JPH06339195A - Electromagnetic acoustic transducer - Google Patents

Abstract

PURPOSE:To improve the sound pressure level by arranging a diaphragm made of a magnetic material, a coil and a rubber magnet on the inside of a container whose sound emitting side has sound emitting holes and whose back surface side has sound leakage holes. CONSTITUTION:The electromagnetic acoustic transducer 10 is made up of a lower container 1 being a container body, a lid body 2 sharing with a yoke plate, a diaphragm 3, a coil 4 and a rubber magnet 5. The lower container 1 is made of an ABS plastic, etc., forming a cylinder with a bottom and a sound leakage hole 11 is formed on the bottom surface and an acoustic resistance cloth 12 choking the sound leakage hole 11 is adhered to the surface of the inner side bottom surface. Then the lid body 2 is placed and fixed from the upper part of the opening part by a 1st step difference section 13 and a coil bobbin body 6 is mounted and fixed by a 2nd step difference section 14 and a 3rd step difference section 15 mounts and fixes the diaphragm 3 made of a magnetic substance metallic material. Thus, the air vibrated in a front gas chamber A is emitted externally via a sound emitting hole 22 and transduced into an audible acoustic signal corresponding to a current signal.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electromagnetic acoustic transducer, and more particularly to an electromagnetic acoustic transducer having high sound pressure sensitivity.

[0002]

2. Description of the Related Art As shown in FIG. 4, an electromagnetic acoustic transducer 40 includes a vibrating plate 30 and a coil 4 inside a container body composed of a lower container 1 and an upper container (hereinafter referred to as a lid) 2. Further, the magnetic flux generating means in which the magnet 50 and the magnet 50 are combined are arranged.

A sound leakage hole 11 to which an acoustic resistance cloth 12 is attached is formed on the bottom surface of the lower container 1. At the center of the lid body 2, a protrusion 21 that protrudes toward the inside of the container 1 is formed.

The diaphragm 30 is made of thin aluminum,
A small disk-shaped armature 31 made of 42Ni—Fe alloy or the like is arranged in order to improve the magnetization efficiency by the magnetic flux emitted from the protruding portion 21 of the lid body 2 and made of a non-magnetic material such as SUS304. This amateur 31
Was generally attached and fixed to the central portion of the diaphragm 30 via spot welding or an adhesive layer made of an epoxy resin adhesive.

The coil 4 and the magnet 50 are fixed to a coil bobbin body 6 made of plastic.
Is fixed by winding a wire around the coil bobbin portion 61, and the magnet 50 is bonded around the coil bobbin portion 61.

In the electromagnetic acoustic transducer 40 described above, the diaphragm 30 and the coil bobbin body 6 are fixed to the lower container 1 with an adhesive, and the lid 2 is provided so as to close the opening of the lower container 1. It was fixed by glue or mechanical structure.

As a result, in the container 1, the sound emitting side space (front air chamber A) and the back side space (rear air chamber B) are formed by the vibrating plate 30.
A lid 2 made of a magnetic material such as iron, which is generated by a coil 4 and a magnet 50 which are partitioned into
By the magnetic flux emitted from the protruding portion 21 of the diaphragm 3
0, especially its amateur 31 will be magnetized.

When an alternating current signal corresponding to a voice signal is applied to the coil 4, the intensity of the magnetic flux emitted from the projecting portion 21 of the lid 2 and the direction in which the magnetic flux is generated fluctuate. It will bend and vibrate.

Therefore, the air in the front air chamber A and the air in the rear air chamber B vibrate, and the sound signal of the predetermined frequency is emitted from the sound output hole 22. A magnetic flux corresponding to a voice signal leaks to the outside of the sound emitting side of the outer peripheral container 1, and a hearing-impaired person can obtain a voice signal by capturing the leak magnetic flux with a pickup coil or the like.

In the electromagnetic acoustic transducer 40 described above, a non-magnetic material is used as the material of the diaphragm 30. This is because the vibration coefficient is relatively good and the frequency of the acoustic characteristics can be easily adjusted.

[0011]

However, since the vibrating plate 30 is made of a non-magnetic material, the coil 4 and the magnet 50 are easy to adjust even if the frequency is easy in view of acoustic characteristics.
The magnetic force generated by the magnetic flux was weak, and the sound pressure level was particularly low due to the acoustic characteristics.

The armature 31 is attached to the diaphragm 30 in order to increase the holding force and raise the sound pressure level. However, considering the vibration effect of the attachment of the armature 31 on the diaphragm 30, the armature 31 is There is a limit to the size and thickness of the magnet, and the leakage magnetic flux is still large, so that the magnetic force of the magnet 50, which is the magnetic flux generating means, is finally increased.

That is, the magnet 50 made of crystalline ferrite or the like formed by sintering with a magnetic force of 1500 to 2000 Gauss was used.

As described above, the crystalline ferrite magnet 50 is expensive and, because it is a sintered body, it is liable to be cracked or cracked by mechanical impact, and thus requires careful handling. .

The present invention has been devised in view of the above-mentioned problems, and an object thereof is to increase the magnetic flux holding capacity by replacing the material of the diaphragm with a magnetic material member so that the sound pressure level of the acoustic characteristic is increased. The present invention provides an electromagnetic acoustic transducer capable of obtaining a predetermined characteristic even when the magnetic flux generating means has a relatively small magnetic force.

[0016]

According to the present invention, a vibrating plate made of a magnetic material is vibrated inside a container having a sound emitting hole on the sound emitting side and a sound leaking hole on the back side. It is an electromagnetic acoustic transducer in which a coil and a rubber magnet are arranged.

[0017]

According to the present invention, since the vibrating plate is used from the magnetic material, all the magnetic forces from the coil and the rubber magnet, which are magnetic flux generating means, can affect the vibrating plate, and the leakage magnetic flux is substantially eliminated. . That is, the holding force of the diaphragm is increased, the amplitude of the diaphragm is large, and the sound pressure level on the acoustic characteristics is significantly improved.

Further, in order to maintain a predetermined sound pressure level, the magnetic force on the side of the magnetic flux generating means for vibrating the diaphragm from the magnetic material can be reduced. It is possible to use a rubber magnet in which rubber of about 500 gauss is mixed with magnetic steel components. As a result, the cost can be significantly reduced and the handling of the rubber magnet can be eased.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The electromagnetic acoustic transducer of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is an external view of the electromagnetic acoustic transducer, FIG. 2 is an exploded sectional view thereof, and FIG. 3 is an exploded sectional view thereof. The same parts as in the conventional case are designated by the same reference numerals.

The electromagnetic acoustic transducer 10 of the present invention comprises a lower container 1 serving as a container, a lid 2 also serving as a yoke plate, a diaphragm 3, a coil 4, and a rubber magnet 5.

The lower container 1 is made of ABS plastic or the like, and has a diameter of 20 to 25 mm and a thickness of 3 to 4 as a whole.
It has a bottomed cylindrical shape of mm. Sound leakage hole 1 on this bottom
1 is formed, and an acoustic resistance cloth 12 that closes the sound leak hole 11 is attached to the surface of the inner bottom surface.

Further, the inner side wall has three stepped portions 13 to 13.
15 are provided around. From the upper part on the opening side, the first step portion 13 is for mounting and fixing the lid body 2, and the second step portion 14 is for mounting and fixing the coil bobbin body 6. The stepped portion 15 is for mounting and fixing the diaphragm 3.

The lid 2 is made of a magnetic metal material such as iron plated with Ni, and has a shape to be fitted into the first step portion 13. A projecting portion 21 that projects toward the inside of the container is formed in the center of the lid 2. In addition, this protrusion 2
1 is the yoke part. A plurality of sound emitting holes 22 ... Are formed on the surface of the lid 2.

The vibrating plate 3 is placed and fixed on the third step portion 15, and is made of a magnetic metal material such as SUS430 and Ni--Fe alloy, and its shape is, for example, 1 mm in diameter.
The thickness is 8 mm and the thickness is 0.1 mm. Further, an armature 31 having a diameter of 4.8 mm and a thickness of 0.2 mm, which is made of, for example, 42Ni—Fe alloy, is bonded and fixed to the central portion of the diaphragm 3 with a relatively soft adhesive.

The coil 4 and the rubber magnet 5 are wound around or mounted and fixed on the coil bobbin body 6, respectively.

The coil bobbin body 6 is placed on the second step portion 14 of the lower container 1, and a bobbin portion 61 having a through hole is formed in the central portion thereof.
It is designed to project from a part of the outside. And
Lead terminals 62 and 63 extending outward are formed in this portion.

The coil 4 is constructed by winding a wire on the bobbin portion 61 of the coil bobbin body 6.

The rubber magnet 5 is, for example, a mixture of a rubber component and a magnetic steel component such as Fe-Al-Ni-Co system or Cu-Ni-Fe system, which is solidified.
It has a ring shape so that it is arranged around the. Such a rubber magnet 5 has a magnetic force of about 300 to 1000 gauss.

The coil bobbin body 6 as described above is provided in the lower container 1.
The coil 4 and the rubber magnet 5 can be arranged at predetermined positions in the container 1 by mounting and fixing them on the second step portion 14.

To assemble the above-mentioned components, first, the acoustic resistance cloth 12 is put in the sound leakage hole 11 on the bottom surface of the lower container 1 having a predetermined shape.
Affix.

Further, the armature 31 is bonded to the central portion of the diaphragm 3 with an adhesive.

Further, the bobbin portion 61 of the coil bobbin body 6
Then, a wire is wound to form the coil 4, and both ends of the coil 4 are joined to the lead terminals 62 and 63.
A rubber magnet 5 is attached to the periphery of 1 with an adhesive.

An adhesive is applied to the third step 15 of the lower container 1 described above, and the vibration plate 3 in which the armature 31 is integrated is placed. Next, an adhesive is applied to the second step 14 of the outer peripheral container 1, and the coil bobbin body 41 in which the coil 4 and the rubber magnet 5 are arranged is placed.

Finally, an adhesive is applied to the first step 13 of the lower container 1 and the lid 2 is placed.

At this time, the protruding portion 21 of the yoke portion of the lid body 2
Is inserted into the through hole of the bobbin portion 61 of the coil bobbin body 6, and the tip of the protruding portion 21 is brought close to the central portion of the diaphragm 3. In this state, the diaphragm 3, the coil bobbin body 6, the lid body 2
And the adhesive between the step portions 13 to 15 is cured to integrate them.

Electromagnetic acoustic transducer 1 assembled in this way
0, the intrinsic magnetic flux of the coil 4 causes the protrusion 21 of the lid 2 to
Emitted toward the diaphragm 3 and the amateur 31,
The diaphragm 3 and the armature 31 will be magnetized.
The distance between the protrusion 21 and the diaphragm 3 in this state is set to, for example, 0.1 to 0.5 mm.

Next, when a predetermined AC signal corresponding to an audio signal is applied to the coil 4 wound around the coil bobbin body 41, a magnetic flux is generated in the coil 4 according to the direction and magnitude of the current flow. The alternating magnetic flux and the magnetic flux combined with the above-mentioned unique magnetic flux of the rubber magnet 5 affect the diaphragm 3 and the armature 31 from the protrusion 21 of the lid 2.

As a result, the diaphragm 3 and the amateur 31
Is attracted to and pulled away from the projecting portion 21 of the lid body 2, causing the diaphragm 3 to undergo flexural vibration, and the diaphragm 3
The air in the front air chamber A and the rear air chamber B in the container partitioned by is vibrated.

As a result, the vibrated air in the front air chamber A is discharged to the outside through the sound output hole 22 and converted into an audible acoustic signal corresponding to the current signal. Further, since the magnetic flux alternating with the coil 4 is also generated in the external direction via the lid body 2, a magnetic field is generated, so that a hearing-impaired person can obtain an audio signal by using a pickup coil that captures this magnetic field.

A characteristic point of the present invention is that the diaphragm 3 is made of a magnetic material such as 42 alloy, SUS430, and iron. Therefore, the vibration plate 3 is generated by the magnetic flux from the coil 4 and the rubber magnet 5 that are magnetic flux generating means.
Since the whole is magnetized, the magnetic holding capacity is increased. Therefore, the degree of influence on the diaphragm 3 is increased, and the sound pressure level of the acoustic characteristics is greatly improved.

Here, the armature 31 is for concentrating the holding force in the central portion of the diaphragm 3 and for increasing the influence of vibration particularly in the central portion of the diaphragm 3, which is different from the conventional non-magnetic material. The vibrating plate 3 is not formed to generate a holding capacity.

Further, in the present invention, the sound leakage hole formed in the lower container 1 is to facilitate the frequency adjustment of the acoustic characteristics, which is the reason why the diaphragm 3 made of a non-magnetic material has been used conventionally. 11 and the acoustic resistance cloth 12 to which it is attached are adjusted according to the opening degree of the mesh.

As described above, according to the present invention, the diaphragm 3
Since the whole is magnetized, the leakage flux is virtually eliminated,
All of the magnetic flux generated from the coil 4 and the rubber magnet 5 can affect the diaphragm 3.

As a result, the sound pressure level on the acoustic characteristic can be dramatically improved. According to the measurement by the inventor, it was confirmed that the sound pressure level of the acoustic characteristics was improved by 12 to 20 dB only by changing the material of the diaphragm from the conventional SUS304 to SUS430 which is an example of the invention.

Further, this means that a practically sufficient sound pressure level can be achieved even if the magnetic force from the magnetic flux generating means is lowered. For example, the impedance of the coil 4 can be increased as compared with the conventional case. It is possible, and it is possible to adopt the magnet 5 having a weak magnetic force.

Conventionally, the magnetic force of the magnet 51 is 1000
Since a magnet made of crystalline ferrite or the like formed by sintering is used because about -1500 gauss is required, in the present invention, the magnetic force is 300 to 1000.
Since Gauss is sufficient, a rubber magnet 5 that is inexpensive, strong against mechanical shock, and lightweight can be used as the magnet.

As a result, the magnet can be easily handled, the workability is improved, the mechanical shock is strong, and the inexpensive electromagnetic acoustic transducer can be achieved.

Further, in the present invention, in order to increase the impedance of the coil, the impedance of the conventional coil 3 is used with an impedance of 300Ω or less in consideration of the decrease of the generated magnetic flux. Further, since the output impedance of the amplifier of the op amp of the external drive circuit is large, it is necessary to connect the buffer transistor in order to reduce the output impedance.

On the other hand, in the present invention, the coil 4 is replaced by 7
Even if the impedance is increased to about 20Ω (for example, a coil that turns a wire rod having a diameter of 0.03 to 0.35 mm for 800 to 1200 turns), the sound pressure level does not pose a practical problem. Therefore, it is possible to set the impedance that follows the output impedance of the op amp of the drive circuit, and the drive circuit operational amplifier can be directly driven by omitting the transistor for buffer as in the conventional case. It can be a bowl.

In the above embodiment, the shape of the lid body 2 and the coil bobbin body 6, the fixing method, the structure of the container 1 and the like can be variously changed, and the coil bobbin body 6 can be omitted and directly. Various modifications such as adhering the coil 4 and the magnet 5 to the lid 2 are possible.

[0052]

As described above, according to the present invention, by replacing the material of the vibrating plate with a magnetic member, an electromagnetic type acoustic transducer having an increased storage capacity and an improved sound pressure level is achieved. it can.

Further, as a magnet of the magnetic flux generating means,
Even if the magnetic force is relatively small, the specified characteristics can be obtained and the cost is low.
A lightweight and shock-resistant rubber magnet can be used, and cost reduction can be achieved.

Furthermore, since the coil of the magnetic flux generating means can have a high impedance, it can be operated by directly connecting it to the operational amplifier of the drive circuit.

[Brief description of drawings]

FIG. 1 is an external perspective view of an electromagnetic acoustic transducer of the present invention.

FIG. 2 is a sectional structural view of an electromagnetic acoustic transducer of the present invention.

FIG. 3 is an exploded structural view of the electromagnetic acoustic transducer of the present invention.

FIG. 4 is a cross-sectional structure diagram of a conventional electromagnetic acoustic transducer.

[Explanation of symbols]

 10 ... Electromagnetic acoustic transducer 1 ... Lower container 2 ... Lid 12 ... Sound leakage hole 11 ... Acoustic resistance cloth 21 ... Projection 22 ... Sound output holes 3, 31 ... Vibrating plate 4 ... Coil 5 ... Rubber magnet 51 ... Magnet

Claims (1)

[Claims] 1. A vibrating plate made of a magnetic material, and a coil and a rubber magnet for vibrating the vibrating plate are arranged inside a container having a sound emitting hole on the sound emitting side and a sound leaking hole on the back side. An electromagnetic acoustic transducer characterized by the above.