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JPH10234097

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DESCRIPTION JPH10234097
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an
electrostatic electroacoustic transducer, in particular, by using a thin metal foil as a diaphragm,
preferably beryllium copper, titanium, stainless steel, aluminum or nickel. The present invention
relates to an electrostatic electroacoustic transducer such as a speaker, a headphone, and a
microphone capable of obtaining a wide band and good sound quality.
[0002]
2. Description of the Related Art Generally, a speaker is an electroacoustic transducer that
converts electrical signals into sound waves which are vibrations of air, such as a cone dynamic
speaker and an electrostatic speaker.
[0003]
For example, as shown in FIG. 6, the cone-type dynamic speaker 10 uses, as a mechanical plate,
conical cone paper 12 in terms of material characteristics such as mechanical strength and sound
pressure characteristics.
In the magnetic field generated between the center pole 16 and the yoke 18 by the permanent
magnet 14, there is a voice coil 20 attached to the inward end of the cone paper 12, and the
current flowing through the voice coil 20 is Cone 12 vibrates according to Fleming's left-hand
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rule.
[0004]
As described above, the cone type dynamic speaker 10 as described above uses the cone paper
12 from the viewpoint of the sound pressure characteristics as the diaphragm and the material
characteristics, but as shown in FIG. An acoustic distortion λ occurs in the inner central portion
of The distortion λ is considered to occur due to interference because the vector of the sound
wave w2 generated from the other side opposite to the sound wave w1 generated from one side
of the cone paper 12 is not parallel.
[0005]
This acoustic distortion λ causes a phenomenon of losing the sharpness of the sound emitted
from the speaker 10 or blurring the localization of the sound image.
[0006]
Therefore, an electrostatic loudspeaker using a flat diaphragm capable of solving various
problems of the cone dynamic loudspeaker 10 has been put into practical use.
[0007]
As shown in FIGS. 7 and 8, in this electrostatic speaker 30, for example, a flat circular diaphragm
32 and a fixed plate 34 also serving as a flat circular electrode are interposed between the ring
spacer members 36. One capacitor is configured by arranging the electrode 38 formed on one
plate surface of the diaphragm 32 and the fixed plate 34 so as to face each other.
[0008]
Then, by applying a voltage between the electrode 38 and the fixed plate 34, an electrostatic
force acts between the diaphragm 32 and the fixed plate 34, and the diaphragm 32 is vibrated by
this electrostatic force. In order to produce an acoustic output proportional to the signal voltage,
a bias voltage E is superimposed on the signal voltage e and applied between the electrode 38
and the fixed plate 34.
[0009]
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In this electrostatic speaker 30, since the driving force is applied to the entire surface of the
diaphragm 32, as shown in FIG. 9, it is difficult to cause divided vibration, and the acoustic
distortion λ generated in the cone dynamic speaker 10 Nor.
Moreover, since the diaphragm 32 vibrates in phase, good acoustic characteristics can be
obtained.
[0010]
By the way, there are many known examples of the electrostatic type speaker 30 as described
above, but in these known examples, as shown in, for example, JP-A-52-18577. A thin plastic film
or a polymer film such as polyester is used as the diaphragm 32.
[0011]
Therefore, when the conventional electrostatic speaker 30 is used in a high humidity
environment, a hygroscopic phenomenon may occur in the diaphragm 32, which may cause
sound cracking or the like.
In addition, since the diaphragm 32 made of a polymer film has low mechanical strength and low
elastic modulus, the vibration speed of the diaphragm 32 can not follow the audio signal when
the amplitude of the audio signal is increased and the sound signal is not received. Phenomena
such as loss of sharpness and blurring of the localization of the sound image may occur.
Therefore, there is a disadvantage that the amplitude (sound volume) of the audio signal can not
be increased so much.
[0012]
On the other hand, in a magnet type speaker, it is known to use a metal plate such as titanium as
a diaphragm.
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This is because the high specific modulus of the metal allows the zone to be broadened.
However, since these are not assumed to be electrostatic speakers, handling of various
parameters such as thickness is different.
[0013]
Furthermore, for example, JP-B-56-53920 discloses an example using a diaphragm having a
thickness of about 40 to 60 μm. This example focuses only on the mechanical strength, and is
considered to be still an insufficient value in consideration of high followability to an audio signal
and lightness.
[0014]
The present invention has been made in consideration of such problems, and it is possible to
increase the drive amplitude of the diaphragm without deteriorating the sound quality even in a
high humidity environment, and to improve the volume. It is an object of the present invention to
provide an electrostatic electroacoustic transducer capable of
[0015]
The electrostatic electroacoustic transducer according to the present invention as set forth in
claim 1 is constructed using a metal foil having a thickness of 0.5 μm or more and 30 μm or
less as a diaphragm.
[0016]
As a result, since the metal foil is not hygroscopic, the sound quality is not impaired even if the
electrostatic electroacoustic transducer is used in a high humidity environment.
In addition, since the metal foil is a high elastic modulus material, the drive amplitude of the
diaphragm can be increased, which makes it possible to increase the volume.
In addition, since the diaphragm is a flat diaphragm, the interference of sound does not occur as
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in a cone type dynamic speaker using a conical cone paper, and the sound quality can be further
improved.
[0017]
Here, when a metal foil having a thickness of more than 30 μm is used as a diaphragm, the force
due to static electricity does not sufficiently vibrate, and a loud sound can not be obtained. If a
metal foil having a thickness of less than 0.5 μm is used as a diaphragm, the mechanical
strength is extremely low and it can not be practically used as a diaphragm.
[0018]
The metal foil is preferably any of beryllium copper, titanium, stainless steel, aluminum and
nickel, in consideration of high specific elastic modulus, practicability, manufacturing cost, mass
productivity and the like.
[0019]
The electrostatic electroacoustic transducer according to the present invention includes a
microphone, headphones and the like in addition to the speaker.
However, the feature that the amplitude of the diaphragm can be increased is best exhibited in
the case of a transducer that emits sound, such as a speaker or a headphone.
[0020]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, several embodiments
in which the electrostatic electroacoustic transducer according to the present invention is applied
to, for example, an electrostatic speaker (hereinafter referred to simply as an electrostatic
loudspeaker according to the embodiment and Will be described with reference to FIGS.
[0021]
First, as shown in FIG. 1, the electrostatic speaker 50A according to the first embodiment
includes, for example, a diaphragm 52 of a plane polygon shape (including a circle) and an
electrode of the plane polygon shape (including a circle) as well. A plate 54 and a plate 54 are
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stacked, for example, with a ring-shaped spacer member 56 interposed therebetween.
[0022]
Further, in the electrostatic loudspeaker 50A according to the first embodiment, one bias power
supply 58 (bias voltage E) having the diaphragm 52 side as the positive electrode between the
diaphragm 52 and the electrode plate 54 and the audio signal e. Source (voice signal source) is
connected.
[0023]
The adhesion between the spacer member 56 and the electrode plate 54 and the adhesion
between the diaphragm 52 and the spacer member 56 are performed using, for example, an
adhesive.
Further, the spacer member 56 uses an insulator such as plastic, thermosetting phenolic resin,
acrylic resin or the like.
Although not shown, in order to electrically connect the diaphragm 52 to the outside, the spacer
member 56 may be appropriately insulated from the electrode plate 54 by using a metal ring if
necessary. .
[0024]
In the electrostatic loudspeaker 50A according to the first embodiment, the diaphragm 52 is
formed of a metal foil having a thickness of 0.5 μm or more and 30 μm or less.
[0025]
Since the metal foil is not hygroscopic, the sound quality is not impaired even if the electrostatic
speaker 50A is used in a high humidity environment.
Further, since the metal foil is a high elastic modulus material, the drive amplitude of the
diaphragm 52 can be increased, which makes it possible to increase the volume.
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In addition, since the diaphragm 52 is a flat diaphragm, no sound interference occurs as in the
cone-type dynamic speaker 10 using cone-shaped cone paper, and the sound quality can be
further improved.
[0026]
By the way, if the thickness of the metal foil which comprises the diaphragm 52 exceeds 30
micrometers, the diaphragm 52 will not fully vibrate with the force by static electricity, but a
loud sound can not be obtained. Therefore, the thickness of the metal foil is preferably 20 μm or
less. In this case, the drive amplitude of the diaphragm 52 can be further increased, which is
advantageous in sound quality and volume.
[0027]
Here, one experimental example is shown. In this experimental example, the thickness of the
diaphragm 52 made of metal foil is appropriately changed to see how the force necessary for the
diaphragm 52 to obtain a certain distortion (such as deflection) changes. It is. The experimental
results are shown in FIG. In FIG. 2, since the force on the vertical axis differs depending on
various conditions such as the size of the electrostatic speaker 50A, the magnitude of the bias
voltage E, and the distance between the diaphragm 52 and the electrode plate 54, they are
shown by absolute values. Absent.
[0028]
From the experimental results in FIG. 2, it can be seen that the required force is rapidly increased
when the thickness of the diaphragm 52 exceeds 30 μm. When the thickness is 20 μm or less,
it vibrates with a relatively small force. From this, as described above, when a metal foil having a
thickness of more than 30 μm is used as the diaphragm 52, the force by static electricity does
not sufficiently vibrate, and a loud sound can not be obtained. Therefore, the thickness of the
diaphragm 52 is preferably 20 μm or less. When a metal foil having a thickness of less than 0.5
μm is used as the diaphragm 52, the mechanical strength is extremely low and it can not be
practically used as the diaphragm 52.
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[0029]
As a metal foil which comprises the diaphragm 52, either of beryllium copper, titanium, stainless
steel, aluminum, and nickel can be used, for example. FIG. 3 shows the specific elastic modulus
(elastic modulus / density) of the various metals and the specific elastic modulus of polyester (the
material of the conventional diaphragm) as a comparative example.
[0030]
Among the various metals, any of the metals is one digit higher than a polymer film such as
polyester, which has conventionally been used as a diaphragm material. In addition, the elastic
modulus is also high by one to two digits, and even if the drive voltage of the diaphragm 52 is
increased by increasing the applied voltage e of the audio signal source 60, it can follow
sufficiently.
[0031]
In addition, a ceramic can be coated on a metal foil to increase the elastic modulus. In this case,
SiC, SiN, ZrO2, Al2O3, diamond or the like can be used as the ceramic.
[0032]
Next, an electrostatic speaker 50B according to a second embodiment will be described with
reference to FIG.
[0033]
As shown in FIG. 4, the electrostatic speaker 50B according to the second embodiment has, for
example, a flat polygonal shape (including a circular shape) and one electrode plate 72 on which
a large number of through holes 70 are formed. Similarly, the other electrode plate 76 which is
also in the form of a plane polygon (including a circle) and on which a large number of through
holes 74 are formed is overlapped with, for example, a ring-shaped spacer member 78
interposed therebetween. A diaphragm 80 is stretched parallel to the plate surfaces of the
electrode plates 72 and 76 so as to partition the space between the pair of electrode plates 72
and 76 in the direction intermediate portion.
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[0034]
Further, in the electrostatic speaker 50B according to the second embodiment, two bias power
supplies 82 and 84 (both of which have a positive electrode between the pair of electrode plates
72 and 76 with one electrode plate 72 side as a positive electrode) E) is connected, and an audio
signal source 86 is connected between the contact points a of the bias power supplies 82 and 84
and the diaphragm 80.
The adhesion between the spacer member 78 and the pair of electrode plates 72 and 76 and the
adhesion between the diaphragm 80 and the spacer member 78 are performed using, for
example, an adhesive.
[0035]
Also in the electrostatic speaker 50B according to the second embodiment, the diaphragm 80 is
formed of a metal foil having a thickness of 0.5 μm or more and 30 μm or less, and beryllium
copper, titanium, or the like as the metal foil. It is made to use either stainless steel, aluminum or
nickel.
[0036]
Therefore, as in the case of the electrostatic speaker 50A according to the first embodiment, even
if the electrostatic speaker 50B is used under a high humidity environment, the drive amplitude
of the diaphragm 80 can be reduced without deteriorating the sound quality. The volume can be
increased, which makes it possible to increase the volume.
And since it is a flat diaphragm 80, a sound quality can be improved further.
[0037]
Next, an electrostatic speaker 50C according to a third embodiment will be described with
reference to FIG.
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The parts corresponding to those in FIG. 4 are denoted by the same reference numerals and the
description thereof will be omitted.
[0038]
An electrostatic speaker 50C according to the third embodiment has substantially the same
configuration as the electrostatic speaker 50B according to the second embodiment, as shown in
FIG. An electret film (plastic film having electrification property) 90 having a large number of
through holes 88 is attached to the respective opposing surfaces of and 76, and two bias power
sources 82 and 84 (see FIG. 4) are omitted. It has composition.
[0039]
For example, since the electret film 90 is pre-charged as shown in FIG. 5, one electrode plate 72
is positively charged and the other electrode plate 76 is negatively charged in the absence of a
signal. It is equivalent to a state in which a bias voltage E is applied between the electrode plates
72 and 76, with the one electrode plate 72 side being positive.
Therefore, it is possible to omit the two bias power supplies 82 and 84 which were necessary in
the first embodiment, and it is possible to promote miniaturization and weight reduction of the
electrostatic speaker 50C.
[0040]
Also in the electrostatic speaker 50C according to the third embodiment, similarly to the
electrostatic speaker 50B according to the second embodiment, a metal foil having a thickness of
0.5 μm or more and 30 μm or less is used. The diaphragm 80 is configured, and any one of
beryllium copper, titanium, stainless steel, aluminum, and nickel is used as the metal foil.
[0041]
Therefore, as with the electrostatic speaker 50B according to the second embodiment, the drive
amplitude of the diaphragm 80 can be increased without impairing the sound quality, and this
makes it possible to increase the volume. .
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And since it is a flat diaphragm 80, a sound quality can be improved further.
[0042]
In each said embodiment, although the example which applied the electrostatic-type
electroacoustic transducer based on this invention to the electrostatic-type speaker was shown, it
can apply to a microphone and headphones besides others.
[0043]
In the electrostatic speaker 50A according to the first embodiment shown in FIG. 1, a titanium
foil 5 μm thick is used as the diaphragm 52, the electrode plate 54 is aluminum, and the spacer
member 56 is an organic polymer resin (thermosetting As a phenol resin etc., the single-type
electrostatic speaker of 50 mm diameter was assembled.
[0044]
When the bias voltage E of the bias power source 58 was 200 V DC and the signal e of the audio
signal source 60 was 100 Vrms AC, clear sound was generated over 20 Hz to 20 kHz.
In an electrostatic speaker 50B according to the second embodiment shown in FIG. 4, a beryllium
copper alloy having a thickness of 10 μm and an effective diameter of 100 mmφ is used as a
diaphragm 80, and a pair of electrode plates 72 and 76 is a through hole having a diameter of 2
mm. Using a copper plate provided with a large number of 70 and 74, and further installing a
pair of electrode plates 72 and 76 at intervals of 3 mm on both sides of the diaphragm 52, a
push-pull electrostatic speaker was produced .
[0045]
When the bias voltage E in each of the two bias power supplies 82 and 84 is 500 V DC and the
signal e of the audio signal source 86 is a voltage signal of AC 250 Vrms, sound with a sufficient
sound pressure from 20 Hz to 20 kHz is generated.
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In an electrostatic speaker 50C according to the third embodiment shown in FIG. 5, a beryllium
copper alloy having a thickness of 10 μm and an effective diameter of 100 mmφ is used as a
diaphragm 80, and a pair of electrode plates 72 and 76 is a through hole having a diameter of 2
mm. By using a copper plate provided with a large number of 70 and 74 and installing a pair of
electrode plates 72 and 76 at intervals of 3 mm on both sides of the diaphragm 80, a push-pull
type electrostatic speaker was produced. In this case, an electret film having a thickness of 25
μm and a potential difference of 500 V between both surfaces of the film was used as the
electret film 90.
[0046]
Then, when the signal e of the audio signal source 86 was a voltage signal of AC 200 Vrms,
sound with sufficient sound pressure was generated from 20 Hz to 20 kHz.
[0047]
The electrostatic electro-acoustic transducer according to the present invention is not limited to
the above-described embodiment, and it goes without saying that various configurations can be
adopted without departing from the scope of the present invention.
[0048]
As described above, according to the electrostatic electroacoustic transducer according to the
present invention, a metal foil having a thickness of 0.5 μm or more and 30 μm or less is used
as the diaphragm.
[0049]
Therefore, the sound quality is not impaired even in a high humidity environment, and further,
the drive amplitude of the diaphragm can be increased, and the effect of improving the volume
can be achieved.
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