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JPH0662699

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DESCRIPTION JPH0662699
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
electromagnetic acoustic transducer, and more particularly to the structure of adhesive bonding
of an armature on a diaphragm.
[0002]
2. Description of the Related Art As shown in FIG. 1, an electromagnetic acoustic transducer has a
magnetic flux in which a diaphragm 3, a coil 4 and a magnet 5 are combined in the interior of a
container comprising an outer peripheral container 1 and a lid 2. The generation means was
arranged.
[0003]
A sound leakage hole 11 is formed on the bottom of the outer peripheral container 1, and an
acoustic resistance cloth 12 is attached to the sound leakage hole 11.
A step portion 15 on which the diaphragm 3 is placed is formed on the inner wall of the outer
peripheral container 1.
[0004]
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The lid 2 doubles as a yoke plate, and a protrusion 21 projecting to the inside of the container is
formed at its center. The coil 4 and the magnet 5 are disposed on the inner surface of the yoke
plate 2 so as to surround the projecting portion 21. Further, a plurality of sound output holes 22
are formed in the yoke plate 2 so as to avoid the coil 4 and the magnet 5.
[0005]
The diaphragm 3 is made of thin aluminum, stainless steel, or Fe--Ni alloy, and 42 Ni--Fe is used
to improve the magnetization efficiency by the magnetic flux emitted from the projecting portion
of the yoke plate 2. A small disc-like armature 31 made of an alloy or the like is disposed.
Generally, the armature 31 is attached and fixed to the central portion of the diaphragm 3 via an
adhesive layer made of spot welding or an epoxy resin adhesive.
[0006]
In the above-described electromagnetic acoustic transducer 10, the diaphragm 3 is fixed to the
step portion 15 of the outer peripheral container 1 via an adhesive, and the yoke plate 2 is
further closed so as to close the opening of the outer peripheral container 1. The double lid is
fixed by an adhesive or mechanical structure.
[0007]
Thus, the inside of the container 1 is divided by the diaphragm 3 into the sound emission side
space (front air chamber A) and the back surface side space (rear air chamber B), and the coil 4
and magnet disposed on the sound emission side The diaphragm 3, in particular, the armature
31 thereof is magnetized by the magnetic flux generated from 5 and emitted from the projecting
portion 21 of the yoke plate 2.
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 projecting portion 21 of the yoke plate 2 and
the direction of generation of the magnetic flux fluctuate, and the diaphragm 3 bends and
vibrates accordingly. It will be. Accordingly, the air in the front air chamber A and the rear air
chamber B vibrates, and an 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
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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.
[0008]
In the above-described electromagnetic acoustic transducer 10, in order to improve the
characteristics of the acoustic signal emitted from the sound emission hole 22, in particular the
sound pressure sensitivity, the diaphragm 3 is used. It is important to make it thin as 50 to 100
μm to increase the amount of bending due to bending vibration.
[0009]
As described above, even if the deflection amount of the diaphragm 3 is increased,
conventionally, the armature 31 is fixed by spot welding, epoxy resin adhesive or the like.
However, due to the presence of the armature 31 which is not easily bent, the original deflection
of the diaphragm 3 is largely prevented, and it is not possible to expect sufficient sound pressure
sensitivity.
[0010]
The present invention has been made in view of the above-mentioned problems, and its object is
to improve the connection structure of the armature and to improve the sound pressure
sensitivity sufficiently. To provide.
[0011]
SUMMARY OF THE INVENTION The present invention is an electromagnetic acoustic transducer
in which a diaphragm on which an armature is disposed is vibrated by alternating magnetic flux
generated by a coil, wherein the armature is a Shore D after curing. The electromagnetic acoustic
transducer is characterized in that it is attached to the diaphragm via an adhesive layer having a
hardness of 30 to 50.
[0012]
As described above, since the armature is attached to the diaphragm via the adhesive layer
having a relative elasticity of 30 to 50 in Shore D hardness after curing, the armature's repulsion
that prevents the deflection of the diaphragm. The force is relieved by the adhesive layer.
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Therefore, even if the thickness of the diaphragm is reduced and the amount of deflection is
increased, the armature can sufficiently follow the amount of deflection, and as a result, the
acoustic characteristics, particularly the sound pressure sensitivity, can be dramatically
increased.
[0013]
Hereinafter, the electromagnetic acoustic transducer of the present invention will be described in
detail with reference to the drawings.
[0014]
FIG. 1 shows a cross-sectional view of the electromagnetic acoustic transducer, and FIG. 2 shows
an exploded cross-sectional view thereof.
[0015]
The electromagnetic acoustic transducer 10 according to the present invention comprises an
outer peripheral case 1, a lid serving also as a yoke plate 2, a diaphragm 3, a coil 4 and a magnet
5.
[0016]
The outer peripheral 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.
Further, three step portions 13 to 15 are provided circumferentially on the inner side wall.
From the upper part on the opening side, the first step 13 mounts and fixes the yoke plate 2, and
the second step 14 mounts and fixes the lower plate 42 of the coil bobbin 45. , And the second
step portion 15 is for mounting and fixing the diaphragm 3
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[0017]
The yoke plate 2 is made of a magnetic metal material such as iron and has a shape to be fitted
to the first step portion 13.
At the central portion of the yoke plate 2, a projecting portion 21 projecting to the inside of the
container is formed.
In addition, a plurality of sound output holes 22 are formed on the surface of the yoke plate 2.
[0018]
The diaphragm 3 is mounted on and fixed to the third step portion 15 and is made of a magnetic
metal material such as a Ni--Fe alloy, and its shape is, for example, 18 mm in diameter and 100
μm in thickness.
An armature 31 made of, for example, 42 Ni-Fe alloy and having a diameter of 5 to 8 mm and a
thickness of 100 μm is attached to the central portion of the diaphragm 3 by the adhesive layer
32.
[0019]
The coil 4 is wound around a coil bobbin 45 consisting of an upper plate 41, a lower plate 42,
and a core body 44 in which a through hole 43 is formed, by a predetermined turn. For example,
the lower plate 42 is placed and fixed on the second step portion 14 of the outer peripheral
container 1 and the coil 4 is disposed at a predetermined position in the container.
[0020]
Further, the projecting portion 21 of the yoke plate 2 is inserted through the through hole 43 of
the core body 44, and the coil 4 is disposed around the projecting portion 21.
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5
[0021]
The magnet 5 has a ring shape and is disposed at a position around the coil 4.
[0022]
As the arrangement method, the magnet 5 is directly adhered and fixed to the yoke plate 2 or the
magnet 5 is adhered and fixed onto the lower plate 42 of the coil bobbin 45, and then the inner
side surface of the yoke plate 2 is further provided. Contact or proximity, and adhesively placed
on it
[0023]
In assembling the above-described components, first, the acoustic resistance cloth 12 is attached
to the sound leakage hole 11 on the bottom surface of the outer peripheral container 1 having a
predetermined shape.
[0024]
Further, the armature 31 is brought into contact with the central portion of the diaphragm 3 via
an adhesive, and the adhesive is hardened to integrate the armature 31 with the diaphragm 3.
[0025]
Furthermore, the coil 4 of a predetermined number of turns is wound around the core 44 of the
coil bobbin 45. Subsequently, the magnet 5 is brought into contact with the surface of the lower
plate 42 of the coil bobbin 45 via an adhesive. After hardening, the magnet 5 is placed around
the coil 4.
[0026]
An adhesive is applied to the third step 15 of the outer peripheral 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
lower plate 42 of the coil bobbin 45 on which the coil 4 and the magnet 5 are disposed is placed.
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[0027]
Finally, an adhesive is applied to the first step 13 of the outer peripheral container 1, and the
yoke plate 2 also serving as a lid is placed.
At this time, the projecting portion 21 of the yoke plate 2 is inserted into the through hole 43
formed in the core body 44 of the coil bobbin 45, 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 45, the yoke plate 2 and the
step portions 13 to 15 is cured to perform integration.
[0028]
In the electromagnetic acoustic transducer 10 thus assembled, a magnetic flux unique to the
magnet 5 is generated from the projecting portion 21 of the yoke plate 2 to magnetize the
diaphragm 3 and the armature 31.
The distance between the protrusion 21 and the diaphragm 3 in this state is set to, for example,
0.2 to 0.5 mm.
[0029]
Next, when a predetermined alternating current signal corresponding to the audio signal is given
to the coil 4 wound around the coil bobbin 45, magnetic flux is generated in the coil 4 according
to the flow direction and magnitude of the current, The magnetic flux combined with the
alternating magnetic flux and the intrinsic magnetic flux of the above-mentioned magnet 5
affects the diaphragm 3 and the armature 31 from the projecting portion 21 of the yoke plate 2
[0030]
As a result, the diaphragm 3 and the armature 31 are drawn to and pulled away from the
projecting portion 21 of the yoke plate 2, causing the diaphragm 3 to bend and vibrate, and the
inside of the container partitioned by the diaphragm 3 The air in the air chamber A and the rear
air chamber B is vibrated.
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[0031]
Thus, 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.
In addition, since the magnetic flux alternatingly generated by the coil 4 is also generated in the
external direction through the yoke plate 2, the deaf person can obtain an audio signal if a
pickup coil for capturing this magnetic field is used.
[0032]
The characteristic point of the present invention is that the adhesive layer 32 for attaching the
armature 31 to the central portion of the diaphragm 3 is set to 30 to 50 in Shore D hardness.
[0033]
In order to obtain the adhesive layer 32 having a Shore D hardness of 30 to 50, it is an adhesive
made of an epoxy resin or an acrylic resin in consideration of the amount and kind of reaction
diluent as the adhesive. .
As the curing method, after the armature 31 coated with an adhesive is attached to the
diaphragm 3, the adhesive layer 32 can be achieved by curing by irradiation of ultraviolet light,
application of heat, standing at normal temperature, or the like.
[0034]
As described above, since the Shore D hardness of the adhesive layer 32 is 30 to 50, the adhesive
layer 32 has a predetermined elasticity.
The thickness of the adhesive layer 32 is set to 3 to 10 μm.
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[0035]
By integrating the diaphragm 3 and the armature 31 with the adhesive layer 32 as described
above, the magnetization efficiency of the entire diaphragm 3 can be improved, but in order to
improve the acoustic characteristics, particularly the sound pressure sensitivity, the diaphragm 3
The thickness of the diaphragm 3 is reduced to increase the amount of deflection of the
diaphragm 3.
At this time, if the Shore D hardness of the adhesive layer 32 is 30 to 50, even if the armature 31
is fixed to the diaphragm 3, it is possible to suppress blocking of the diaphragm 3 and high
sound pressure sensitivity
[0036]
The inventor used an epoxy resin (Shore D hardness 70 to 80 after curing) and an acrylic resin
(Shore D hardness 30 to 50 after curing) respectively on the diaphragm 3 under the same
conditions. Paste to create an acoustic transducer and compare sound pressure sensitivity
[0037]
In the conventional acoustic transducer in which the diaphragm 3 and the armature 31 are
attached via an adhesive composed mainly of epoxy resin, the sound pressure sensitivity is 93 dB
(0.1 Vrms). In the present invention, the sound pressure sensitivity is 95 to 96 dB (0.1 Vrms)
[0038]
Furthermore, if the Shore D hardness after curing is less than 30, the sound pressure sensitivity
becomes 93 dB or less.
It is considered that this is because the space between the armature 31 and the diaphragm 31
lowers the magnetization efficiency.
[0039]
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Therefore, the Shore D hardness of the adhesive (after curing) for integrating the diaphragm 3
and the armature 31 is preferably in the range of 30 to 50.
[0040]
Further, in the present invention, it has been confirmed that the variation in characteristics can
be reduced by as much as 20%, and the production yield can be greatly improved.
[0041]
In the above embodiment, the shape of the yoke plate and the coil bobbin, the fixing method, the
structure of the container, and the like can be variously changed. Further, the coil bobbin is
omitted and the coil and magnet are directly attached to the yoke plate. Various changes such as
bonding are possible
[0042]
As described above, according to the present invention, since Shore D hardness after curing of
the adhesive layer between the diaphragm and the armature is set to 30 to 50, the flexural
vibration of the diaphragm is prevented. Become an electromagnetic type acoustic transducer
that can maximize the acoustic characteristics, especially the sound pressure characteristics.
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