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JP2012090023

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DESCRIPTION JP2012090023
In a variable directional microphone unit and a variable directional microphone that switch
directivity by switching electric circuits, a circuit for switching directivity does not become a load
and does not become a noise source. SOLUTION: A pair of microphone elements 10 and 20 are
arranged back to back, and output signal systems of the pair of microphone elements 10 and 20
are respectively connected to a hot side terminal and a cold side terminal of balanced output, and
one of the pair of microphone elements An inverting amplifier 24 is connected to the output
signal system, the input resistance or feedback resistance of the inverting amplifier 24 is divided,
and switching means 30 is provided for switching the signal extraction point by arbitrarily
selecting the dividing point of the input resistance or feedback resistance. The directivity of the
balanced output signal is made variable by switching the output on one side of the balanced
output by the switching means 30. [Selected figure] Figure 1
Variable directional microphone unit and variable directional microphone
[0001]
The present invention relates to a variable directional microphone unit and a variable directional
microphone that can switch directivity by switching of an electric circuit, and in spite of the
simple circuit configuration, there is no increase in noise, and a dual Variable directivity can be
realized over a wide range from directivity to omnidirectionality.
[0002]
Conventionally, as a microphone whose directivity is variable, one using a microphone unit in
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1
which two capacitor type microphone elements are back-to-back is known (see, for example,
Patent Document 1 and Patent Document 2).
Each of the two microphone elements has a cardioid characteristic, and is made variable
directivity by adjusting the output of each element or adjusting the polarization voltage of each
element as described in Patent Document 1. ing. As an example of a microphone unit in which
two capacitor type microphone elements are back-to-back, those described in Patent Document 3
and Patent Document 4 are also known.
[0003]
An example of directivity that can be obtained by a microphone unit in which two capacitor-type
microphone elements are back-to-back is shown in FIG. 3, and a conventional capacitor-type
microphone that can obtain various directivity as shown in FIG. Examples of units are shown in
FIG. 4 and FIG.
[0004]
In FIG. 3, the solid line of the curve shown in the upper stage shows the directivity characteristic
of the front microphone element, and the broken line shows the directivity characteristic of the
rear microphone element.
In the example of this figure, the front element is fixed in unidirectionality, and switches the
output and the polarity of the rear element. The lower part of FIG. 3 shows directivity that can be
obtained as a microphone unit by switching the output and the polarity of the rear side
microphone element. The example shown by “3” in the center in the left-right direction shows
a single directivity which is not influenced by the rear element, and hence the output of the rear
element is zero and can be obtained only with the front element. There is. As the output of the
rear element is gradually increased centering on this uni-directionality, the directivity changes
from “3” to the right or left according to the polarity of the output. The left side from "3"
shows the case where the output polarity of the rear element is made negative, and when the
output of the rear element is maximized, it becomes bi-directional as shown in "1" and the output
of the rear element If you make it smaller, it becomes hypercardioid directivity as shown in
“2”. The right side from "3" shows the case where the output polarity of the rear element is
made positive. When the output of the rear element is maximized, it becomes omnidirectional as
shown in "5" and the output of the rear element becomes Becomes smaller (wide cardioid) as
shown in "4".
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[0005]
A circuit example of a conventional variable directional condenser microphone which can be
switched to various directivity as shown in FIG. 3 is shown in FIG. In FIG. 4, the condenser
microphone unit 50 has a first microphone element 51 having a fixed pole 55 common to the
diaphragm 53, and a second microphone element 52 having a diaphragm 54 and the common
fixed pole 55 described above. ing. By applying a fixed polarization voltage to the diaphragm 53
of one of the two microphone elements 51 and 52 and switching the polarization voltage applied
to the diaphragm 54 of the other microphone element 52, The directivity of the microphone unit
50 can be switched.
[0006]
In the example shown in FIG. 4, a +60 V DC power supply and a −60 V DC power supply are
provided, and +60 V is always applied to the diaphragm 53 of one microphone element 51. The
+60 V and -60 V power supplies are divided into two steps (for example, 60 V and 30 V) by
voltage dividing resistors 61 and 62 and voltage dividing resistors 63 and 64, respectively, to
generate five steps of voltages including 0 V It has become. The five-step voltage is selected by
the switch 56 and applied to the diaphragm 54 of the other microphone element 52. 0 V is
applied to the fixed electrodes 55 (also referred to as “back plates”) of both elements.
[0007]
When the switch shown in FIG. 4 selects the contact point 1, the polarization voltage of the first
microphone element 51 is +60 V, whereas the polarization voltage of the second microphone
element 52 is −60 V. The microphone unit of the directivity characteristic in which the output of
the microphone element on the rear surface is subtracted from the output of the microphone
element on the front surface as shown in FIG. When the switch selects the contact point 2, the
polarization voltage of the microphone element 52 becomes a voltage (for example, -30 V)
between -60 V and 0 V, and the microphone of hypercardioid directivity characteristic as shown
in "2" of FIG. Become a unit. When the switch selects the contact point 3, the polarization voltage
of the microphone element 52 becomes 0 V, and a microphone unit which outputs signals only
from the cardioid directivity characteristic as shown by "3" in FIG. 3, that is, the front microphone
element. When the switch selects the contact point 4, the polarization voltage of the microphone
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element 52 becomes a voltage (for example, 30 V) between 0 V and +60 V, and the microphone
unit with wide cardioid directional characteristics as shown in “4” of FIG. Become. When the
switch selects the contact point 5, the polarization voltage of the microphone element 52
becomes +60 V, and the output of the back microphone element is output to the output of the
nondirectional, ie front microphone element as shown in "5" of FIG. It becomes a microphone
unit of the added directional characteristic.
[0008]
Another circuit example of a conventional variable directional condenser microphone unit which
can be switched to various directivity is shown in FIG. In FIG. 5, reference numerals 10 and 20
respectively indicate condenser microphone elements. In FIG. 5, the two condenser microphone
elements 10 and 20 are drawn to be independent independently, but are assembled integrally
back and forth with the fixed electrodes back to back or with the fixed electrodes in common.
The microphone element 10 has a diaphragm 11 and a fixed electrode 12 opposed thereto, and
the output signal thereof is output as an impedance converter 13 including an FET and the like, a
hot side signal of balanced output through a buffer amplifier 15. It has become. The microphone
element 20 also has the diaphragm 21 and the fixed electrode 22 opposed thereto, and the
output signal thereof is output as the cold side signal of the balanced output through the
impedance converter 23 including the FET and the like, the buffer amplifier 25. It has become.
[0009]
The microphone element 10 side is a front element, the element 20 is a rear element, and the
microphone element 20 includes a directional switching circuit including an inverting amplifier
24 as described below between the impedance converter 23 and the buffer amplifier 25. Is
incorporated. The output of the impedance converter 23 is connected to the first contact of a
changeover switch having five changeover contacts and to the inverting input terminal of the
inverting amplifier 24 via the input resistor Rs. The noninverting input terminal of the inverting
amplifier 24 is grounded. The output terminal of the inverting amplifier 24 is connected to the
fifth contact of the changeover switch, and the output terminal of the inverting amplifier 24 and
the inverting input terminal are connected via a feedback resistor Rf. The gain of the inverting
amplifier 24 is determined by the ratio of the feedback resistor Rf to the input resistor Rs.
[0010]
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Between the output terminal of the impedance converter 23 and the output terminal of the
inverting amplifier 24, an attenuator formed by connecting resistors R1, R2, R3 and R4 in series
is connected. The resistors R1, R2, R3 and R4 are substantially voltage dividing resistors. The
connection point of the resistors R1 and R2 is to the second contact of the changeover switch,
the connection point of the resistors R2 and R3 is to the third contact of the changeover switch,
and the connection point of the resistors R3 and R4 is to the fourth contact of the changeover
switch , Each connected. The values of the voltage dividing resistors R1, R2, R3 and R4 are
arbitrary, but all have the same resistance value here. The movable contact of the changeover
switch is connected to the input terminal of the buffer amplifier 25, and the output terminal of
the buffer amplifier 25 is output as the cold side signal of the balanced output.
[0011]
Now, assuming that the changeover switch selects the first contact 1 as shown in FIG. 5, the
output of the impedance converter 23 is directly input to the buffer amplifier 25. Therefore, the
buffer amplifier 25 outputs the non-inverted output signal of the microphone element 20 at the
maximum level, and this output signal is output as the cold side signal of the balanced output. As
a result, the directional characteristics of the signal balancedly output from OUT + and OUT- as
the microphone unit output become bi-directional as shown by 1 in FIG. When the changeover
switch selects the second contact 2, the non-inverted output signal of the microphone element 20
is divided by the voltage dividing resistor, and this divided voltage signal is input to the buffer
amplifier 25. The buffer amplifier 25 outputs the non-inverted output signal of the microphone
element 20 at an intermediate level, and this output signal is output as the cold side signal of the
balanced output. As a result, the directivity characteristic of the signal balancedly output from
OUT + and OUT- as the microphone unit output becomes hypercardioid directivity as shown by 2
in FIG.
[0012]
When the changeover switch selects the third contact point 3, the middle point of the voltage
dividing resistors R1, R2, R3 and R4, that is, the connection point of the resistors R2 and R3 is
selected. Both will be zero. Therefore, the directional characteristics of the signal balancedly
output from OUT + and OUT- as the microphone unit output become the cardioid directivity or
unidirectionality as shown by 3 in FIG. When the changeover switch selects the fourth contact
point 4, the inverted output of the inverting amplifier 24 is divided by the voltage dividing
resistor and inputted to the buffer amplifier 25, and this output signal is outputted as the cold
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side signal of the balanced output. As a result, the directivity of the signal balancedly output from
OUT + and OUT- as the microphone unit output becomes the directivity of wide cardioid as
shown by 4 in FIG. When the changeover switch selects the fifth contact point 5, the inverted
output level of the inverting amplifier 24 is inputted as it is to the buffer amplifier 25 and this
output signal is outputted as the cold side signal of the balanced output. As a result, the
directional characteristics of the signal balancedly output from OUT + and OUT- as the
microphone unit output become non-directional as shown by 5 in FIG.
[0013]
JP-A-7-143595 JP-A-2008-67286 JP-A-2008-118260 JP-A-2010-103637
[0014]
The conventional variable directional condenser microphone unit as shown in FIG. 4 assumes a
condenser unit that is not an electret type, and therefore can not be applied to an electret
condenser microphone unit.
In addition, a DC voltage of about 60 V, which is required as a polarization voltage, is required,
and a DC voltage source with both positive and negative polarities needs to be provided.
However, assuming a microphone using a power supply battery, even when using a plurality of
power supply batteries in series, the voltage is several volts and the polarization voltage is
insufficient. Therefore, a DC-DC converter is incorporated to boost the DC voltage, but since the
DC-DC converter uses an oscillator with an oscillation frequency of, for example, 1 MHz, this
transmission signal serves as a noise source for the audio signal. There are In addition, there is a
problem that the voltage dividing resistance acts as a load on the DC-DC converter, and if the DCDC converter's ability is enhanced, the power supply battery will be depleted.
[0015]
According to the conventional variable directional condenser microphone unit as shown in FIG. 5,
since the inverting amplifier and the output circuit of the inverting amplifier are connected to
one output signal system of the microphone elements forming a pair, It is necessary to flow a
current through this voltage dividing resistor, and this current becomes the load of the inverting
amplifier. In other words, this load needs to be driven by an inverting amplifier. In order to
reduce the load on the inverting amplifier, it is sufficient to increase the value of the voltage
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dividing resistor. However, if the value of the voltage dividing resistor is increased, the voltage
dividing resistor becomes a noise source and the SN ratio of the audio signal is degraded. Will
occur.
[0016]
The present invention solves the problems of the prior art as described above, that is, in the
variable directional microphone unit and the variable directional microphone in which the
directivity is switched by switching the electric circuit, the directivity is switched. It is an object
of the present invention to prevent the circuit of (1) from becoming a load and a noise source.
[0017]
In the present invention, a pair of microphone elements are disposed back to back, and the
output signal system of the pair of microphone elements is connected to the hot side terminal
and the cold side terminal of the balanced output, respectively, and one output signal of the pair
of microphone elements An inverting amplifier is connected to the system, the input resistance or
feedback resistance of the inverting amplifier is divided, and switching means for switching the
signal output point by arbitrarily selecting the dividing point of the input resistance or feedback
resistance, the switching The most important feature is that the directivity of the balanced output
signal is made variable by switching the output on one side of the balanced output by means.
[0018]
One of the pair of back-to-back microphone elements is directly connected to one of the balanced
outputs, and the input resistance or feedback resistance of the inverting amplifier connected to
the other output signal system of the balanced outputs is divided, The signal extraction point is
switched by arbitrarily selecting the dividing point of the input resistor or the feedback resistor
by the switching means.
In the switching operation by the switching means, the level and the polarity of the output signal
in the other output signal system of the balanced output are switched, and the directivity of the
balanced output signal is switched.
The directivity is switched by switching the signal extraction point by selecting the dividing point
of the input resistor or the feedback resistor, so that the circuit for switching the directivity does
not become a load and does not become a noise source.
03-05-2019
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[0019]
It is a circuit diagram showing an example of a variable directivity microphone unit concerning
the present invention. It is a circuit diagram showing another example of the variable directivity
microphone unit concerning the present invention. It is a pattern figure which shows the
example of the various directivity which can be switched by a variable directivity microphone. It
is a circuit diagram showing an example of the conventional variable directivity microphone unit.
It is a circuit diagram showing another example of the conventional variable directional
microphone unit.
[0020]
Hereinafter, embodiments of a variable directional microphone unit and a variable directional
microphone according to the present invention will be described with reference to FIGS. 1 to 3.
The same reference numerals as in the conventional example shown in FIG. 5 denote the same
parts.
[0021]
In FIG. 1, reference numerals 10 and 20 respectively indicate condenser microphone elements.
The microphone element 10 has the diaphragm 11 and the fixed electrode 12 opposed thereto,
and the output signal thereof is output as the hot side signal OUT + of balanced output through
the impedance converter 13 including the FET and the like, the buffer amplifier 15 It has
become. The microphone element 20 also has the diaphragm 21 and the fixed electrode 22
opposed thereto, and the output signal thereof is output as the cold side signal OUT- of the
balanced output through the impedance converter 23 including the FET and the like, the buffer
amplifier 25. It is supposed to be. The two condenser microphone elements 10 and 20 are, for
example, assembled separately and independently, assembled with the respective fixed electrodes
12 and 22 back to back, or assembled together back and forth with the fixed electrodes in
common. There is. Therefore, the pair of microphone elements 10 and 20 are disposed back to
back.
[0022]
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The microphone element 10 side is a front element, the element 20 is a rear element, and the
microphone element 20 includes a directional switching circuit including an inverting amplifier
24 as described below between the impedance converter 23 and the buffer amplifier 25. Is
incorporated. The output signal of the impedance converter 23 is input to the inverting input
terminal of the inverting amplifier 24 through the input resistor, and the input resistor is
composed of two input resistors Rs1 and Rs2 connected in series. The noninverting input
terminal of the inverting amplifier 24 is grounded. A feedback resistor is connected between the
output terminal and the inverting input terminal of the inverting amplifier 24. The feedback
resistor is composed of two feedback resistors Rf1 and Rf2 connected in series. The gain of the
inverting amplifier 24 is determined by the ratio of the feedback resistance to the input
resistance. As described above, the input resistance is divided by two resistances Rs1 and Rs2,
the feedback resistance is divided by two resistances Rf1 and Rf2, and these division points and
non-division points are switched by the switching switch 30, The output of one side is switched
to make the directivity of the balanced output signal variable. Although the values of the two
input resistors Rs1 and Rs2 and the two feedback resistors Rf1 and Rf2 are described to be the
same, they may be set to different values according to the design concept.
[0023]
The changeover switch 30 has five changeover contacts (fixed contacts), and the movable contact
is connected to the input terminal of the buffer amplifier 25. The first switching contact “1” of
the changeover switch 30 is connected to the output terminal of the impedance converter 23.
The second switching contact "2" of the changeover switch 30 is connected to the connection
point of the input resistors Rs1 and Rs2. The third switching contact “3” of the changeover
switch 30 is connected to the inverting input terminal of the inverting amplifier 24. The fourth
switching contact "4" of the changeover switch 30 is connected to the connection point of the
feedback resistors Rf1 and Rf2. The fifth switching contact “5” of the changeover switch 30 is
connected to the output terminal of the inverting amplifier 24.
[0024]
The operation of the embodiment configured as described above will be described below. As
shown in FIG. 1, when the changeover switch 30 selects the contact “1”, the output of the
impedance converter 23 is directly input to the buffer amplifier 25. Therefore, the output of the
rear microphone element 20 is directly input from the impedance converter 23 to the buffer
03-05-2019
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amplifier 25 without passing through the inverting amplifier 24, and is output as a cold-side
signal of the balanced output. The cold side signal has the same polarity and directivity as the hot
side signal, and becomes negative polarity indicated by a broken line at "1" in FIG. 3 on the
receiving side of the balanced output. Therefore, on the receiving side of the balanced output, the
directivity characteristic of the cardioid outputted from one microphone element 10 side (hot
side) and the cardioid directivity of the opposite polarity outputted from the other microphone
element 20 side (cold side) Together with the characteristics, it becomes a bi-directional output.
[0025]
When the contact point "2" is selected by the changeover switch 30, the connection point of the
input resistances Rs1 and Rs2 of the inverting amplifier 24, that is, the division point of the input
resistance is selected to take out a signal. Output as the cold side signal of the balanced output.
The cold-side signal of this balanced output is a signal of positive polarity with low level cardioid
directivity as shown by a broken line in "2" of FIG. On the receiving side of the balanced output,
the polarity of the cold side signal is inverted to minus. Therefore, on the reception side of the
balanced output, the signal of the cardioid directivity characteristic outputted from one
microphone element 10 side (hot side) and the cold side signal are combined to become the
hypercardioid directivity characteristic.
[0026]
When the contact point "3" is selected by the changeover switch 30, the inverting input terminal
of the inverting amplifier 24 is selected, and the input signal level to the buffer amplifier 25
becomes zero. As a result, as shown by "3" in FIG. 3, as the cold side signal of the balanced
output, only the signal having the cardioid directivity characteristic outputted from one
microphone element 10 side is balanced and output.
[0027]
When the contact point "4" is selected by the changeover switch 30, the connection point of the
feedback resistors Rf1 and Rf2 of the inverting amplifier 24, that is, the dividing point of the
feedback resistors is selected to take out a signal. Output as the cold side signal of the balanced
output. The cold-side signal of this balanced output is a signal of negative polarity with low level
cardioid directivity as shown by a broken line in "4" of FIG. On the receiving side of the balanced
03-05-2019
10
output, the polarity of the cold side signal is inverted to positive. Therefore, on the reception side
of the balanced output, the signal of the cardioid directivity characteristic outputted from one
microphone element 10 side (hot side) and the cold side signal are combined to become the wide
cardioid directivity characteristic.
[0028]
When the contact point “5” is selected by the changeover switch 30, the output signal from
the output terminal of the inverting amplifier 24 is inputted to the buffer amplifier 25 as it is.
The gain of the inverting amplifier 24 is determined by the value obtained by combining the
input resistors Rs1 and Rs2 and the value obtained by combining the feedback resistors Rf1 and
Rf2. The output signal is a full level and negative polarity signal having a cardioid directivity
characteristic as shown by a broken line in "5" of FIG. This signal passes through the buffer
amplifier 25 and becomes the cold side signal of the balanced output, and on the receiving side
of the balanced output, the polarity of the cold side signal is inverted to plus. Therefore, on the
receiving side of the balanced output, it becomes an omnidirectional directional pattern in
combination with the hot side output of the balanced output having the cardioid directional
characteristic output from one microphone element 10 side.
[0029]
Thus, in the embodiment shown in FIG. 1, the inverting amplifier 24 in which the input resistance
and the feedback resistance are divided into the output signal system on one side of the balanced
output, and the division point of the input resistance and the feedback resistance of the inverting
amplifier 24 The directivity of the balanced output signal is made variable by providing
switching means 30 for switching the signal taking point by arbitrarily selecting. Since the input
resistance and the feedback resistance do not load the inverting amplifier 24, consumption of the
power supply can be suppressed, and the values of the input resistance and the feedback
resistance of the inverting amplifier 24 do not change by switching. , The gain of the inverting
amplifier 24 does not fluctuate. Further, since it is not necessary to make the input resistance
and the feedback resistance high, noise generated from the resistance can be reduced. Since the
directivity is not switched by switching the polarization voltage of the condenser microphone, the
present invention is also applicable to an electret condenser microphone. Since there is no need
to boost the DC power supply voltage, there is no need to incorporate a DC-DC converter.
[0030]
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In the embodiment shown in FIG. 1, both the input resistance and the feedback resistance of the
inverting amplifier 24 are divided, and one directivity is selected from among the entire dividing
points of the input resistance and the feedback resistance to switch the directivity. However, only
the input resistance may be divided and one of these division points may be selected, or only the
feedback resistance may be divided and one of these division points may be selected. . However,
if only the input resistance or the feedback resistance is divided and division points are selected,
the directivity switching range is limited, so if the directivity switching range is made wider, the
input resistance It is desirable to divide both of and the feedback resistance so as to select one of
the division points.
[0031]
A second embodiment is shown in FIG. This embodiment differs from the first embodiment in
that a center tap variable resistor 31 is used as a directivity switching means. The center tap of
the variable resistor 31 is connected to the inverting input terminal of the inverting amplifier 24,
and one side of the variable resistor 31 is the input resistance Rs of the inverting amplifier 24
and the other side is the feedback resistor Rf of the inverting amplifier 24. It has become. The
slider of the variable resistor 31 is connected to the input terminal of the buffer amplifier 25 so
that the signal appearing on the slider is output as one side of the balanced output, that is, the
cold side signal in the example of FIG. The variable resistor 31 may be one that can be arbitrarily
operated by the user, or even if it is a semi-fixed resistance that keeps the adjustment position
semi-fixed after adjusting the directivity once. Good. The other configuration is the same as the
configuration of the embodiment shown in FIG.
[0032]
Now, as shown in FIG. 2, assuming that the slider of the center tap variable resistor 31 is at the
same position as the center tap, the switching means 30 in the embodiment shown in FIG. Since
it becomes the same as the selected one, the directivity characteristic of the balanced output
signal becomes the cardioid shown in "3" of FIG.
[0033]
When the slider of the variable resistor 31 is slid toward the input resistance Rs, the input
resistance Rs becomes substantially the same as divided, and in the embodiment of FIG. This
03-05-2019
12
division point is selected to take out a signal, which is the same as outputting this signal as a
cold-side signal of balanced output through the buffer amplifier 25.
The cold-side signal of this balanced output is a signal of positive polarity with low level cardioid
directivity as shown by a broken line in "2" of FIG. On the receiving side of the balanced output,
the polarity of the cold side signal is inverted to minus. Therefore, on the reception side of the
balanced output, the signal of the cardioid directivity characteristic outputted from one
microphone element 10 side (hot side) and the cold side signal are combined to become the
hypercardioid directivity characteristic.
[0034]
When the slider reaches the beginning of the input resistance Rs, the directivity of the signal
which is balanced and output becomes bi-directional as shown by "1" in FIG. Since the input
resistance Rs and feedback resistance Rf of the inverting amplifier 24 do not change, the gain of
the inverting amplifier 24 is constant.
[0035]
When the slider of the variable resistor 31 is slid from the center position toward the feedback
resistor Rf, it becomes substantially the same as selecting the feedback resistor Rf division point
of the inverting amplifier 24 and extracting the signal, and this signal is a buffer amplifier 25 is
output as a cold side signal of the balanced output. The cold-side signal of this balanced output is
a signal of negative polarity with low level cardioid directivity as shown by a broken line in "4" of
FIG. On the receiving side of the balanced output, the polarity of the cold side signal is inverted to
positive. Therefore, on the reception side of the balanced output, the signal of the cardioid
directivity characteristic outputted from one microphone element 10 side (hot side) and the cold
side signal are combined to become the wide cardioid directivity characteristic.
[0036]
When the slider reaches the end of the input resistance Rs, the directivity characteristic of the
signal which is balanced and output becomes non-directivity shown by "5" in FIG.
[0037]
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13
According to the embodiment shown in FIG. 2, the same effect as the embodiment shown in FIG.
1 described above is obtained, and since the variable resistor 31 with center tap is used as the
directivity switching means, the configuration is simple. Thus, the directivity can be switched
steplessly and continuously.
[0038]
The variable directional microphone unit according to the present invention described above can
be configured as a variable directional microphone by incorporating it into a microphone case
and further incorporating a microphone connector for performing balanced output in the
microphone case.
[0039]
The variable directional microphone unit and the variable directional microphone according to
the present invention can be used indoors as well as indoors such as a studio, and have optimum
directivity according to the place of use, purpose of use, and other various conditions. It can be
adjusted.
[0040]
Reference Signs List 10 microphone element 11 diaphragm 13 impedance converter 15 buffer
amplifier 20 microphone element 22 diaphragm 23 impedance converter 24 inverting amplifier
25 buffer amplifier 30 switching unit 31 variable resistor as switching unit
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