Acoustic device

Abstract

This acoustic device is provided with: a diaphragm that generates sound by vibrating; a frame that supports the diaphragm; and a stopper portion that is provided between the diaphragm and the frame and that, when the diaphragm is pressed toward the frame side, comes into abutment with a part of the diaphragm to suppress deformation of the diaphragm. When the diaphragm is pressed toward the frame side, the diaphragm and a stopper portion A abut on each other by line contact.

Description

sound equipment

[0001] The present disclosure relates to acoustic devices.

[0002] Japanese Patent Application Laid-Open Publication No. 2021-034864 discloses an acoustic device that generates sound by vibrating a vibrating body having a diaphragm portion and an edge portion joined to the outer periphery of the diaphragm portion. In the acoustic device described in this document, the internal space of the main body case and the external space are separated by the vibrating body. In addition, a vibrating body restricting portion is provided at a position opposite the edge portion of the vibrating body. When the air pressure in the internal space of the main body case suddenly decreases, the vibrating body is sucked toward the inside of the main body case, and at this time, the edge portion of the vibrating body comes into contact with the vibrating body restricting portion. This prevents the edge portion from deforming in an inverted manner.

[0003] Incidentally, the configuration of the acoustic device described in JP 2021-034864 A is useful from the viewpoint of suppressing the inversion of the edge portion when the air pressure in the internal space of the main body case suddenly drops, but there is room for improvement from the viewpoint of suppressing deformation of the diaphragm (diaphragm portion).

[0004] In consideration of the above, an object of the present disclosure is to provide an acoustic device that can suppress deformation of the diaphragm.

[0005] The acoustic device of the first aspect comprises a diaphragm that generates sound by vibrating, a frame that supports the diaphragm, and a stopper portion that is provided between the diaphragm and the frame and that a part of the diaphragm abuts against when the diaphragm is pressed toward the frame, thereby suppressing deformation of the diaphragm; when the diaphragm is pressed toward the frame, the diaphragm and the stopper portion abut at a line.

[0006] In the acoustic device of the first aspect, sound is generated by the vibration of a diaphragm. This diaphragm is supported by a frame. In the acoustic device of the first aspect, when the diaphragm is pressed toward the frame, the diaphragm and the stopper portion come into contact with each other at a line. This makes it possible to prevent the diaphragm from deforming when pressed toward the frame.

[0007] The second aspect of the acoustic device is the acoustic device of the first aspect, wherein the outer periphery of the diaphragm and the frame are connected via an edge member, a portion of which deforms as the diaphragm vibrates, and a joint where a portion of the edge member and the outer periphery of the diaphragm are joined together in a superimposed state, and when the diaphragm is pressed toward the frame, the joint and the stopper portion come into contact.

[0008] In the acoustic device of the second aspect, the outer periphery of the diaphragm and the frame are connected via an edge member, a portion of which deforms as the diaphragm vibrates. Here, a portion of the edge member and the outer periphery of the diaphragm are joined together in an overlapping state, forming a joint. In the acoustic device of the second aspect, when the diaphragm is pressed toward the frame, the joint and the stopper portion come into contact. This makes it possible to suppress deformation of the diaphragm when the diaphragm is pressed toward the frame.

[0009] The acoustic device of the third aspect is the acoustic device of the second aspect, wherein the thickness of the portion of the edge member that is joined to the outer periphery of the diaphragm is greater than the thickness of the portion of the edge member that deforms as the diaphragm vibrates.

[0010] In the acoustic device of the third aspect, compared to a configuration in which the thickness of the edge member at the portion joined to the outer periphery of the diaphragm and the thickness of the edge member at the portion that deforms as the diaphragm vibrates are set to the same dimension, the outer periphery of the diaphragm can be more effectively reinforced by the edge member, i.e., the joint that abuts against the stopper portion can be more effectively reinforced.

[0011] An acoustic device of a fourth aspect is an acoustic device of any one of the first to third aspects, in which a voice coil is fixed to the inner periphery of the diaphragm, and the voice coil and the frame are connected via a damper, and the frame is provided with a damper regulating portion that regulates displacement of the damper toward the frame, and the distance that the voice coil moves to the position where the damper abuts the damper regulating portion is set to be equal to or greater than the distance that the voice coil moves to the position where the diaphragm abuts the stopper portion.

[0012] In the acoustic device of the fourth aspect, the distance that the voice coil moves to the position where the damper abuts against the damper restricting portion is set to be equal to or greater than the distance that the voice coil moves to the position where the diaphragm abuts against the stopper portion, thereby making it possible to prevent the movement of the damper from being impeded by the stopper portion.

[0013] The fifth aspect of the acoustic device is the acoustic device of the fourth aspect, wherein a yoke is provided around the voice coil, and the distance that the voice coil moves to the position where the diaphragm abuts the stopper portion is set to be less than the distance that the voice coil moves to the position where the voice coil abuts the yoke.

[0014] In the acoustic device of the fifth aspect, the distance that the voice coil moves to the position where the diaphragm abuts the stopper portion is set to be less than the distance that the voice coil moves to the position where the voice coil abuts the yoke, thereby making it possible to prevent the voice coil from abutting the yoke before the diaphragm abuts the stopper portion.

[0015] An acoustic device of a sixth aspect is the acoustic device of any one of the first to fifth aspects, wherein the stopper portion is formed integrally with the frame.

[0016] In the acoustic device of the sixth aspect, an increase in the number of parts of the acoustic device can be suppressed compared to a configuration in which the stopper portion is formed separately from the frame.

[0017] An acoustic device according to a seventh aspect is the acoustic device according to any one of the first to sixth aspects, wherein the surface of the stopper portion facing the diaphragm is curved.

[0018] In the acoustic device of the seventh aspect, the contact pressure between the stopper portion and the joint portion can be reduced compared to a configuration in which the surface of the stopper portion facing the diaphragm is not curved.

[0019] The acoustic device of the eighth aspect is an acoustic device of any one of the first to seventh aspects, in which when the diaphragm is pressed toward the frame, the outer periphery of the diaphragm abuts against the stopper portion.

[0020] In the acoustic device of the eighth aspect, when the diaphragm is pressed toward the frame, the outer periphery of the diaphragm comes into contact with the stopper portion, thereby preventing the outer periphery of the diaphragm from deforming in an inverted manner relative to the inner periphery.

[0021] The acoustic device of the ninth aspect is an acoustic device of any one of the first to eighth aspects, in which a plurality of the stopper portions are arranged in a radial direction of the diaphragm, and when the diaphragm is pressed toward the frame, the diaphragm abuts against the plurality of stopper portions.

[0022] In the acoustic device of the ninth aspect, the plurality of stoppers are arranged in a radial direction of the diaphragm, and when the diaphragm is pressed toward the frame, the diaphragm abuts against the plurality of stoppers. In this configuration, compared to a configuration in which a single stopper is provided, an increase in contact pressure between the diaphragm and the stopper can be suppressed.

[0023] The acoustic device according to the present disclosure has the excellent effect of being able to suppress deformation of the diaphragm.

[0024] Fig. 1 is a cross-sectional perspective view of an acoustic device cut along the front-rear direction; Fig. 2 is a side cross-sectional view of an acoustic device cut along the front-rear direction; Fig. 3 is an enlarged side cross-sectional view of an acoustic device cut along the front-rear direction; Fig. 4 is a cross-sectional view corresponding to Fig. 3 showing another example of an edge member; Fig. 5 is a cross-sectional view corresponding to Fig. 3 showing another example of a stopper portion.

[0025] An acoustic device 10 according to an embodiment of the present disclosure will be described using Figures 1 to 3. The acoustic device 10 according to this embodiment is mounted on a vehicle, as an example, and can be used as an external sound system (ESS) such as a warning horn or an acoustic vehicle alerting system (AVAS). The front and rear sides of the acoustic device 10 are indicated by arrows FR and RR, respectively. Hereinafter, when simply referring to the front and rear directions, this refers to the front and rear directions of the acoustic device 10, unless otherwise specified.

[0026] 1 and 2, the acoustic device 10 includes a box-shaped main baffle 12 and a front cover 14 attached to the front of the main baffle 12. The acoustic device 10 also includes an acoustic device body 16 that is supported by the main baffle 12 while being disposed within the main baffle 12. Note that cross-sectional hatching has been omitted in FIGS. 1 and 2 to make the drawings easier to see.

[0027] The main baffle 12 is formed in a cylindrical shape with a bottom and an open front side. Specifically, the main baffle 12 has a rear wall portion 12A formed in a disk shape with its thickness direction in the front-to-rear direction. The main baffle 12 also has a cylindrical portion 12B extending forward from the radially outer end of the rear wall portion 12A and having an axial direction in the front-to-rear direction.

[0028] The front cover 14 is formed in a cylindrical shape with a bottom and an open rear side. Specifically, the front cover 14 includes a front wall portion 14A disposed forward of a diaphragm 28 (described later). The front cover 14 also includes a cylindrical portion 14B extending rearward from the outer circumferential edge of the front wall portion 14A and having an axial direction extending in the front-to-rear direction. The rear end of the cylindrical portion 14B is joined to the front end of the cylindrical portion 12B of the main baffle 12. This forms a space between the main baffle 12 and the front cover 14 in which the acoustic device body 16 is disposed. The joint between the rear end of the cylindrical portion 14B and the front end of the cylindrical portion 12B of the main baffle 12 is sealed with a sealant (e.g., adhesive). This ensures watertightness of the joint between the rear end of the cylindrical portion 14B and the front end of the cylindrical portion 12B of the main baffle 12.

[0029] The center of the front wall 14A forms a convex portion 14C that protrudes toward the diaphragm 28, which will be described later. The rear surface of this convex portion 14C is disposed along the front surface of the diaphragm 28. A plurality of elongated through-holes 14D are formed in the front wall 14A at locations corresponding to the convex portion 14C. A plurality of drain holes 14E are also formed around the convex portion 14C in the front wall 14A.

[0030] A second front cover 18 is attached from the front side to the center of the front wall portion 14A of the front cover 14. This second front cover 18 covers from the front side the portion of the front wall portion 14A that covers a diaphragm 28 and an edge member 30, which will be described later. In other words, the diaphragm 28 and the edge member 30, which will be described later, are protected from the front side by the front wall portion 14A of the front cover 14 and the second front cover 18. The second front cover 18 also has a plurality of second through holes 18A and a plurality of second drainage holes 18B formed therein.

[0031] As shown in Figures 2 and 3, the acoustic device main body 16 includes a frame 20, a magnetic circuit section 22 supported by the frame 20, a voice coil 24 arranged within the frame 20, a damper 26 provided between the voice coil 24 and the frame 20, a diaphragm 28 fixed to the voice coil 24, and an edge member 30 connecting the diaphragm 28 and the frame 20.

[0032] The frame 20 is formed in a generally stepped cylindrical shape with a larger opening at the front than at the rear. The opening at the front of the frame 20 is closed by a diaphragm 28 and an edge member 30, which will be described later.

[0033] The magnetic circuit unit 22 applies a magnetic field to the voice coil 24, which will be described later. The magnetic circuit unit 22 includes a yoke 32 formed in a cylindrical shape with a bottom, a disk-shaped magnet 34 fixed to the bottom surface of the yoke 32, and a disk-shaped top plate 36 laminated on the magnet. The yoke 32 and the top plate 36 are made of a soft magnetic material. The yoke 32 opens toward the front and is disposed so as to close the opening on the rear side of the frame 20. A gap is formed between the yoke 32 and the magnet 34 / top plate 36, and a portion of the voice coil 24, which will be described later, is disposed in this gap.

[0034] The voice coil 24 includes a cylindrical bobbin 38 and a coil 40 formed around the bobbin 38. The diaphragm 28, which will be described later, is fixed to the front end of the bobbin 38. The coil 40 is formed by winding a linear conductor made of a conductive material around the bobbin 38. A pair of end portions of the conductor forming the coil 40 are connected to a pair of terminals, not shown, respectively.

[0035] The damper 26 is formed in a disk shape with an opening formed in its radial center and a wave-like shape that repeatedly curves back and forth along the radial direction. The voice coil 24 is inserted into the opening formed in the center of the damper 26. The inner periphery of the damper 26 is joined to the bobbin 38 of the voice coil 24, and the outer periphery of the damper 26 is joined to the frame 20. Thus, the bobbin 38 and the frame 20 are connected via the damper 26.

[0036] The diaphragm 28 is circular when viewed from the front-to-rear direction, with a concave opening at the front. The diaphragm 28 includes an annular outer peripheral portion 28A that constitutes the radially outer portion of the diaphragm 28, and an inner peripheral portion 28B that constitutes the radially central portion of the diaphragm 28 and is integrally formed with the outer peripheral portion 28A. The outer peripheral portion 28A is funnel-shaped, narrowing from the front to the rear. The inner peripheral portion 28B is convex toward the rear and concave toward the front. Arrow R indicates the radially outer side of the diaphragm 28, and arrow C indicates the circumferential direction of the diaphragm 28. The radial direction of the diaphragm 28 (the direction of arrow R and the opposite direction to arrow R) and the circumferential direction of the diaphragm 28 (the direction of arrow C and the opposite direction to arrow C) are perpendicular to the front-to-rear direction. Hereinafter, unless otherwise specified, when simply referring to the radially outer and inner directions, this refers to the radially outer and inner directions of the diaphragm 28. Furthermore, when simply referring to the circumferential direction, this refers to the circumferential direction of the diaphragm 28, unless otherwise specified.

[0037] The edge member 30 is made of an elastic material such as rubber and has a ring shape when viewed from the front-to-rear direction. A radially outer end of the edge member 30 is joined to the front end of the frame 20. Furthermore, a radially inner end of the edge member 30 is joined to the radially outer end of the outer peripheral portion 28A of the diaphragm 28 in a state where the radially outer end of the outer peripheral portion 28A overlaps the radially outer end of the outer peripheral portion 28A in the front-to-rear direction.

[0038] Next, the configuration of the main parts of this embodiment will be described.

[0039] 3 , in the acoustic device main body 16 of this embodiment, the radially inner end 30A of the edge member 30 and the radially outer end 28A1 of the outer periphery 28A of the diaphragm 28 are joined together in an overlapping state to form a joint 42. At the joint 42, the radially inner end 30A of the edge member 30 is disposed forward of the radially outer end 28A1 of the outer periphery 28A of the diaphragm 28. Here, in this embodiment, the thickness of the portion of the edge member 30 joined to the outer periphery 28A of the diaphragm 28 (the radially inner end 30A) is the same as the thickness of the portion 30B of the edge member 30 that deforms in response to vibration of the diaphragm 28.

[0040] A stopper portion 20A protruding forward is provided at the radially intermediate portion of the frame 20. This stopper portion 20A is formed in a generally cylindrical shape with its axial direction aligned in the front-to-rear direction. Furthermore, a surface 20B (the surface at the front end) of the stopper portion 20A at the tip end in the protruding direction is gently curved so as to be convex forward in a cross-sectional view taken along the radial direction. The surface 20B at the tip end in the protruding direction of this stopper portion 20A faces a joint 42 between the edge member 30 and the outer peripheral portion 28A of the diaphragm 28 in the front-to-rear direction. The stopper portion 20A may be formed continuously along the circumferential direction or may be interrupted in part of the circumferential direction. The stopper portion 20A may also be formed in a scattered manner along the circumferential direction. As shown in FIG. 2 , the stopper portion 20A of this embodiment has a plurality of openings 20C that penetrate the stopper portion 20A in the radial direction. Therefore, wiring 44 connected to the voice coil 24 can be routed through these openings 20C. In FIG. 3, the opening 20C is not shown.

[0041] As shown in FIG. 3 , a damper restricting portion 20D that is convex toward the front is formed at the rear opening of the frame 20. The damper 26 contacts the damper restricting portion 20D, thereby limiting the displacement of the damper 26. The state shown in FIG. 3 is a state in which no current is applied to the voice coil 24. The position of the voice coil 24 in this state is referred to as the neutral position. In this embodiment, the distance the voice coil 24 moves to the position where the damper 26 contacts the damper restricting portion 20D (the distance from the neutral position toward the rear) is set to be equal to or greater than the distance the voice coil 24 moves to the position where the joint 42 between the edge member 30 and the outer periphery 28A of the diaphragm 28 contacts the stopper portion 20A (the distance from the neutral position toward the rear).

[0042] In addition, in this embodiment, the distance (movement distance from the neutral position toward the rear) that the voice coil 24 moves to the position where the joint 42 between the edge member 30 and the outer peripheral portion 28A of the diaphragm 28 abuts the stopper portion 20A is set to a distance that is less than the distance (movement distance from the neutral position toward the rear) that the voice coil 24 moves to the position where the voice coil 24 abuts the bottom 32A of the yoke 32.

[0043] (Operations and Effects of the Present Embodiment) Next, operations and effects of the present embodiment will be described.

[0044] 1 to 3, in the acoustic device 10 of this embodiment, current is passed through the coil 40 of the voice coil 24 via various wiring paths (not shown) and external connectors (not shown), etc. As a result, as the voice coil 24 moves in the front-to-rear direction, the diaphragm 28 vibrates, generating sound.

[0045] Furthermore, in the acoustic device 10 of this embodiment, when the diaphragm 28 is pressed toward the frame 20 due to water entering from the front side of the acoustic device 10, the joint 42 between the edge member 30 and the outer periphery 28A of the diaphragm 28 comes into linear contact with the stopper portion 20A. This causes the outer periphery 28A of the diaphragm 28 to be supported by the stopper portion 20A, and it is possible to prevent the outer periphery 28A of the diaphragm 28 from deforming in an inverted manner relative to the inner periphery 28B.

[0046] Furthermore, in the acoustic device 10 of this embodiment, the distance that the voice coil 24 moves to the position where the damper 26 abuts against the damper restricting portion 20D (the distance that it moves rearward from the neutral position) is set to be equal to or greater than the distance that the voice coil 24 moves to the position where the joint 42 between the edge member 30 and the outer periphery 28A of the diaphragm 28 abuts against the stopper portion 20A (the distance that it moves rearward from the neutral position). This makes it possible to prevent the movement (displacement) of the damper 26 from being hindered by the stopper portion 20A.

[0047] Furthermore, in the acoustic device 10 of this embodiment, the distance that the voice coil 24 moves to the position where the joint 42 between the edge member 30 and the outer periphery 28A of the diaphragm 28 abuts against the stopper portion 20A (the distance that the voice coil 24 moves rearward from the neutral position) is set to a distance that is less than the distance that the voice coil 24 moves to the position where the voice coil 24 abuts against the bottom 32A of the yoke 32 (the distance that the voice coil 24 moves rearward from the neutral position). This makes it possible to prevent the voice coil 24 from abutting against the bottom 32A of the yoke 32 before the joint 42 between the edge member 30 and the outer periphery 28A of the diaphragm 28 abuts against the stopper portion 20A.

[0048] Furthermore, in the acoustic device 10 of this embodiment, the stopper portion 20A is formed integrally with the frame 20. This makes it possible to prevent an increase in the number of parts of the acoustic device 10 compared to a configuration in which the stopper portion 20A is formed separately from the frame 20.

[0049] Furthermore, in the acoustic device 10 of this embodiment, the surface 20B on the tip side in the protruding direction of the stopper portion 20A is gently curved. In this configuration, the contact pressure between the stopper portion 20A, the edge member 30, and the joint portion 42 between the outer periphery 28A of the diaphragm 28 and the stopper portion 20A can be reduced compared to a configuration in which the surface 20B on the tip side in the protruding direction of the stopper portion 20A is not curved.

[0050] In the above-described example, the surface 20B on the tip side of the protruding direction of the stopper portion 20A is curved, but the present disclosure is not limited to this. Whether or not the surface 20B on the tip side of the protruding direction of the stopper portion 20A is curved can be determined appropriately taking into account the expected contact pressure between the stopper portion 20A and the joint portion 42.

[0051] In the above-described example, the stopper portion 20A is formed integrally with the frame 20, but the present disclosure is not limited to this. Whether or not the stopper portion 20A is formed integrally with the frame 20 can be determined appropriately in consideration of the configuration of the frame 20, the manufacturing method, etc.

[0052] Furthermore, in the above-described example, the distance the voice coil 24 moves to the position where the joint 42 between the edge member 30 and the outer periphery 28A of the diaphragm 28 abuts the stopper portion 20A (the distance it moves rearward from the neutral position) is set to be less than the distance the voice coil 24 moves to the position where the voice coil 24 abuts the bottom 32A of the yoke 32 (the distance it moves rearward from the neutral position), but the present disclosure is not limited to this. For example, if there is no problem even if the voice coil 24 abuts the bottom 32A of the yoke 32 before the joint 42 between the edge member 30 and the outer periphery 28A of the diaphragm 28 abuts the stopper portion 20A, each distance may be set outside the above range.

[0053] In the above-described example, the distance the voice coil 24 moves to the position where the damper 26 abuts the damper restricting portion 20D (the distance it moves rearward from the neutral position) is set to be equal to or greater than the distance the voice coil 24 moves to the position where the joint 42 between the edge member 30 and the outer periphery 28A of the diaphragm 28 abuts the stopper portion 20A (the distance it moves rearward from the neutral position), but the present disclosure is not limited to this. For example, if it is not expected that the movement (displacement) of the damper 26 will be hindered by the stopper portion 20A, each distance may be set outside the above range.

[0054] Furthermore, in the above-described example, the thickness of the portion of the edge member 30 joined to the outer periphery 28A of the diaphragm 28 (the radially inner end 30A) is the same as the thickness of the portion 30B of the edge member 30 that deforms with vibration of the diaphragm 28. However, the present disclosure is not limited to this. For example, as shown in FIG. 4 , the thickness of the portion of the edge member 30 joined to the outer periphery 28A of the diaphragm 28 (the radially inner end 30A) may be greater than the thickness of the portion 30B of the edge member 30 that deforms with vibration of the diaphragm 28. In this configuration, compared to the configuration shown in FIG. 3 , the radially outer end 28A1 of the outer periphery 28A of the diaphragm 28 can be effectively reinforced by the edge member 30. That is, the joint 42 that abuts against the stopper portion 20A can be effectively reinforced.

[0055] Furthermore, in the above-described example, the stopper portion 20A is provided at one radial location, but the present disclosure is not limited thereto. For example, as shown in FIG. 5 , a configuration in which multiple stopper portions 20A are provided at multiple radial locations may be used. In the example shown in FIG. 5 , the multiple stopper portions 20A are arranged radially in a row at positions facing the outer periphery of the vibration plate 28. This configuration can suppress an increase in contact pressure between the vibration plate 28 and the stopper portion 20A compared to a configuration in which a single stopper portion 20A is provided (a configuration in which the stopper portion 20A is provided at one radial location). Note that in the example shown in FIG. 5 , the stopper portion-forming member 46 is joined to the frame 20, and some of the multiple stopper portions 20A are formed on the stopper portion-forming member 46.

[0056] In addition, although the present embodiment has described a configuration in which the diaphragm 28 and the edge member 30 are separate members, the present disclosure is not limited to this. For example, the diaphragm 28 and the edge member 30 may be integrally formed (a configuration in which the joint 42 is not formed).

[0057] The above describes one embodiment of the present disclosure, but the present disclosure is not limited to the above, and it goes without saying that it can be implemented in various other modified forms within the scope that does not deviate from the gist of the present disclosure.

[0058] The disclosure of Japanese Patent Application No. 2023-140568, filed on August 30, 2023, is incorporated herein by reference in its entirety.

Claims

1. An acoustic device comprising: a diaphragm that generates sound by vibrating; a frame that supports the diaphragm; and a stopper portion provided between the diaphragm and the frame, with which a part of the diaphragm comes into contact when the diaphragm is pressed towards the frame, suppressing deformation of the diaphragm; wherein when the diaphragm is pressed towards the frame, the diaphragm and the stopper portion come into contact at a line.

2. The acoustic device of claim 1, wherein the outer periphery of the diaphragm and the frame are connected via an edge member, a portion of which deforms in response to vibration of the diaphragm, and a joint is formed in which a portion of the edge member and the outer periphery of the diaphragm are joined in a superimposed state, and when the diaphragm is pressed towards the frame, the joint and the stopper portion come into contact.

3. The acoustic device according to claim 2, wherein the thickness of the portion of said edge member joined to the outer periphery of said diaphragm is greater than the thickness of the portion of said edge member that deforms in response to vibration of said diaphragm.

4. An acoustic device as claimed in any one of claims 1 to 3, wherein a voice coil is fixed to the inner periphery of the diaphragm and the voice coil and the frame are connected via a damper, the frame is provided with a damper regulating portion which regulates the displacement of the damper towards the frame, and the distance which the voice coil moves to the position where the damper abuts against the damper regulating portion is set to be equal to or greater than the distance which the voice coil moves to the position where the diaphragm abuts against the stopper portion.

5. The acoustic device according to claim 4, wherein a yoke is provided around the voice coil, and the distance that the voice coil moves to the position where the diaphragm abuts against the stopper portion is set to a distance that is less than the distance that the voice coil moves to the position where the voice coil abuts against the yoke.

6. The acoustic device according to claim 1, wherein said stopper portion is formed integrally with said frame.

7. The acoustic device according to claim 1, wherein the surface of said stopper portion facing said diaphragm is curved.

8. The acoustic device according to claim 1, wherein when the diaphragm is pressed towards the frame, the outer periphery of the diaphragm comes into contact with the stopper portion.

9. The acoustic device according to claim 1, wherein a plurality of the stopper portions are arranged in a radial direction of the diaphragm, and when the diaphragm is pressed towards the frame, the diaphragm comes into contact with the plurality of the stopper portions.

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