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JPH0256200

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
complete, reliable or fit for specific purposes. Critical decisions, such as commercially relevant or
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DESCRIPTION JPH0256200
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
loudspeaker, in particular an inductive loudspeaker. SUMMARY OF THE INVENTION According
to the present invention, in a speaker, by forming a diaphragm so that the electrical resistance of
the conductive portion is lower than the electrical resistance of the vibrating portion, the
occurrence of leakage current flowing in the vibrating portion can be prevented. It is something
that can be done. [Prior Art] In a conventional electrodynamic speaker, a driving force is obtained
by supplying an audio signal current to a voice coil in a direct current magnetic field. The voice
signal current is normally supplied to the voice coil from the outside by a lead wire fixed to a
cone paper as a diaphragm. [Problems to be Solved by the Invention] However, the conventional
electrodynamic speaker has a disadvantage that the lead wire is easily cut by the reciprocating
motion of the diaphragm because the speaker is provided with the lead wire. On the other hand,
even when the lead wire is not cut, distortion of the sound is likely to occur because the linearity
in reciprocating motion of the diaphragm is disturbed, and the lead wire itself resonates to
generate abnormal noise. there were. Furthermore, there is a disadvantage that the assembly is
troublesome because the lead wire must be drawn out from the narrow gap of the speaker for
positioning, bonding and fixing during manufacture. Therefore, Japanese Patent Publication No.
56-27039 discloses an induction type speaker from which a lead wire is removed as a speaker
for solving the various defects described above. The speaker disclosed in the above publication
removes the lead wire and arranges the drive coil in the vicinity of the voice coil wound around
the voice coil bobbin. Then, an audio signal current is supplied to the drive coil, and an audio
signal is supplied from the drive coil to the voice coil by magnetic induction. That is, when an AC
signal from the power amplifier of the audio frequency flows to the drive coil, an AC magnetic
flux corresponding to the input waveform is generated from the drive coil by the AC signal.
Interlock. On the other hand, since the voice coil is short-circuited by itself, a short-circuit current
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flows in the voice coil by the above-mentioned alternating current magnetic flux. Since the voice
coil is located in the magnetic field created by the pole piece and the surrounding magnetic pole,
the voice coil exerts a force proportional to the product of the strength of the magnetic field and
the short circuit current. This force causes the cone to vibrate from the voice coil through the
voice coil bobbin and sound is emitted from the cone like a normal speaker. In the technique
disclosed in the above-mentioned publication, although the various defects caused by the lead
wire are eliminated because the lead wire is removed, the following problems are separately
caused. .
Since the voice coil is generally fixed to the voice coil bobbin with an adhesive, there is a
disadvantage that the driving force generated in the voice coil is difficult to be directly
transmitted to the cone. Also, although the voice coil necessarily generates heat due to the short
circuit current, it has a disadvantage that it is difficult to dissipate the heat well. Then, in order to
improve the sensitivity of the speaker, it is required to narrow the gap (magnetic gap) between
the coil bobbin and the drive coil and wind the voice coil many times in the gap. Therefore, the
diameter of the metal wire used for the voice coil necessarily becomes smaller, and the heat
capacity of the metal wire becomes smaller. As a result, coupled with the problem of heat
dissipation as described above, the voice coil is easily disconnected due to heat generation, which
results in the disadvantage that the current capacity is limited. Furthermore, there is a
disadvantage that the paper voice coil bobbin is carbonized due to the repeated heat generation
described above. Therefore, an induction type speaker from which a voice coil has been removed
is proposed in Japanese Utility Model Laid-Open No. 50-105438. That is, in this speaker, a
diaphragm having an annular conductive portion in a magnetic gap portion in a magnetic circuit
is vibratably supported by a damper, and a feed coil electrically coupled to the conductive
portion by a mutual induction action is opposed Are arranged. The speaker generates an
induction current based on mutual induction in the annular conductive portion formed in a part
of the diaphragm, and causes the diaphragm to act on the DC magnetic field at the position of the
magnetic gap with the induction current. To excite the In the technique disclosed in the abovementioned publication, since the voice coil as well as the lead wire is removed, various defects
caused by the lead wire, the voice coil and the like are eliminated. However, the above-mentioned
diaphragm has usually to be formed of metal because of the necessity of generating an induced
current in the conductive portion which is a part of the diaphragm. When the diaphragm is made
of metal, it is heavy (therefore, there is a problem that the sensitivity of the speaker is lowered.
Further, since the conductive portion in the diaphragm and the portion other than the conductive
portion in the diaphragm are not insulated at all, the induced current induced in the conductive
portion goes out of the conductive portion and becomes a leakage current, which is an induced
current The problem is that the Since this leakage current is not useful for driving the
diaphragm, the force for driving the diaphragm is also weakened, and as a result, the sensitivity
of the speaker is lowered. Therefore, improvement of these problems has been desired.
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Therefore, an object of the present invention is to provide a speaker which can reduce the weight
of the diaphragm and prevent the occurrence of leakage current to enhance the sensitivity.
[Means for Solving the Problems] A loudspeaker according to the present invention comprises a
diaphragm including a vibrating portion and an annular conductive portion, a feed coil disposed
to face the conductive portion with a predetermined gap, and a feed coil. And a magnetic circuit
to be attached, and the vibrating plate is formed so that the electric resistance of the conductive
part is lower than the electric resistance of the vibrating part. [Operation] When an alternating
current as a voice signal is supplied to the feeding coil, an alternating magnetic flux is generated.
Since the annular conductive portion closely interlinks with the above-mentioned alternating
current magnetic flux, induced currents of the same frequency are induced in the abovedescribed conductive portion by mutual induction phenomenon. Since the electrical resistance of
the conductive part is lower than the electrical resistance of the vibrating part, the induced
current is more likely to flow in the conductive part, but the induced current is more difficult to
flow in the vibrating part. As a result, more induced current flows through the conductive
portion, and it is possible to prevent the occurrence of leakage current which is not useful for
driving the diaphragm. The above-mentioned induced current works with the DC magnetic field
in the magnetic gap to excite the diaphragm, but since the leakage current is eliminated, the
driving force of the diaphragm can be increased to drive the diaphragm more sensitively. And the
sensitivity of the speaker can be improved. Further, the entire diaphragm can be further reduced
in weight, and the sensitivity of the speaker can be improved. Embodiments of the present
invention will now be described with reference to the drawings. This embodiment is an
application of the present invention to a dome-shaped speaker as shown in FIG. 1 to FIG. The
description will be made in the following order. (A) First Embodiment (B) Second Embodiment (C)
Third Embodiment (D) Fourth Embodiment (E) Fifth Embodiment (F) Sixth Embodiment (A 1) First
Embodiment A first embodiment according to the present invention is shown in FIG. In the
configuration shown in FIG. 1, the speaker 1 is mainly composed of a diaphragm 2, a damper 9, a
primary feeding coil 3, a plate 4, a magnet 5, a yoke plate 6, and a pole piece 11. ing. The domeshaped diaphragm 2 includes a vibrating portion 15 which is thin and hemispherically shaped,
and a conductive portion 8 which is thickly and annularly formed at the opening edge portion 7.
The diaphragm 2 is entirely made of a good conductor, for example, a metal such as aluminum,
beryllium, or magnesium.
The diaphragm 2 is vibratably supported by the damper 9 in a state where the conductive
portion 8 is positioned in the magnetic gap portion 10. The above-mentioned magnetic gap 10 is
annularly formed between the plate 4 and the pole piece 1 of the yoke plate 6. The damper 9 has
a spring property and is formed in an annular shape. The inner peripheral side of the damper 9 is
connected to the periphery of the conductive portion 8, and the outer peripheral side is fixed on
the plate 4. The primary feeding coil 3 electrically couples the annular conductive portions 8 by
mutual induction action, and is disposed opposite to the conductive portions 8 with a
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predetermined gap. The primary feeding coil 3 is disposed to face the outer periphery
corresponding position or the inner periphery corresponding position of the conductive portion
8. The primary feed coil 3 in the illustrated example is fixed to one side end face 12 of the plate 4
so as to correspond to the outer periphery of the annular conductive portion 8. When the
primary feeding coil 3 is provided at a position corresponding to the inner circumference of the
conductive portion 8, the primary feeding coil 3 is fixed to the outer circumference 13 of the
pole piece 11. The primary feeding coil 3 may be provided at both the outer periphery
corresponding position or the inner periphery corresponding position of the conductive portion
8. The plate 4, the magnet 5, the yoke plate 6, and the pole piece 11 constitute a magnetic
circuit. That is, as shown in FIG. 1, the magnet 5 is fixed to the outer peripheral portion on the
yoke plate 6, and the plate 4 is fixed to the outer peripheral portion on the magnet 5. A magnetic
circuit is formed with the magnetic gap 10 separated by a path from the magnet 5 to the plate 4
and from the magnet 5 to the yoke plate 6 and the pole piece 11. Next, an example of the
formation of the diaphragm 2 will be described. In the first embodiment, when the diaphragm 2
is formed, integral drawing is performed on the cylindrical body 16 as a member for forming the
diaphragm 2 by a press. In this case, the vibrating portion 15 is thinly squeezed to a necessary
minimum thickness, and the conductive portion 8 is squeezed thick. As described above, by
thickening the conductive portion 8 to increase the cross-sectional area of the conductive portion
8 and thinning the vibrating portion 15 to reduce the cross-sectional area of the vibrating
portion 15, on the other hand, the entire diaphragm 2 is lighter. On the other hand, the
resistance of the conductive portion 8 is lowered and the resistance of the vibrating portion 15 is
raised. Next, the operation of the speaker 1 will be described. When an alternating current as an
audio signal is supplied to the primary feeding coil 3, an alternating magnetic flux corresponding
to the input waveform is generated. Since the annular conductive portion 8 closely interlinks
with the above-mentioned alternating current magnetic flux, induced currents of the same
frequency are induced in the conductive portion 8 by the mutual induction phenomenon.
Since the conductive portion 8 is located in the magnetic gap 10, a force proportional to the
product of the strength of the DC magnetic field in the magnetic gap 10 and the induced current
acts on the conductive portion 8. That is, the induction current of the conductive portion 8 acts
on the DC magnetic field in the magnetic gap portion 10 to drive the diaphragm 2 directly to
emit a sound wave. As described above, since the conductive portion 8 is thick and the vibrating
portion 15 is thin as much as necessary, the entire diaphragm 2 can be reduced in weight, and
the sensitivity of the speaker 1 can be improved. Further, since the cross sectional area of the
conductive portion 8 is increased and the cross sectional area of the vibrating portion 15 is
decreased, the resistance of the conductive portion 8 is relatively decreased and the resistance of
the vibrating portion 15 is relatively increased. Therefore, more induced current flows through
the conductive portion 8, and the occurrence of leakage current can be prevented. By preventing
the occurrence of the leakage current, the driving force of the diaphragm 2 can be increased, the
diaphragm 2 can be driven more sharply, and the sensitivity of the speaker 1 can be improved.
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(B) Second Embodiment The second embodiment differs from the first embodiment in the
method of forming the diaphragm 2. An example of formation of the diaphragm 2 in the second
embodiment is shown in FIG. The main point of the formation of the diaphragm 2 is to reduce
only the thickness of the range corresponding to the vibrating portion 15 in the cylindrical body
16 by cutting. The outer peripheral surface 17 of the cylindrical body 16 having a thickness t16
as shown in FIG. 2A is cut until it has a minimum thickness t15, leaving only the lower portion
18. Thereby, the diaphragm 2 as shown in FIG. 2B is formed. That is, the diaphragm 2 includes a
thin vibrating portion 15 which is cut from thickness t16 to thickness t15, and a thick conductive
portion 8 which has a thickness t16 in a non-cutting state. By the way, when the concave portion
25 as shown by the dotted line in FIG. 2B is formed, the cross-sectional area is reduced, and the
resistance value between the conductive portion 8 and the vibrating portion 15 can be increased.
By providing such a recess 25, it is possible to adjust the high frequency cutoff frequency. As
described above, this second embodiment shows an example in which the diaphragm 2 is formed
by cutting, but as a method other than cutting, for example, sputtering, oxidation treatment, etc.
are also possible. If the diaphragm 2 is made of aluminum, oxidation treatment, so-called alumite
treatment is particularly effective. In this case, if colored alumite treatment, for example, black, is
performed, it can be made to be excellent in design, and the heat dissipation performance is also
improved.
The other contents are the same as those in the first embodiment, and the redundant description
will be omitted. (C) Third Embodiment The third embodiment differs from the first and second
embodiments in the method of forming the diaphragm 2. An example of formation of the
diaphragm 2 in the third embodiment is shown in FIG. Hereinafter, description will be made with
reference to FIG. The opening edge 30 of the cylindrical body 16 formed with the minimum
necessary thickness is folded back to form the annular conductive portion 8. Thereby, the
diaphragm 2 is formed. The means for forming the diaphragm 2 can be selected appropriately as
a press or the like. The other contents are the same as those of the first embodiment, and the
redundant description will be omitted. (D) Fourth Embodiment The fourth embodiment differs
from the first embodiment in the method of forming the diaphragm 2. An example of the
formation of the diaphragm 2 in the fourth embodiment is shown in FIG. The point of formation
of the diaphragm 2 in the fourth embodiment is to make the thickness L8 of the conductive
portion 8 larger than the thickness t16 of the cylindrical body 16 by plating. A metal having
good conductivity, for example, only on the lower portion 18 of the outer peripheral surface 17
of the cylindrical body 16 [thickness t16] formed thin to the minimum necessary thickness as
shown in FIG. 4A. By applying metal plating such as gold, silver and copper, as shown in FIG. 4B,
the diaphragm 2 in which the plating portion 36 is formed thicker toward the outer periphery is
configured. That is, the diaphragm 2 is composed of a thin vibrating portion 15 which is not
laminated and has a thickness t15, and a thick conductive portion 8 which is formed of a plating
portion 36 and which has a thickness t8. Further, FIG. 4C shows the case where the plating
portion 36 is formed on the inner peripheral surface 35 of the cylindrical body 16, and the case
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where the plating portion 36 is formed on the inner and outer peripheral surface 35.17 in the
fourth embodiment. . Although not described in detail, each of them has the label portion 36
formed by the same method as in FIG. 4B, thereby obtaining a desired function. In the fourth
embodiment, an example of the stick processing is described, but the present invention is not
limited to the stick processing, and may be performed by sputtering, for example. The other
contents are the same as those of the first embodiment, and the redundant description will be
omitted. (E) Fifth Embodiment The fifth embodiment differs from the first embodiment in the
method of forming the diaphragm 2. An example of formation of the diaphragm 2 in the fifth
embodiment is shown in FIG. The point of formation of the diaphragm 2 in the fifth embodiment
is that the thickness of the conductive portion 8 is made larger than the thickness t16 by fitting
the conductive ring 40 to the opening edge 30 of the cylindrical body 16 .
As shown in FIG. 5A, on the outer peripheral surface 17 of the lower portion 18 of the cylindrical
body 16 (thickness is also 16) formed to be as thin as necessary, it is formed of a material having
good conductivity. The conductive ring 40 as shown in B is fitted. Thus, the diaphragm 2 as
shown in FIG. 5C is formed. The other contents are the same as those of the first embodiment,
and the redundant description will be omitted. (F) Sixth Embodiment The sixth embodiment
differs from the first embodiment in the formation of the diaphragm 2. An example of the
formation of the diaphragm 2 in the sixth embodiment is shown in FIG. The main point of the
formation of the diaphragm 2 in the sixth embodiment is that, in the vibrating portion 15 of the
diaphragm 2 formed thin, a large number of portions 45 (hereinafter referred to as non-passing
portions) where no DC magnetic field passes at all. It is providing a hole. The above-mentioned
non-passing portion 45 is a range in which the DC magnetic field does not pass when the
diaphragm 2 is moved to the lowermost position (direction of arrow Do in FIG. 7) as shown in
FIG. It means the lowermost part. In the example shown in FIG. 6A, round holes 46, in the
example shown in FIG. 6B, horizontally long holes 47, and in the example shown in FIG. 6C, many
vertically long holes 48 are formed in the non-passing portion 45 respectively. ing. As described
above, by forming the holes 46.47.48 in the non-passing portion 45 of the DC magnetic field, the
entire diaphragm 2 is reduced in weight, and the cross-sectional area of the portion through
which current flows in the non-passing portion 45 is reduced. The resistance is increased to
prevent the occurrence of leakage current. Also, depending on the state of formation of the holes
46 and 47.
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