JPH10234098

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DESCRIPTION JPH10234098
[0001]
The present invention relates to an electrostatic electroacoustic transducer, and in particular, by
using a thin ceramic flat plate as a diaphragm, preferably a zirconia flat plate, a wide band and a
good sound quality can be obtained. The present invention relates to electrostatic electroacoustic
transducers such as speakers, headphones, and microphones.
[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
rule.
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[0004]
The cone type dynamic speaker 10 as described above uses the cone paper 12 in terms of sound
pressure characteristics and material characteristics as a diaphragm, but as shown in FIG.
Acoustic distortion λ occurs. 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, conventionally, an electrostatic loudspeaker using a flat diaphragm capable of solving
various problems of the cone dynamic loudspeaker 10 has been put to 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]
In this electrostatic speaker 30, since the driving force is applied to the entire surface of the
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diaphragm 32, as shown in FIG. 9, it is difficult to cause divided vibration, and the acoustic
distortion generated in the cone dynamic speaker 10 is also generated. It does not occur.
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, for example, in Japanese Patent Application Laid-Open No. 61-7797, it is
proposed to use a ceramic flat plate as a diaphragm.
The purpose of this is to prevent the interference of the sound waves generated by the cone type
dynamic speaker 10 and to remove the resonance.
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[0013]
However, since the above-mentioned example of a proposal assumes a speaker of a magnet type
to the last, and does not assume an electrostatic type speaker, handling of various parameters,
such as thickness, is different.
[0014]
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.
[0015]
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
[0016]
The electrostatic electroacoustic transducer according to the present invention as set forth in
claim 1 is constructed using a ceramic flat plate having a thickness of 1 μm or more and 30 μm
or less as a diaphragm.
[0017]
Thereby, since the ceramic flat plate is not hygroscopic, the sound quality is not impaired even if
the electrostatic electroacoustic transducer is used in a high humidity environment.
Further, since the ceramic flat plate is a high elastic modulus material, it is possible to increase
the drive amplitude of the diaphragm, which makes it possible to increase the volume.
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In addition, since the diaphragm is a flat diaphragm, the interference of sound does not occur as
in a cone type dynamic speaker using a conical cone paper, and the sound quality can be further
improved.
[0018]
Here, if a ceramic flat plate 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 ceramic flat plate having a thickness of less than 1 μm is used as a diaphragm, the
mechanical strength is extremely low and it can not be practically used as a diaphragm.
[0019]
And it is preferable to use a zirconia as a ceramic plane plate which comprises the said
diaphragm.
[0020]
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 speaker.
[0021]
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.
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[0022]
First, as shown in FIG. 1, the electrostatic loudspeaker 50A according to the first embodiment
has, for example, a flat polygonal shape (including a circular shape) and a diaphragm 54 having
an electrode film 52 formed on the surface. And an electrode plate 56 having a planar polygonal
shape (including a circular shape) in the same manner, for example, with a ring-shaped spacer
member 58 interposed therebetween.
[0023]
Further, in the electrostatic loudspeaker 50A according to the first embodiment, one of the
diaphragm 54 side between the electrode film 52 formed on the surface of the diaphragm 54
and the electrode plate 56 is a positive electrode. A bias power supply 60 (bias voltage E) and a
generation source (audio signal source) 62 of the audio signal e are connected.
[0024]
The adhesion between the spacer member 58 and the electrode plate 56 and the adhesion
between the diaphragm 54 and the spacer member 58 are performed using, for example, an
adhesive.
Further, the spacer member 58 uses an insulator such as plastic, thermosetting phenol resin,
acrylic resin or the like.
Although not shown, the spacer member 58 is appropriately insulated from the electrode plate
56 by using a metal ring as necessary in order to connect the electrode film 52 to the outside.
[0025]
In the electrostatic speaker 50A according to the first embodiment, the diaphragm 54 is formed
of a ceramic flat plate having a thickness of 1 μm or more and 30 μm or less.
[0026]
Since the ceramic flat plate is not hygroscopic, the sound quality is not impaired even if the
electrostatic speaker 50A is used in a high humidity environment.
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Further, since the ceramic flat plate is a high elastic modulus material, the drive amplitude of the
diaphragm 54 can be increased, which makes it possible to increase the volume.
Moreover, since the diaphragm 54 is flat, interference of sound does not occur as in a cone-type
dynamic speaker using cone-shaped cone paper, and the sound quality can be further improved.
[0027]
In FIG. 1, the electrode plate 56 may be made of ceramic and an electrode as a fixed electrode
may be formed thereon. In this case, the ceramic integrated electrostatic speaker 50A is
obtained, and the corrosion resistance is improved.
[0028]
By the way, if the thickness of the ceramic flat plate constituting the diaphragm 54 exceeds 30
μm, the diaphragm 54 does not vibrate sufficiently by the force of static electricity, and a loud
sound can not be obtained. Therefore, the thickness of the ceramic flat plate is preferably 20 μm
or less. In this case, the drive amplitude of the diaphragm 54 can be further increased, which is
advantageous in sound quality and volume.
[0029]
Here, one experimental example is shown. In this experimental example, the thickness of the
diaphragm 54 formed of a ceramic flat plate was appropriately changed to observe how the force
necessary for the diaphragm 54 to obtain a constant strain (flexure, etc.) changes. It is a thing.
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 54 and the electrode plate 56,
absolute values are shown. Absent.
[0030]
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From the experimental results shown in FIG. 2, it can be seen that the required force rapidly
increases when the thickness of the diaphragm 54 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
ceramic flat plate having a thickness of more than 30 μm is used as the diaphragm 54, a force
due to static electricity does not sufficiently vibrate and a loud sound can not be obtained.
Therefore, the thickness of the diaphragm 54 is preferably 20 μm or less. When a ceramic flat
plate having a thickness of less than 1 μm is used as the diaphragm 54, the mechanical strength
is extremely low and it can not be practically used as the diaphragm 54.
[0031]
It is preferable to use zirconia as the ceramic flat plate that constitutes the diaphragm 54.
Zirconia has a high elastic modulus of 200 GPa and a density of 5.9 g / cm 3, so the specific
elastic modulus (elastic modulus / density) is 3.4 × 10 12 cm 2 / sec 2, and the material of the
conventional plastic diaphragm For example, as compared with the elastic modulus of 2 GPa,
density of 1.38 g / cm 3, and specific elastic modulus of 0.14 × 10 12 cm 2 / sec 2 of polyester,
it is advantageous as sound quality improvement.
[0032]
In particular, zirconia having yttria added in an amount of 2 to 4 mol%, which is mainly
tetragonal, or mainly tetragonal or cubic, has a bending strength as high as about 400 to 1000
MPa, and the diameter of crystal particles constituting the sintered body is also 0.1 Since it is as
small as about 0.5 μm, it is extremely convenient for processing as a thin flat plate.
[0033]
Besides the above-mentioned zirconia, for example, ceramics such as silicon nitride, silicon
carbide, and alumina are preferably used as the material of the diaphragm 54 of the electrostatic
speaker 50A because they are easily processed as a thin flat plate having a high elastic modulus.
can do.
[0034]
FIG. 3 shows the specific elastic modulus of the various ceramics and the specific elastic modulus
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of polyester (material of the conventional diaphragm) as a comparative example.
These various ceramics are higher in specific modulus by one to two digits than polymer films
conventionally used as diaphragm materials for any ceramics, for example, polyester.
Further, the elastic modulus is also high by two orders of magnitude, and even if the drive
voltage of the diaphragm 54 is increased by increasing the applied voltage e of the audio signal
source 62, the actuator 54 can sufficiently follow.
[0035]
The ceramic flat plate is obtained, for example, by firing a green sheet formed by a known
forming method such as a doctor blade or a reverse roll coater. In addition, a method of forming
on an organic film by printing, a method of depositing or precipitating from an alkoxide solution
or the like on an organic film, a method of forming a conductive layer on an organic film and
forming a film by electrophoresis may be applicable. It is.
[0036]
On the other hand, any conductive film can be used as the electrode film 52 formed on the
surface of the diaphragm 54. For example, metal films such as gold, silver, aluminum, copper, etc.
or oxidized films such as ITO It can also be obtained by a method of forming various transparent
electrode films including an object by sputtering, for example.
[0037]
Next, an electrostatic speaker 50B according to a second embodiment will be described with
reference to FIG.
[0038]
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
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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. An electrode film 82 is formed thereon.
[0039]
Further, in the electrostatic speaker 50B according to the second embodiment, two bias power
supplies 84 and 86 having a positive electrode on the side of one electrode plate 72 between the
pair of electrode plates 72 and 76 (both bias voltages E) is connected, and an audio signal source
88 is connected between contact points a of the bias power supplies 84 and 86 and an electrode
film 82 formed on the surface of 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.
[0040]
Also in the electrostatic speaker 50B according to the second embodiment, the diaphragm 80 is
formed of a ceramic flat plate having a thickness of 1 μm or more and 30 μm or less, and
zirconia, silicon nitride, or the like as the ceramic flat plate. Either silicon carbide or alumina is
used.
[0041]
Therefore, as in the case of the electrostatic loudspeaker 50A according to the first embodiment,
the use of the electrostatic loudspeaker 50B in a high humidity environment does not impair the
sound quality, and the diaphragm 80 The drive amplitude 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.
[0042]
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Next, an electrostatic speaker 50C according to a third embodiment will be described with
reference to FIG.
The parts corresponding to those in FIG. 4 are denoted by the same reference numerals and the
description thereof will be omitted.
[0043]
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 properties) 92 having a large number of
through holes 90 is attached to the respective opposing surfaces in the and 76, and two bias
power sources 84 and 86 (see FIG. 4) are omitted. It has composition.
[0044]
For example, since the electret film 92 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 of FIG.
Therefore, the two bias power supplies 84 and 86, which were required in the first embodiment,
can be omitted, and the reduction in size and weight of the electrostatic speaker 50C can be
promoted.
[0045]
Also in the electrostatic speaker 50C according to the third embodiment, a ceramic flat with a
thickness of 1 μm or more and 30 μm or less is the same as the electrostatic speaker 50B
according to the second embodiment. The diaphragm 80 is composed of a face plate, and any
one of zirconia, silicon nitride, silicon carbide and alumina is used as the ceramic flat plate.
[0046]
Therefore, similarly to the electrostatic speaker 50B according to the second embodiment, the
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sound quality is not impaired, and the drive amplitude of the diaphragm 80 can be increased,
thereby increasing the volume. It becomes possible.
And since it is a flat diaphragm 80, a sound quality can be improved further.
[0047]
As described above, the electric field necessary for the electrostatic type is formed by forming
the electret film 92 on the pair of electrode plates 72 and 76 as in the electrostatic speaker 50C
according to the third embodiment. As in the electrostatic speakers 50A and 50B according to
the first and second embodiments, any method using DC bias voltage E may be used.
[0048]
In addition, as in the electrostatic loudspeaker 50A according to the first embodiment, as in the
electrostatic loudspeakers 50B and 50C according to the single type in which the electrode plate
56 is only one, and the second and third embodiments. In addition, any of the push-pull type in
which the electrode plates 72 and 76 are on both sides of the diaphragm 80 is possible.
[0049]
Further, the distance between the electrode plate and the diaphragm can be set arbitrarily in the
range of about 0.2 mm to 5 mm, and the bias voltage E can be set arbitrarily from about 50 V to
several thousand V.
The voltage of the AC signal (audio signal e) can also be arbitrarily set to about 0 to 1000 Vrms.
[0050]
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.
[0051]
Zirconia containing 3 mol% of yttria was molded with a doctor blade, peeled from the carrier
film, and fired at 1400 ° C. in air to prepare a zirconia of 5 μm in thickness in which the crystal
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phase is mainly tetragonal.
[0052]
Aluminum was formed on the surface of the zirconia by vapor deposition to obtain a diaphragm
54 having an effective diameter of about 50 mm.
[0053]
Then, in the electrostatic speaker 50A according to the first embodiment shown in FIG. 1, the
diaphragm 54 is used, the electrode plate 56 is made of copper, and the spacer member 58 is
made of organic polymer resin (thermosetting phenolic resin or the like) , And the distance
between the diaphragm 54 and the electrode plate 56 was 2 mm, and the single-type
electrostatic speaker 50A was assembled.
[0054]
In the assembled electrostatic speaker 50A, when the bias voltage E of the bias power source 60
was 500 V DC and the signal e of the audio signal source 62 was a voltage signal of AC 300
Vrms, clear sound was generated from 20 Hz to 20 kHz.
A 10 μm thick zirconia was prepared with the same composition as in Example 1 above, and ITO
was formed on both sides by sputtering to produce a diaphragm 80 having an effective diameter
of 100 mm.
[0055]
In the electrostatic speaker 50B according to the second embodiment shown in FIG. 4, a large
number of through holes 70 and 74 each having a diameter of 2 mm are provided as the pair of
electrode plates 72 and 76 using the diaphragm 80. A push-pull electrostatic speaker 50B was
produced by using a copper plate and further installing a pair of electrode plates 72 and 76 on
both sides of the diaphragm 80 at intervals of 3 mm.
[0056]
When the bias voltage E in each of the two bias power supplies 84 and 86 is 500 V DC and the
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signal e of the audio signal source 88 is a voltage signal of AC 250 Vrms in the produced
electrostatic speaker 50 B, sufficient from 20 Hz to 20 kHz. Sound pressure sound was
generated.
A composition obtained by adding 1 wt% of high purity magnesia to high purity alumina was
molded by a doctor blade method, and fired at 1600 ° C. to produce alumina of 15 μm
thickness.
Thereafter, ITO was formed on both sides of the alumina by sputtering to prepare a diaphragm
80 having an effective diameter of 100 mm.
[0057]
In the electrostatic speaker 50C according to the third embodiment shown in FIG. 5, a large
number of through holes 70 and 74 each having a diameter of 2 mm are provided as the pair of
electrode plates 72 and 76 using the diaphragm 80. A push-pull electrostatic speaker 50C was
produced by placing a pair of electrode plates 72 and 76 on both sides of the diaphragm 80 at
intervals of 3 mm using a copper plate.
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 92.
[0058]
When the signal e of the audio signal source 88 was a voltage signal of AC 200 Vrms in the
produced electrostatic speaker 50C, sound with sufficient sound pressure was generated from 20
Hz to 20 kHz.
[0059]
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.
[0060]
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As described above, according to the electrostatic electroacoustic transducer according to the
present invention, a ceramic flat plate with a thickness of 1 μm or more and 30 μm or less is
used as the diaphragm.
[0061]
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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