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JP2006349979

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This translation is machine-generated. It cannot be guaranteed that it is intelligible, accurate,
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DESCRIPTION JP2006349979
An object of the present invention is to provide a noise reduction device capable of noise
reduction even without a sound insulation wall. SOLUTION: With respect to an apparatus 10
generating low frequency noise and noise, a plurality of control speakers 21 are surrounded by
control poles 20 linearly arranged at regular intervals in a columnar support without
surrounding the periphery by a sound insulation wall. . When the low frequency sound generated
by the device 10 and the sound of the frequency opposite to the phase generated by the device
10 (broken line) are generated on the opposite side to the device 10, the low generated from the
device 10 outside the control pole 20 There is an effect that the noise of the frequency (solid
line) mutually interferes and the noise is reduced. [Selected figure] Figure 1
Noise reduction device
[0001]
The present invention relates to a noise reduction device that reduces noise. In particular, low
frequency noise and noise can be reduced without using a sound insulation wall.
[0002]
The sound wave transmitted from the noise source is detected by the detection microphone, and
the sound wave in reverse phase to the sound wave propagated by the sound is output from the
speaker to be detected by another detection microphone installed at a predetermined position.
Active noise control (ANC) is known to reduce noise.
04-05-2019
1
[0003]
As such an active noise control, for example, as shown in FIG. 10, the detection microphone 1
and the control speaker 5 are disposed closer to the noise source S than the soundproofing fence
B to reduce the sound of the upper edge E. Patent Document 1 discloses an active control type
soundproofing device that reduces the noise at the sound receiving point M.
This device detects an incident sound wave from the noise source S to the soundproofing rod B
by the detection microphone 1 and calculates the amplitude and phase of the incident sound
wave from the detection signal in a DSP (digital signal processor) 3 instantaneously to obtain an
antiphase The system generates a sound wave signal of the following and sends the sound wave
signal to the control speaker 5 installed near the upper edge E, and radiates the control sound
wave toward the noise source S to cancel the noise potential at the upper edge E is there.
[0004]
In addition, Patent Document 2 discloses an active acoustic control device for the purpose of
improving soundproof performance by making the device simple and small. In this active
acoustic control device, an active acoustic control unit is provided at the upper end of the
soundproof wall, and the transmission characteristic G determined by the acoustic wave detector,
control circuit, amplifier and acoustic generator of the active acoustic control unit is negative
infinity or negative infinity. It is adjusted to be a large neighborhood or a neighborhood of -1 or 1.
[0005]
Further, Patent Document 3 discloses a noise reduction device for sufficiently reducing noise
from a noise source in an open space. The noise reduction device includes a speaker for
outputting an interference sound wave for canceling out the propagation sound wave from the
noise source into the space, a detection microphone for detecting the sound propagation sound
wave and converting it into an electric signal, and an interference sound wave output from the
speaker A plurality of muffling units each including a drive signal generation unit for generating
a signal and a drive signal generation unit as an electric signal correction unit that corrects an
interference sound wave detected by the detection microphone. Japanese Patent Publication No.
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2
7-82347 "Active Control Type Soundproof Device" Patent No. 3388961 "Active Sound Control
Device" Japanese Patent Application Laid-Open No. 2003-66969 "Muffing Device and Method"
[0006]
In order to apply the above-mentioned conventional technology to road noise and noise from a
factory, a noise barrier is always required, and the following problems remain. That is, in order to
apply the conventional system to road noise and the like, it is necessary to arrange the systems
side by side in the direction along the soundproof fence B (the direction orthogonal to the sheet),
but Since the control sound wave (interference sound wave) of the control speaker 5 is spread
over a wide range, the control sound pressure is increased at the other part of the upper edge E
to increase the sound, and the muffling effect may be reduced. The Moreover, when there is a
private house etc. in the position away from the soundproofing fence B, when reducing noise in
the position of the private house, comparatively big energy of a control sound wave is needed. In
addition, if the energy of the control sound wave is increased to reduce the noise at the position
of the private house, it affects the muffling area of the adjacent system, and the sound pressure
of the control sound wave is increased to cause loud noise, resulting in muffling effect May have
been reduced.
[0007]
The present invention is made in view of the above-mentioned subject, and an object of the
present invention is to provide a noise reduction device which can reduce noise even if there is
no sound insulation wall.
[0008]
A noise reduction device according to claim 1 of the present invention for solving the abovementioned problems is a device in which noise generating equipment is surrounded by a control
pole or control net formed by arranging a plurality of control speakers and noise generated from
the equipment The noise is reduced by generating a sound wave of the opposite phase to that of
the control speaker from the control speaker.
[0009]
A noise reduction device according to a second aspect of the present invention for solving the
above-mentioned problems is characterized in that in the first aspect, the control pole or control
net is provided with a detection microphone for capturing the noise generated from the device. .
04-05-2019
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[0010]
The noise reduction device according to claim 3 of the present invention for solving the abovementioned problems is the noise reduction device according to claim 1, wherein on the device
side, a detection microphone capturing noise generated from the device or a vibration sensor
capturing vibration generated by the device It is characterized by having.
[0011]
A noise reduction device according to a fourth aspect of the present invention for solving the
above-mentioned problems is characterized in that in the second aspect, the control speakers in
the same control pole or control net are independently controlled. .
[0012]
A noise reduction device according to claim 5 of the present invention for solving the above
problems is the mutual feedback canceller for suppressing interference between the control
speakers in the same control pole or control net in claim 2 or 4. It is characterized in that it is
provided.
[0013]
A noise reduction apparatus according to claim 6 of the present invention for solving the abovementioned problems is provided, in claim 5, provided with a mutual feedback canceller for
suppressing interference between the control speakers among a plurality of control poles or
control nets. It is characterized by
[0014]
The noise reduction device according to claim 7 of the present invention for solving the abovementioned problems is the detection according to claim 1, 2, 3, 4, 5 or 6, wherein the control
speaker detects noise generated from the device in the device. A muffling unit is configured by
combining a microphone or a vibration sensor for capturing a vibration generated by the device,
or an error sensor disposed at a position on the opposite side of the device where noise should
be reduced.
[0015]
In the noise reduction device according to claim 8 of the present invention for solving the abovementioned problems, in claim 1, 2, 3, 4, 5, 6 or 7, the device is a fixed sound source or a moving
sound source, and the fixed sound source , The at least two side surfaces are surrounded by the
04-05-2019
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muffling unit, and for the moving sound source, at least one side surface is surrounded by the
muffling unit.
[0016]
A noise reduction device according to a ninth aspect of the present invention for solving the
above-mentioned problems is a linear, two-dimensional or three-dimensional one as the control
speaker in the first, second, third, fourth, fifth, sixth or seventh aspect. It is characterized by
using a speaker array arranged in.
[0017]
A noise reduction apparatus according to claim 10 of the present invention for solving the above
problems is the parametric speaker having sharp directivity as the control speaker according to
claims 1, 2, 3, 4, 5, 6, 7 or 8. It is characterized by using.
[0018]
A noise reduction device according to claim 11 of the present invention for solving the abovementioned problems is characterized in that in claim 1, 2, 3, 4, 5, 6, 7 or 8, holes or slits are
arranged at regular intervals as the control speaker. It is characterized by using a directional
speaker with an end impedance control speaker in which an end impedance control speaker is
attached to both ends of the tubular body.
[0019]
In the noise reduction device according to the first aspect of the present invention, the noise
generated from the device is surrounded by a control pole or a control net formed by arranging a
plurality of control speakers, around the device generating noise which is low frequency sound.
Since the sound wave of the opposite phase is generated from the control speaker, the low
frequency noise can be reduced without using the sound insulation wall.
[0020]
The noise reduction device according to claim 2 of the present invention has the same effect as
the invention according to claim 1, and further, since the control pole or control net is provided
with a detection microphone for capturing noise generated from the device. There is also an
advantage that control poles or control nets can be installed independently, and the system can
be simplified.
04-05-2019
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[0021]
The noise reduction device according to claim 3 of the present invention exhibits the same effect
as the invention according to claim 1 and, on the device side, detects a noise generated from the
device or a vibration generated by the device. Since the vibration sensor is provided for
capturing, there is also an advantage that howling of the control speaker can be prevented since
the detection microphone is separated from the control speaker or the vibration detection sensor
is used instead of the detection microphone.
[0022]
The noise reduction device according to claim 4 of the present invention exhibits the same effect
as that of the invention according to claim 2, and furthermore, since the control speakers in the
same control pole or control net are controlled independently of each other. There is also an
advantage that the control circuit of each control speaker becomes single degree of freedom and
the cost can be reduced.
[0023]
The noise reduction device according to claim 5 of the present invention produces the same
effect as that of the invention according to claim 2 or 4, and further suppresses interference
between the control speakers in the same control pole or control net. Since the mutual feedback
canceller is provided, the control sound pressure from each control speaker can be increased
without being influenced by the low frequency noise generated from the device, and there is also
an advantage that the control performance can be improved.
[0024]
The noise reduction device according to claim 6 of the present invention exhibits the same
effects as the invention according to claim 5, and also provides mutual feedback for suppressing
interference between the control speakers among a plurality of control poles or control nets.
Since the canceller is provided, there is an advantage that the control sound pressure from each
control speaker can be further increased without being influenced by the low frequency noise
generated from the device, and the control performance can be further improved.
[0025]
The noise reduction device according to claim 7 of the present invention produces the same
effect as that of the invention according to claim 1, 2, 3, 4, 5 or 6, and the control speaker is
generated from the device in the device Since the muffling unit is configured by combining a
detection microphone that captures noise, a vibration sensor that captures the vibration
generated by the device, or an error sensor disposed at a position on the opposite side of the
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device where noise should be reduced Each time there is an advantage that the control speaker
can be controlled based on the sensing microphone, the vibration sensor or the error sensor.
[0026]
The noise reduction device according to claim 8 of the present invention exhibits the same
effects as the invention according to claims 1, 2, 3, 4, 5, 6 or 7, and the device is a fixed sound
source or a moving sound source. As for the fixed sound source, at least two side surfaces thereof
are surrounded by the muffling unit, and at least one side surface of the moving sound source is
surrounded by the muffling unit, the sound insulating wall is not limited to the fixed sound
source. There is an advantage that low frequency noise can be reduced without providing it.
[0027]
The noise reduction device according to claim 9 of the present invention has the same effects as
the invention according to claims 1, 2, 3, 4, 5, 6, 7 or 8, and further, it is linear and flat as the
control speaker. The use of a speaker array arranged in a three-dimensional or three-dimensional
manner has an advantage that the directivity of the control sound wave can be enhanced and the
sound increase area can be reduced.
[0028]
A noise reduction device according to claim 10 of the present invention has the same effects as
the inventions according to claims 1, 2, 3, 4, 5, 6, 7 or 8, and, in addition, sharp directivity as the
control speaker. In particular, the directivity of the control sound wave can be enhanced, and the
region of increased sound can be eliminated or reduced, since the use of the parametric speaker
having such a configuration.
[0029]
The noise reduction device according to claim 11 of the present invention exhibits the same
effects as the invention according to claims 1, 2, 3, 4, 5, 6, 7 or 8, and further, as the control
speaker, holes at regular intervals. Or because it uses a directional speaker with an end
impedance control speaker in which an end impedance control speaker is attached to one end of
a tube in which a slit is arranged, cost is lower than arranging a large number of speakers, and
one end of the tube is absorbed There is an advantage that the apparatus itself becomes compact
because the sound absorption coefficient of low frequency sound is better than in the case of
using materials such as materials.
[0030]
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7
The best mode for carrying out the present invention is shown in FIGS. 1 (a) and 1 (b).
As shown in FIGS. 1 (a) and 1 (b), with respect to the device 10 generating low frequency noise
and noise, a plurality of control speakers 21 are linearly spaced at regular intervals within the
columnar support without surrounding the periphery with a sound insulation wall. It encloses by
the control pole 20 arrange | positioned at.
Each control speaker 20 is arranged facing outwards, that is to say opposite to the device 10.
The distance between the control speakers 21 is, for example, a pitch equal to or less than a
quarter of the wavelength of the target sound.
[0031]
Therefore, when the low frequency sound generated from the device 10 and the sound of the
frequency opposite to the phase are generated from each control speaker 21 on the opposite side
to the device 10 as shown by the broken line in the figure, The low frequency sound shown by
the solid line in the figure generated from the device 10 interferes with each other to reduce the
noise.
[0032]
Here, each control pole 20 is provided with detection microphones (not shown), and these
control microphones are controlled so that low frequency sound generated from the device 10
can be captured and sounds in reverse phase can be output for each control pole 20. If the
speakers 21 are controlled, the control poles 20 can be installed independently, which has an
advantage of simplifying the system.
[0033]
In addition, the device 10 is provided with a detection microphone or a vibration detection
sensor (these are collectively referred to as detection sensors), and these detection sensors
capture low frequency sound or vibration generated from the device 10 and output sound in
reverse phase. If it is possible to control the control speaker 21, there is also an advantage that
howling of the control speaker 21 can be prevented because the detection microphone is
separated from the control speaker 21 or a vibration detection sensor is used instead of the
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detection microphone.
[0034]
Furthermore, each control speaker 21 in the same control pole 20 can be controlled
independently, which has an advantage that the control circuit of each control speaker 21
becomes a single degree of freedom and the cost can be reduced.
[0035]
Also, a mutual feedback canceller as described later can be added so that the respective control
speakers in the same control pole 20 do not interfere with each other, so that the control sound
pressure from each control speaker 21 can be increased, and the control performance is
improved. There is also an advantage that can be improved.
[0036]
Furthermore, in each control speaker in the same control pole 20, not only the mutual feedback
canceller can be added, but also the mutual feedback canceller can be added as described later so
as not to interfere between the plurality of control poles 20. Then, the control sound pressure
from each control speaker 21 can be further increased, and there is also an advantage that the
control performance can be further improved.
[0037]
Example 1 of the present invention is shown in FIGS. 2 (a) and 2 (b).
In the present embodiment, as a device that generates noise, both fixed sound sources and
moving sound sources are targeted.
[0038]
That is, FIG. 2 (a) shows the muffling unit 50 (shown by black circles in the figure) at a constant
interval on one side surface (Y-Z plane) of the moving sound source 30 such as a vehicle
traveling in the Y direction in the figure. They are arranged in a mesh shape in the vertical and
horizontal directions.
04-05-2019
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This is called a control net.
The frequency of the noise generated by the moving sound source 30 is approximately 250 Hz to
2 kHz.
FIG. 2 (b) shows a fixed sound source 40 such as a transformer, in which meshing units 50
(shown by black circles in the drawing) are meshed at regular intervals on the two side surfaces
(X-Z plane and Y-Z plane). The fixed sound source 40 has a vibration sensor 41 attached thereto.
[0039]
For the moving sound source 30, the muffling unit 50 can not be arranged in the moving
direction, but can be arranged above the moving sound source 30.
For the fixed sound source 40, the muffling unit 30 can be disposed on the other side surfaces
other than the two side surfaces shown in the drawing.
The noise reduction unit 50 has three aspects as described below, in combination with a
detection microphone, a vibration sensor, and an error sensor.
[0040]
The first mode comprises a control speaker 51 and a detection sensor (microphone) 52 disposed
between the control speaker 51 and the sound sources 30, 40 as shown in FIG. 3 (a). .
The second mode uses the vibration sensor 41 as the control speaker 51 and the detection
sensor (microphone) 52 disposed between the control speaker 51 and the sound sources 30, 40.
The third mode comprises a control speaker 51 and an error sensor 53 disposed on the opposite
04-05-2019
10
side of the sound sources 30 and 40 with respect to the control speaker 51, as shown in FIG. 3
(b).
[0041]
[Detection Sensor] The detection sensor 52 is disposed closer to the sound sources 30, 40 than
the control speaker 51, captures low-frequency sound or noise generated by the sound sources
30, 40, and outputs sound in reverse phase from the control speaker 51. Perform feed forward
control as you do.
For example, as shown in FIG. 4 and FIG. 5, based on the low frequency sound or noise captured
by the detection sensor 52 or the vibration sensor 41, the drive signal generation unit 54
generates a sound of the opposite phase and It is an output.
Such control is similarly performed in the control pole 20 shown in FIG.
As the detection sensor 52, a detection microphone consisting of a nondirectional microphone or
a directional microphone or a vibration sensor is used.
[0042]
[Error Sensor] The error sensor 53 is disposed farther from the sound sources 30, 40 than the
control speaker 51, captures low-frequency sound generated by the sound sources 30, 40, and
outputs sound in reverse phase from the control speaker 51. Feedback control is performed to
minimize noise at the position where the error sensor 53 is disposed.
For example, it is arranged in a private house adjacent to a road or a factory.
As the error sensor 53, a nondirectional microphone or a directional microphone is used.
[0043]
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[Control Speaker] As the control speaker 51, a general nondirectional speaker or a directional
speaker is used, and in addition, a special directional speaker as described below can be used.
[0044]
<Linear Arrangement Speaker Array> A plurality of speaker units are arranged in a horizontal
row, and these speaker units are electrically connected in parallel.
When an audio signal is input to each speaker unit, it is radiated to the outside as a sound wave
from each speaker, and in a direction perpendicular to the array axis of the speaker units, the
distance from each speaker unit is approximately equal if it is separated from the speakers to
some extent. To be considered, the sound waves arriving from each speaker unit all have the
same phase, and the sound waves reinforce each other.
Therefore, the directivity is high on the central axis of the speaker.
[0045]
<Directivity-Controlled Speaker Array> The directivity-controlled speaker array system shown in
FIG. 6 includes a plurality of FIR (finite response length digital filter) filters 70, 71,... 7n, a
plurality of amplifiers 80, 81,. A plurality of speaker units 90, 91a... 9na, 91b... 9nb, a detection
microphone 52, and a drive signal generation unit 60 are provided.
The plurality of speaker units 90, 91a... 9na, 91b... 9nb are arranged linearly, two-dimensionally
or three-dimensionally.
The FIR filters 70, 71,..., 7n have filter characteristics that bring the directivity of the system most
closely to the desired ones in accordance with the characteristics of the speaker units 90, 91a,.
[0046]
04-05-2019
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Therefore, when low frequency sound and noise are detected by the detection microphone 52,
sound signals of opposite phases are generated by the drive signal generation unit 60, and the
FIR filters 70, 71,... 7n, and a plurality of amplifiers 80, 81,. When output from a plurality of
speaker units 90, 91a... 9na, 91b... 9nb, noise can be effectively reduced at a certain point.
In addition, using a planar arrangement speaker array in which a plurality of speakers are
arranged in a plane, driving is performed by a signal given a delay amount according to the
difference between the path from the center of the array to the focus and the path from each
speaker unit to the focus As a result, the same effect as described above can be obtained.
[0047]
<Speaker Array with Mutual Feedback Canceller> It is also possible to provide a mutual feedback
canceller in the speaker array.
For example, as shown in FIG. 8, when the muffling apparatus 100 includes two muffling units
110a and 110b, and two muffling units 110a and 110b are juxtaposed, the muffling unit 110a,
When 110b are arranged in parallel, not only from the muffling unit 110a but also from the
muffling unit 110b, an interference sound wave for reducing the propagation sound wave of the
noise from the noise source 120 is output.
[0048]
Therefore, the magnitudes of the propagating sound waves from the noise source 120 detected
by the detection microphones 111a of the muffling unit 110a and the detection microphones
111b of the muffling unit 110b differ due to the attenuation depending on the distance of the
propagation sound waves.
Therefore, in order to cancel the propagation sound waves of noise from the noise source 120,
an interference sound wave having a characteristic of F is output from the speaker 112a of the
muffling unit 110a and an interference sound wave having a characteristic of F1 is output from a
speaker 112b of the muffling unit 110b. Be done.
04-05-2019
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Here, the case where the muffling unit 110b interferes with the muffling unit 110a will be
described as an example.
The propagated sound waves of the noise from the noise source 120 are detected by the
detection microphone 111 b of the muffling unit 110 b and converted into an electric signal.
Then, this electrical signal is sent from the detection microphone 111b to the drive signal
generation unit 113b.
[0049]
Therefore, the drive signal generation unit 113b of the muffling unit 110b generates a drive
signal having a characteristic of W1 based on the detected electrical signal of the propagation
sound wave.
The electrical signal having the characteristic W1 is generated based on a value predetermined to
reduce the detected propagating sound wave at a predetermined position.
The drive signal having the characteristic of W1 is sent from the drive signal generation unit
113b to the speaker 112b.
The speaker 112b outputs an interference sound wave having a characteristic of F1 based on the
electric signal having a characteristic of W1 sent in this way, and attenuates the interference
sound wave of the noise from the noise source 120 to reduce the noise. .
Similarly, in the muffling unit 110a, an electric signal having a characteristic of W is generated.
The interference sound wave having the characteristic of F1 output from the speaker 112b of the
muffling unit 110b is detected by the detection microphone 111a of the muffling unit 110a
arranged in parallel.
[0050]
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However, the muffling unit 110a simultaneously detects the propagation sound wave of the noise
from the noise source 120 and the interference sound wave having the characteristic of F1
output from the muffling unit 110b provided in parallel, and reduces both sound waves. Howling
occurs when an interference sound wave is output. Therefore, when an interference sound wave
having a characteristic of F1 output from the muffling unit 110b is detected by the detection
microphone 111a of the muffling unit 110a, a feedback canceller for eliminating the influence of
the interference sound wave having the characteristic of F1. Provide a mechanism. In order that
the muffling unit 110a is not affected by the interference sound wave having the characteristic of
F1 output from the muffling unit 110b, an electric signal having the characteristic of F1 'which is
the opposite characteristic to the characteristic of F1 in the muffling unit 110a It is good to give
Although the muffling unit 110a and the muffling unit 110b are configured independently of
each other, they are connected to each other in order to exchange electric signals having the
characteristic of F1 '.
[0051]
Therefore, the drive signal generation unit 113a of the muffling unit 110a performs feedback on
the electrical signals of the sound waves detected by the detection microphone 111a using an
electrical signal having a characteristic of F1 ', and this is detected. Correct by increasing or
decreasing the electrical signal. The electric signal having the characteristic of F1 'can be
arbitrarily changed in consideration of the influence of the interference sound wave having the
characteristic of F1 on the muffling unit 110a if the characteristic of F1 is measured in advance.
In this way, in the muffling unit 110a, an interference sound wave for reducing only the
propagation sound wave of the noise from the noise source 120 without causing howling due to
the influence of the interference sound wave output from the muffling unit 110b arranged in
parallel. Can be generated.
[0052]
<Parametric Speaker> A parametric speaker is a superdirectivity that adopts the principle
(nonlinearity) of obtaining sound in the audible range by using a distortion component that
generates distortion components in the process of strong ultrasonic waves propagating through
air. It is a speaker. That is, in the parametric speaker, if two ultrasonic waves SW1 and SW2
respectively having different frequencies f1 and f2 are emitted from a sound source toward a
specific propagation medium, these two ultrasonic waves SW1 and SW2 interfere with each
other. As a result, so-called beats occur in which the vibration changes periodically in a strong
04-05-2019
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and weak manner.
[0053]
The frequency of the combined carrier wave in this case is (f1 + f2) / 2, and the frequency of the
amplitude modulation wave corresponding to the beat is represented by (f1-f2) / 2 (where f1>
f2). Therefore, if the component waveforms in this case are large-amplitude sound waves both of
which are sufficiently large, they are gradually distorted as a synthetic secondary waveform in
the secondary wave sound source area, and a difference sound corresponding to (f1-f2) is finally
generated. Disappear. Assuming that the sound waves SW1 and SW2 are primary waves and the
difference sound is a secondary wave, the secondary wave functions as a virtual sound source
until the primary wave is attenuated, and a virtual sound source with a very long propagation
distance is formed. Even if the frequency of the sound is an audio frequency, the directivity will
be very sharp.
[0054]
<Directional Speaker with End Impedance Control Speaker> As shown in FIG. 9, the directional
speaker 200 with end impedance control speaker has end impedance at both ends of a tube 210
in which holes (slits) 230 are arranged at regular intervals. The control speakers 220a and 220b
are attached.
[0055]
This directional impedance speaker 200 with end impedance control speaker is an improvement
of the superdirective speaker disclosed in Japanese Patent Laid-Open No. 11-234784.
That is, in the superdirective speaker disclosed in JP-A-11-234784, a speaker is attached to one
end of a tube in which holes (slits) are arranged at regular intervals, and a sound absorbing
material or the like is placed on the other end. Directivity can only be obtained in the longitudinal
direction. On the other hand, in the directional speaker 200 with end impedance control speaker,
when the A end on the left side in the figure is controlled as a non-reflecting end, the sound
leaking from the hole (slit) 230 interferes and the longitudinal direction of the tube 210 When
high directivity is obtained in the X direction in a certain figure, and the A end on the left side in
the figure is controlled as a reflection end, the sound leaking from the hole (slit) 230 interferes
and intersects the longitudinal direction of the tube 210 In the figure, high directivity is obtained
04-05-2019
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in the Y direction. Furthermore, when the A end on the left side in the figure is controlled as an
intermediate reflection end, the sound leaking from the hole (slit) 230 interferes, and it is not
omnidirectional but intermediate directivity. There is a feature that can be obtained.
[0056]
The principle is as follows ("Active control of duct acoustic impedance", Shoji Nishimura, Keizo
Onishi, Takanori Arai, Proceedings of the Acoustical Society of Japan, September 1996). That is,
based on the Filtered-X-LMS algorithm in which the difference between the measured reflected
sound wave and the desired reflected sound wave is an error signal, the acoustic impedance at
the duct end is arbitrarily and actively controlled. As shown in FIG. 7, a pair microphone is used
as the control microphone, and the incident sound wave Pi (t) and the reflected sound wave Pr (t)
are separately measured by the equations (1) to (4).
[0057]
[0058]
Here, P (t) and u (t) are the sound pressure and particle velocity at the control point, P1 (t) and
P2 (t) and the sound pressure of each control microphone, ρ is the density, c is the speed of
sound, Δr Is the spacing of the paired microphones.
The control speaker is disposed farther from the error microphone as viewed from the sound
source to control the reflected sound. Assuming that the target acoustic impedance at the control
point is Z (f), the complex sound pressure reflectance R (f) at that point is given by equation (5).
Here, S is a duct area. Considering that the sound pressure reflectance is a transfer function from
incident sound to reflected sound, the reflected sound p'r (t) to be the target at the control point
is the measured incident sound Pi (t) and reflectance The convolution of the impulse response r
(t) is expressed as in equations (6) and (7). Therefore, when the error signal e (t) is defined as
equation (8), adaptive control by the Filtered-X-LMS algorithm is possible as shown in FIG. Note
that r (t) is generally a delay system, and can be described by an FIR filter.
[0059]
04-05-2019
17
In order to verify the validity of the above control method, a sound source speaker is disposed at
one end of the tube, a control speaker is disposed at the other end, and the signal from the
control microphone is calculated by the DSP using equations (1) to (8) And have been input to
the ANC. Note that the sound source speaker and the control speaker are laterally opposite to the
speakers 220b and 220a in FIG. As a reference signal, an input signal of a sound source speaker
was used for simplicity. The results are shown in FIG. As shown in FIG. 11, R (f) = 0, that is, e (t) =
pr (t) is obtained by performing control with the non-reflection end as a target (system on). That
is, it can be seen that, by applying control, absorption coefficient (Absorption Coefficient)
becomes almost zero and control as intended is realized. Also, it can be seen that the reverse
characteristic is obtained when the system is off.
[0060]
The present invention is a noise reduction device that reduces low frequency noise and noise
without using a sound insulation wall, and is widely applied not only to road noise to moving
sound sources but also to fixed sound sources such as transformers in factories. It is applicable.
[0061]
It is explanatory drawing which shows the optimal embodiment of this invention.
It is explanatory drawing which shows the Example with respect to a moving sound source or a
fixed sound source. It is an explanatory view showing a muffling unit. It is a block diagram
showing a muffling unit. It is a block diagram showing a muffling unit. FIG. 5 is a block diagram
illustrating a linear speaker array. FIG. 6 is a circuit diagram showing active control of duct
acoustic impedance. It is a block diagram of the speaker array which provided the feedback
canceller mechanism. It is a structural view of a directional speaker with an end impedance
control speaker. It is explanatory drawing which shows a prior art example. It is a graph which
shows the test result of active control of duct acoustic impedance.
Explanation of sign
[0062]
10 Transformers and other devices that generate low frequency noise (noise) 20 Control pole 21
Control speaker 30 Moving sound source such as vehicle 40 Fixed sound source such as
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transformer 41 Vibration sensor 50 Silencer unit (control net) 51 Control speaker 52 Detection
sensor (Microphone) 53 Error sensor 54, 60 Drive signal generation unit 70, 71, ... 7 n FIR filter
80, 81, ... 8 n Amplifier 90, 91 a ... 9 na, 91 b ... 9 nb Speaker unit 100 Silencer 110a, 110b
Silencer 111a, DESCRIPTION OF SYMBOLS 111b Detection microphone 112a, 112b Speaker
113a, 113b Driving signal production | generation part 120 Noise source 200 Directional
speaker 210 with an end impedance control speaker Tube body 220a, 220b End impedance
control speaker 230 hole (slit)
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