first embodiment, since the diameter of the through-hole 50B on the plate member side is smaller than the through-hole 30A on the diaphragm side, the plate member 50 can be brought into contact with the entire surface of the diaphragm 12, and the transmission of stress generated at the fitting portion between the first case 22 and the second case 24 to the diaphragm 12 can be effectively suppressed. Furthermore, since the inner diameter of the recess 24B of the second case 24 is smaller than the through-hole 50B on the plate member side, even if the plate member 50 deforms to the point of being crushed between the first case 22 and the second case 24, it is possible to suppress the plate member 50 from getting stuck between the projection 22B and the recess 24B.

[0068] In the first embodiment, the bolt 40 is screwed into the projection 22B from the sound output direction side. As a result, the distortion of the second case 24, which is located on the sound output direction side of the first case 22 and the second case 24, tends to be large. However, since the plate member 50 is located on the sound output direction side of the diaphragm 12, the distortion generated in the second case 24 can be effectively suppressed.

[0069] In the first embodiment, the first case 22 and the second case 24 are engaged by the claw portion 22C, and as shown in Figure 3, a notch 50C is formed in the plate member 50 at a position corresponding to the claw portion 22C. Therefore, the plate member 50 can be easily positioned during assembly by utilizing the notch 50C. <Second Embodiment>

[0070] In the first embodiment, the plate member 50 is made of an elastic material to suppress the transmission of stress generated at the fitting portion between the first case 22 and the second case 24 to the diaphragm 12. In the second embodiment, the plate member 50 is made of a highly rigid metal material. Detailed explanations of the configuration similar to that of the first embodiment will be omitted.

[0071] The plate member 50 in the second embodiment is made of a highly rigid metal. The dimensions of the plate member 50 are substantially the same as those in the first embodiment. It is preferable to form the plate member 50 to a thickness between 0.4 mm and 0.6 mm, as making it too thick would increase its weight, and making it too thin would increase processing costs. Furthermore, considering the impact on the magnetic circuit, it is preferable to form the plate member 50 from a non-magnetic metal.

[0072] In the second embodiment, by using a highly rigid metal member as the plate member 50, it is possible to suppress the transmission of stress generated at the fitting portion between the first case 22 and the second case 24 to the diaphragm 12.

[0073] Furthermore, if the plate member 50 is made of metal, it is less susceptible to deterioration over time than elastic materials such as rubber, thus ensuring long-term reliability. In addition, metal members make it easier to achieve highly accurate dimensions during processing. Other functions are the same as in the first embodiment.

[0074] [Supplementary Explanation] The electroacoustic converter 10 according to the first and second embodiments has been described above, but it goes without saying that the invention can be implemented in various forms without departing from the spirit of the present invention. For example, in the first and second embodiments, the plate member 50 is arranged on the rear side of the diaphragm 12, but the invention is not limited to this, and the plate member 50 may be arranged on the front side of the diaphragm 12, as shown in the modified example in Figure 6. Alternatively, plate members may be arranged on both the front and rear sides of the diaphragm 12.

[0075] As shown in Figure 6, in this modified example, the plate member 50 is not placed on the rear side of the diaphragm 12. On the other hand, the plate member 50 is placed on the front side of the diaphragm 12. The plate member 50 is inserted through the projection 22B of the first case 22. Note that by placing the plate member 50 on the first case 22 side, the distance between the first yoke 18 and the diaphragm 12 increases by the thickness of the plate member 50, so it is preferable to adjust it so that the distance is the same as in the embodiment. For example, the part of the first case 22 that holds the first yoke 18 may be raised to make the adjustment.

[0076] Furthermore, in the first and second embodiments, the first case 22 is provided with a projection 22B and the second case 24 is provided with a recess 24B, but the invention is not limited thereto. For example, the first case 22 may be provided with a recess and the second case 24 may be provided with a projection. Moreover, the insertion direction of the bolt 40 and the presence or absence of the claw portion 22C are not limited, and for example, a structure without the claw portion 22C may be used.

[0077] Furthermore, while the first and second embodiments described an electroacoustic transducer 10 mounted on headphones, which are audio equipment, the invention is not limited to this and may be mounted on audio equipment other than headphones.

Claims

1. An electroacoustic transducer comprising: a planar diaphragm on which a coil is formed in a predetermined pattern on the surface of an insulating thin film; a first yoke positioned at a distance from the diaphragm so as to face one side of the diaphragm and having a first magnet on the side facing the diaphragm; a second yoke positioned at a distance from the diaphragm so as to face the other side of the diaphragm and having a second magnet on the side facing the diaphragm; a first case that holds the first yoke; and a second case positioned on the opposite side of the diaphragm from the first case and holding the second yoke, wherein the diaphragm is sandwiched between the first case and the second case via a plate member outside of the first and second yokes.

2. The electroacoustic converter according to claim 1, wherein a plurality of diaphragm-side through holes are formed on the diaphragm outside the coil, the plate member is formed in a frame shape and has plate member-side through holes formed at positions corresponding to the diaphragm-side through holes, and one of the first case and the second case is provided with a projection that is inserted into the diaphragm-side through holes and the plate member-side through holes.

3. The electroacoustic converter according to claim 2, wherein the other of the first case and the second case has a recess into which the projection is inserted, and the projection and the recess are fastened together by a bolt.

4. The electroacoustic transducer according to claim 3, wherein the diameter of the through-hole on the plate member side is smaller than that of the through-hole on the diaphragm side, and the inner diameter of the recess is smaller than that of the through-hole on the plate member side.

5. The electroacoustic converter according to claim 3, wherein the plate member is positioned on the sound output direction side of the diaphragm, and the bolt is screwed into the projection from the sound output direction side.

6. The electroacoustic converter according to claim 1, wherein one of the first case and the second case is provided with a claw portion that engages with the other, and the plate member has a notch formed at a position corresponding to the claw portion.

7. The electroacoustic transducer according to claim 1, wherein the plate member is made of an elastic material.

8. The electroacoustic transducer according to claim 1, wherein the plate member is made of a highly rigid material.

9. Headphones equipped with an electroacoustic converter according to any one of claims 1 to 8.

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