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JPH06339195

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DESCRIPTION JPH06339195
[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 diaphragm 30 and a coil 4 inside a container body comprising a lower container 1 and
an upper container (hereinafter referred to as a lid) 2. And the magnetic flux generation means
which combined the magnet 50 was arrange ¦ positioned, respectively.
[0003]
A sound leakage hole 11 to which an acoustic resistance cloth 12 is attached is formed on the
bottom surface of the lower case 1.
At the center of the lid 2 is formed a protrusion 21 that protrudes to the inside of the container
1.
[0004]
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The diaphragm 30 is made of a thin non-magnetic material such as aluminum or SUS304, and a
small circle of 42 Ni-Fe alloy or the like to improve the magnetization efficiency due to the
magnetic flux emitted from the projecting portion 21 of the lid 2. A plate-like amateur 31 is
disposed. Generally, the armature 31 is attached and fixed to the central portion of the
diaphragm 30 via an adhesive layer made of spot welding or an epoxy resin adhesive.
[0005]
The coil 4 and the magnet 50 are fixed to a plastic coil bobbin body 6, the coil 4 is fixed by
winding a wire around the coil bobbin portion 61, and the magnet 50 is bonded around the coil
bobbin portion 61 There is.
[0006]
The above-described electromagnetic type acoustic transducer 40 is fixed to the lower container
1 with the diaphragm 30 and the coil bobbin body 6 via an adhesive, and the lid 2 is an adhesive
or the like so as to close the opening of the lower container 1. It was fixed by mechanical
structure etc.
[0007]
As a result, the inside of the container 1 is divided by the diaphragm 30 into the sound emission
side space (front air chamber A) and the back surface side space (rear air chamber B), and is
generated from the coil 4 and magnet 50 disposed on the sound emission side. Then, the
diaphragm 30, in particular, the armature 31 is magnetized by the magnetic flux emitted from
the projecting portion 21 of the lid 2 made of a magnetic material such as iron.
[0008]
Then, when an alternating current signal corresponding to the audio signal is given to the coil 4,
the strength of the magnetic flux emitted from the projection 21 of the lid 2 and the direction of
generation of the magnetic flux fluctuate, and the diaphragm 30 is bent and vibrated accordingly.
It will be.
[0009]
Accordingly, the air in the front air chamber A and the rear air chamber B vibrates, and an
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acoustic signal of a predetermined frequency is emitted from the sound emission hole 22.
In addition, the magnetic flux corresponding to the audio signal leaks to the sound emitting side
outside of the outer peripheral container 1, and the deaf person can obtain the audio signal by
capturing the leakage magnetic flux with a pickup coil or the like.
[0010]
In the above-described electromagnetic acoustic transducer 40, a nonmagnetic material is used
as the material of the diaphragm 30.
This is because the vibration coefficient is relatively good and the adjustment of the frequency of
the acoustic characteristic is easy.
[0011]
However, since the diaphragm 30 is a nonmagnetic material, the magnetic force holding power
of the magnetic flux generated from the coil 4 and the magnet 50 is particularly easy in terms of
acoustic characteristics, even if the frequency adjustment is easy. The sound pressure level was
particularly low in terms of acoustic characteristics.
[0012]
The armature 31 is attached to the diaphragm 30 to increase the sound pressure level by
strengthening the holding force, but in consideration of the vibration effect of the diaphragm 30
due to the attachment of the amateur 31, the size and size of the armature 31 The thickness is
also limited, and the leakage flux is still large, and finally, the magnetic force of the magnet 50
which is the magnetic flux generating means is enhanced.
[0013]
That is, the magnet 50 which consists of crystal system ferrite etc. which were formed by
sintering of about 1500-2000 gauss of magnetic force was used.
[0014]
As described above, since the magnet 50 of the crystalline ferrite is expensive and is a sintered
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body, it is likely to cause chipping and cracking due to mechanical impact, requiring careful
handling.
[0015]
The present invention has been made in view of the above problems, and its object is to increase
the magnetic flux holding capacity and improve the sound pressure level of acoustic
characteristics by replacing the material of the diaphragm with a magnetic member. Further, the
present invention provides an electromagnetic acoustic transducer in which predetermined
characteristics can be obtained even when the magnetic flux generation means has a relatively
small magnetic force.
[0016]
SUMMARY OF THE INVENTION According to the present invention, a diaphragm made of a
magnetic material and a diaphragm made of a magnetic material are vibrated inside a container
having a sound emission hole on the sound emission side and a sound leakage hole on the back
side. It is an electromagnetic acoustic transducer in which a coil and a rubber magnet are
disposed.
[0017]
According to the present invention, since the diaphragm is made of a magnetic material, all the
magnetic forces from the coil and the rubber magnet, which are magnetic flux generating means,
can affect the diaphragm and leakage flux is substantially eliminated. .
That is, the holding power at the diaphragm is increased, the amplitude of the diaphragm is large,
and the sound pressure level on the acoustic characteristics is greatly improved.
[0018]
Also, in order to maintain the predetermined sound pressure level, the magnetic force on the side
of the magnetic flux generating means for applying vibration to the diaphragm from the
magnetic material can be reduced. A mixed rubber magnet such as a magnetic steel component
can be used for the rubber of
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This can significantly reduce the cost and further ease the handling of the rubber magnet.
[0019]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT The electromagnetic acoustic
transducer according to the present invention will be described in detail with reference to the
drawings.
[0020]
FIG. 1 is an external view of an 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 prior art are given the same reference numerals.
[0021]
The electromagnetic acoustic transducer 10 according to the present invention is composed of a
lower case 1 serving as a case body and a lid 2 serving also as a yoke plate, a diaphragm 3, a coil
4, and a rubber magnet 5.
[0022]
The lower container 1 is made of ABS plastic or the like, and has a bottomed cylindrical shape
with a diameter of 20 to 25 mm and a thickness of 3 to 4 mm as a whole.
A sound leakage hole 11 is formed on the bottom surface, and an acoustic resistance cloth 12 for
closing the sound leakage hole 11 is attached to the surface of the inner bottom surface.
[0023]
Further, three step portions 13 to 15 are provided circumferentially on the inner side wall.
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The first step 13 mounts and fixes the lid 2 from the upper portion on the opening side, and the
second step 14 mounts and fixes the coil bobbin body 6. The step portion 15 is for mounting and
fixing the diaphragm 3.
[0024]
The lid 2 is made of a magnetic metal material such as iron plated with Ni, and has a shape fitted
to the first step portion 13.
At the central portion of the lid 2 is formed a projecting portion 21 projecting to the inside of the
container.
The projecting portion 21 is a yoke portion.
Further, on the surface of the lid 2, a plurality of sound emission holes 22 are formed.
[0025]
The diaphragm 3 is mounted and fixed to the third step portion 15 and is made of a magnetic
metal material such as SUS 430 or Ni--Fe alloy, and its shape is, for example, 18 mm in diameter
and 0.1 mm in thickness. .
Further, an armature 31 made of, for example, 42Ni-Fe alloy and having a diameter of 4.8 mm
and a thickness of 0.2 mm is adhesively fixed to the central portion of the diaphragm 3 by a
relatively soft adhesive.
[0026]
The coil 4 and the rubber magnet 5 are respectively wound or mounted on the coil bobbin body
6.
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[0027]
The coil bobbin body 6 is mounted 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, and protrudes from a
part of the lower container 1 to the outside It is supposed to
Further, lead terminals 62 and 63 extending to the outside are formed in this portion.
[0028]
The coil 4 is configured by winding a wire around the bobbin portion 61 of the coil bobbin body
6.
[0029]
The rubber magnet 5 is, for example, one obtained by mixing and solidifying a rubber component
and a magnet steel component such as Fe-Al-Ni-Co-based or Cu-Ni-Fe-based, and is disposed
around the bobbin portion 61 It has a ring shape.
Such a rubber magnet 5 has a magnetic force of about 300 to 1000 gauss.
[0030]
By placing and fixing such a coil bobbin body 6 on the second step portion 14 of the lower
container 1, the coil 4 and the rubber magnet 5 can be disposed at a predetermined position in
the container 1.
[0031]
First, the acoustic resistance cloth 12 is attached to the sound leakage hole 11 on the bottom of
the lower container 1 having a predetermined shape.
[0032]
Further, an adhesive is bonded to the armature 31 at the central portion of the diaphragm 3.
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[0033]
Furthermore, a wire is wound around the bobbin portion 61 of the coil bobbin body 6 to form
the coil 4, both ends of the coil 4 are joined to the lead terminals 62 and 63, and further, the
rubber magnet 5 is bonded around the bobbin portion 61. Glue with an agent.
[0034]
An adhesive is applied to the third step 15 of the lower container 1 described above, and the
diaphragm 3 integrated with the armature 31 is placed.
Next, an adhesive is applied to the second step 14 of the outer peripheral container 1, and the
coil bobbin body 41 on which the coil 4 and the rubber magnet 5 are disposed is placed.
[0035]
Finally, an adhesive is applied to the first step 13 of the lower container 1 and the lid 2 is placed.
[0036]
At this time, the projecting portion 21 of the yoke portion of the lid 2 is inserted into the through
hole of the bobbin portion 61 of the coil bobbin body 6, and the tip of the projecting portion 21
approaches the central portion of the diaphragm 3.
In this state, the adhesive between the diaphragm 3, the coil bobbin body 6, the lid 2 and the step
portions 13 to 15 is cured to perform integration.
[0037]
In the electromagnetic acoustic transducer 10 thus assembled, the intrinsic magnetic flux of the
coil 4 is emitted from the projection 21 of the lid 2 toward the diaphragm 3 and the armature 31
to magnetize the diaphragm 3 and the armature 31. It will be.
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The distance between the protrusion 21 and the diaphragm 3 in this state is set to, for example,
0.1 to 0.5 mm.
[0038]
Next, when a predetermined alternating current signal corresponding to the audio signal is given
to the coil 4 wound around the coil bobbin body 41, a magnetic flux is generated in the coil 4
according to the flow direction and the magnitude of the current. The generated magnetic flux
and the magnetic flux synthesized with the above-mentioned inherent magnetic flux of the
rubber magnet 5 affect the diaphragm 3 and the armature 31 from the projecting portion 21 of
the lid 2.
[0039]
As a result, the diaphragm 3 and the armature 31 are attracted to the projecting portion 21 of
the lid 2 and pulled apart, causing the diaphragm 3 to flex and vibrate, and the front air chamber
A in the container partitioned by the diaphragm 3 And vibrate the air in the rear air chamber B.
[0040]
As a result, the vibrated air of the front air chamber A is discharged to the outside through the
sound emission hole 22 and converted into an audible acoustic signal corresponding to the
current signal.
Further, the magnetic flux alternatingly generated by the coil 4 is also generated in the external
direction through the lid 2, so that a deaf person can obtain an audio signal by using a pickup
coil for capturing this magnetic field.
[0041]
The characteristic point of the present invention is that the diaphragm 3 is made of a magnetic
material such as 42 alloy, SUS430, iron or the like.
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For this reason, since the whole diaphragm 3 is magnetized by the magnetic flux from the coil 4
and the rubber magnet 5 which are magnetic flux generating means, the magnetic force holding
capacity becomes large.
Therefore, the degree of influence on the diaphragm 3 is increased, and the sound pressure level
of the acoustic characteristics is greatly improved.
[0042]
Here, the armature 31 is for concentrating the holding power at the central portion of the
diaphragm 3 to increase the influence of vibration particularly at the central portion of the
diaphragm 3, and is a diaphragm made of a conventional nonmagnetic material. 3 is not formed
to generate a holding capacity.
[0043]
Also, in the present invention, it is easy to adjust the frequency of the acoustic characteristics,
which is the reason for using the diaphragm 3 made of nonmagnetic material conventionally. Is
adjusted by the degree of opening of the mesh of the acoustic resistance cloth 12 to be attached.
[0044]
As described above, according to the present invention, since the entire diaphragm 3 is
magnetized, the leakage flux is substantially eliminated, and all the magnetic fluxes generated
from the coil 4 and the rubber magnet 5 affect the diaphragm 3. Can.
[0045]
Thereby, the sound pressure level on acoustic characteristics can be dramatically improved.
According to the measurement of the present inventor, it was confirmed that the sound pressure
level of the acoustic characteristics is 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 present
invention.
[0046]
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Also, this means that a sound pressure level sufficient for practical use is achieved even if the
magnetic force from the magnetic flux generating means is reduced, and for example, it is
possible to increase the impedance of the coil 4 compared to the prior art. , It becomes possible
to adopt a magnet 5 with weak magnetic force.
[0047]
Conventionally, since the magnet 51 needs to have a magnetic force of about 1000 to 1500
gauss, a magnet made of crystal ferrite or the like formed by sintering is used, but in the present
invention, the magnetic force is about 300 to 1000 gauss. Since it is sufficient, a lightweight
rubber magnet 5 that is inexpensive, resistant to mechanical impact, and lightweight can be used
as the magnet.
[0048]
As a result, the magnet can be easily handled, the workability can be improved, and an
inexpensive electromagnetic acoustic transducer can be achieved that is resistant to mechanical
impact.
[0049]
Further, in the present invention, the impedance of the conventional coil 3 has been used with an
impedance of 300 Ω or less in consideration of a decrease in generated magnetic flux, in order
to achieve high impedance of the coil.
Further, since the output impedance of the amplifier of the op amp of the external drive circuit is
large, it has been necessary to connect a buffer transistor in order to lower the output
impedance.
[0050]
On the other hand, in the present invention, even if the impedance of the coil 4 is increased to
about 720 Ω (for example, a coil that turns a wire rod with a diameter of 0.03 to 0.35 mm 800
to 1200), the sound pressure level is practically It does not matter.
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Therefore, since it is possible to set the impedance following the output impedance of the op amp
of the drive circuit, it is possible to omit the buffer transistor and drive it directly with the drive
circuit operational amplifier as in the prior art. Can be
[0051]
In the above embodiment, the shape of the lid 2 and the coil bobbin body 6, the fixing method,
the structure of the container 1 and the like can be changed variously, and the coil bobbin body
6 is omitted. Various modifications are possible, such as bonding the coil 4 and the magnet 5 to
each other.
[0052]
As described above, according to the present invention, by replacing the material of the
diaphragm with a magnetic member, the storage capacity is increased, and an electromagnetic
acoustic transducer having an improved sound pressure level is achieved. it can.
[0053]
Further, even if the magnetic force is relatively small, predetermined characteristics can be
obtained as the magnet of the magnetic flux generating means, and a low cost, light weight,
impact resistant rubber magnet can be used, and cost reduction can be achieved.
[0054]
Furthermore, since the coil of the magnetic flux generating means can be made high in
impedance, it can be operated by being directly connected to the operational amplifier of the
drive circuit.
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