JP3192372B2 - Thin electromagnetic transducer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic transducer having a thin structure, and more particularly, to an electromagnetic transducer having an integral structure and multi-polarized magnets, and disposed so as to face each other with a space therebetween. The present invention relates to a thin electromagnetic transducer having a vibrating film having a meandering coil pattern and a buffer member interposed between the permanent magnet and the vibrating film. This thin electromagnetic transducer is useful for, for example, a flat speaker, a headphone, or a microphone.

[0002]

2. Description of the Related Art An electromagnetic transducer having a flat plate structure combining a permanent magnet and a vibrating membrane is conventionally known. This type of electromagnetic converter generally includes a permanent magnet structure, a vibrating film arranged to face the permanent magnet, and a support member that fixes the vibrating film to the permanent magnet structure at a peripheral portion. are doing.

Here, a permanent magnet structure used in a conventional electromagnetic converter of this type is composed of a large number of rod-shaped permanent magnets that have been subjected to double-sided double-pole magnetization (magnetization in the vertical direction of the structure). The magnetic poles are arranged in parallel and alternately different from each other, and are fixedly connected to each other by a non-magnetic structural member. As the vibrating membrane, a thin resin film having a coil formed of a meandering conductive wire pattern formed on the surface or inside thereof is used. Then, the vibrating membrane is combined with the permanent magnet structure in such a positional relationship that the linear portions of the meandering conductive wire pattern correspond to just the middle portions of the bar-shaped permanent magnets arranged in parallel. Actually, the configuration is such that the diaphragm is fixed to the permanent magnet structure via a spacer at the periphery of the diaphragm.

Magnetic lines of force pass between the magnetic poles of adjacent bar-shaped permanent magnets, and a magnetic field is generated that crosses the linear portion of the conductive pattern of the vibrating membrane. Then, when the coil of the diaphragm is energized,
An electromagnetic force is generated according to Fleming's left-hand rule, and the diaphragm is displaced in the thickness direction. According to this principle, a vibration corresponding to the drive current to the coil is generated, and a sound wave is generated. The sound waves are radiated outside through the space between the bar-shaped permanent magnets.

[0005]

In order to improve the performance of the conventional permanent magnet structure, it is desirable to arrange the elongated rod-shaped permanent magnets as densely as possible. However, if the permanent magnet to be used is a sintered magnet (ferrite magnet), for example, it becomes more difficult to manufacture with high precision as the shape is elongated (warping or other deformation occurs during firing), and It becomes difficult to have sufficient mechanical strength. Further, since a large magnetic force acts between the bar-shaped permanent magnets, it is very difficult to accurately assemble the elongated bar-shaped permanent magnets close to each other. Also, since the bar-shaped permanent magnets are separated from each other, magnetic poles appear not only on both sides in the thickness direction but also on the edges and part of the side surfaces of the upper and lower surfaces and the side surfaces. The magnetic flux flies in the direction (linearly in the gap portion), and the number of magnetic force lines interlinking with the coil (linear portion of the conductor pattern) of the essential diaphragm is reduced, which also has a problem that the driving efficiency is deteriorated. .

As a result, many rod-shaped permanent magnets are
It has to be arranged with a wide space between each other, which requires a wide space between the permanent magnet structure and the diaphragm.
At that point, the conversion efficiency is deteriorated, and the entire electromagnetic converter becomes thick.

Further, in the prior art, since a structure in which the vibrating film is firmly pressed by the spacer at the peripheral portion is adopted, a fulcrum is generated at the peripheral portion, resulting in a so-called "becove" vibration, and the drive current is reduced. However, there is a problem that it is difficult to generate a reproduced sound that is faithful to the above, and the amplitude cannot be increased.

An object of the present invention is to solve the above-mentioned drawbacks of the prior art and to provide an electromagnetic converter which is easy to manufacture and thin. Another object of the present invention is to suppress the generation of abnormal noise (noise) due to resonance in the peripheral portion of the diaphragm, so that the diaphragm can freely vibrate locally and entirely.
An object of the present invention is to provide a thin electromagnetic transducer which is designed so that a large vibration amplitude can be obtained and which outputs a sound faithful to a drive current.

[0009]

According to the present invention, there is provided a permanent magnet plate, and a vibrating membrane disposed so as to face the permanent magnet plate.
A thin electromagnetic transducer comprising a buffer member interposed between the vibration film and the permanent magnet plate, and a support member for regulating a relative position of the vibration film with respect to the permanent magnet plate. The permanent magnet plate has a band-shaped N
A multi-pole magnetized pattern in the form of parallel stripes in which poles and S poles appear alternately is formed, and has an integral structure in which a large number of exhaust through holes are arranged at positions of a neutral zone in the magnetized pattern. Further, the vibrating membrane has a structure in which a coil made of a meandering (reciprocating) shape conductor pattern is printed and wired on a thin and flexible resin film, and the conductor pattern has a straight line portion corresponding to a neutral zone of the permanent magnet plate. The supporting member is not fixed at the peripheral portion and the displacement in the in-plane direction is regulated by the support member, but is supported so as to be freely displaceable in the thickness direction. Further, the cushioning member has a structure in which a plurality of sheets having the same size as the vibrating membrane are stacked, being soft and breathable, and has a gap between the sheet and the permanent magnet plate or the vibrating membrane. It is arranged as follows.

The permanent magnet plate and the cushioning member may be provided only on one side of the diaphragm, but they are respectively disposed on both sides of the diaphragm so as to sandwich the diaphragm. It is preferable that the neutral zones are fixed at intervals so that the neutral zones coincide with each other and the same poles face each other. In that case, the structure need not always be symmetric with respect to the vibrating membrane. Therefore, both permanent magnet plates are
The same material and the same shape may be used, or different materials and different shapes (thicknesses) may be used. The permanent magnet plate may be, for example, a sintered magnet, a plastic magnet, a metal magnet, or the like.

The meandering (reciprocating) conductor pattern serving as a coil may be formed on only one side of the resin film,
It may be formed on both sides. Also, one conductor pattern may be formed one by one corresponding to the center line of each neutral zone of the permanent magnet plate, or a plurality of conductor patterns may be provided. When a plurality of conductor patterns are arranged side by side in one neutral zone, it is necessary to distribute the conductor patterns so as to be completely symmetric with respect to the center line. In any case, it is necessary to maintain a parallel positional relationship between the center line and the conductor pattern.

It is preferable that a high-permeability magnetic plate (for example, an iron plate or a nickel-iron alloy plate) for preventing magnetic flux leakage be adhered to the surface of the permanent magnet plate opposite to the surface facing the diaphragm. In this case, it is necessary to form a similar exhaust through-hole at the same position as the exhaust through-hole formed in the permanent magnet plate, so that sound waves generated inside are radiated smoothly to the outside.

[0013]

BEST MODE FOR CARRYING OUT THE INVENTION Belt-shaped N poles and S poles alternately appear as parallel stripes on the surface of a permanent magnet plate due to magnetization.
The magnetic field component (absolute value) perpendicular to the surface of the permanent magnet plate is largest near the N pole and S pole, and smallest near the boundary between the N pole and S pole. This is because the component of the magnetizing magnetic field is defined as viewed in the vertical direction. Since there is no magnetic field of the vertical component near the boundary between the N pole and the S pole, this region is called a neutral zone. On the other hand, the horizontal component of the magnetic field (the component parallel to the surface of the permanent magnet plate) is the smallest near the N and S poles and the largest near the boundary between the N and S poles (neutral zone). This means
This is apparent from the fact that the magnetic field lines pass from the adjacent N pole to the S pole in an arc shape. The magnetic field component that contributes to vibrating the vibrating membrane in the thickness direction is not a vertical component but a horizontal component (Fleming's left-hand rule). The horizontal component of the magnetic field works most effectively not in the vicinity of each pole but in the position of the neutral zone as described above. Therefore, if the linear portion of the conductor pattern is provided at a position corresponding to the neutral zone, the magnetic force lines pass in a direction crossing the linear portion of the conductor pattern in the plane of the diaphragm. Therefore, in such a configuration, the coil (conductor pattern)
When a driving current is supplied to the device, an electromagnetic force is generated most efficiently by the interaction between the current and the magnetic field, and the vibrating film vibrates in the thickness direction. The sound waves generated thereby are emitted to the outside through the exhaust through holes formed in the permanent magnet plate (and the high-permeability magnetic plate). This is the principle of sound generation of the electromagnetic converter according to the present invention, and the principle of the electromagnetic conversion itself is the same as that of a conventional electromagnetic converter of this type.

One of the features of the present invention is that a parallel-striped multipolar magnetized pattern is formed on almost the entire surface of the surface, and a large number of exhaust through holes are arranged at positions of a neutral zone in the magnetized pattern. The point is that a permanent magnet plate having an integral continuous structure (a structure that is not a combination of individual magnets) is used as a magnetic drive source. Another feature of the present invention is that the vibrating membrane is not fixed at the peripheral portion and is supported so as to be freely displaceable only in the thickness direction. Still another feature of the present invention is that a cushioning member having a structure in which a plurality of soft and air permeable sheets are stacked is provided so as to have a gap between the permanent magnet plate and the vibration film.

Whether the permanent magnet plate is a sintered magnet, a non-sintered magnet, a flexible magnet, a solid structure magnet, or a material (ferrite magnet, rare earth magnet, neodymium-iron-boron magnet) Etc.), characteristics, etc., thickness and shape (square, rectangular, circular, oval, etc.) and structure (whether it is a single permanent magnet plate or a structure in which multiple permanent magnet plates are bonded together, etc.) Is optional and
It is selected as appropriate according to the characteristics, cost, manufacturing necessity, use condition, etc. due to design problems. The size of the magnetic pole (magnitude of magnetization), the pole pitch, and the like are also arbitrary. There is a configuration in which the permanent magnet plate is disposed on only one side of the diaphragm, and a configuration in which the permanent magnet plates are disposed on both sides. Conversely, there is also a configuration in which vibration films are arranged on both sides of the permanent magnet plate so as to sandwich the permanent magnet plate. The conductive wire pattern may be provided on one side of the resin film of the vibration film, or may be provided on both sides. In some cases, the vibrating membrane is composed of a plurality of resin films. The conductor pattern is arranged so as to correspond to the neutral zone in the permanent magnet plate, and may be arranged one by one in each neutral zone (one-turn configuration) or may be arranged in plurals (multi-turn configuration). .

[0016]

FIG. 1 is an explanatory view showing an embodiment of a flat speaker which is a kind of a thin electromagnetic transducer according to the present invention. In the figure, A shows the entire configuration, and B shows the main part in an enlarged manner (however, the buffer member is not shown). The flat loudspeaker includes a permanent magnet plate 10, a vibration film 12 arranged to face the permanent magnet plate 10, a buffer member 14 interposed between the vibration film 12 and the permanent magnet plate 10, A support member 16 is provided for regulating the position of the vibration film 12 with respect to the permanent magnet plate 10. The permanent magnet plate 10 and the buffer member 14 are symmetrically arranged on both surfaces of the vibration film 12 so that the same type sandwiches the vibration film 12.

As shown in FIG. 2, the permanent magnet plate 10 is, for example, a square flat plate made of a sintered ferrite magnet, and has a strip-shaped N pole and S
A multi-pole magnetized pattern in the form of parallel stripes in which the poles alternately appear, and a neutral zone nz of the magnetized pattern
And an integral structure in which a large number of exhaust through holes 18 are arranged at the position. The exhaust through-holes 18 are formed at a constant pitch along the neutral zone nz, and are arranged in a staggered pattern by being shifted by half a pitch from the exhaust through-holes 18 of the adjacent neutral zone nz. They may be arranged in a square lattice shape so that they are located at the same position in adjacent neutral zones.However, if the magnetization pitch is small, the hole interval is small, so that the mechanical strength of the permanent magnet plate may be reduced and the permanent magnet plate may be cracked. It is more preferable to form a staggered lattice as described above. The shape of the exhaust through-hole 18 may be circular or oval, but the dimensions and shape are selected appropriately and they are precisely arranged.
If it is too small, the sound wave generated inside will not be sufficiently emitted to the outside, and if it is too large, the volume of the permanent magnet plate 10 will be reduced, the working magnetic field will be weakened, and the mechanical strength will also be reduced.

Such a permanent magnet plate 10 can be easily manufactured, for example, by laminating and integrating unsintered multi-hole magnet sheets and sintering them. For multipolar magnetization, use a magnetizing jig with a structure in which electric wires are embedded in each narrow groove of a magnetizing yoke in which a number of narrow grooves are engraved in parallel, and closely contact the magnetizing jig with the permanent magnet plate By supplying a pulse current, a multi-pole magnetized pattern in the form of parallel stripes in which magnetic poles appear in a band shape on the surface of the permanent magnet plate can be formed. In this case, a portion facing the narrow groove is a neutral zone.

As shown in FIG. 2, the vibrating membrane 12 is, for example, a biaxially stretched polyethylene terephthalate film having a thickness of about 30 μm or less (trade name: Mylar).
Alternatively, the coil 22 having a meandering conductive pattern is printed on a thin and flexible resin film 20 such as an aromatic polyimide film (trade name: Kapton). The coil 22 is located at a position where its linear portion corresponds to the neutral zone nz of the permanent magnet plate 10,
The support member 16 is provided in parallel with the neutral zone and is not completely fixed at the peripheral portion. The displacement in the in-plane direction is regulated by the support member 16, but is supported so as to be freely displaceable in the thickness direction.

Returning to FIG. 1, the cushioning member 14 is soft and air-permeable (sound waves can pass freely).
A plurality of sheets 24 having substantially the same size as the vibrating membrane 12 are stacked, and the sheet 24 and the permanent magnet plate 10
Alternatively, it is provided so as to have an appropriate gap with the vibration film 12. As the sheet 24, for example, a thin nonwoven fabric is preferable, and the sheet 24 is interposed in a state where about three sheets (2 to 5 sheets) are stacked. Here, the “overlapping state” means a state in which the members are not overlapped and adhered, but are simply overlapped in a sparse state so that they can be individually vibrated (displaced).
The thickness and material of the non-woven fabric and the number of sheets to be overlapped vary depending on design conditions and the like. The cushioning member 14 holds the vibration membrane 12 during operation.
Other than sound waves that are faithful to the sound source, such as preventing abnormal sound (noise other than normal vibration sound) from colliding with the permanent magnet plate 10 and preventing the occurrence of split vibration of the diaphragm itself (preventing chattering sound). And has the function of appropriately controlling the occurrence of. FIG. 1
In (A), the cushioning member 14 made of a nonwoven fabric is drawn by a broken line, but sheets of substantially the same size as the diaphragm are stacked as described above.

The two permanent magnet plates 10 are held by a support member 16. The support member 16 is formed by a combination of a support rod 26 provided at each of the four corners and a nut 28 screwed at both ends thereof. The two permanent magnet plates 10 are firmly mechanically fixed by the supporting members 16 so as to maintain a constant positional relationship with each other. Vibrating membrane 1 located between
2 has four holes 13 (see FIG. 2) at the four corners.
By virtue of the support rod 26 being inserted into the vibrating membrane 12 and being fitted with a precision of the order of microns, the position of the vibrating membrane 12 is regulated in the in-plane direction, but it can be freely displaced in the thickness direction. If the vibrating membrane 12 is displaced in the lateral direction and deviates from the magnetization pattern of the permanent magnet plate 10, it is difficult to efficiently generate sound waves. Therefore, the coil linear part is supported so as not to deviate from the neutral zone. Similarly, the nonwoven fabric serving as the cushioning member may have a configuration in which a hole is provided at a corner and the support bar 26 is inserted and supported. In any case, as in the case of the vibrating membrane, it is necessary to be able to freely displace in the thickness direction.

Further, in this embodiment, a high-permeability magnetic plate 30 for preventing magnetic flux leakage is adhered to the surface of the permanent magnet plate 10 opposite to the surface facing the vibrating membrane. An exhaust through hole 32 similar to the exhaust through hole 18 formed in the plate 10 is formed at the same position so as to communicate with each other. As the high magnetic permeability magnetic plate 30, for example, an iron plate or a nickel-iron alloy (permalloy) plate is suitable.

In the above-described configuration, strip-shaped N-poles and S-poles alternately appear on the surface of the permanent magnet plate 10 (the surface facing the vibration film) to form a parallel stripe magnetized pattern. Since the linear portion of the coil 22 of the diaphragm 12 is provided at a position corresponding to the neutral zone (boundary line between the north pole and the south pole), the linear portion of the coil 22 crosses the plane of the diaphragm 12 in the plane of the diaphragm 12. The lines of magnetic force pass in any direction (an example of the lines of magnetic force is indicated by an arrow in FIG. 1B). Therefore, when a drive current is supplied to the coil 22, an interaction between the current and the magnetic field generates an electromagnetic force in the thickness direction, and the vibrating membrane 12 vibrates.
Sound waves generated by this vibration are applied to the exhaust through holes 18, 32 formed in the permanent magnet plate 10 and the high-permeability magnetic plate 30.
To be released to the outside.

In the electromagnetic transducer according to the present invention, it is considered that the sound waves are respectively generated from the local portions of the vibrating membrane 12 (the minute regions in the linear portion of the coil 22). That is, the vibration film 12
The periphery (edge) is not completely fixed,
Since the coil 22 is in a free state in which it can be displaced in the thickness direction, when a driving current flows through the coil 22, the vibrating membrane 1 is subjected to electromagnetic force according to Fleming's left-hand rule at that portion.
2 will locally vibrate freely. The resultant vibration obtained by combining the local vibrations reaches the ear of the listener and is recognized as a sound. Supporting the peripheral part in a free state prevents such local vibrations from being hindered even in the vicinity of the periphery, performs faithful sound conversion, and increases the sound wave generation efficiency as a whole device That's why.

In the permanent magnet plate 10, magnetic lines of force are generated from an arbitrary north pole on the surface to an adjacent south pole. As described above, the vertical component of the magnetic field is largest near the north pole and south pole, but is smallest near the boundary between the north pole and south pole. On the other hand, the horizontal component of the magnetic field is smallest near the north pole and south pole, and largest near the boundary between the north pole and south pole. In the case of one permanent magnet plate, the lines of magnetic force are generated substantially concentrically. However, in the case of the above embodiment in which two permanent magnet plates are arranged to face each other, the two permanent magnet plates face each other so that the same poles face each other (N pole and N pole face each other, and S pole and S pole face each other). Therefore, as shown in FIG. 1B, the magnetic lines of force from the N pole to the S pole of one permanent magnet plate and the N lines of the other permanent magnet plate
Magnetic lines of force from the pole to the S pole are pressed against each other and deformed so that components in the horizontal direction (direction passing through the plane of the diaphragm 12) are balanced and increased at the center. Since this horizontal component contributes to the generation of sound waves, such a facing arrangement of the permanent magnet plates is particularly preferable when the coil is configured with a plurality of turns (when a plurality of conductive wire patterns are passed through one neutral zone). In addition, it is preferable because the conductive pattern area can be increased. Of course, the electromagnetic conversion efficiency also increases.

The conductor pattern serving as a coil may be a simple one-turn configuration as shown in FIG. 2 or a plural-turn configuration. FIG. 3 shows an example of two turns. A coil 22 is formed on the surface of the resin film 20 in which a conductor pattern is provided two by two in parallel. In the case of a multi-turn configuration, the neutral zones are arranged as close as possible to the center line of the neutral zone so as to be symmetrical. Coil 22 and permanent magnet plate 1 for two turns
FIG. 4 shows the relationship with the 0 magnetic pole. By making such a relationship, the vibration caused by the component of the force parallel to the plane, which occurs in the conductor pattern at a position deviated from the center line of the neutral zone, is canceled, and the vibrating membrane vibrates in the direction perpendicular to the plane as efficiently as possible Can be done.

As shown in FIG. 5A, the vibrating membrane may have a configuration in which the coil 22 is formed on one side of the resin film 20 or a configuration in which the coil 22 is formed on both sides of the resin film 20 (B in FIG. 5). reference). In some cases, as shown in FIG.
It is also possible to have a configuration in which a plurality of sheets are stacked and arranged by folding back. However, when superposing resin films with coils formed on both sides, insert another insulating film between them,
It is necessary to take measures such as applying insulation treatment to the coil surface.

FIG. 6 is an explanatory view showing another embodiment of the thin electromagnetic transducer according to the present invention. The embodiment shown in FIG.
It is a single-sided drive type of permanent magnet plate. On one side (lower side in the figure) of the vibrating membrane 12, a cushioning member 1 made of a plurality of nonwoven fabrics
4, a permanent magnet plate 10 is arranged on the other side, and a multi-hole holding plate 60 is arranged on the opposite side (the upper side in the figure) via a buffer member 14 made of a plurality of nonwoven fabrics, and the four corners are fixed by the support member 16. . In FIG. 6, for the sake of simplicity of the drawing, most of the buffer member 14 is omitted, but is actually substantially the same size as the diaphragm. Here, it is needless to say that the diaphragm 12 and the cushioning member 14 are not fixed around, and can be freely displaced in the vertical direction as a whole. Although not shown, a high-permeability magnetic plate is preferably provided on the lower surface side of the permanent magnet plate 10.

The present invention has various other applications. For example, when performing multi-polar magnetization on both sides of a permanent magnet plate,
As shown in FIG. 6B, a configuration in which the vibration films 12 are arranged on both sides of the permanent magnet plate 70 is also possible. That is, the buffer members 14 are arranged between the permanent magnet plate 70 and the vibration film 12 and between the vibration film 12 and the multi-hole pressing plate 60, respectively, and are fixed by the support members 16 at the corners. The method of fixing is the same as in each of the above embodiments.
The holding plate 60 is fixed, but the diaphragm 12 and the cushioning member 14 can be freely displaced in the thickness direction. Further, as shown in FIG. 6C, instead of this multi-hole holding plate,
It is also possible to adopt a configuration in which another permanent magnet plate 10 is provided.

The configuration shown in FIG. 6A requires only one permanent magnet plate, so that the sound pressure generated is small but simple, and it has the advantage of being light and thin. In the configuration of FIG. 6B, both diaphragms can be driven simultaneously. In FIG. 6C,
Although it is slightly thicker, the generated sound pressure can be increased.

As the permanent magnet plate used in the present invention, any permanent magnet plate can be used in addition to the sintered ferrite magnet described in the above embodiment. For example, a rare-earth permanent magnet, a neodymium-iron-boron (Nd-Fe-B) -based permanent magnet, or another metal-based magnet may be used. A sintered or solid permanent magnet may be used, or a plastic magnet hardened with resin may be used. In the configuration where a plurality of permanent magnet plates are arranged,
Different types of permanent magnet plates may be combined. For example, a configuration in which a sintered magnet is used for the main part and a plastic magnet is used for the sub part is also possible. Further, one permanent magnet plate may be configured by bonding a plurality of types of different permanent magnet plates.

The shape of the permanent magnet plate, in other words, the shape of the electromagnetic transducer may be a square or rectangular structure, or a circular or elliptical shape. Of course, any other shape may be used. Since it is thin, not only a flat plate shape but also an arbitrary curved surface shape (for example, a swollen curved surface shape or a bent corrugated surface shape) can be used. The overall thickness is appropriately determined according to the structure, the state of use, the required performance, and the like. The size of each pole (magnitude of magnetization) and the pole pitch in the strip-shaped parallel magnetized pattern may also be appropriately determined according to the usage state, required performance, and the like.

As described above, the vibration film may have a single structure or a structure in which a plurality of vibration films are stacked. Usually, a flexible copper-clad printed film is photo-etched to produce a vibrating membrane having a desired coil pattern. The coil integrated with the resin sheet by such a printed wiring technique may have a single-turn configuration or a multiple-turn configuration. Further, a configuration in which the coils are formed on both upper and lower surfaces of the resin sheet may be employed. In this case, it is possible to connect the conductive patterns on the upper and lower surfaces by a technique such as a through hole. The cross-sectional shape, material, length, and the like of the conductor pattern serving as a coil are determined and determined from the design impedance of the speaker and the like.

[0034]

According to the present invention, since the multi-pole magnetized permanent magnet plate having the integral structure as described above is used, it can be manufactured easily and with high accuracy, and can have sufficient mechanical strength. Even a fine magnetized pattern can be formed with high precision.
Further, since the magnetic poles appear only on the surface facing the diaphragm, the lines of magnetic force hardly pass in unnecessary directions, and the number of lines of magnetic force interlinking with the coils of the diaphragm of interest is increased, and the driving efficiency is improved. Also,
Since the magnetization pattern can be formed densely, the distance between the permanent magnet structure and the vibrating membrane can be reduced, and in that respect, the conversion efficiency can be improved and the entire electromagnetic converter can be made thinner.

In the present invention, since the vibrating membrane is supported so that it can be freely displaced in the thickness direction at the peripheral portion, there is no fulcrum at the peripheral portion, a reproduced sound faithful to the drive current is generated, and the amplitude is increased. There is an advantage that can be increased. Since a buffer member made of nonwoven fabric is interposed between the vibrating membrane and the permanent magnet, the vibrating membrane does not collide with the permanent magnet and prevents unnecessary noise (such as chattering noise) from being generated. it can.

[Brief description of the drawings]

FIG. 1 is an explanatory view showing one embodiment of an electromagnetic converter according to the present invention.

FIG. 2 is a perspective view showing a structure and a mutual positional relationship between a permanent magnet plate and a vibrating membrane.

FIG. 3 is an explanatory view showing another example of the vibration film.

FIG. 4 is an explanatory diagram showing the structure and mutual positional relationship between a permanent magnet plate and a vibrating membrane.

FIG. 5 is an explanatory view showing another example of the vibration film.

FIG. 6 is an explanatory view showing another configuration example of the electromagnetic converter according to the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Permanent magnet plate 12 Vibration film 14 Buffer member 16 Support member 20 Resin film 22 Coil 30 High permeability magnetic plate

Continuation of the front page (56) References JP-A-61-184094 (JP, A) JP-A-54-98611 (JP, A) JP-A-55-96795 (JP, A) JP-A 64-37197 (JP) , U) (58) Fields surveyed (Int. Cl. ⁷ , DB name) H04R 9/00 H04R 7/18 H04R 9/04 104

Claims (4)

(57) [Claims] 1. A permanent magnet plate, a vibrating film arranged so as to face the permanent magnet plate, a buffer member interposed between the vibrating film and the permanent magnet plate, and a permanent magnet plate of the vibrating film The permanent magnet plate has a multi-pole magnetized pattern of parallel stripes in which strip-shaped N-poles and S-poles appear alternately on substantially the entire surface of the diaphragm facing surface. The vibrating membrane is a thin and flexible resin film, and a coil made of a meandering conductive wire pattern is printed on a thin flexible resin film by wiring. The straight line portion of the conductive wire pattern is provided at a position corresponding to the neutral zone of the permanent magnet plate, and is not fixed at the peripheral portion, and the displacement in the in-plane direction is restricted by the support member. However, the buffer member is supported so that it can be freely displaced in the thickness direction.The buffer member has a structure in which a plurality of sheets having the same size as the vibrating membrane are soft and breathable, and a plurality of sheets are stacked. A thin electromagnetic transducer, which is disposed so as to have a gap between a sheet and the permanent magnet plate or the vibrating membrane. 2. A permanent magnet plate and a cushioning member are respectively arranged on both sides of the diaphragm so as to sandwich the diaphragm, and both permanent magnet plates have the same neutral zone and the same poles face each other. 2. The thin electromagnetic transducer according to claim 1, wherein the electromagnetic transducer is fixed at an interval in a positional relationship. 3. The thin electromagnetic transducer according to claim 2, wherein a vibrating membrane having a meandering conductive pattern formed on both surfaces of the resin film is used. 4. A high-permeability magnetic plate for preventing magnetic flux leakage is adhered to the surface of the permanent magnet plate opposite to the surface opposed to the vibrating membrane, and the high-permeability magnetic plate is also provided with an exhaust formed on the permanent magnet plate. 4. The thin type according to claim 1, wherein a plurality of exhaust through holes similar to the exhaust through holes are formed so that the exhaust through hole of the permanent magnet plate and the exhaust through hole of the high-permeability magnetic plate communicate with each other. Electromagnetic transducer.