speaker

Abstract

This speaker provides a mechanism that effectively dissipates the heat generated by the voice coil into the surrounding space. [Solution] In the speaker 1, the magnetic circuit section 10 has a magnetic gap G formed between the rear inner yoke 12c and the rear outer yoke 13, which are formed in the rear portion of the center yoke 12, and the voice coil 25 is located within the magnetic gap G located behind the magnetic circuit section 10. The magnetic gap G is open to the external space behind the magnetic circuit section 10, and at least in the front-rear neutral position, a part of the voice coil 25 protrudes into the external space. Therefore, the heat of the voice coil 25 can be dissipated into the external space behind it.

Description

Technical Field

[0001] The present invention relates to a speaker capable of effectively releasing heat generated from a voice coil vibrating within a magnetic gap of a magnetic circuit section. [[ID=)7]]

Background Art

[0002] In a speaker, a voice coil is wound around a bobbin that vibrates together with a diaphragm, and the voice coil is positioned within a magnetic gap of a magnetic circuit section. The diaphragm is driven by an electromagnetic force generated by a drive current flowing through the voice coil and a magnetic field crossing the voice coil. However, there is a problem that the voice coil generates heat due to Joule heat during vibration. Since the voice coil is configured by winding a plurality of turns of a conducting wire around a bobbin, its mass is relatively large, and this mass contributes to increasing the load of a vibrating portion including the diaphragm. Although it is possible to reduce the mass by reducing the cross-sectional area of the conducting wire constituting the voice coil, if a thin conducting wire is used, the Joule heat increases, and the conducting wire may be melted during the operation of the speaker. Therefore, in the magnetic circuit section, it is necessary to adopt a structure that can release heat generated from the voice coil to the external space.

[0003] In the speaker described in Patent Document 1, a plurality of through holes penetrating the outer peripheral side and the inner peripheral side are radially formed in a magnet constituting a magnetic circuit, and outside air can easily flow into the inside of the semi-closed magnetic circuit. In the speaker described in Patent Document 2, a through hole is formed in a center pole of a magnetic circuit, and a groove communicating with the through hole is formed on the bottom surface of a bottom plate integrated with the center pole. This speaker can release the air existing in the space surrounded by the bobbin to the outside through the through hole and the groove even when the bottom surface of the magnetic circuit is pressed against the inner wall surface of the housing. In the speaker described in Patent Document 3, a plurality of slits penetrating the upper and lower surfaces are radially provided on the outer peripheral portion of a center pole, and a ventilation hole is formed on the bottom surface of a bowl-shaped yoke. By providing the slits and the ventilation hole, the air permeability is improved to prevent an excessive rise in temperature.

Prior Art Documents

[0004] [Patent Document 1] Japanese Patent Application Publication No. 8-9494 [Patent Document 2] Japanese Patent Publication No. 2002-262387 [Patent Document 3] Japanese Utility Model Publication No. 5-9099 [Overview of the project] [Problems that the invention aims to solve]

[0005] The speaker described in Patent Document 1 requires the use of a special magnet with multiple through-holes arranged radially, which is impractical. Furthermore, drilling holes inside the magnet reduces its volume, leading to a decrease in magnetic force. In the speakers described in Patent Documents 2 and 3, the magnetic gap where the voice coil is located is positioned in front of the magnetic circuit. As a result, heat emitted from the voice coil tends to accumulate in the space inside the magnetic circuit, making it difficult to efficiently dissipate the heat to the outside with only ventilation holes opening at the bottom of the magnetic circuit.

[0006] The present invention aims to solve the above-mentioned conventional problems and to provide a speaker that can efficiently dissipate heat from the voice coil within the magnetic gap to the outside space by opening the magnetic gap to the outside space. [Means for solving the problem]

[0007] The present invention relates to a speaker having a frame and a support portion including a magnetic circuit portion fixed to the rear of the frame, a diaphragm vibrating freely on the frame, a bobbin that vibrates together with the diaphragm, and a voice coil provided on the bobbin, The magnetic circuit section has a drive magnet, and a magnetic gap is formed between a rear inner yoke and a rear outer yoke located behind the drive magnet, with the voice coil positioned inside the magnetic gap. The magnetic gap is characterized by being open to the space behind the magnetic circuit portion.

[0008] The speaker of the present invention has a magnetic circuit section having a magnetic gap formed between a front inner yoke and a front outer yoke located in front of the drive magnet. The bobbin can be configured to include a voice coil located inside the magnetic gap between the front inner yoke and the front outer yoke, and a voice coil located inside the magnetic gap between the rear inner yoke and the rear outer yoke.

[0009] In the speaker of the present invention, it is preferable that, at least when the bobbin is in a neutral position in the front-to-back vibration direction, a portion of the voice coil protrudes from the rear surface of the magnetic circuit towards the rear space.

[0010] In the speaker of the present invention, an operating hole is formed in the support portion between the diaphragm and the magnetic circuit portion, which penetrates in the front-to-back direction and leads to the magnetic gap. A portion of the bobbin vibrates back and forth inside the operating hole. For example, the operating hole is formed in the yoke that constitutes the magnetic circuit section.

[0011] The speaker of the present invention has a bobbin formed with an open notch at its front end and a continuous portion located between adjacent notches. Multiple of the continuous sections can be configured to vibrate back and forth within the multiple operating holes.

[0012] In the speaker of the present invention, it is preferable that a reinforcing member is provided in front of the operating hole, connecting a plurality of the continuous sections. The reinforcing member may be a cap fitted to the front end of the bobbin. [Effects of the Invention]

[0013] In the speaker of the present invention, a magnetic gap is formed between a rear inner yoke and a rear outer yoke located behind a drive magnet in a magnetic circuit portion, and the magnetic gap is opened to a rear space. Preferably, when at least the bobbin is in a neutral position in the front-rear vibration direction, a part of the voice coil protrudes from the rear surface of the magnetic circuit portion toward the rear space. Therefore, heat generated from the voice coil can be effectively released to the rear space, and it is easy to prevent the temperature of the voice coil and its surroundings from becoming high.

Brief Description of the Drawings

[0014] [Figure 1] It shows a speaker of the first embodiment of the present invention, a perspective view including a longitudinal section, [Figure 2] A partially exploded perspective view showing a bobbin, a voice coil, and a magnetic circuit portion provided in the speaker shown in FIG. 1, [Figure 3] It shows the magnetic circuit portion shown in FIGS. 1 and 2 in a plane, a cross-sectional view of the speaker shown in FIG. 1 cut along line III-III, [Figure 4] A partially perspective view showing a modified example of the present invention provided with a reinforcing member for reinforcing the bobbin, [Figure 5] A longitudinal sectional view showing a speaker of the second embodiment of the present invention, [Figure 6] It shows an operation hole formed in the magnetic circuit portion of the speaker shown in FIG. 5, a partial cross-sectional view of the speaker shown in FIG. 4 cut along line VI-VI, [Figure 7] It shows simulation results for explaining the effects of the present invention, (A) shows an example model of the present invention, and (B) shows a comparative example model, [Figure 8] A diagram showing changes in the average temperature around the voice coil in the example model and the comparative example model shown in FIG.

Modes for Carrying Out the Invention

[0015] In the speaker 1 according to an embodiment of the present invention, the Y1 - Y2 direction is the front - rear direction, the Y1 direction is the front, and the Y2 direction is the rear. The sound - emitting direction of the speaker 1 varies depending on the usage form, and the Y1 direction may be used as the sound - emitting direction, or the Y2 direction may be used as the sound - emitting direction. In FIG. 1, a central axis O extending in the front - rear direction (Y1 - Y2 direction) is shown. The main part of the speaker 1 has a substantially rotation - symmetric structure centered on the central axis O.

[0016] The speaker 1 shown in FIG. 1 has a frame 2. The frame 2 is formed of a non - magnetic material or a magnetic material and has a tapered shape with a diameter gradually expanding toward the front (Y1 direction). The frame 2 has a rear fixing portion 2a in the rear (Y2 direction), and an opening 2b is formed in the rear fixing portion 2a.

[0017] A magnetic circuit portion 10 is fixed to the rear fixing portion 2a of the frame 2. The magnetic circuit portion 10 is a so - called outer - magnet type and has a ring - shaped drive magnet 11 centered on the central axis O. A center yoke 12 is provided in the magnetic circuit portion 10. The center yoke 12 is integrally formed with a center pole 12a located inside the drive magnet 11 and a front yoke 12b that projects from the front of the center pole 12a to the periphery. In the center yoke 12, a portion behind the center pole 12a functions as a rear inner yoke 12c. The drive magnet 11 is fixed to the rear surface of the front yoke 12b, and a ring - shaped rear outer yoke 13 is fixed to the rear surface of the drive magnet 11. The center yoke 12 and the rear outer yoke 13 are formed of a magnetic material, that is, a magnetic metal material. The rear outer yoke 13 is located on the outer peripheral portion of the rear inner yoke 12c, which is the rear portion of the center yoke 12, and a magnetic gap G is formed along the circumference centered on the central axis O between the outer peripheral surface of the rear inner yoke 12c and the inner peripheral surface of the rear outer yoke 13.

[0018] The magnetic circuit portion 10 is installed on the rear surface of the rear fixing portion 2a of the frame 2, and the rear fixing portion 2a and the front yoke 12b of the magnetic circuit portion 10 are fixed by a plurality of fixing screws 9. The frame 2 and the magnetic circuit portion 10 constitute a "support portion".

[0019] As shown in Figures 1 and 2, the center yoke 12 has multiple operating holes 14 formed at the boundary between the center pole 12a and the front yoke 12b. At least a portion of the operating holes 14 are formed to penetrate from front to back. As shown in Figure 3, when the magnetic circuit section 10 is viewed in plan, a portion of the center pole 12a, a portion of the rear outer yoke 13, and a portion of the magnetic gap G are visible inside each operating hole 14. As shown in Figure 1, the internal space of the operating hole 14 is connected to the magnetic gap G through the gap 15 between the outer surface of the center pole 12a and the inner surface of the drive magnet 11.

[0020] A bobbin 20 is provided in the center of speaker 1. The bobbin 20 is cylindrical in shape with a central axis O. As shown in Figure 2, the bobbin 20 has a cylindrical portion 21 located at the rear (Y2 direction), a plurality of notches 22 formed continuously from the front of the cylindrical portion 21 to the front end of the bobbin 20, and a plurality of continuous portions 23 which are parts of the cylinder remaining between adjacent notches 22, 22. The plurality of notches 21 and the plurality of continuous portions 23 are positioned alternately in the circumferential direction of the cylinder. A voice coil 25 is provided at the rear end of the bobbin 20. The voice coil 25 is formed by winding a wire multiple times around the outer circumference of the cylindrical portion 21 of the bobbin 20.

[0021] As shown in Figure 2, the bobbin 20 is assembled to the magnetic circuit section 10 from the rear (Y2 direction) towards the front (Y1 direction). During assembly, the continuous section 23 of the bobbin 20 is inserted from the rear into the magnetic gap G of the magnetic circuit section 10, and the continuous section 23 is inserted into the operating hole 14 through the gap 15 between the outer surface of the center pole 12a and the inner surface of the drive magnet 11. As shown in Figure 1, once the bobbin 20 is assembled to the magnetic circuit section 10, the front ends of the multiple continuous sections 23 protrude forward from their respective operating holes 14, the cylindrical section 21 of the bobbin 20 is located inside the gap 15 and inside the magnetic gap G, and the voice coil 25 is located inside the magnetic gap G. The magnetic circuit section 10 and the voice coil 25 constitute the "magnetic drive section".

[0022] As shown in Figure 1, a diaphragm 3 is provided inside the front portion of the frame 2. The diaphragm 3 has a two-piece structure in which a rear plate portion 4 and a front plate portion 5 are assembled with a gap between them, and each is a cone shape. An elastically deformable edge member 5a is integrally formed on the outer edge of the front plate portion 5 of the diaphragm 3, and the edge member 5a is joined to the front end peripheral portion 2c of the frame 2. When the magnetic circuit portion 10 is fixed to the rear surface of the rear fixing portion 2a of the frame 2 with fixing screws 9, the operating hole 14 of the magnetic circuit portion 10 appears inside the opening 2b of the rear fixing portion 2a. The continuous portion 23 of the bobbin 20 passes through the operating hole 14, and its front end portion 23a is bonded to the inner surface of the central hole 4a formed in the rear plate portion 4 of the diaphragm 3. An inner circumferential fixing portion 2d is formed on the inner surface of the middle section of the frame 2, and the outer circumferential portion of the elastically deformable damper member 6, which has a corrugated cross-section, is fixed to the inner circumferential fixing portion 2d of the frame 2 with adhesive. The inner circumferential edge 6a of the damper member 6 is bonded and fixed to the outer circumferential surface of the continuous portion 23 of the bobbin 20.

[0023] The diaphragm 3, bobbin 20, and voice coil 25 are supported so as to be able to vibrate freely in the front-rear direction (Y1-Y2 direction) relative to the frame 2 (relative to the support part) by the elastic deformation of the edge member 5a and damper member 6. The diaphragm 3, bobbin 20, and voice coil 25 constitute a "vibrating part" that vibrates in the front-rear direction (Y1-Y2 direction) relative to the "support part" which includes the frame 2.

[0024] Next, we will explain the sound production operation of speaker 1. During sound production, a drive current is supplied to the voice coil 25 based on the audio signal output from the audio amplifier. In the magnetic circuit section 10, the drive magnetic flux F emitted from the drive magnet 11 passes from the front yoke 12b, which is part of the center yoke 12, through the rear inner yoke 12c, across the magnetic gap G, and reaches the rear outer yoke 13. The electromagnetic force excited by the drive magnetic flux F traversing the voice coil 25 within the magnetic gap G and the drive current flowing through the voice coil 25 causes the vibrating section, including the bobbin 20, voice coil 25, and diaphragm 3, to vibrate in the front-to-back direction (Y1-Y2 direction), generating sound pressure corresponding to the frequency of the drive current, and emitting sound forward or backward.

[0025] When speaker 1 is operating, Joule heat is generated due to the amount of drive current flowing through the voice coil 25 and the electrical resistance of the voice coil 25, causing the temperature of the voice coil 25 to rise, and the temperature inside the narrow space of the magnetic gap G also rises. However, since the magnetic gap G is open to the external space behind the magnetic circuit section 10, and the internal space of the magnetic gap G is directly connected to the external space behind it, heat inside the magnetic gap G can easily escape to the external space behind it. In addition, when the bobbin 20 is in a neutral position in at least the front-to-back vibration direction, the rear end 25a of the voice coil 25 protrudes from the bottom surface of the magnetic circuit section 10 into the external space behind it, and preferably, the rear end 25a protrudes from the bottom surface of the magnetic circuit section 10 into the external space behind it throughout the entire range of movement of the bobbin 20 as it moves back and forth. As a result, it becomes possible to directly radiate the heat of the voice coil 25 into the external space, which suppresses the temperature rise around the magnetic gap G and prevents phenomena such as the conductors constituting the voice coil 25 melting due to high heat.

[0026] Figure 7 shows the models used in the simulation to verify the effects of the present invention. (A) is an embodiment model of the present invention, in which the magnetic gap G is directly opened to the external space behind the magnetic circuit section 10, and the voice coil 25 protrudes to the rear of the magnetic circuit section, at least in the neutral position. (B) is a comparative example model, in which a ventilation hole 31 penetrating from front to back is formed in the center pole, similar to the known technology described in Patent Document 2. In the settings of each model, the voice coil is made of copper, the bobbin is made of polypropylene (PP), and the yoke including the center pole is made of iron. In the simulation, the voice coil was set to move ±10 mm from the neutral position in the front-to-back direction at a frequency of 60 Hz, and the power supplied to the voice coil, which is the heat-generating part, was set to 150 W. Figure 8 shows the average temperature of the heat-generating part on the vertical axis and the operating time on the horizontal axis. In Figure 8, (i) shows the temperature change of the embodiment model, and (ii) shows the temperature change of the comparative example model. In this simulation, the saturation temperature of the heat-generating part centered on the voice coil in the embodiment model is about 20% lower compared to the comparative example model.

[0027] In the speaker 1 of the present invention, it is preferable that the damper member 6 is made of a material that is substantially impermeable to air. The damper member 6 is generally made of a fibrous structure, but by impregnating the fibrous structure with resin, it can be made to be an airtight structure. Since the internal space of the bobbin 20 is covered by the front plate portion 5 located above it, if the damper member 6 has a structure that is substantially impermeable to air, when the damper member 6 vibrates up and down together with the diaphragm 3, the air between the damper member 6 and the magnetic circuit portion 10, which is a nearly closed space, will flow from the operating hole 14 through the gap 15 into the magnetic gap G, making it easier to discharge the air in the magnetic gap G into the space behind the magnetic circuit portion 10. Note that "substantially impermeable to air" means that when the damper member 6 vibrates back and forth at the frequency and amplitude of vibration used in the speaker 1, the pressure change of the air due to this vibration is not sufficient for air to pass through the damper member 6.

[0028] Figure 4 shows a modified example of the present invention. In the structure shown in Figure 4, after the bobbin 20 is assembled to the magnetic circuit section 10 from rear to front, a plurality of continuous sections 23 protruding forward from the operating hole 14 of the magnetic circuit section 10 are connected to each other by a reinforcing member 26, thereby reinforcing the bobbin 20. The reinforcing member 26 is formed in a ring shape from the same lightweight resin sheet as the bobbin 20 and is bonded to the outer or inner circumferential surface of all continuous sections 23. By providing the reinforcing member 26, the bobbin 20 having the notched section 22 can be reinforced, and distortion of the bobbin 20 due to vibration can be suppressed.

[0029] As shown in Figure 4, a cap 27 can be used as a reinforcing member. The cap 27 has a top plate 27a and a partially cylindrical peripheral portion 27b, and the peripheral portion 27b is fitted onto the outer surface of all continuous portions 23 and fixed with adhesive. By using the cap 27 as a reinforcing member, the relative positions of adjacent continuous portions 23 become aligned with the cylindrical surface, thereby increasing the reinforcing effect of the bobbin 20.

[0030] Figure 5 shows a speaker 101 according to a second embodiment of the present invention. The magnetic circuit section 110 provided in the speaker 101 is a so-called external magnet type and has a ring-shaped drive magnet 111 located on the outside of the bobbin 120. A ring-shaped rear outer yoke 112 is fixed to the rear surface of the drive magnet 111, and a ring-shaped front outer yoke 113 is fixed to the front surface of the drive magnet 111. A center yoke 114 is provided inside the bobbin 120. The rear outer yoke 112, the front outer yoke 113, and the center yoke 114 are made of magnetic material. The rear portion of the center yoke 114 functions as a rear inner yoke 114a, and a rear magnetic gap G1 is formed between the outer circumferential surface of the rear inner yoke 114a and the inner circumferential surface of the rear outer yoke 112. The front portion of the center yoke 114 functions as a front inner yoke 114b, and a front magnetic gap G2 is formed between the outer circumferential surface of the front inner yoke 114b and the inner circumferential surface of the front outer yoke 113.

[0031] The front outer yoke 113 and the center yoke 114 are fixed to the rear surface of the magnetic circuit bracket 117, and the magnetic circuit bracket 117 is fixed to the rear fixing portion 2a of the frame 2 with fixing screws 9. The magnetic circuit bracket 117 is made of a magnetic or non-magnetic material. Multiple operating holes 115 are formed in the magnetic circuit bracket 117, passing through from front to back, and the operating holes 115 are connected to the front magnetic gap G2 and the rear magnetic gap G1 through the gap 116 on the outer circumference of the center yoke 114.

[0032] The bobbin 120 has a cylindrical portion 121, a notched portion 122, and a continuous portion 123. A rear voice coil 125 and a front voice coil 126 are provided on the outer circumferential surface of the cylindrical portion 121, spaced apart in the front-to-back direction (Y1-Y2 direction). The rear voice coil 125 and the front voice coil 126 are constructed by winding a single wire in opposite directions. When the bobbin 120 is incorporated into the magnetic circuit portion 110 from the rear, and the continuous portion 123 is made to protrude forward through the operating hole 115, and the front end of the continuous portion 123 is joined to the central hole 4a of the rear plate portion 4 of the diaphragm 3, the rear voice coil 125 is located in the rear magnetic gap G1, and the front voice coil 126 is located in the front magnetic gap G2.

[0033] In the magnetic circuit section 110 shown in Figure 5, the drive magnetic flux F1 emitted from the drive magnet 111 crosses the front magnetic gap G2 from the front outer yoke 113, crosses the rear magnetic gap G1 from the center yoke 114, and returns to the drive magnet 111 via the rear outer yoke 112. Since both the front voice coil 126 in the front magnetic gap G2 and the rear voice coil 125 in the rear magnetic gap G1 exert a driving force that is symmetrical in the front-rear direction, it becomes possible to maintain linearity in the front-rear direction of the vibrating part. In the speaker 101 of Figure 5, the rear magnetic gap G1 is open to the external space behind the magnetic circuit section 110, and a part of the rear voice coil 125 protrudes into the rear external space, making it easier to dissipate heat from the rear voice coil 125. Also, since the front magnetic gap G2 and the front voice coil 126 are close to the rear external space, it is also easier to dissipate heat from the front voice coil 126 to the rear.

[0034] In the magnetic circuit section 110 shown in Figure 5, the circumferential path of the drive magnetic flux F1 emitted from the drive magnet 111 is almost completed by the front outer yoke 113, the center yoke 114, and the rear outer yoke 112. Since the operating hole 115 formed in the magnetic circuit bracket 117 is not located on the circumferential path of the drive magnetic flux F1, the operating hole 115 does not act as a magnetic resistance to the drive magnetic flux F1. Therefore, as shown in Figure 6, even if the operating hole 115 formed in the magnetic circuit bracket 117 is made to be long in the circumferential direction, it does not affect the driving of the vibrating part in any way. Therefore, as shown in Figure 6, the circumferential width dimension W1 of the notch 122 of the bobbin 120 can be reduced, and the circumferential width dimension W2 of the continuous section 123 can be increased. As a result, the bobbin 120 can maintain high strength even with the notch 122.

[0035] In the second embodiment shown in Figure 5, the magnetic circuit bracket 117 may be omitted, and the front outer yoke 113 and the center yoke 114 may be directly fixed to the rear fixing portion 2a of the frame 2 with fixing screws 9. In this case, an operating hole is formed in the rear fixing portion 2a of the frame 2 through which the continuous portion 123 of the bobbin 120 passes.

[0036] The magnetic circuit section 10 shown in Figure 1 and the magnetic circuit section 110 shown in Figure 5 are external magnet type, with the drive magnet provided on the outer circumference of the bobbin. However, these magnetic circuit sections can also be configured as internal magnet type. That is, in the magnetic circuit section 10 shown in Figure 1, the disc-shaped drive magnet and the rear inner yoke may be arranged inside the bobbin 20. Similarly, in the magnetic circuit section 110 shown in Figure 5, the disc-shaped drive magnet, the rear inner yoke, and the front inner yoke may be arranged inside the bobbin 120. [Explanation of Symbols]

[0037] 1,101 speakers 2 frames 3 Vibration plate 10 Magnetic circuit section 11 Fixed magnets 12c Rear inner yoke 13. Rear outer yoke 14 Operating holes 20 bobbins 21 Cylindrical section 22 Notch 23 consecutive sections 25 Voice coil 26 Reinforcement members 27 caps 110 Magnetic circuit section 112 Rear outer yoke 113 Front outer yoke 114a Rear inner yoke 114b Anterior lateral yoke 120 bobbins 121 Cylindrical section 122 Notch 123 Continuous section 125 Rear voice coil 126 Front voice coil G magnetic gap G1 Rear magnetic gap G2 forward magnetic gap O center axis

Claims

1. A speaker having a frame and a support portion including a magnetic circuit portion fixed to the rear of the frame, a diaphragm supported on the frame so as to be vibrable, a bobbin that vibrates together with the diaphragm, and a voice coil provided on the bobbin, The magnetic circuit section has a drive magnet, and a magnetic gap is formed between a rear inner yoke and a rear outer yoke located behind the drive magnet, with the voice coil positioned inside the magnetic gap. A speaker characterized in that the magnetic gap is open to the space behind the magnetic circuit section.

2. The magnetic circuit section has a magnetic gap formed between a front inner yoke and a front outer yoke located in front of the drive magnet. The speaker according to claim 1, wherein the bobbin is provided with a voice coil located inside the magnetic gap between the front inner yoke and the front outer yoke, and a voice coil located inside the magnetic gap between the rear inner yoke and the rear outer yoke.

3. The speaker according to claim 1 or 2, wherein at least when the bobbin is in a neutral position in the front-to-back vibration direction, a portion of the voice coil protrudes from the rear surface of the magnetic circuit portion toward the rear space.

4. Between the diaphragm and the magnetic circuit, the support portion has an operating hole that penetrates in the front-rear direction and leads to the magnetic gap. The speaker according to claim 1 or 2, wherein a part of the bobbin vibrates back and forth inside the operating hole.

5. The speaker according to claim 4, wherein the operating hole is formed in the yoke constituting the magnetic circuit portion.

6. The bobbin has an open notch at its front end and a continuous section located between adjacent notches. The speaker according to claim 4, wherein a plurality of the continuous portions vibrate back and forth inside a plurality of the operating holes.

7. The speaker according to claim 6, wherein a reinforcing member connecting a plurality of the continuous portions is provided in front of the operating hole.

8. The speaker according to claim 7, wherein the reinforcing member is a cap fitted to the front end of the bobbin.

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