JP2008092560A - Electroacoustic transducer - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a large acoustic pressure by vibrating a diaphragm with a large amplitude. <P>SOLUTION: An electroacoustic transducer includes a yoke 1 having an annular intermediate yoke portion 1a, an inner yoke portion 1b and an outer yoke portion 1c; a permanent magnet 3 provided on the outer yoke portion 1c so as to surround the inner yoke portion 1b and forming a magnetic gap between itself and the inner yoke portion 1b; a voice coil inserted into the magnetic gap; and a diaphragm 4 supporting the voice coil. The diaphragm 4 has an outer annular portion 4a which is fixed to an inner peripheral surface of the outer yoke portion 1c and extended toward the inner yoke portion 1b, an inner portion 4b arranged to face a distal end opening 1e of the inner yoke portion 1b, and a cylindrical portion 4c connected between the inner portion and the outer annular portion. The inner portion 4b of the diaphragm has a dome portion that is convex toward the distal end opening. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a structure of an electrodynamic electroacoustic transducer suitable for mounting on a relatively small electronic device having a function such as a speaker, a receiver (earphone), or a microphone.

  In recent years, mobile phones and other small information devices that handle images and audio have become more and more multifunctional, image information is required to have a large area, and additional functions such as cameras are also required. The electroacoustic transducer is required to be installed in a narrower space, despite severe requirements for both sound quality and volume.

  FIG. 14 shows a typical structure of a speaker as such an electroacoustic transducer disclosed in Japanese Patent Laid-Open No. 2001-309487. Reference numeral 1 denotes a cup-shaped yoke made of a soft magnetic material, which is molded in a plastic (non-magnetic) frame 11. A disc-shaped permanent magnet 3 magnetized in the vertical direction and a disc-shaped top plate 9 made of a soft magnetic material mounted on the permanent magnet are provided in the central portion. A magnetic circuit is formed through a magnetic gap G between the peripheral edge of 9 and the upper edge of the yoke 1.

  The diaphragm 4 is a thin plastic plate having a substantially disk shape. A ring-shaped outer peripheral portion 4 a of the diaphragm 4 is bonded and fixed to a step portion formed on the inner wall surface of the frame 11 via a spacer 5. In the diaphragm 4, a ring-shaped outer peripheral dome 4b, a thin ring-shaped flat portion 4c, and a central dome 4e are formed in this order on the inner side of the outer peripheral portion 4a. The outer dome 4b and the central dome 4e are curved in order to provide the appropriate elasticity and rigidity necessary for the diaphragm 4 to generate sound vibrations, and a plurality of fine grooves (radial, ring, or Elasticity and rigidity are adjusted by forming a shallow irregular shape such as a spiral.

  A cylindrical voice coil 6 is bonded and fixed to the flat portion 4 c and inserted into the magnetic gap G. The terminal line of the voice coil is usually guided to the outside with the diaphragm surface facing, but the illustration is omitted. By causing a voice current to flow through the voice coil 6, the voice coil 6 moves up and down within the magnetic gap G and vibrates the diaphragm 4 to emit sound. A protector 10 formed in a shallow cup shape such as a metal plate is provided so as to cover the upper surface of the diaphragm 4, and a sound emitting hole 7 is provided in the protector. Note that a line indicating the upper edge of the yoke 1 and a line indicating the lower edge of the voice coil 6 that should be visible in the back of the cross section of FIG. 14 are not shown for the sake of clarity.

  FIG. 15 shows a speaker having another structure disclosed in Japanese Patent Laid-Open No. 2001-169390. Although the basic shape structure is the same as that shown in FIG. 14, the diaphragm 4 has a U-shaped bent portion 4f, and the voice coil 6 is directly wound around the outer surface thereof. By doing so, it is said that the voice coil bonding step can be eliminated, the positional accuracy of the voice coil is improved, and the characteristics and quality are stabilized.

FIG. 16 shows a speaker having still another structure disclosed in Japanese Patent Laid-Open No. 55-135500. In this speaker, a yoke 1 having a center pole 1 ′, an annular frame 11 provided on the outer peripheral edge of the yoke 1, and an annular permanent magnet 2 attached to the inner peripheral surface of the annular frame 11 are provided. Have. The permanent magnet is magnetized in the radial direction. A magnetic gap G is formed between the inner peripheral surface of the permanent magnet and the center pole 1 ′ of the yoke 1, and the voice coil 6 set in the magnetic gap has a center. It is set so as to be attached around a cylindrical portion 4g of the diaphragm 4 raised so as to surround the pole 1 '.
JP 2001-309487 A JP 2001-169390 A JP 55-135500 A

  In the electroacoustic transducer shown in FIG. 14, the positioning accuracy when the voice coil is bonded to the flat portion of the diaphragm becomes a problem. If the positioning accuracy is poor, it is necessary to widen the magnetic gap, the magnetic resistance increases, and the magnetic flux density in the magnetic gap cannot be increased. In the electroacoustic transducer shown in FIG. 15, the problem of the voice coil positioning accuracy can be solved, but there is a limit to narrowing the magnetic gap because of the U-shaped bent portion 4f of the diaphragm. In the electroacoustic transducer of FIG. 16, the positioning accuracy of the voice coil can be improved and the magnetic gap can be narrowed. However, since the cross-sectional area of the center pole is small and the diameter of the voice coil is small, the vibration of the diaphragm 4 The area of the end face portion of the cylindrical portion 4g that is the center of the diaphragm 4 is small, the vibration amount of the vibration of the diaphragm 4 based on the vibration of the voice coil 6 is small, and therefore the sound pressure (volume) is small.

  The object of the present invention is to improve the conventional electroacoustic transducer as described above.

That is, the present invention
An annular intermediate yoke portion, a cylindrical inner yoke portion extending in the axial direction of the intermediate yoke portion from the radially inner periphery of the intermediate yoke portion, and extending in the axial direction from the radially outer periphery of the intermediate yoke portion A yoke having a cylindrical outer yoke portion having an inner peripheral surface forming a cylindrical space with the outer peripheral surface of the inner yoke portion;
At least one permanent magnet provided to surround the inner yoke portion at a position away from the intermediate yoke portion in the axial direction, and is magnetized in the radial direction of the yoke portion, and the inner yoke portion At least one permanent magnet forming a magnetic gap with the outer peripheral surface of
A cylindrical voice coil inserted in the axial direction in the cylindrical space and extending in the axial direction in the magnetic gap;
A diaphragm that supports the voice coil, and is attached to an inner circumferential surface of the outer yoke portion or an outer annular portion that extends toward the inner yoke portion and extends toward the inner yoke portion, and a tip opening of the inner yoke. A diaphragm having an inner portion disposed so as to face each other, and a cylindrical portion connected between a radially outer peripheral edge of the inner portion and a radially inner peripheral edge of the outer annular portion. An electroacoustic transducer is provided.

  In this electroacoustic transducer, since the inner part of the diaphragm is arranged so as to face the front end opening of the inner yoke part, even if the vibration at the inner part is large, The contact with the inner yoke portion is unlikely to occur, and accordingly, the diaphragm can be vibrated with a large amplitude to obtain a large sound pressure.

In particular,
The outer yoke portion of the yoke is longer in the axial direction than the inner yoke portion, and the permanent magnet is attached to the portion longer in the axial direction than the inner yoke portion of the outer yoke portion,
The outer annular portion of the diaphragm is positioned between the inner yoke portion and the outer yoke portion,
The cylindrical portion of the diaphragm extends in the axial direction from the radially inner peripheral edge of the outer annular portion of the diaphragm and is connected to the radially outer peripheral edge of the inner side of the diaphragm at a position exceeding the tip opening of the yoke. be able to.

  Since the outer annular portion of the diaphragm is set at the above position, the permanent magnet can be set close to the intermediate yoke portion, and the electroacoustic transducer can be made thin.

More specifically,
The voice coil can be fixed on the inner part of the diaphragm adjacent to the inner peripheral surface of the cylindrical part of the diaphragm.

  When the voice coil is fixed to the outer part of the diaphragm, when the diaphragm is vibrated, the vicinity of the connecting part between the outer part and the cylindrical part of the diaphragm and the connection between the cylindrical part and the inner part Whereas the deflection due to the vibration occurs in the two portions near the portion, the deflection of the diaphragm due to the vibration is mainly caused by the inner part of the diaphragm by setting the voice coil as described above. One near the portion where the voice coil is fixed. For this reason, generation of noise during vibration of the diaphragm is less likely to occur.

The voice coil has a planar shape having a pair of long sides that are opposed to each other with a gap when viewed from the axial direction, and a pair of short sides that connect both ends of the long side,
At least one permanent magnet is arranged on the outer side of each long side portion of the voice coil and is made of a soft permanent magnet and has a shape surrounding the voice coil. A ring-shaped magnet support having a side surface,
A rod-shaped permanent magnet can be fixed to the inner surface of the magnet support, and the outer surface of the magnet support can be fixed to the inner peripheral surface of the outer yoke portion.

  Here, the planar shape of the voice coil includes not only a rectangular shape but also an elliptical or elliptical shape. The magnet support can be made of a soft magnetic material or plastic. The magnet support may be ring-shaped or may include a pair of rod-shaped magnet support segments facing the long sides of the voice coil.

  Further, at least one permanent magnet has a rod-shaped additional permanent magnet disposed outside each short side portion of the voice coil and facing the short side portion, and the additional permanent magnet is an inner surface of the magnet support. It can be made to adhere to.

  Contrary to the above, a permanent magnet may be fixed to the outer peripheral surface of the magnet support, and the permanent magnet may be fixed to the inner peripheral surface of the outer yoke portion. In order to make sure that the permanent magnets are firmly fixed to the magnet support, the surface of the magnet support on which the permanent magnets are fixed can be L-shaped to increase the mutual contact surfaces.

  The inner side of the diaphragm can have a convex dome toward the tip opening. By providing the dome part, the rigidity of the inner part of the diaphragm can be increased, the area of the inner part can be increased, and the inner yoke part is cylindrical and has an opening at the tip. Therefore, when the inner portion vibrates, the contact between the dome portion and the inner yoke portion is unlikely to occur, and therefore, the diaphragm can be vibrated with a large amplitude and a large sound pressure can be obtained. .

  Further, the voice coil can be fixed on the diaphragm adjacent to the outer peripheral surface of the cylindrical portion of the diaphragm.

  Further, the voice coil has a planar shape having a pair of long side portions opposed to each other with a space therebetween when viewed from the axial direction, and a pair of short side portions connecting both ends of the long side portion. And the at least one permanent magnet is opposed to the long side portions on both sides of the short side portion from an intermediate portion located opposite to the short side portions of the voice coil outside the voice coil. A pair of U-shaped permanent magnets having a pair of extending portions extending in the direction, and the tips of the pair of U-shaped permanent magnets can face each other.

Hereinafter, an embodiment of an electroacoustic transducer according to the present invention will be described with reference to the accompanying drawings.
1 to 4 show a speaker as an electroacoustic transducer according to the present invention. The speaker has a flat oval shape as a whole so as to be suitable for a small information device such as a mobile phone.

  The speaker includes a yoke 1 formed by drawing a plate of a soft magnetic material such as permalloy or soft iron by drawing, a bottom plate 2 made of a nonmagnetic material, a permanent magnet 3, a diaphragm 4, and a voice coil 6.

  The yoke 1 and the bottom plate 2 form a casing of the speaker. The speaker is mounted on a mother board (not shown) of a small information device such as a mobile phone to which the speaker is attached by contacting the bottom plate 2, but the bottom plate 2 may be configured by a part of the mother board. In the illustrated example, the bottom plate 2 is provided with an opening 2a for releasing the back pressure when the diaphragm 4 vibrates and reducing the resistance of vibration.

  As shown in FIG. 1, the yoke 1 has an oval shape as a whole when viewed in the axial direction of the yoke. As shown in FIGS. 2 and 3, the yoke extends in the axial direction of the intermediate yoke portion (downward in FIG. 2) from the annular intermediate yoke portion 1a and the radially inner peripheral edge of the intermediate yoke portion 1a. A cylindrical inner yoke portion 1b and a cylindrical outer yoke having an inner peripheral surface that extends in the axial direction from the radially outer peripheral edge of the intermediate yoke portion 1a and forms a cylindrical space between the outer peripheral surface of the inner yoke portion. Part 1c. An oblong reinforcing plate 1d as seen in FIG. 1 is provided at the central portion in the axial direction of the inner yoke portion 1b. The reinforcing plate 1d has a plurality of sound emitting holes 7 along its length. Is provided.

  The permanent magnet 3 is fixed to the inner peripheral surface of a portion of the outer yoke portion 1c that extends in the axial direction relative to the inner yoke portion 1b, and has an oval ring shape. The permanent magnet 3 is magnetized in the radial direction of the yoke 1 (left-right direction as viewed in FIGS. 2 and 3), and forms a magnetic gap G between the outer peripheral surface of the inner yoke portion 1b. ing.

  The diaphragm 4 has an end portion fixed on the permanent magnet 3 via the spacer 5 at a position adjacent to the inner peripheral surface of the outer yoke portion 1c, and an outer annular portion 4a extending from the end portion toward the inner yoke portion 1b. An inner portion 4b arranged to face the opening 1e of the inner yoke 1b (the lower end in FIG. 1), a radially outer periphery of the inner portion 4b, and a radially inner periphery of the outer annular portion 4a And a cylindrical portion 4c connected to each other. In order to increase the rigidity of the diaphragm 4, the outer annular portion 4 a has a cross section convex upward as seen in FIG. 1, and the inner portion 4 b faces the tip opening 1 of the inner yoke portion 1 b. And has a convex dome.

  The voice coil 6 is adjacent to the outer peripheral surface of the cylindrical portion 4c of the diaphragm 4 and is fixed below the outer annular portion 4a, and is set so as to extend in the magnetic gap G in the axial direction.

FIG. 5 shows a modification of the yoke in the speaker.
The permalloy material desirable as the material of the yoke 1 is a difficult-to-work material, and it is not always easy to integrally form a complicated shape by plastic working. Therefore, in this modification, the cup-shaped body 101 having the intermediate yoke portion 1a and the cylindrical outer yoke portion 1c and the cylindrical body 102 having the inner yoke portion 1b are molded from separate plate materials, respectively. The yoke is joined by spot welding or the like. The yoke body 101 is provided with a sound emitting hole 7.

  FIG. 6 shows a speaker according to another embodiment of the present invention. In this speaker, unlike the speaker shown in FIGS. 1 to 4, the outer peripheral edge of the diaphragm 4 is sandwiched between the permanent magnet 3 and a step portion 1f provided on the inner peripheral surface of the outer yoke portion 1c. It is fixed. Incorporate an adhesive if necessary. With this structure, the spacer 5 can be omitted, the number of parts can be reduced, and the positioning accuracy of the diaphragm 4 can be improved. Further, the inner yoke portion 1b is not provided with the reinforcing portion 1d as shown in FIG. 2, and the hole of the inner yoke portion 1b is used as the sound emitting hole 7, thereby eliminating the need for processing the sound emitting hole 7. . Since the opening area as the sound emitting hole is large, there is an advantage that the acoustic resistance is small.

  FIG. 7 is a bottom view of a speaker according to another embodiment of the present invention, and the bottom plate 2 and the diaphragm 1 are removed in order to clarify the features thereof. In this loudspeaker, the voice coil 6 as a whole has a pair of long side portions 6a arranged opposite to each other with a space therebetween, and a pair of short side portions 6b connecting both ends of the long side portion. It has an elongated shape. Further, in this speaker, the permanent magnet 3 is disposed on the outside of each long side portion 6a of the voice coil 6, and a pair of rod-like permanent magnets 3a facing the long side portion 6a and the outside of each short side portion 6b. And a pair of rod-like permanent magnets 3b facing the short side 6b. By using such a bar-shaped magnet as the permanent magnet, the manufacturing cost of the speaker is reduced and substantially the same as that of the speaker using one ring-shaped permanent magnet shown in FIGS. A speaker having the following characteristics can be realized. There is also an advantage that it is possible to quickly respond to a request for a design change in the size or shape of the speaker.

  FIG. 8 is a view similar to FIG. 7 showing a speaker according to still another embodiment of the present invention. In this speaker, narrow bar-shaped permanent magnets 3a are respectively arranged opposite to the long side portion 6a of the voice coil 6, and the outer yoke portion 1c of the outer yoke portion 1c is interposed via a magnet support 8 made of a bar-shaped soft magnetic member. It is fixed to the inner peripheral surface.

  Even if the inner and outer positions of the permanent magnet 3 and the magnet support 8 are reversed from those in FIG. 8, a speaker having the same characteristics can be obtained. In this embodiment, since there is no magnet material etc. outside the short side 6b of the voice coil 6, the longitudinal size of the speaker can be reduced. Alternatively, the length of the long side portion 6a of the voice coil can be increased with respect to the length of the speaker.

FIG. 9 is a view similar to FIG. 7 showing a speaker according to another embodiment.
In this speaker, two rod-like permanent magnets 3 are arranged on the inner peripheral surface of the outer yoke portion 1c, and a magnet support 8 made of a ring-shaped soft magnetic member is fixed inside the permanent magnets 3. By doing so, an annular magnetic gap G can be formed between the inner yoke portion 1b and the magnet support 8 even though the number of permanent magnets 3 is two, and the voice coil 6 can be made efficient. It can be driven well.

  FIG. 10 is a view similar to FIG. 7 showing a speaker according to still another embodiment. In this speaker, a “C” -shaped permanent magnet 3 is fixed to the inner peripheral surface of the inner yoke portion 1b. By doing in this way, the characteristic equivalent to the speaker using the oval permanent magnet 3 shown in FIGS. 1 to 4 can be obtained.

  FIG. 11 is a graph showing the results of measuring the acoustic characteristics of a speaker having a structure similar to the speaker shown in FIG. The input was a sine wave of 0.179 Vrms (100 Hz to 10 kHz), and the sound pressure output was recorded. As shown in the figure, fh (resonance point at which the sound pressure decreases at a high frequency) is slightly low, but at a frequency lower than that, a sound pressure level equivalent to that of a conventional speaker can be achieved even though the speaker is thin. ing.

  FIG. 12 shows a speaker according to still another embodiment of the present invention. In this embodiment, the ring-shaped permanent magnet 3 is fixed on the outer peripheral surface of the inner yoke portion 1b, and the cylindrical portion 4c of the diaphragm 4 is lowered in height (the height is the height of the voice coil). This is used only for positioning the voice coil 6 and disposed outside the magnetic gap, and the yoke 1 and the permanent magnet 3 are both disposed on one side of the diaphragm 4 (upper side in FIG. 12). This is different from the above-described embodiment.

  Also in this embodiment, the positioning of the voice coil can be facilitated, and the speaker can be made thinner and smaller and the number of parts can be minimized.

FIG. 13 is a view similar to FIG. 2 showing a speaker according to another embodiment of the present invention.
In this speaker, the yoke 1 has the same overall configuration as the speaker of FIG. 6, but the voice coil 6 is disposed adjacent to the inner peripheral surface of the cylindrical portion 4 </ b> C of the diaphragm 4, and the inner portion of the diaphragm 4 is arranged. It is fixed on 4b. Although not shown in FIG. 13, the permanent magnet 3 is a pair of rod-like permanent magnets arranged so as to face the long side portions outside the long side portions 6 a of the voice coil, The pair of permanent magnets is fixed to the inner peripheral surface of a ring-shaped magnet support 8 (as shown in FIG. 9) disposed on the outer periphery of the pair of permanent magnets. By assembling the permanent magnets to the magnet support 8 and incorporating them as a unit, the assembly work can be facilitated. The magnet support 8 has an L-shaped cross section as shown in FIG. 17 so that the contact surface with the permanent magnet can be increased, and the permanent magnet can be stably fixed in a stable state. . As for the magnet support, the embodiment using the soft magnetic member has been described, but a plastic member can also be used. In the figure, reference numerals 12 and 13 denote ring-shaped members for fixing the outer peripheral edge of the diaphragm 4. When an impact such as a drop is applied to the electroacoustic transducer, the permanent magnets drop off to the yoke side. Also work not to. The link-like member 13 is provided with an inclined surface so as not to hinder the vibration of the diaphragm. Reference numeral 14 denotes a protector attached to the outer peripheral surface of the outer yoke portion.

These are the top views of the speaker as 1st Embodiment as an electroacoustic transducer which concerns on this invention. FIG. 2 is a cross-sectional view taken along the line II-II in FIG. FIG. 3 is a sectional view taken along line III-III in FIG. 1. FIG. 2 is an enlarged cross-sectional view of a diaphragm and related members of the speaker of FIG. 1. These are sectional drawings which show the modification of the yoke of the speaker of FIG. These are sectional drawings similar to FIG. 2 of the speaker which concerns on the 2nd Embodiment of this invention. These are bottom views which show the member which comprises the magnetic circuit of the speaker based on the 3rd Embodiment of this invention, and in order to clarify the principal part, the baseplate and diaphragm of the said speaker are abbreviate | omitted and shown. These are figures similar to FIG. 7 which shows the member which comprises the magnetic circuit of the speaker which concerns on the 4th Embodiment of this invention. These are figures similar to FIG. 7 which shows the member which comprises the magnetic circuit of the speaker which concerns on the 5th Embodiment of this invention. These are figures similar to FIG. 7 which shows the member which comprises the magnetic circuit of the speaker which concerns on the 6th Embodiment of this invention. These are the acoustic characteristic figures of the speaker which concerns on this invention. These are figures similar to FIG. 2 which shows the speaker which concerns on the 7th Embodiment of this invention. These are figures similar to FIG. 2 which shows the speaker which concerns on the 8th Embodiment of this invention. These are sectional drawings of the conventional speaker. These are sectional views of other conventional types of speakers. These are sectional drawings of the conventional another type of speaker. These are sectional drawings which show the modification of a magnet support body.

Claims (16)

An annular intermediate yoke portion, a cylindrical inner yoke portion extending in the axial direction of the intermediate yoke portion from the radially inner periphery of the intermediate yoke portion, and extending in the axial direction from the radially outer periphery of the intermediate yoke portion A yoke having a cylindrical outer yoke portion having an inner peripheral surface forming a cylindrical space with the outer peripheral surface of the inner yoke portion;
At least one permanent magnet provided so as to surround the inner yoke portion at a position away from the intermediate yoke portion in the axial direction, and is magnetized in the radial direction of the yoke so that the inner yoke portion At least one permanent magnet forming a magnetic gap with the outer peripheral surface;
A cylindrical voice coil inserted in the axial direction in the cylindrical space and extending in the axial direction in the magnetic gap;
A diaphragm that supports the voice coil, and is attached to an inner circumferential surface of the outer yoke portion or an outer annular portion that extends toward the inner yoke portion and extends toward the inner yoke portion, and a tip opening of the inner yoke. An electroacoustic having an inner portion disposed so as to oppose, and a cylindrical portion connected between a radially outer peripheral edge of the inner portion and a radially inner peripheral edge of the outer annular portion converter. The outer yoke portion of the yoke is longer in the axial direction than the inner yoke portion, and the permanent magnet is attached to a portion of the outer yoke portion that is longer in the axial direction than the inner yoke portion,
The outer annular portion of the diaphragm is positioned between the inner yoke portion and the outer yoke portion;
The cylindrical portion of the diaphragm extends in the axial direction from the radially inner periphery of the outer annular portion of the diaphragm and extends to the radially outer periphery of the inner portion of the diaphragm at a position exceeding the tip opening of the yoke. The electroacoustic transducer according to claim 1 connected.   The electroacoustic transducer according to claim 2, wherein the voice coil is fixed on the inner portion of the diaphragm adjacent to the inner peripheral surface of the cylindrical portion of the diaphragm. The voice coil has a planar shape having a pair of long sides opposed to each other as viewed from the axial direction and a pair of short sides connecting both ends of the long sides. And
The at least one permanent magnet is disposed outside each long side portion of the voice coil and is arranged to surround the voice coil, and has an inner surface and an outer surface. A magnet support,
The rod-shaped permanent magnet is fixed to the inner side surface of the magnet support, and the outer surface of the magnet support is fixed to the inner peripheral surface of the outer yoke portion. Electroacoustic transducer.   The at least one permanent magnet further includes a rod-shaped additional permanent magnet disposed outside each short side portion of the voice coil and opposed to the short side portion, and the additional permanent magnet is the magnet support. The electroacoustic transducer according to claim 4, wherein the electroacoustic transducer is fixed to the inner surface of the electroacoustic transducer.   The electroacoustic transducer according to claim 1, wherein the inner portion of the diaphragm has a convex dome portion toward the tip opening.   The electroacoustic transducer according to claim 1, wherein the voice coil is fixed on the diaphragm adjacent to an outer peripheral surface of the cylindrical portion of the diaphragm.   The voice coil has a planar shape having a pair of long sides opposed to each other as viewed from the axial direction and a pair of short sides connecting both ends of the long sides. The at least one permanent magnet is arranged so as to surround the voice coil, and the magnet is provided at a position corresponding to each of the long sides of the voice coil and an annular magnet support having an inner peripheral surface and an outer peripheral surface. The electroacoustic transducer according to claim 1, further comprising a permanent magnet fixed between an outer peripheral surface of the support and an inner peripheral surface of the outer yoke portion.   The voice coil has a planar shape having a pair of long sides opposed to each other as viewed from the axial direction and a pair of short sides connecting both ends of the long sides. The at least one permanent magnet is opposed to the long side portions on both sides of the short side portion from an intermediate portion located opposite to the short side portions of the voice coil outside the voice coil. A pair of U-shaped permanent magnets having a pair of extending portions, and the ends of the pair of extending portions of the pair of U-shaped permanent magnets are opposed to each other. The electroacoustic transducer according to claim 1.   The electroacoustic transducer according to claim 4 or 8, wherein a cross section of the magnet support is L-shaped, and the rod-shaped permanent magnet is supported by the magnet support so as to engage with the L-shape.   2. The electroacoustic transducer according to claim 1, further comprising a bottom plate attached to an end of the outer yoke portion away from the intermediate yoke portion and having an opening.   The electroacoustic transducer according to claim 4, wherein the magnet support is made of a soft magnetic material.   The electroacoustic transducer according to claim 4, wherein the magnet support is made of plastic.   The electroacoustic transducer according to claim 4, wherein the magnet support has a ring shape.   5. The electroacoustic according to claim 4, wherein the magnet support includes a pair of rod-shaped magnet supports that are disposed outside the long sides of the voice coil and to which a rod-shaped permanent magnet facing the long sides is fixed. converter. An annular intermediate yoke portion, a cylindrical inner yoke portion extending in the axial direction of the intermediate yoke portion from the radially inner periphery of the intermediate yoke portion, and extending in the axial direction from the radially outer periphery of the intermediate yoke portion A yoke having a cylindrical outer yoke portion having an inner peripheral surface forming a cylindrical space with the outer peripheral surface of the inner yoke portion;
At least one permanent magnet attached to the outer peripheral surface of the inner yoke portion at a position away from the intermediate yoke portion in the axial direction, magnetized in the radial direction of the yoke, and At least one permanent magnet forming a magnetic gap with the inner peripheral surface;
A cylindrical voice coil inserted in the cylindrical space in the axial direction and extending in the axial direction in the magnetic gap;
An annular coil support portion that is on the outer side in the axial direction of the annular space and supports the voice coil, a tubular portion raised from the radially inner periphery of the coil support portion toward the annular space, and the tubular portion An electroacoustic transducer having a diaphragm having an inner portion disposed so as to close the tip opening of the inner yoke portion and to face the tip opening portion of the inner yoke portion.

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