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JP2013034196

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DESCRIPTION JP2013034196
An object of the present invention is to suppress an influence on an output caused by a change in
distance between an electrode of an electrostatic electroacoustic transducer and a vibrating body.
When a power supply of a drive circuit is turned on, a measurement unit measures a voltage
applied from a bias power supply to a vibrating body, and the electrostatic speaker and the
resistor function as a capacitor. The time constant τ of the configured integration circuit is
measured. The adjustment unit 142 calculates the distance between the vibrating body 10 and
the electrode 20 from the area S of the vibrating body 10, the dielectric constant ε of the elastic
member 30, the resistance value R of the resistor R1 and the obtained time constant τ. The
control unit 140 controls the bias power supply 120 according to the calculated distance d to
adjust the bias voltage applied to the vibrator 10. [Selected figure] Figure 4
Drive circuit and electrostatic electroacoustic conversion system
[0001]
The present invention relates to an electrostatic electroacoustic transducer and a circuit related
to the electroacoustic transducer.
[0002]
As a flexible, foldable or bendable electrostatic speaker, for example, there is an electrostatic
speaker disclosed in Patent Document 1.
04-05-2019
1
In this electrostatic speaker, a polyester film on which aluminum is vapor-deposited is
sandwiched between two cloths woven by conductive yarn, and ester wool is disposed between
the film and the cloth. There is. In this electrostatic speaker, when a bias voltage is applied to a
film serving as a vibrating body and an audio signal boosted by a transformer is supplied to a
cloth serving as an electrode, the vibrating body vibrates in accordance with a change in the
audio signal. The sound is emitted.
[0003]
JP 2008-54154 A
[0004]
The electrostatic loudspeaker disclosed in Patent Document 1 includes ester wool in order to
maintain the distance between the cloth and the film, but the thickness of the ester wool varies.
For this reason, the manufactured electrostatic type speaker will differ in thickness individually.
The sound pressure of the sound emitted from the electrostatic speaker is inversely proportional
to the square of the distance between the film and the cloth, so if the thickness of the ester wool
is different in each of a plurality of manufactured electrostatic speakers, Even if the same audio
signal is input, there arises a problem that the sound pressure of the output sound is individually
different. Moreover, about ester wool, thickness can change with secular change or
environmental change. As described above, the sound pressure of the sound emitted from the
electrostatic speaker is inversely proportional to the square of the distance between the film and
the cloth, so when the thickness of the ester wool changes due to aging or environmental
changes, the same effect occurs. Even if an audio signal is input, the sound pressure of the sound
emitted at the time of a new product is different from the sound pressure of the sound emitted
after aging or after environmental change. In addition, a configuration in which a vibrating body
is sandwiched between a pair of electrodes can also be used as an electrostatic microphone.
When such a configuration is used as an electrostatic microphone, a signal corresponding to the
sound reaching the vibrator can be obtained from the electrode of the electrostatic microphone.
Also in this case, the sound pressure of the sound collected after the aging or the environmental
change is different from the sound pressure of the sound collected at the time of the new
product.
[0005]
The present invention has been made under the above-described background, and provides a
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2
technique for suppressing the influence on the output due to the change in the distance between
the electrode of the electrostatic electroacoustic transducer and the vibrator. To aim.
[0006]
In order to solve the problems described above, the present invention is a drive circuit for driving
an electrostatic speaker including a vibrator and an electrode facing the vibrator, the resistor
including the drive circuit and the electrostatic type. The time constant of the integrating circuit
configured with the speaker is measured, and at least the bias voltage output to the vibrator or
the acoustic signal supplied to the electrode is controlled based on the time constant to emit the
sound from the electrostatic speaker A drive circuit comprising control means for adjusting the
sound pressure of the sound being played.
[0007]
In the present invention, the drive circuit comprises: amplifying means for amplifying the input
acoustic signal; and boosting means for boosting the acoustic signal amplified by the amplifying
means and supplying the boosted acoustic signal to the electrode A bias power supply for
outputting a bias voltage to be applied to the vibrator, and a resistor having one end connected
to the bias power supply and the other end connected to the vibrator, the control means
including the resistor And measuring the time constant of the integration circuit constituted by
the electrostatic speaker, and controlling at least the bias power supply or the amplification
means based on the time constant to thereby control the sound of the sound emitted from the
electrostatic speaker The pressure may be adjusted.
Further, in the present invention, the drive circuit is connected to an amplification means for
amplifying an input acoustic signal, a first resistor whose one end is connected to the
amplification means, and the other end of the first resistor. A boosting unit for boosting an
acoustic signal supplied from the amplifying unit via the first resistor and supplying the boosted
acoustic signal to the electrode; and a bias for outputting a bias voltage applied to the vibrator. A
power source, and a second resistor having one end connected to the bias power source and the
other end connected to the vibrating body, the control means including an acoustic signal before
passing through the first resistor; The acoustic signal after passing through the first resistor is
measured, and based on the measurement result, at least the bias power supply or the
amplification means is controlled to control the sound pressure of the sound emitted from the
electrostatic speaker. The configuration may be adjusted.
04-05-2019
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[0008]
In the present invention, the control means may be configured to adjust the sound pressure by
controlling the bias power supply to adjust the bias voltage.
In the present invention, the control means may be configured to adjust the sound pressure by
controlling the amplification means to adjust the amplification factor of the amplification means.
[0009]
The present invention also provides an electroacoustic transducer system comprising an
electrostatic speaker including a vibrator and an electrode facing the vibrator, and a drive circuit
having any one of the above-described configurations. Further, the present invention includes a
plurality of electrostatic type speakers including a vibrator and an electrode facing the vibrator,
and the electroacoustic conversion including a drive circuit having any one of the abovedescribed configurations for each of the plurality of electrostatic speakers. Supply system.
[0010]
Further, according to the present invention, there is provided a drive circuit for generating an
acoustic signal from a signal output from an electrode of an electrostatic microphone including a
vibrating body and an electrode facing the vibrating body, wherein the resistor is included in the
drive circuit. And driving means for controlling the acoustic signal by controlling a time constant
of an integration circuit constituted by the above-mentioned electrostatic microphone and
controlling at least a bias voltage output to the vibrator based on the time constant. Provide a
circuit. The present invention also provides an electrostatic electroacoustic transducing system
including the above-described drive circuit that generates an acoustic signal, and an electrostatic
microphone including a vibrating body and an electrode facing the vibrating body.
[0011]
ADVANTAGE OF THE INVENTION According to this invention, the influence on the output
resulting from the change of the distance between the electrode of an electrostatic
electroacoustic transducer and a vibrating body can be suppressed.
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4
[0012]
FIG. 1 is an external view of an electrostatic speaker 1 according to an embodiment of the
present invention.
1. AA sectional view taken on the line of FIG. The exploded view of electrostatic type speaker 1.
FIG. 2 shows a configuration of a drive circuit 100. FIG. 2 shows a configuration of a drive circuit
100A. The figure which showed the frequency characteristic of the integrating circuit comprised
with resistor R3 and the electrostatic type speaker 1. FIG. The figure for demonstrating the
relationship between the frequency characteristic of an integrating circuit, and the distance
between a vibrator and an electrode. FIG. 2 is a diagram showing an electrical configuration
according to an electrostatic microphone 2.
[0013]
First Embodiment FIG. 1 is an external view of an electrostatic speaker 1 (electrostatic
electroacoustic transducer) according to an embodiment of the present invention, and FIG. 2 is a
cross-sectional view of the electrostatic speaker 1 taken along line A-A. FIG. 3 is an exploded view
of the electrostatic speaker 1, and FIG. 4 is a diagram showing a configuration of a drive circuit
100 for driving the electrostatic speaker 1. As shown in FIG. In the figure, the directions are
indicated by the orthogonal X-axis, Y-axis, and Z-axis, and the horizontal direction when the
electrostatic speaker 1 is viewed from the front is the X-axis direction, and the depth direction is
the Y-axis direction. The height direction is the direction of the Z axis. Further, in the drawings,
those in which “•” is described in “o” means an arrow directed from the back to the front of
the drawing. Further, in the drawings, those in which “x” is described in “o” means an arrow
directed from the front to the back of the drawing.
[0014]
As shown in the figure, the electrostatic loudspeaker 1 has a vibrator 10, electrodes 20U and
20L, elastic members 30U and 30L, and protection members 60U and 60L. In the present
embodiment, the configurations of the electrode 20U and the electrode 20L are the same, and
the configurations of the elastic member 30U and the elastic member 30L are the same. For this
reason, in these members, when it is not particularly necessary to distinguish between a member
04-05-2019
5
having a suffix “U” and a member having a suffix “L”, the descriptions such as “L” and
“U” are omitted. . Further, the configurations of the protective member 60U and the protective
member 60L are the same. For this reason, also in these members, when it is not particularly
necessary to distinguish between a member whose code end is "U" and a member whose code
end is "L", the descriptions such as "L" and "U" are omitted. Do. Further, the dimensions of the
respective members in the figure are different from the actual dimensions so that the shapes and
positional relationships of the respective members can be easily understood.
[0015]
(Configuration of Each Part of Electrostatic Speaker 1) First, each part of the electrostatic speaker
1 will be described. The rectangular vibrator 10 as viewed from the point on the Z-axis is one of
films (insulating layers) of insulating and flexible synthetic resin such as PET (polyethylene
terephthalate) or PP (polypropylene). It has a sheet-like structure in which a conductive metal is
vapor-deposited on the surface of the metal layer to form a conductive film (conductive layer). In
the present embodiment, the conductive film is formed on one side of the film, but may be
formed on both sides of the film. The vibrating body 10 may have a configuration in which a
conductive metal is rolled to form a film.
[0016]
The elastic member 30 is a non-woven fabric in this embodiment and can pass air and sound
without passing electricity, and its shape is rectangular when viewed from a point on the Z axis.
Also, the elastic member 30 has elasticity, and deforms when an external force is applied, and
returns to its original shape when an external force is removed. The elastic member 30 may be a
member having insulation, sound transmission, and elasticity, and it may be formed by applying
heat to the batt and compressing it, woven cloth, and synthetic resin having insulation. Or the
like. Further, the elastic member 30 may have a configuration in which air does not pass as long
as sound passes therethrough. For example, a sponge of an elastic and discontinuous bubble may
be formed into a sheet to be the elastic member 30. In the present embodiment, the length of the
elastic member 30 in the X-axis direction is longer than the length of the vibrating body 10 in
the X-axis direction, and the length of the elastic member 30 in the Y-axis direction is greater
than the length of the vibrating body 10 in the Y-axis direction It is getting longer.
[0017]
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6
The electrode (fixed electrode) 20 has a configuration in which a conductive metal is deposited
on one surface of a film (insulating layer) of insulating synthetic resin such as PET or PP to form
a conductive film (conductive layer) It has become. The shape and the area of the conductive film
are the same as the shape and the area of the vibrating body 10. The electrode 20 is rectangular
when viewed from a point on the Z axis. The electrode 20 has a plurality of holes penetrating
from the front surface to the back surface to allow air and sound to pass therethrough, but in the
drawings, the illustration of the holes is omitted. In the present embodiment, the length in the Xaxis direction and the length in the Y-axis direction of the electrode 20 are the same as the elastic
member 30. Further, as in the case of the vibrating body 10, the electrode 20 may be formed into
a film by rolling a conductive metal.
[0018]
The protective member 60 is a cloth having an insulating property. The protective member 60 is
rectangular when viewed from a point on the Z-axis, and allows passage of air and sound. In the
present embodiment, the length in the X axis direction of the protective member 60 and the
length in the Y axis direction are the same as those of the elastic member 30.
[0019]
(Structure of Electrostatic Speaker 1) Next, the structure of the electrostatic speaker 1 will be
described. In the electrostatic loudspeaker 1, the vibrating body 10 is disposed between the
lower surface of the elastic member 30U and the upper surface of the elastic member 30L. The
adhesive is applied to the elastic member 30U and the elastic member 30L with a width of
several mm from the edge in the left-right direction and the edge in the depth direction, and the
portion to which the adhesive is applied The inner side is not fixed to the elastic member 30U
and the elastic member 30L. In addition, the adhesive is applied to the elastic member 30U and
the elastic member 30L with a width of several mm from the edge to the inside, and they are
fixed to each other.
[0020]
The electrode 20U is bonded to the upper surface of the elastic member 30U. The electrode 20L
is bonded to the lower surface of the elastic member 30L. The electrode 20U is coated with an
04-05-2019
7
adhesive with a width of several mm from the lateral edge and the edge in the depth direction
and is adhered to the elastic member 30U, and the electrode 20L is formed from the lateral edge
and the edge in the depth direction An adhesive is applied to the inside with a width of several
mm and is adhered to the elastic member 30L. The electrode 20 is in a state where it is not fixed
to the elastic member 30 inside the portion to which the adhesive is applied. The electrode 20U
is in contact with the elastic member 30U at the side with the conductive film, and the electrode
20L is in contact with the elastic member 30L at the side with the conductive film. The
conductive film of the electrode 20 and the vibrator 10 face each other with the elastic member
30 interposed therebetween. That is, the electrostatic speaker 1 has a configuration in which the
elastic member 30 which is a dielectric is provided between two conductors of the electrode 20
and the vibrating body 10, and functions as a capacitor.
[0021]
The protective member 60U is bonded to the top surface of the electrode 20U. The protective
member 60L is bonded to the lower surface of the electrode 20L. An adhesive is applied to the
protective member 60U with a width of several mm from the lateral edge and the edge in the
depth direction and is adhered to the electrode 20U. The protective member 60L has the lateral
edge and the edge in the depth direction. An adhesive is applied in a width of several mm from
the inside to adhere to the electrode 20L. The protective member 60 is in a state where it is not
fixed to the electrode 20 inside the portion to which the adhesive is applied.
[0022]
(Electrical Configuration of Electrostatic Loudspeaker 1) Next, the electrical configuration of the
electrostatic loudspeaker 1 will be described. As shown in FIG. 4, the electrostatic speaker 1
includes a drive circuit 100 including an amplification unit 130, a transformer 110, a bias power
supply 120 for applying a DC bias voltage to the vibrating body 10, and a control unit 140. Is
connected. The electrostatic loudspeaker 1 and the drive circuit 100 constitute a loudspeaker
system.
[0023]
The electrode 20U is connected to one terminal T1 of the secondary side of the transformer 110,
and the electrode 20L is connected to the other terminal T2 of the secondary side of the
04-05-2019
8
transformer 110. The terminals T1 and T2 function as output means for outputting an acoustic
signal to the electrostatic speaker 1. The vibrating body 10 is also connected to the bias power
supply 120 via the resistor R1 (second resistor). The terminal T3 at the midpoint of the
transformer 110 is connected to the ground GND, which is the reference potential of the drive
circuit 100, via the resistor R2. Further, one terminal T5 on the primary side of the transformer
110 is connected to the ground GND.
[0024]
The amplification unit 130 is an amplification unit that amplifies an input acoustic signal and
outputs the amplified acoustic signal. The amplification unit 130 is connected to one end of the
resistor R3 (first resistor), and outputs the amplified acoustic signal to the resistor R3. The other
end of the resistor R3 is connected to the other terminal T4 on the primary side of the
transformer 110, and the acoustic signal amplified by the amplification unit 130 is supplied to
the transformer 110.
[0025]
The control unit 140 according to the present embodiment is a microcomputer including a
central processing unit (CPU), a read only memory (ROM), and a random access memory (RAM).
In the control unit 140, when the program stored in the ROM is executed, the measurement unit
141 and the adjustment unit 142 are realized. The measuring unit 141 has a function of
sampling the voltage of the line connecting the vibrating body 10 and the resistor R1, that is, the
voltage applied to the vibrating body 10, and measuring the instantaneous value of the voltage.
The measurement unit 141 sends data representing the measured voltage to the adjustment unit
142. The adjustment unit 142 has a function of controlling the bias power supply 120 based on
the data sent from the measurement unit 141 and adjusting the bias voltage applied to the
vibrator 10. The control unit 140 may be an application specific integrated circuit (ASIC) instead
of a microcomputer.
[0026]
Operation of First Embodiment Next, the operation of the first embodiment will be described.
First, when the power supply (not shown) of the drive circuit 100 is turned on, the adjustment
unit 142 controls the bias power supply 120 to apply a bias voltage to the vibrating body 10.
04-05-2019
9
The bias power supply 120 is controlled such that the voltage applied to the vibrating body 10
becomes a predetermined voltage V1 when the power is turned on. The measurement unit 141
samples the voltage applied to the vibrator 10 to measure an instantaneous value of the voltage,
and sequentially sends data representing the measured voltage to the adjustment unit 142. The
adjustment unit 142 observes the voltage represented by the data sent from the measurement
unit 141.
[0027]
In addition, since the electrostatic type speaker 1 functions as a capacitor as described above, the
integrating circuit is configured by the resistor R 1 and the electrostatic type speaker 1. For this
reason, when the application of the bias voltage is started, the voltage applied to the vibrator 10
does not rise in a pulse shape and gradually rises with a time constant. The adjustment unit 142
observes the change of the bias voltage represented by the data sent from the measurement unit
141, and the time from when the measured voltage reaches 0 V to a voltage of 63.2% of the
voltage V1, ie, the resistor R1. The time constant τ of the integrating circuit configured by the
electrostatic speaker 1 is measured. Here, assuming that the resistance value of the resistor R1
connected to the bias power supply 120 is R and the electrostatic capacitance of the electrostatic
speaker 1 is C, an integrating circuit configured by the resistor R1 and the electrostatic speaker 1
The time constant τ of is τ = RC. Since the resistance value of the resistor R1 is predetermined,
when the time constant τ is obtained, the capacitance of the electrostatic speaker 1 can be
obtained from the equation of C = τ / R.
[0028]
The electrostatic capacity of the electrostatic speaker 1 is S of the area of the conductive film of
the vibrating body 10 and the electrode 20, ε of the dielectric constant between the electrode
20 and the vibrating body 10, ε of the electrode 20 and the vibrating body 10 If the distance
between them is d, then C = 2εS / d. If this equation is modified, d = 2εS / C, but since the
capacitance is C = τ / R, it can be transformed to d = 2εSR / τ. The adjustment unit 142 stores
the area S, the dielectric constant ε, and the resistance value R in advance, and stores the area S,
the dielectric constant ε, the resistance value R, and the value of the distance d from the
measured time constant τ. calculate.
[0029]
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10
Next, assuming that the sound pressure of the sound emitted from the electrostatic speaker 1 is
p, the bias voltage is Vdc, and the voltage of the acoustic signal boosted by the transformer 110
is Vsig, the sound pressure p, the bias voltage Vdc, the acoustic The voltage Vsig of the signal
and the distance d have a relationship of p∝Vdc · Vsig / d <2>. For example, in the case of a
configuration in which the bias voltage Vdc is not controlled, even if an acoustic signal of the
same level is input to the electrostatic speaker 1, it is new before the distance d changes with
new and after the distance d changes with aging. The sound pressure of the emitted sound will
be different.
[0030]
Therefore, the adjustment unit 142 controls the bias power supply 120 according to the
calculated distance d. Specifically, in the present embodiment, the above-described operation is
performed before the electrostatic speaker 1 is shipped from the factory to calculate the distance
d, and the calculated distance d is stored as the distance d in the adjustment unit 142. ing. The
adjustment unit 142 compares the distance d1 stored as the initial value with the distance d
calculated by the above-described operation. When the distance d and the distance d1 are equal,
the adjustment unit 142 controls the bias power supply 120 such that the voltage applied to the
vibrating body 10 becomes the voltage V1. Further, when the distance d and the distance d1 are
different, the adjustment unit 142 calculates a bias voltage Vdc in which the calculation result of
V1 · Vsig / d1 <2> and the calculation result of Vdc · Vsig / d <2> are the same. The bias power
supply 120 is controlled so that the calculated bias Vdc is applied to the vibrator 10. The voltage
applied to the vibrator 10 decreases as the distance d decreases, and increases as the distance d
increases.
[0031]
Next, when an AC acoustic signal is input to the amplification unit 130, the input acoustic signal
is amplified and supplied to the primary side of the transformer 110. The acoustic signal boosted
by the transformer 110 as boosting means and outputted from the terminal T2 is boosted by the
transformer 110 and the polarity of the signal is opposite to that of the acoustic signal outputted
from the terminal T1. When a positive acoustic signal is output from the terminal T1 and a
negative acoustic signal is output from the terminal T2, a positive voltage is applied to the
electrode 20U, and a negative voltage is applied to the electrode 20L. Since a positive voltage is
applied to the vibrating body 10 by the bias power supply 120, the electrostatic attractive force
between the vibrating body 10 and the electrode 20U to which a positive voltage is applied is
04-05-2019
11
weakened while a negative voltage is applied. Electrostatic attraction with the electrode 20L is
increased. Then, the vibrator 10 is displaced to the electrode 20L side (opposite direction as the
Z direction) according to the difference between the electrostatic attractive force acting on the
electrode 20U side and the electrostatic attractive force acting on the electrode 20L side.
[0032]
When a negative acoustic signal is output from the terminal T1 and a positive acoustic signal is
output from the terminal T2, a negative voltage is applied to the electrode 20U, and a positive
voltage is applied to the electrode 20L. Since a positive voltage is applied to the vibrating body
10 by the bias power supply 120, the electrostatic attractive force between the vibrating body 10
and the electrode 20L to which the positive voltage is applied is weakened, and a negative
voltage is applied. The electrostatic attractive force with the electrode 20U is increased. Then, the
vibrator 10 is displaced to the electrode 20U side (Z-axis direction) according to the difference
between the electrostatic attractive force acting on the electrode 20U side and the electrostatic
attractive force acting on the electrode 20L side.
[0033]
Thus, the vibrating body 10 is displaced (deflection) in the positive direction of the Z-axis and the
negative direction of the Z-axis in accordance with the acoustic signal (deflection), and the
displacement direction changes sequentially to become vibration, and the vibration state ( A
sound wave corresponding to the frequency, amplitude, phase) is generated from the vibrator 10.
The generated sound waves pass through the elastic member 30 having sound permeability, the
electrode 20 and the protection member 60 and are emitted as sound to the outside of the
electrostatic speaker 1.
[0034]
In the present embodiment, as described above, the bias voltage is controlled according to the
distance between the vibrating body 10 and the electrode 20, so even if the change in the
distance between the vibrating body 10 and the electrode 20 changes, It is possible to suppress
the change in the sound pressure of the sound emitted from the electrostatic speaker 1.
[0035]
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12
In the first embodiment, the sound pressure is controlled by controlling the bias voltage applied
to the vibrator 10. However, the configuration for controlling the sound pressure is not limited to
this configuration.
The adjustment unit 142 may control the amplification unit 130 to control the voltage of the
acoustic signal S2 supplied to the transformer 110. Specifically, the adjustment unit 142 controls
the amplification factor of the amplification unit 130 so that the calculation result of V1 · Vsig /
d1 <2> and the calculation result of V1 · Vsig / d <2> become the same. The amplification factor
of the signal S2 is adjusted. In this configuration, the amplification factor decreases as the
distance d decreases, and increases as the distance d increases. Further, the adjustment unit 142
controls the sound pressure of the sound emitted from the electrostatic speaker 1 by adjusting
not only one of the bias voltage and the voltage of the acoustic signal S 2 but also both of them.
It is also good.
[0036]
In the first embodiment, since the time constant τ changes according to the distance d, the time
constant before shipment is stored, and the stored time constant is compared with the measured
time constant. By comparison, it can be seen whether the distance d has become shorter or
longer. Therefore, when the time constant τ is shorter than at the time of shipment (when the
distance d is long), the bias voltage is increased, and when the time constant τ is longer than at
the time of shipment (the distance d is short) In the case of (1), the bias voltage may be lowered.
In the case of this configuration as well, the voltage of the sound signal S2 may be controlled by
adjusting the voltage of the sound signal S2 instead of the bias voltage, and both the bias voltage
and the voltage of the sound signal S2 may be controlled. The sound pressure of the emitted
sound may be controlled.
[0037]
Second Embodiment Next, a second embodiment of the present invention will be described. FIG.
5 is a diagram showing the configuration of a drive circuit 100A according to a second
embodiment of the present invention. The electrostatic loudspeaker 1 and the drive circuit 100A
constitute a loudspeaker system. In the second embodiment of the present invention, the
configuration of the electrostatic speaker is the same as that of the first embodiment. In the
second embodiment, the configuration of a drive circuit for driving the electrostatic speaker 1 is
04-05-2019
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different from that of the first embodiment. Therefore, the description of the electrostatic
speaker 1 connected to the drive circuit 100A is omitted, and the drive circuit 100A having a
configuration different from that of the first embodiment will be described. In the drive circuit
100A, the same components as those of the drive circuit 100 of the first embodiment are
denoted by the same reference numerals and the description thereof is omitted.
[0038]
The control unit 140A is a microcomputer, and when the program stored in the ROM is executed,
the measurement unit 141A and the adjustment unit 142A are realized. Of the voltage value of
the acoustic signal (acoustic signal S1) supplied from the amplification unit 130 to the resistor
R3 (first resistor) and the acoustic signal (acoustic signal S2) after passing through the resistor
R3 of the measurement unit 141A. It has a function to sample voltage values. In addition, the
measurement unit 141A performs a fast Fourier transform process on the voltage value obtained
by sampling to obtain the amplitudes of the plurality of frequency components included in the
acoustic signal S1 and the amplitudes of the plurality of frequency components included in the
acoustic signal S2. Is equipped. Data representing the amplitude obtained by the fast Fourier
transform process is sent from the measurement unit 141A to the adjustment unit 142A. The
adjustment unit 142A controls the bias power supply 120 based on the data sent from the
measurement unit 141A, and has a function of adjusting the bias voltage applied to the vibrating
body 10.
[0039]
Operation of Second Embodiment Next, the operation of the second embodiment will be
described. First, when the power supply (not shown) of the drive circuit 100A is turned on, the
bias power supply 120 is controlled by the adjustment unit 142A, and a bias voltage is applied to
the vibrator 10. The bias power supply 120 is controlled such that the voltage applied to the
vibrating body 10 becomes a predetermined voltage V1 when the power is turned on.
[0040]
Next, when the acoustic signal is supplied to the amplification unit 130, the amplified acoustic
signal is output from the amplification unit 130 and supplied to the transformer 110. The
acoustic signal output from the amplification unit 130 is also supplied to the measurement unit
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141A. The measurement unit 141A performs fast Fourier transform processing on the voltage
value obtained by sampling the acoustic signal S1, and obtains an amplitude for each of a
plurality of frequency components of the acoustic signal S1. Further, the measurement unit 141A
performs fast Fourier transform processing on the voltage value obtained by sampling the
acoustic signal S2, and obtains an amplitude for each of a plurality of frequency components of
the acoustic signal S2. The measurement unit 141A sends data of each amplitude obtained by the
fast Fourier transform process to the adjustment unit 142A.
[0041]
The adjustment unit 142A calculates the ratio of the amplitudes of the acoustic signal S1 and the
acoustic signal S2 for each of a plurality of frequency components based on the data sent from
the measurement unit 141A. In addition, since the electrostatic type speaker 1 functions as a
capacitor as described above, the integrating circuit is configured by the resistor R 3 and the
electrostatic type speaker 1. Therefore, if the amplitude ratio is interpolated for the frequency
components among the plurality of frequency components based on the calculated amplitude
ratio for each of the plurality of frequency components, for example, frequency characteristics as
shown in FIG. 6 can be obtained. . That is, the frequency characteristic of the integrating circuit
can be obtained from the amplitude ratio of the plurality of frequency components calculated
and obtained.
[0042]
When the adjustment unit 142A analyzes the calculated amplitude ratio and obtains the
frequency characteristic, the obtained frequency characteristic is analyzed and the cutoff
frequency fc of the integration circuit (the amplitude ratio of the signal output from the
integration circuit is 1 / √ The frequency to be 2) is obtained (FIG. 6). Note that the cutoff
frequency fc of the integrating circuit is fc = 1 /, where the resistance value of the resistor R3 is
R, the capacitance of the electrostatic speaker 1 is C, and the winding ratio of the transformer
110 is 1: n. It is represented by (2πRn <2> C). In addition, the electrostatic capacitance of the
electrostatic speaker is C = 2εS / d. For this reason, the distance d between the electrode 20 and
the vibrating body 10 can be obtained from these equations by obtaining the cut-off frequency
fc.
[0043]
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15
Next, the adjustment unit 142A controls the bias power supply 120 according to the calculated
distance d. Specifically, in the present embodiment, the above-described operation is performed
before the electrostatic speaker 1 is shipped from the factory to calculate the distance d, and the
calculated distance d is stored as the distance d in the adjustment unit 142A. ing. The adjustment
unit 142A compares the distance d1 stored as the initial value with the distance d calculated by
the above-described operation.
[0044]
The adjustment unit 142A compares the distance d1 stored as the initial value with the distance
d calculated by the above-described operation. When the distance d and the distance d1 are
equal, the adjustment unit 142A controls the bias power supply 120 so that the voltage applied
to the vibrating body 10 becomes the voltage V1. Further, when the distance d and the distance
d1 are different, the adjustment unit 142A calculates a bias voltage Vdc in which the calculation
result of V1 · Vsig / d1 <2> and the calculation result of Vdc · Vsig / d <2> are the same. The bias
power supply 120 is controlled so that the calculated bias Vsig is applied to the vibrator 10. The
voltage applied to the vibrator 10 decreases as the distance d decreases, and increases as the
distance d increases.
[0045]
In the present embodiment, the distance d is calculated from the cutoff frequency fc, and the bias
voltage is controlled based on the calculated distance d as in the first embodiment, so the
distance between the vibrator 10 and the electrode 20 Even if the change of the change of the
sound pressure of the electrostatic speaker 1 is changed, the change of the sound pressure of the
sound emitted from the electrostatic speaker 1 can be suppressed.
[0046]
In the second embodiment, the acoustic signal is sampled and fast Fourier transform processing
is performed, and the distance d is calculated using the cutoff frequency fc obtained from the
result of the fast Fourier transform processing, and the calculated distance d is calculated.
Although the bias voltage is controlled, the configuration for controlling the bias voltage is not
limited to this configuration.
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For example, in the case where the frequency characteristic of the integrating circuit is the
frequency characteristic shown by the solid line in FIG. 7 at the distance d1 before shipment,
when the distance d becomes short and the capacitance C becomes large, the gain in the high
region becomes small in the integrating circuit. Therefore, the frequency characteristic shown by
the two-dot chain line in FIG. 7 is obtained. Further, when the distance d becomes long and the
electrostatic capacitance C becomes small, the gain in the high region becomes large in the
integrating circuit, so that the frequency characteristic shown by the dashed dotted line in FIG. 7
is obtained. Focusing on the predetermined high frequency fh in FIG. 7, let G2 be the amplitude
ratio before shipment, G1 be the amplitude ratio when the distance d is short, and G3 be the
amplitude ratio when the distance d be long. The amplitude ratio is G3> G2> G1, and it can be
seen that the amplitude ratio increases as the distance d increases. Therefore, the amplitude ratio
of the component of the frequency fh included in the acoustic signal is measured and stored
before the electrostatic speaker 1 is shipped from the factory, and the stored amplitude ratio is
compared with the measured amplitude ratio. If so, it can be known whether the distance d has
become longer or shorter than at the time of shipping. Then, the bias voltage may be lowered
when the distance d is shorter than at the time of shipping, and the bias voltage may be
increased when the distance d is shorter than at the time of shipping. Note that the measurement
signal of a predetermined frequency is superimposed on the acoustic signal input to the
amplification unit 130, and the amplitude of the superimposed signal is measured before and
after the resistor R3, and the bias power is supplied according to the ratio of the measured
amplitudes. 120 may be controlled. Here, the frequency of the measurement signal is preferably,
for example, a frequency of 20 kHz or more.
[0047]
Further, the configuration for obtaining the amplitude ratio for high frequency components is not
limited to the configuration for performing the fast Fourier transform processing. For example, a
first band pass filter for passing a signal of frequency fh is provided between the line connecting
the amplifying unit 130 and the resistor R3 and the measuring unit 141A, and the line
connecting the resistor R3 and the transformer 110 and measurement A second band pass filter
for passing a signal of frequency fh is also provided between unit 141A. The measurement unit
141A samples the voltage value of the signal that has passed through the band pass filter, the
amplitude of the signal that has passed through the first band pass filter from the minimum value
and the maximum value of the voltage values obtained by sampling, and the second band pass
Find the amplitude of the signal that has passed through the filter. The adjustment unit 142A
calculates a ratio between the amplitude of the signal that has passed through the first band pass
filter and the amplitude of the signal that has passed through the second band pass filter. Also in
this configuration, it is possible to compare the amplitude ratio stored in advance and the
measured amplitude ratio, and to know whether the distance d has become longer or shorter
04-05-2019
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than at the time of shipping.
[0048]
Further, in the second embodiment described above, the measurement unit 141A outputs the
voltage of the acoustic signal (acoustic signal S1) supplied from the amplification unit 130 to the
resistor R3 and the acoustic signal after passing through the resistor R3 (acoustic The voltage of
the signal S2) is sampled, but the voltage of the acoustic signal input to the amplification unit
130 and the voltage of the acoustic signal (acoustic signal S2) after passing through the resistor
R3 are sampled and included in the acoustic signal The amplitude ratio may be obtained for the
plurality of frequency components to be input before being input to the amplification unit 130
and after passing through the resistor R3.
[0049]
Further, in the second embodiment, the bias voltage Vdc and the amplification factor of the
amplification unit 130 can be arbitrarily determined by obtaining the distance d between the
electrode 20 and the vibrating body 10 temporally or periodically not only when the power is
turned on but also temporally or periodically. The control may be performed at the timing of
[0050]
In the second embodiment, the phase characteristic is determined by fast Fourier transform
processing for the acoustic signal S1 and the acoustic signal S2, the cutoff frequency is identified
from the phase difference between the two signals, and the distance d is determined from the
identified cutoff frequency. You may get it.
That is, when obtaining the cutoff frequency, either the amplitude ratio or the phase difference of
the acoustic signal may be used as long as it is a frequency response.
[0051]
In the second embodiment, the cutoff frequency measured before shipment is stored in the
adjustment unit 142A, and the bias voltage is determined according to the comparison result
between the measured cutoff frequency and the cutoff frequency stored in the adjustment unit
142A. May be controlled.
04-05-2019
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Specifically, when the cut-off frequency obtained by measurement is lower than the cut-off
frequency stored in advance, adjustment unit 142A lowers bias voltage Vdc, and the cut-off
frequency obtained by measurement is stored in advance. When it is higher than the off
frequency, the bias voltage Vdc is increased.
[0052]
[Modifications] Although the embodiment of the present invention has been described above, the
present invention is not limited to the above-described embodiment, and can be practiced in
various other forms. For example, the above-described embodiment may be modified as follows
to implement the present invention. The above-described embodiment and the following
modifications may be combined with each other.
[0053]
In each of the above-described embodiments, the distance between the electrode 20 and the
vibrating body 10 is stored in a table in which the bias voltage applied at this distance is
associated with the distance obtained by measurement. The bias power supply 120 may be
controlled to have a bias voltage applied. In addition, since the cutoff frequency according to the
distance between the electrode 20 and the vibrating body 10 can also be specified by the
measurement by the control unit 140A, the cutoff frequency is associated with the bias voltage in
the table, and the cutoff calculated by the adjustment unit 142A. The bias power supply 120 may
be controlled to have a bias voltage associated with the off frequency.
[0054]
In the embodiment described above, the electrostatic speaker 1 is a push-pull electrostatic
speaker, but the electrostatic speaker connected to the drive circuit 100 is not limited to the
push-pull type, and a single type May be an electrostatic speaker.
[0055]
In the embodiment described above, although the bias voltage is measured to achieve the time
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constant τ after the drive circuit 100 is powered on, the change of the bias voltage is measured
after the drive circuit 100 is powered off. The time constant τ may be determined.
In this configuration, the distance d is calculated based on the time constant τ measured when
the power is turned off, and the bias voltage Vdc is set using the calculated distance d the next
time the drive circuit 100 is powered on. You may
[0056]
In the present invention, a plurality of sets of the electrostatic speaker 1 and the drive circuit
100 or a plurality of sets of the electrostatic speaker 1 and the drive circuit 100A may be
arranged to form a single speaker system. For example, in the case where a plurality of
electrostatic loudspeakers 1 are arranged side by side, the distance between the vibrator 10 and
the electrode 20 may be different in each electrostatic loudspeaker 1. In this case, if the
electrostatic speaker 1 is driven by the drive circuit 100 or the drive circuit 100A according to
the present invention, even if the distance between the vibrator 10 and the electrode 20 in each
electrostatic speaker 1 is different, the bias power supply The sound pressure of the sound
emitted from each electrostatic type speaker 1 can be made uniform by controlling 120 or the
amplification unit 130.
[0057]
In the embodiment described above, the configuration in which the electrode, the vibrator, and
the elastic member are stacked is used as an electrostatic speaker that converts an acoustic
signal into sound, but this configuration is an electrostatic type that converts sound into an
acoustic signal. Microphones (electrostatic electroacoustic transducers) are also possible. FIG. 8 is
a diagram showing a configuration of an electrostatic microphone 2 according to the present
modification and an acoustic signal generation circuit 200 that generates an acoustic signal
representing a sound collected by the electrostatic microphone 2. In the present modification, the
electrostatic microphone 2 includes the same members as the electrostatic speaker 1 described
above. Therefore, the members constituting the electrostatic microphone 2 include the respective
members of the electrostatic speaker 1. The same reference numerals are given and the
description thereof is omitted. Further, the configuration of the acoustic signal generation circuit
200 is the same as that of the drive circuit 100 except that the direction in which the sound
reaches the electrostatic microphone 2 and the signal flow is different from that of the drive
circuit 100. The components provided are given the same reference numerals as the components
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provided in the drive circuit 100, and the description of each component is omitted. The
transformation ratio of the transformer 110 and the resistance value of each resistor are
appropriately adjusted.
[0058]
In the electrostatic microphone 2, the electrode 20 as a conductor and the vibrating body 10 as a
conductor are disposed opposite to each other at a distance, and the electrode 20 and the
vibrating body 10 are capacitors configured by parallel flat conductors. It is functioning. Since a
bias voltage is applied to the vibrator 10, when no sound reaches the electrostatic microphone 2,
a constant charge is accumulated in the capacitor. When the sound reaches the electrostatic
microphone 2, the vibrator 10 vibrates by the sound that has reached. When the vibrating body
10 vibrates, the distance between the vibrating body 10 and the electrodes 20U and 20L
changes, so that the capacitance between the vibrating body 10 and the electrode 20 changes.
[0059]
For example, when the vibrating body 10 is displaced toward the electrode 20U, the distance
between the electrode 20U and the vibrating body 10 is shortened, and the capacitance between
the electrode 20U and the vibrating body 10 is increased. Further, the distance between the
electrode 20L and the vibrating body 10 becomes longer, and the capacitance between the
electrode 20L and the vibrating body 10 becomes smaller. Thus, when the capacitance changes,
the potential of the electrode 20U changes so that the potential difference between the electrode
20U and the vibrating body 10 decreases, and the potential of the electrode 20L such that the
potential difference between the electrode 20L and the vibrating body 10 increases. Changes.
Here, since a potential difference occurs between the electrode 20U and the electrode 20L,
current flows in the secondary coil of the transformer 110.
[0060]
Further, when the vibrating body 10 is displaced to the electrode 20L side, the distance between
the electrode 20L and the vibrating body 10 becomes short, and the capacitance between the
electrode 20L and the vibrating body 10 becomes large. Further, the distance between the
electrode 20U and the vibrating body 10 becomes longer, and the capacitance between the
electrode 20U and the vibrating body 10 becomes smaller. Then, the potential of the electrode
04-05-2019
21
20L changes so that the potential difference between the electrode 20L and the vibrating body
10 becomes smaller, and the potential of the electrode 20U changes so that the potential
difference between the electrode 20U and the vibrating body 10 becomes larger. Here, a
potential difference occurs between the electrode 20U and the electrode 20L, and a current flows
in the secondary coil of the transformer 110 in the direction opposite to that when the vibrating
body 10 is displaced in the direction of the electrode 20U.
[0061]
When current flows in the secondary coil of the transformer 110, current also flows in the
primary coil of the transformer 110 in response to this current. The signal that has flowed to the
primary side coil is amplified by the amplification unit 130 and the amplified signal is output
from the amplification unit 130 as an acoustic signal representing the sound collected by the
electrostatic microphone 2.
[0062]
In the present modification, when the impedance of the transformer 110 is low, the frequency
characteristic at a low frequency may be degraded due to the influence of the load capacity of
the electrostatic microphone 2. In this case, in place of the transformer 110, an amplifier with
high impedance may be connected to the electrodes 20U and 20L to suppress a decrease in
frequency characteristics. Further, even in the configuration shown in FIG. 5, the amplification
unit 130 may output an acoustic signal in accordance with the signal that has flowed to the
primary coil of the transformer 110.
[0063]
DESCRIPTION OF SYMBOLS 1 ... Electrostatic type speaker, 2 ... Electrostatic type microphone, 10
... Vibrator, 20, 20 U, 20 L ... Electrode, 30, 30 U, 30 L ... Elastic member, 60, 60 U, 60 L ...
Protective member, 100 ... Drive circuit, DESCRIPTION OF SYMBOLS 110 ... Transformer, 120 ...
Bias power supply, 130 ... Amplification part, 140 ... Control part, 141, 141A ... Measurement
part, 142, 142A ... Adjustment part, 200 ... Sound signal generation circuit, R1-R3 ... Resistor
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