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JP2001333486

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DESCRIPTION JP2001333486
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
microphone device.
[0002]
2. Description of the Related Art A microphone unit machine is arranged by coaxially arranging
two omnidirectional microphone units so that the diaphragms face each other, and using the sum
signal of the outputs of the two microphone units as an output signal. A microphone device
capable of effectively reducing vibration noise generated by dynamic vibration has been
developed (Japanese Patent Application No. 62-230278). This kind of microphone device has
been widely used until now, mainly for applications such as a microphone device of a camera
integrated video recorder.
[0003]
The above-mentioned conventional microphone device will be described below with reference to
the drawings. FIG. 3 shows an outline of a nondirectional microphone unit used in the
conventional and inventive microphone devices. In the same figure, 1 shows a microphone unit
main body, 2 shows a diaphragm. Also, 3 is a terminal (+ terminal) that outputs a positive voltage
when the diaphragm is pushed toward the back of the microphone unit, and 4 is a terminal that
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outputs a negative voltage when the diaphragm is pushed toward the back of the microphone
unit (-Terminal).
[0004]
Here, when the microphone unit 1 is vibrated at a velocity v in a direction parallel to the
diaphragm 2 (y direction in FIG. 3), the diaphragm 2 hardly vibrates. However, when vibrating at
a velocity v in a direction perpendicular to the diaphragm 2 (x direction in FIG. 3), the diaphragm
2 vibrates largely. Therefore, even if there is no sound wave incident on the microphone unit, if a
force is applied in the x-axis direction of the microphone unit for some reason, a voltage is
generated at the output terminals 3 and 4, and the generated sound vibrates. It becomes noise.
[0005]
The vibration noise is generated not only when a force is directly applied in the x direction, but
also when a force is applied in an oblique direction, due to a component force of the force
converted into the x direction. For example, as shown in FIG. 5, assuming that the angle formed
by the direction (x direction) perpendicular to the diaphragm 2 and the vibration direction is θ,
the velocity component contributing to the generation of vibration noise can be represented by v
cos θ it can.
[0006]
When considering the cause of generation of vibration noise mentioned above, vibration noise
can be reduced if two microphone units are arranged opposite to each other so that vibration
components in the direction perpendicular to the diaphragms of those microphone units cancel
each other. I understand. FIG. 4 shows a conventional microphone device to which this principle
is applied. In the figure, 1 and 2 represent microphone units, and 9 and 10 represent respective
diaphragms. The microphone units 1 and 2 are disposed close to each other so that the
diaphragms face each other at a distance d, and are fixed by the connector 3. It is desirable that
the connector 3 be made of a material as strong as possible so that the microphone units 1 and 2
vibrate as much as possible when the entire microphone device is excited. In addition, a hole 4 is
opened in the connector 3 so as not to disturb the sound wave incident on the diaphragms of the
microphone units 1 and 2 as much as possible.
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[0007]
An output terminal 5 outputs a positive voltage when the diaphragm 9 of the microphone unit 1
is pushed toward the back of the microphone unit and outputs a negative voltage when the
diaphragm 9 moves in the opposite direction. The diaphragm 6 of the microphone unit 1 outputs
a negative voltage. It is an output terminal that outputs a negative voltage when pressed in the
back direction and outputs a positive voltage when pressed in the opposite direction. Similarly, 7
is an output terminal that outputs a positive voltage when the diaphragm 10 of the microphone
unit 2 is pushed in the back direction of the microphone unit and outputs a negative voltage
when the diaphragm 10 of the microphone unit 2 is pushed in the opposite direction. It is an
output terminal that outputs a positive voltage when a negative voltage is pushed in the opposite
direction when the diaphragm 10 is pushed in the rear direction.
[0008]
The positive voltage output terminal 5 of the microphone unit 1 and the positive voltage output
terminal 7 of the microphone unit 2 are directly connected, and this is used as the positive
voltage output terminal 11 of the entire microphone device. Similarly, the negative voltage
output terminal 6 of the microphone unit 1 and the negative voltage output terminal 8 of the
microphone unit 2 are directly connected, and this is used as the negative voltage output
terminal 12 of the entire microphone device.
[0009]
Here, when the entire microphone device is excited, vibrations in the same direction occur in the
diaphragm 9 of the microphone unit 1 and the diaphragm 10 of the microphone unit 2. However,
since the microphone units 1 and 2 are disposed opposite to each other, when the diaphragm 9
of the microphone unit 1 moves, for example, in a direction approaching the back of the
microphone unit, the diaphragm 10 of the microphone unit 2 simultaneously has the same speed.
Move in the direction away from That is, since the output voltages of the microphone units 1 and
2 generated due to the vibration are in opposite phase to each other, the output signal of the
vibration noise component is canceled if the two are added.
[0010]
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On the other hand, sound waves incident on the microphone units 1 and 2 through the holes 4
opened in the connector 3 are simultaneously moved to the microphone unit 1 when, for
example, the diaphragm 9 of the microphone unit 1 approaches the back of the microphone unit
Similarly, the diaphragm 10 of 2 moves toward the back of the microphone unit, that is, the
output voltages of the microphone units 1 and 2 become in phase with each other, so the output
signals for the sound waves are added together by adding them together. Doubled.
[0011]
SUMMARY OF THE INVENTION The above-mentioned microphone device can obtain the
maximum effect when sound waves of the same phase are always incident on the diaphragms of
the two microphone units disposed oppositely from the principle of operation. It is supposed to
be.
However, in an actual microphone device, the phase of the incident sound wave is disturbed by
the influence of a structure or the like in the vicinity of the microphone unit, so that not only the
original vibration noise reduction effect can not be sufficiently obtained, but conversely an
adverse effect occurs. was there. Especially in the high frequency range where the wavelength is
short, there is a problem that the sensitivity of the high range is lowered or the high / low range
frequency characteristic is disturbed by peak / dip and the sound quality is affected. The It is an
object of the present invention to overcome the above-mentioned drawbacks of conventional
microphone devices.
[0012]
SUMMARY OF THE INVENTION In order to solve the above problems, the present invention
provides a microphone device comprising the following means. That is, two nondirectional
microphone units are disposed coaxially with the diaphragms facing each other, and low
frequency components are extracted from the sum signal of the outputs of the two microphone
units, By adding a signal obtained by adding high frequency components extracted from the
output of one of the two microphone units as an output signal, vibration noise generated by
mechanical vibration of the microphone unit is removed, Further, the present invention provides
a microphone device in which high frequency characteristics can be obtained well.
[0013]
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According to another aspect of the present invention, there is also provided a microphone device
comprising the following means. That is, two nondirectional microphone units are disposed
coaxially with the diaphragms facing each other, and low frequency components are extracted
from the sum signal of the outputs of the two microphone units, Vibration noise generated by
mechanical vibration of the microphone unit by using as an output signal a signal obtained by
adding the result of extracting high frequency components from the outputs of other microphone
units arranged in the vicinity of the two microphone units. The present invention also provides a
microphone device which can obtain a high frequency characteristic well while removing the
[0014]
In the above microphone device, a cutoff frequency (cutoff frequency) of a filter circuit for
extracting a low frequency component from a sum signal of outputs of the two microphone units,
and either one (or two) of the two. By making it possible to change the cutoff frequency of the
filter circuit that extracts high frequency components from the output of another microphone
unit placed in the vicinity of this microphone unit, the maximum vibration noise can be achieved
without loss of sound quality. It is possible to obtain the removal effect.
[0015]
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS In describing the embodiment of
the present invention, the above-mentioned conventional microphone device will be discussed
again.
In the microphone device shown in FIG. 4, the output signal of the microphone unit 1 is Vout1,
the output signal of the microphone unit 2 is Vout2, and the sum signal of these outputs is Vout.
Here, although both the microphone units 1 and 2 define Vout for only the positive output
terminal, the following description is similarly established only by considering the sign of the
voltage inverted for the negative output terminal.
[0016]
Furthermore, the output signal Vout1 of the microphone unit 1 can be divided into an output Vs1
caused by an incident sound wave and an output Vn1 caused by vibration. つまり、
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Vout1=Vs1+Vn1 ・・・ (1)である。 Similarly, the microphone unit 2 can also be
expressed as Vout2 = Vs2 + Vn2 (2). At this time, the characteristics of the two microphone units
are exactly the same, and the arrangement distance d between the two microphone units is
sufficiently small with respect to the wavelength of the audible sound, and the connector 3 and
the hole 4 opened there are incident. It is an ideal shape that does not cause reflection of sound
waves or disturbance of phase, and therefore, if sound waves are incident on two microphone
units under exactly the same conditions, Vs1 = Vs2 ··· at a certain time It can be said that (3).
[0017]
Also, if the mechanical coupling of the microphone units 1 and 2 by the connector 3 is
sufficiently strong and the vibrations of the two microphone units when excited across the entire
microphone device are exactly the same, at a certain time, Vn1 = -Vn2 (4) Accordingly, the sum
signal Vout becomes Vout = Vout1 + Vout2 = Vs1 + Vn1 + Vs2 + Vn2 = 2Vs1 (2) (5), the output
signal originating from the incident sound wave is doubled, and the output signal originating
from the vibration becomes zero. In this way, the vibration noise is canceled while the output for
the target sound is increased, so that the S / N ratio for the vibration noise is greatly improved.
[0018]
The above is the description of the operation principle of the microphone device for reducing
vibration noise by opposingly arranging two nondirectional microphone units, but the
microphone device using this principle satisfies the following conditions Sometimes it produces
the ideal effect. (1) the electrical characteristics and mechanical characteristics of the two
microphone units are the same, (2) the sound waves incident on the two microphone units have
the same phase and magnitude, (3) 2 The diaphragms of the individual microphone units should
be identical to external vibration.
[0019]
However, in a real microphone device, all the above conditions are not ideal. Among the above
conditions (1) to (3), it is known that (1) and (3) do not become so much obstacles from many
practical examples such as a camera integrated video recorder and the like. The difference in
sensitivity between the two microphone units causes a problem that the output signal Vs due to
the sound wave is not exactly doubled or the output signal Vn due to the vibration is not
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completely zero, and the magnitude of the vibration noise reduction effect is large Although it is
effective if it is not completely ideal as long as it has a certain effect on hearing, there are many
cases where a sufficient noise reduction effect is actually obtained by a mass-produced
microphone unit on the market. In the mass-produced microphone units on the market,
individual differences in phase characteristics are also observed. However, no adverse side effect
is recognized as a side effect other than the magnitude of the noise reduction effect in many past
examples. As to the problem of the strength of the connector 3 for fixing two microphone units, a
vibration noise reduction effect sufficient for practical use is obtained by using materials, parts
and fixing mechanisms which can be mass-produced.
[0020]
However, with regard to the above (2), problems have been recognized in past actual examples.
That is, it is practically difficult to design the shape of a microphone device in which sound waves
of the same phase and the same level are incident on two microphone units arranged opposite to
each other. Ideally, two point collection sound sources having no size should be arranged as close
as possible in free space where there are no obstacles in the periphery. In order not to prevent
ideal sound wave incidence, it is desirable that no connector be present.
[0021]
Here, as to the level difference between the sound waves incident on the two microphone units, it
has been mentioned earlier that it slightly affects the vibration noise reduction effect and does
not cause much problems. Therefore, the reason why in the actual microphone device, the sound
waves of the same phase are prevented from being input to the two microphone units will be
described. First, because a microphone unit has a size and sound waves have to be incident on
the diaphragms of two microphone units disposed opposite to each other, a physical distance d is
required between the two microphone units. . Therefore, a difference arises in the time which an
incident sound wave reaches the diaphragm of two microphone units.
[0022]
As shown in FIG. 5, when the sound source is at a position sufficiently separated from the
microphone unit, the sound waves reach two microphone units, where θ is the angle between
the direction perpendicular to the diaphragm and the incident direction of the sound wave. The
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difference in distance is dcosθ. The phase difference between the sound waves of the two
microphone units is maximized when θ = 0, and the distance difference is d. As an example of an
actual past microphone device for a camera integrated type video recorder, a device with d of
about 5 mm exists, in this case a frequency at which the phase difference of sound waves input
to two microphone units is 180 °. That is, Vs1 = -Vs2, and the sum signal of the outputs of the
two microphone units becomes zero, that is, the frequency at which equation 5 becomes zero as
in Vout = Vout1 + Vout2 = Vs1 + Vn1 + Vs2 + Vn2 = 0 (6) Is about 34.7 kHz (in the case of 25 °
C.) and its odd multiple.
[0023]
This situation is shown in the graph in which the horizontal axis represents frequency and the
vertical axis represents output voltage. Thus, the distance d between the microphone units has an
adverse effect that the high range is attenuated. This effect also extends to the audible band.
[0024]
Also, in order to connect the two microphone units firmly, the connector 3 as described with
reference to FIG. 4 is also required. Therefore, a space surrounded by the two microphone units
disposed opposite to each other and the connector is created. A sound wave whose wavelength is
shorter than the size of this space causes reflection, resonance, etc. in this space, and the
condition that the sound waves must always be incident on the two microphone units with the
same phase is prevented.
[0025]
For example, when looking at a conventional camera integrated video recorder, there is a typical
numerical example of an opposed arrangement microphone device in which the diameter of the
microphone unit is 6 mm and the microphone unit distance d is 5 mm. In this case, the half
wavelength is 6 mm. The frequency of the sound wave becomes 28.9 kHz, and the frequency of
the sound wave whose half wavelength becomes 5 mm becomes 34.7 kHz (both in the case of 25
° C.), which also affects the high frequency characteristics of the audible band.
[0026]
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The next problem is the effect of a windscreen or a wire grill (microphone grille) covering the
microphone device.
These become acoustic resistance and cause different amounts of delay depending on the
traveling path of the sound wave, and disturb the phase relationship between the sound waves
incident on the two microphone units at different positions.
[0027]
Furthermore, when considering an application example of an actual microphone device, there is a
structure in the vicinity of the periphery of the microphone device that is not related to sound
collection, and this is an obstacle to disturb the phase. For example, considering a microphone
device having a shape projecting from the main body of a camera integrated video recorder as
shown in FIG. 7, reflection of sound waves occurs on the surface of the video recorder main body
102 in the vicinity of the microphone device 101. By this, the phase relationship between the
sound waves incident on the two microphone units is disturbed. In the microphone device 101 of
FIG. 7, it is assumed that two opposingly arranged microphone units as shown in FIG. 4 are
incorporated.
[0028]
In FIG. 7, a sound wave (direct sound) that has come out of a sound source and directly reached
the microphone device 101 enters the microphone unit 1 of FIG. 4 and comes out of the sound
source and is reflected by the video recorder body 102 and reaches the microphone device 101.
(Indirect sound) is assumed to be incident on the microphone unit 2 of FIG. Since the arrival path
is different between the direct sound and the indirect sound, it is considered that the phases do
not match. If the phase difference between the two is 180 °, the sum signal of the outputs of the
microphone units 1 and 2 will be zero as in equation 6.
[0029]
The frequency characteristic of the sound wave following the same arrival path is similar to that
of Fig. 6, and the output signal becomes zero at a frequency that is an odd multiple of the
frequency when the phase difference between the direct sound and the indirect sound is 180 °.
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Output voltage characteristics such as As described above, since an obstacle existing relatively
far around the microphone device causes a large phase difference between the direct sound and
the indirect sound, the influence of the frequency characteristic extends to the low frequency
range, and the entire microphone device This will cause large disturbances in the frequency
characteristics of
[0030]
For example, in a camera-integrated video tape recorder of the past, as shown in FIG. 7, equipped
with a microphone device protruding from the main body, the difference in reach distance for
direct sound and indirect sound to reach the microphone unit is about 20 mm. There was one
that had a shape, but the frequency of the sound wave for which the half wavelength is 20 mm is
about 8.7 kHz (in the case of 25 ° C.), so the sum signal of the outputs of microphone units 1
and 2 is about 8.7 kHz It cancels out and becomes zero at the frequency of the odd multiple of,
which greatly affects the frequency characteristic of the high range.
[0031]
As described above, in an actual application, a microphone device aiming at a vibration noise
reduction effect by opposing arrangement of two microphone units causes disturbance of
frequency characteristics such as signal level attenuation mainly in a high frequency region. ing.
10 and 11 show frequency characteristics measured by attaching a microphone device to an
actual camera-integrated video recorder. The microphone device is attached at a position
projecting from the camera body as in FIG. 7, and measures the frequency characteristic in the
front direction of the camera. FIG. 10 shows the case where the nondirectional microphone unit
is attached in the front direction as shown in FIG. 8, and FIG. 11 is the case where the same
microphone unit is attached in the opposite arrangement as shown in FIG. As described above,
the frequency characteristics when the microphone units are disposed opposite to each other
cause disturbances such as peaks and dips in the high frequency region, and the sensitivity
decreases in the highest region.
[0032]
Next, consider the frequency band of vibration noise. Vibration noise is caused by vibration that
occurs when the microphone device receives an external impact, and vibration from inside that
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occurs when the microphone device itself or the device to which it is attached has any
mechanical drive mechanism or the like. Generally, the frequency is generally low.
[0033]
For example, as an example of a drive mechanism that generates high frequency vibration noise,
there are a tape drive system and a tape travel system of a DV camera integrated video recorder,
and the head drum which is the drive system that rotates at the highest speed among them. Since
the rotational speed of the above is 9000 rpm, vibrations of 150 Hz and its integral multiples
occur, but the frequency to be aurally sensitive is up to about several kHz at most. That is, the
target of the vibration noise to be reduced may be considered up to about several kHz or less.
[0034]
On the other hand, as described above, the adverse effect caused by the vibration noise reduction
method by arranging two microphone units opposite to each other and taking their sum signal is
a number in consideration of the past embodiments. It occurs in the band above kHz. From this, it
is understood that in order to realize the vibration noise reduction while eliminating the adverse
effect, it is sufficient to limit the frequency band using the sum signal to a low frequency.
[0035]
Next, the microphone device according to the first embodiment of the present invention will be
described. FIG. 1 is a block diagram of a microphone device implemented as a first embodiment
of the present invention. In FIG. 1, 1 and 2 are nondirectional microphone units, and these
microphone units are arranged so that the diaphragms face each other and the faces of the
diaphragms are coaxially aligned. 3, 7 are circuits for adding electric signals, 4 is a low pass filter
(LPF), 5 is a high pass filter (HPF), 6 is an attenuator (ATT) for adjusting the signal level, 8 is It is
a signal output terminal of this microphone device. In this figure, an amplifier for amplifying a
minute signal output from the microphone unit is omitted.
[0036]
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The output signal 9 of the microphone unit 1 and the output signal 10 of the microphone unit 2
are added by the adder 3 to obtain the signal 11 in which the vibration noise is canceled
according to the principle as described above. By passing this through the low pass filter 4, a
high frequency region which may cause disturbance of the frequency characteristic is cut. On the
other hand, by passing the output signal 10 of the microphone unit 2 through the high pass filter
5, the low frequency range where vibration noise becomes a problem is cut.
[0037]
The output of the low pass filter 4 is passed through the attenuator 6 to match the signal level
with the output of the high pass filter 5 and then added to the output signal of the high pass
filter 5 in the adder 7. , The final output of this microphone device is obtained. Here, the cut-off
frequency of low-pass filter 4 and the cut-off frequency of high-pass filter 5 should be selected to
have similar frequency values so that the output signal of adder 7 draws as flat a frequency
characteristic as possible. As described above, the frequency should be selected to be an
intermediate value between the low frequency band where vibration noise is present and the
high frequency band that may cause disturbance of the frequency characteristic. . For example, in
consideration of the practical examples described so far, it is desirable to set the cutoff frequency
around several kHz. The signal input to the high pass filter 5 may be the output signal 9 of the
microphone unit 1 instead of the output signal 10 of the microphone unit 2.
[0038]
Next, a microphone device according to a second embodiment of the present invention will be
described. As shown in FIG. 2, the microphone device according to this embodiment does not
supply the output signal of the microphone unit 1 or 2 to the signal input to the high-pass filter
5, but is prepared separately from these microphone units Use the output of the microphone
unit. Here, it is desirable to arrange the third microphone unit 12 as close as possible within a
range that does not prevent the sound wave incident on the opposingly arranged microphone
units 1 and 2.
[0039]
By performing the processing as described above, vibration noise can be effectively removed on
the principle of vibration noise cancellation using the opposing microphone unit for low
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frequency regions where vibration noise is a problem. This adverse effect can be avoided by
synthesizing a microphone unit output signal that is not the sum signal of the facing microphone
units for a high frequency region that may cause characteristic disturbance. Thus, a microphone
device capable of effectively removing vibration noise can be realized without sacrificing high
frequency characteristics.
[0040]
Next, a microphone device according to a third embodiment of the present invention will be
described. The microphone device of this embodiment is the cut-off frequency (cut of the high
pass filter 5 and the low pass filter 4 in the microphone devices of the first and second
embodiments described with reference to FIG. 1 or FIG. 2). Make the off frequency) a variable
system. As described above, in the high frequency components to be reduced by the low pass
filter 4, the phase of the incident sound wave is disturbed due to the physical shape near the
microphone unit or around the microphone device, and the sensitivity decreases or the frequency
decreases. There is a frequency band that causes sound quality deterioration such as peak-dip of
characteristics, which is different depending on physical conditions such as the mounting
structure of the microphone unit and the shape around the microphone device.
[0041]
The low frequency component to be reduced by the high pass filter 5 is the frequency band of
the vibration applied to the microphone device, which also differs depending on the vibration
condition around the microphone device. Therefore, if the cutoff frequency of the low pass filter
4 and the high pass filter 5 is adjustable, it is possible to achieve both the vibration noise
reduction effect and the good high frequency characteristic under various usage conditions. It is
possible to select the optimum cutoff frequency that can be used, and to improve the overall
sound quality.
[0042]
According to the present invention, two non-directional microphone units, which have been
widely practiced conventionally, are disposed opposite to each other, and the sum signal of each
output is used as an output signal to mechanically connect the microphone units. The
disturbance of the high frequency characteristic which is the fault of the microphone device
which can reduce the vibration noise generated by the vibration is suppressed, the vibration
noise reduction effect and the good high frequency characteristic are compatible, and the overall
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sound quality is improved. can do.
[0043]
Brief description of the drawings
[0044]
1 is a circuit diagram of a microphone device according to a first embodiment of the present
invention.
[0045]
2 is a circuit diagram of a microphone device according to a second embodiment of the present
invention.
[0046]
3 is a schematic view of the microphone unit.
[0047]
4 is a schematic view of a conventional microphone device.
[0048]
5 is a schematic view showing the appearance of the sound wave input to the opposing
microphone unit.
[0049]
62 is an output characteristic diagram of a conventional microphone device in which two
microphone units are disposed to face each other.
[0050]
7 is a diagram showing a sound wave input to the microphone device attached to the video
recorder.
[0051]
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81 is a diagram showing a sound wave input to the microphone device of the microphone unit.
[0052]
FIG. 92 is a diagram showing a sound wave input to the microphone device of the microphone
unit.
[0053]
10 is an output characteristic diagram of a microphone device comprising an opposing
microphone unit.
[0054]
11 is an output characteristic diagram of a microphone device comprising an opposing
microphone unit.
[0055]
Explanation of sign
[0056]
1, 2 ... Microphone unit, 3, 7 ... Adder, 4 ... Low pass filter, 5 ... High pass filter, 6 ... Attenuator for
level adjustment
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