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JP2008179979

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DESCRIPTION JP2008179979
An object of the present invention is to make it possible to reduce noise diffused from a noise
source in a wide range even if the noise has directivity. When noise from a noise source has
directivity, the directivity of noise from the noise source is calculated and calculated by the signal
processing unit based on sound wave information of the sensor microphone and the speaker
proximity microphone 38. According to the directivity, the directivity correction coefficient is
calculated for each speaker 12, the directivity correction coefficient is set in each delay circuit,
and the magnitude of the control sound is corrected according to the directivity correction
coefficient. , Correct the reduced signal amplitude. As a result, the directivity of the control sound
emitted from each speaker 12 and the directivity of the noise become the same, so even if the
noise from the noise source has directivity, it is possible in a wide range including the control
point. , The noise from the noise source is canceled. [Selected figure] Figure 3
Noise reduction device
[0001]
The present invention relates to a noise reduction device, and more particularly to an active
control noise reduction device that reduces noise by active control.
[0002]
Conventionally, environmental standards have been established for road traffic noise and railway
noise, and road construction that does not meet the standards and operation of high-speed
vehicles that do not meet the standards are not permitted.
09-05-2019
1
[0003]
From such a background, sound barriers have been actively developed, and technology
development of active noise control (ANC) has been conducted to reduce the diffracted sound
from the sound barriers by active control.
[0004]
As ANC technology, a plurality of point sound sources are linearly arranged to construct a control
sound source of a finite length, and a control sound is emitted from the control sound source in
the front and diagonal directions, and the width of the control sound source in the length
direction A noise reduction device that reduces noise is known (Patent Document 1).
Japanese Patent Application Publication No. 2006-138130
[0005]
However, in the technology described in Patent Document 1 above, the control sound is emitted
in the direction perpendicular to the length direction from the control sound source of finite
length L, so the range where noise can be reduced is the width L of the control sound source.
Since it is limited to the range, there is a problem that the noise diffused from the noise source in
a circle can not be reduced in a wide range.
Also, there is a problem that it can not be dealt with when the noise source has directivity.
[0006]
The present invention has been made to solve the above-mentioned problems, and it is possible
to reduce the noise diffused from the noise source in a wide range even if the noise from the
noise source has directivity. The purpose is to present a noise reduction device that can
[0007]
In order to achieve the above object, the noise reduction device according to the first invention is
arranged at intervals equal to or less than a length corresponding to half of the wavelength
corresponding to the maximum frequency in the noise frequency band to be reduced. A speaker
09-05-2019
2
unit having a plurality of speakers, a microphone for collecting noise from a noise source and
outputting an acoustic signal corresponding to the collected noise, and the noise source from the
speaker unit based on the acoustic signal The generation means for generating a reduction signal
for reducing noise on the opposite side, and the reduction signal so that the envelope surface of
the wave front of the control sound emitted from the speaker corresponds to the wave front of
the noise Processing means for performing processing for respectively delaying for a time
corresponding to each of the distances between the source and the plurality of speakers emitting
the control sound based on the delayed reduced signal, and the processing means Based on input
means for inputting the selected signal to each of the plurality of speakers, directivity calculation
means for calculating directivity of noise from the noise source, and directivity calculated by the
directivity calculation means, Correct the magnitude of the control sound emitted from each of
the plurality of speakers so that the directivity of the control sound emitted from the plurality of
speakers is the same as the directivity of the noise from the noise source And correction means
for
[0008]
According to the noise reduction device pertaining to the first aspect of the invention, the
microphone collects the noise from the noise source, outputs an acoustic signal corresponding to
the collected noise, and the generation means generates the speaker based on the acoustic signal.
A reduction signal is generated from the unit to reduce noise on the side opposite the noise
source.
[0009]
Then, the processing means emits the control sound based on the noise reduction source and the
reduction signal delayed such that the envelope surface of the wave front of the control sound
emitted from the speaker corresponds to the wave front of noise. A process of delaying each for a
time corresponding to each of the distances to a plurality of speakers is performed.
[0010]
Further, the directivity calculation means calculates the directivity of noise from the noise source
based on the acoustic signal.
Then, based on the directivity calculated by the directivity calculation unit by the correction unit,
the directivity of the control sound emitted from the plurality of speakers is the same as the
directivity of the noise from the noise source. The magnitude of the control sound emitted from
09-05-2019
3
each of the plurality of speakers is corrected.
[0011]
Then, the signal processed by the processing means is input to each of the plurality of speakers
by the input means, and the control sound is emitted by the plurality of speakers of the speaker
unit.
At this time, the envelope of the wave front of the sound wave in which the emitted control
sounds are combined corresponds to the wave front of noise, and the directivity of the control
sound emitted from the plurality of speakers and the noise from the noise source Since the
directivity is the same, noise is reduced by the control sound.
[0012]
As described above, based on the directivity of the noise source, the magnitude of the control
sound is corrected and reduced so that the directivity of the control sound emitted from the
plurality of speakers becomes the same as the directivity of the noise. The control signal is
emitted from each speaker by delaying the reduction signal input to each speaker so that the
envelope of the wavefront of the control sound emitted from the plurality of speakers based on
the signal corresponds to the wavefront of the noise. Thus, even if noise from a noise source has
directivity, noise diffused from the noise source can be reduced in a wide range.
[0013]
A noise reduction device according to a first aspect of the present invention is movable along a
direction in which a plurality of speakers are arranged, and collects noise from a noise source at
a predetermined position with respect to each of the plurality of speakers. The directivity
calculation means further includes a speaker corresponding microphone for outputting an
acoustic signal corresponding to the noise, and the directivity calculation means is configured to
output noise from the noise source based on the sound signal output by the microphone and the
sound signal output by the speaker corresponding microphone. The directivity can be calculated.
Thereby, the directivity of the noise from the noise source can be calculated based on the
acoustic signal corresponding to the noise from the noise source.
09-05-2019
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[0014]
The noise reduction device according to the first aspect of the present invention is a noise which
is installed at a predetermined position with respect to the corresponding speaker corresponding
to each of the plurality of speakers and collects noise from the noise source and collects the
noise. The apparatus further includes a plurality of speaker compatible microphones that output
corresponding audio signals, and the directivity calculation unit is configured to calculate noise
from the noise source based on the audio signals output by the microphones and the audio
signals output by the plurality of speaker compatible microphones. The directivity of can be
calculated.
Thereby, the directivity of the noise from the noise source can be calculated based on the
acoustic signal corresponding to the noise from the noise source.
[0015]
In the noise reduction device according to the first aspect of the present invention, the noise is
emitted from the speaker based on the phase difference calculating means for calculating the
phase difference of the noise from the noise source and the phase difference calculated by the
phase difference calculating means. And delay time correction means for correcting the time
delayed by the processing means such that the envelope surface of the control sound wave front
corresponds to the noise wave front.
Thereby, even if the noise from the noise source has a phase difference, the noise diffused from
the noise source can be reduced in a wide range.
[0016]
Further, the noise reduction device is movable along the arrangement direction of the plurality of
speakers, and collects noise from the noise source at a predetermined position with respect to
each of the plurality of speakers, The system further includes a speaker-compatible microphone
that outputs a corresponding sound signal, and the phase difference calculating means calculates
09-05-2019
5
a phase difference of noise from the noise source based on the sound signal output by the
microphone and the sound signal output by the speaker-compatible microphone. It can be
calculated.
Thereby, based on the acoustic signal corresponding to the noise from a noise source, the phase
difference of the noise from a noise source can be calculated.
[0017]
In addition, the noise reduction device is installed at a predetermined position with respect to the
corresponding speaker corresponding to each of the plurality of speakers, and collects the noise
from the noise source, and an acoustic signal corresponding to the collected noise. The system
further includes a plurality of speaker-compatible microphones that output, and the phase
difference calculation unit calculates the phase difference of noise from the noise source based
on the acoustic signal output by the microphone and the acoustic signal output by the plurality
of speaker-compatible microphones can do. Thereby, based on the acoustic signal corresponding
to the noise from a noise source, the phase difference of the noise from a noise source can be
calculated.
[0018]
A noise reduction device according to a second aspect of the present invention is a speaker unit
including a plurality of speakers arranged at intervals equal to or less than a length
corresponding to 1/2 of a wavelength corresponding to the maximum frequency in the
frequency band of noise to be reduced. And vibration detection means for detecting vibration of a
noise source and outputting a vibration signal corresponding to the detected vibration, and for
reducing noise on the side opposite to the noise source from the speaker unit based on the
vibration signal. Based on the generation means for generating a reduction signal, and the
reduction signal obtained by delaying the reduction signal with the noise source such that the
envelope surface of the wavefront of the control sound emitted from the speaker corresponds to
the wavefront of the noise. Processing means for performing processing for respectively delaying
each of the distances according to the distances to the plurality of speakers emitting the control
sound, and the plurality of speakers for processing the signals processed by the processing
means Sound is emitted from the plurality of speakers based on input means input to each,
directivity calculation means for calculating directivity of noise from the noise source, and
directivity calculated by the directivity calculation means And correction means for correcting
the magnitude of the control sound emitted from each of the plurality of speakers such that the
directivity of the control sound and the directivity of the noise from the noise source are the
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same. ing.
[0019]
According to the noise reduction device pertaining to the second aspect of the invention, the
vibration detection means detects the vibration of the noise source, outputs a vibration signal
corresponding to the detected vibration, and the generation means generates the speaker unit
based on the vibration signal. To generate a reduced signal to reduce noise on the side opposite
the noise source.
[0020]
Then, the processing means emits the control sound based on the noise reduction source and the
reduction signal delayed such that the envelope surface of the wave front of the control sound
emitted from the speaker corresponds to the wave front of noise. A process of delaying each for a
time corresponding to each of the distances to a plurality of speakers is performed.
[0021]
Further, the directivity calculation means calculates the directivity of noise from the noise source
based on the acoustic signal.
Then, based on the directivity calculated by the directivity calculation unit by the correction unit,
the directivity of the control sound emitted from the plurality of speakers is the same as the
directivity of the noise from the noise source. The magnitude of the control sound emitted from
each of the plurality of speakers is corrected.
[0022]
Then, the signal processed by the processing means is input to each of the plurality of speakers
by the input means, and the control sound is emitted by the plurality of speakers of the speaker
unit.
At this time, the envelope of the wave front of the sound wave in which the emitted control
sounds are combined corresponds to the wave front of noise, and the directivity of the control
09-05-2019
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sound emitted from the plurality of speakers and the noise from the noise source Since the
directivity is the same, noise is reduced by the control sound.
[0023]
As described above, based on the directivity of the noise source, the magnitude of the control
sound is corrected and reduced so that the directivity of the control sound emitted from the
plurality of speakers becomes the same as the directivity of the noise. The control signal is
emitted from each speaker by delaying the reduction signal input to each speaker so that the
envelope of the wavefront of the control sound emitted from the plurality of speakers based on
the signal corresponds to the wavefront of the noise. Thus, even if noise from a noise source has
directivity, noise diffused from the noise source can be reduced in a wide range.
[0024]
A noise reduction device according to a second aspect of the present invention is movable along
a direction in which a plurality of speakers are arranged, and collects noise from a noise source
at a predetermined position with respect to each of the plurality of speakers. The microphone
further includes a speaker corresponding microphone for outputting an acoustic signal
corresponding to the noise, and the directivity calculation unit is configured to output from the
noise source based on the vibration signal outputted by the vibration detection unit and the
sound signal outputted by the speaker corresponding microphone. Noise directivity can be
calculated.
Thereby, the directivity of the noise from the noise source can be calculated based on the
vibration signal corresponding to the vibration of the noise source and the acoustic signal
corresponding to the noise from the noise source.
[0025]
The noise reduction device according to the second aspect of the present invention is a noise
which is installed at a predetermined position with respect to the corresponding speaker
corresponding to each of the plurality of speakers and collects noise from the noise source and
collects the noise. The directivity calculation means further includes a plurality of speaker
compatible microphones outputting the corresponding sound signal, and the directivity
calculation unit is configured to output the noise signal from the noise source based on the
09-05-2019
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vibration signal output by the vibration detection unit and the sound signal output by the
plurality of speaker corresponding microphones. Noise directivity can be calculated.
Thereby, the directivity of the noise from the noise source can be calculated based on the
vibration signal corresponding to the vibration of the noise source and the acoustic signal
corresponding to the noise from the noise source.
[0026]
In the noise reduction device according to the second aspect of the present invention, the noise is
emitted from the speaker based on the phase difference calculating means for calculating the
phase difference of the noise from the noise source and the phase difference calculated by the
phase difference calculating means. And delay time correction means for correcting the time
delayed by the processing means such that the envelope surface of the control sound wave front
corresponds to the noise wave front. Thereby, even if the noise from the noise source has a phase
difference, the noise diffused from the noise source can be reduced in a wide range.
[0027]
Further, the noise reduction device is movable along the arrangement direction of the plurality of
speakers, and collects noise from the noise source at a predetermined position with respect to
each of the plurality of speakers, The system further includes a speaker-compatible microphone
that outputs a corresponding sound signal, and the phase difference calculation means
determines the magnitude of noise from the noise source based on the vibration signal output by
the vibration detection means and the sound signal output by the speaker-compatible
microphone. The phase difference can be calculated. Thereby, the phase difference of the noise
from the noise source can be calculated based on the vibration signal corresponding to the
vibration of the noise source and the acoustic signal corresponding to the noise from the noise
source.
[0028]
In addition, the noise reduction device is installed at a predetermined position with respect to the
corresponding speaker corresponding to each of the plurality of speakers, and collects the noise
09-05-2019
9
from the noise source, and an acoustic signal corresponding to the collected noise. The system
further includes a plurality of speaker-compatible microphones that output, and the phase
difference calculation unit is configured to calculate a phase difference of noise from the noise
source based on the vibration signal output by the vibration detection unit and the acoustic
signal output by the plurality of speaker-compatible microphones. Can be calculated. Thereby,
the phase difference of the noise from the noise source can be calculated based on the vibration
signal corresponding to the vibration of the noise source and the acoustic signal corresponding
to the noise from the noise source.
[0029]
In addition, a plurality of speakers of the above speaker unit can be provided on the wall.
[0030]
As described above, according to the noise reduction device of the present invention, the
directivity of the control sound emitted from the plurality of speakers and the directivity of the
noise become the same based on the directivity of the noise source. And correct the magnitude of
the control sound, and delay the reduction signal input to each speaker so that the envelope
surface of the control sound emitted from the plurality of speakers based on the reduction signal
corresponds to the wave front of noise By causing the control sound to be emitted from each
speaker, even if the noise from the noise source has directivity, the noise diffused from the noise
source can be reduced in a wide range. The effect is obtained.
[0031]
Hereinafter, preferred embodiments of the present invention will be described with reference to
the drawings.
In the present embodiment, a case will be described where the present invention is applied to a
noise reduction system that reduces directional noise in a free sound field having no sound
barrier.
[0032]
As shown in FIG. 1, the noise reduction system 10 according to the first embodiment controls a
09-05-2019
10
speaker unit 14 in which a plurality of speakers 12 are arranged in a row, and a control sound
emitted from the speakers 12. Control block 16, a plurality of power amplifiers 36 for amplifying
the signals output from the control block 16 and inputting them to the respective speakers 12,
and installed in the vicinity of the noise source, and collecting the noise from the noise source , A
sensor microphone 18 for outputting an acoustic signal corresponding to the collected noise, a
microphone amplifier 20 for amplifying the acoustic signal, and a signal output from the
microphone amplifier 20 are subjected to reverse filtering to generate a reduced signal. Inverse
filter DSP 22 as generation means for output to the control block 16, and an air for providing
feedback to the inverse filter DSP 22 installed at the control point And Maiku 24, a speaker near
a microphone 38 provided close to the speaker 12, and a signal processing unit 40 as correction
means for performing predetermined signal processing.
As for the control point, since the sound wave from the noise source propagates as a spherical
wave, it may be anywhere on the side opposite to the noise source from the speaker unit 14. The
power amplifier 36 corresponds to the input means of the present invention.
[0033]
In the speaker unit 14, the plurality of speakers 12 are linearly arranged, and the control block
16 controls the control block 16 to emit sound in a frequency band lower than the maximum
frequency of the noise frequency band to be reduced. Be done.
[0034]
Further, the plurality of speakers 12 are arranged at equal intervals, and the distance d is, as
shown by the following equation, of the wavelength λ of the sound of the maximum central
frequency Fmax of the frequency band to be reduced among noise frequency bands. Set to 1/2 or
less.
d≦λ/2
[0035]
For example, in the case of Fmax = 500 kHz, if the sound speed c is 340 m / s, the distance d is
0.34 m. The spacing d of the speakers 12 may be λ / 2 or less, and the maximum central
09-05-2019
11
frequency Fmax of the noise frequency band to be reduced changes to a higher frequency
Fmaxh, and the spacing d is λmaxh / 2 (λmaxh When it becomes larger than = c / Fmaxh), as
shown in FIG. 2, by arranging the rails 13 along the arrangement position of the speakers 12, a
speaker moving means is provided to make each of the speakers movable. By moving the
speakers 12 so that the distance d with respect to the frequency Fmaxh is equal to or less than
λmaxh / 2, by the carriage 15 formed of the self-propelled wheels and the electric motor
provided between the rails 13 and the speakers 12 Good. In addition, you may move the speaker
12 not by mechanical methods, such as an electric motor, but manually.
[0036]
The inverse filter DSP 22 includes an A / D converter 26 that converts an analog signal output
from the microphone amplifier 20 into a digital signal, and a time-invariant inverse filter 28
whose filter coefficient is preset. The filter coefficient of the inverse filter 28 is determined by
either the explicit method or the LMS method, and outputs a signal of the same amplitude and
opposite phase to the signal output from the A / D converter 26.
[0037]
The control block 16 further includes a delay circuit 30 for delaying a signal according to the
arrangement order of the speakers 12 for each of the n speakers 12 and a D / A converter 34 for
converting a digital signal into an analog signal. A plurality of are provided.
[0038]
The delay circuit 30 delays the signal input to the speaker 12 so that the virtual sound sources of
the speaker 12 are arranged in an arc shape centering on the noise source.
The delay time of the signal input to each of the speakers 12 is determined by the signal
processing unit 40 as follows.
[0039]
First, based on the sound wave information, the position of the noise source is determined as
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12
follows. Cross spectrum Φxy (X) of two sound waves x (t) and y (t) from a noise source incident
on the sensor microphone 18 and the speaker proximity microphone 38 (Mi, i = 1, 2,... 9 in this
example) A cross correlation function φxy (τ) which is an inverse Fourier transform of ω) is
obtained.
[0040]
The cross correlation function φ xy (τ) is expressed as follows. For the function of time x (t), y
(t) the autocorrelation function is
[0041]
And the cross correlation function is
[0042]
It is expressed as
Here, when Fourier transforming φxx (τ) and φxy (τ), the power spectrum is
[0043]
And the cross spectrum is
[0044]
It is expressed as
Also, let h (t) be the impulse response of the system and H (ω) be its transfer function,
[0045]
09-05-2019
13
[0046]
となる。
Also, in the frequency domain, it is expressed as follows.
[0047]
[0048]
[0049]
The cross-correlation function φ xy (τ) expressed by the above equation (6) takes the sensor
microphone 18 as time axis zero (base point), and the noise reaches the speaker proximity
microphone 38 (referred to as Mi) from the sensor microphone 18 It is the required time Ti.
Here, when the distance from the speaker proximity microphone 38 to the sensor microphone
18 is di and c is the speed of sound, it is expressed by the following equation.
Ti=di/c
[0050]
Therefore, the distance di from the sensor microphone 18 to the speaker proximity microphone
38 is di = Ti × c. Therefore, with the speaker proximity microphone 38 as the center of a circle,
an arc of radius di is drawn to intersect the arcs Identify the point as the location of the noise
source.
[0051]
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14
When the position of the speaker proximity microphone 38 at the minimum time Tmin of Ti is
the position closest to the noise source and the distance from the sensor microphone 18 to the
speaker proximity microphone 38 is R, the distance R is It is expressed by the following equation.
R=Tmin・c
[0052]
Then, as shown in FIG. 3, the speaker 12 closest to the sensor microphone 18 is used as the
central speaker of the arc-arranged speaker group in a virtual arrangement, and as shown in FIG.
Is calculated by the following equation (9).
[0053]
Δ = {(R <2> + D ± i <2>) <1/2> −R} / c (9)
[0054]
When the position of the noise source moves, the delay time Δ is calculated for each speaker 12
based on the above equation, and the delay time Δ set in the delay circuit 30 corresponding to
each speaker 12 is corrected.
Thus, each of the delay circuits 30 delays the signal by a delay time Δ calculated according to
the distance between the moved noise source and the speaker 12.
[0055]
Further, the signal processing unit 40 calculates the amplitude correction K for correcting the
amplitude of the control sound emitted from the speaker 12 as follows, and sets it in the delay
circuit 30.
When the loudspeakers 12 are arranged in a straight line, the actual loudspeakers 12 are ahead
by a distance corresponding to the delay time Δ with respect to the arc in the virtual
09-05-2019
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arrangement, so a louder sound is produced than when the loudspeakers 12 exist in the virtual
arrangement. Release to control point. Therefore, a correction coefficient Ki for correcting the
magnitude of the control sound to a smaller value is calculated by the following equation (10).
[0056]
Ki = Δi × c / R (I = 1, 2,...) (10)
[0057]
Further, the signal processing unit 40 determines the filter coefficient W (t) of the inverse filter
28 as follows, for example, by an explicit method.
[0058]
First, the cross-correlation function hs (t) of noise x (t) from the noise source entering the sensor
microphone 18 installed near the noise source and noise ys (t) reaching the control point from
the noise source is measured, and A cross correlation function hc between noise x (t) from the
noise source entering the sensor microphone 18 and noise yc (t) emitted from the speaker 12 as
W (t) = δ (t) as the inverse filter t) Measure (measurement of impulse h (t) by cross-correlation
method).
[0059]
Then, assuming that the transfer functions of hs (t) and hc (t) are Hs (ω) and Hc (ω), the inverse
filter W (t) is determined by the following equation (11).
[0060]
Here, F <-1> indicates an inverse Fourier transform.
[0061]
When the filter coefficient of the inverse filter 28 is determined by the MLS method, it is
determined as follows.
[0062]
First, directivity correction Di to be described later of all the N speakers 12 is set (the directivity
09-05-2019
16
of the noise source and the directivity of the control sound source speaker are made the same).
Then, the noise source is activated, and x (t) entering the sensor microphone 18 installed in the
vicinity of the noise source and noise ys (t) from the noise source reaching the control point are
input to the LMS system. The filter coefficient W (t) is determined by automatic identification by
the operation of the method.
[0063]
Further, as shown in FIG. 3, when the noise from the noise source has directivity, the directivity
correction coefficient Di is obtained as follows, and the magnitude of the control sound from each
speaker 12 is corrected. Are set in each delay circuit 30.
When there are a plurality of sound sources (for example, transformer 50 Hz sine wave emission)
and sound waves from the plurality of sound sources interfere with each other to propagate, or
there is a reflective object such as a building around the sound source When the waves reflected
from the object and the reflecting object propagate while interfering with each other, the noise
from the noise source has directivity, and the cross correlation function is in proportion to the
magnitude of the sound incident on each speaker proximity microphone 38 That is, the
amplitude (power) is different reflecting the directivity of noise reduction.
For example, as shown in FIG. 5, the amplitudes of M8 and M9 are large, and the fact that M1
and M2 are small is the result of the directivity of the noise source.
If the magnitude of the control sound emitted from the speaker 12 is the same as the directivity
of the noise source, it is possible to cope with the case where the noise source has directivity.
[0064]
Therefore, the directivity correction coefficient Di is a cross-correlation function of y (t) incident
on the speaker proximity microphone 38 (M6) close to the central speaker 12 of the arcarranged speaker and x (t) incident on the sensor microphone 18 Based on φ <M6> xy (τ), it is
calculated by the following equation (12).
09-05-2019
17
[0065]
[0066]
When the noise source has a phase difference Δtsi, directivity correction Dpi is obtained as
follows, and is set in each delay circuit 30 so as to correct the delay time.
Since noise generated by a sound source generally has a wide band frequency component, it is
generally considered that no significant phase difference occurs even if the noise source has
directivity.
However, if there are complicated directivity due to the fact that there are a plurality of sound
sources and complexity and building reflection of noise, the phase difference changes, so the
phase difference must be corrected.
[0067]
Therefore, when the noise source has directivity and phase difference Δtsi, first, cross
correlation between yi (t) incident on the speaker proximity microphone 38 (Mi) and x (t)
incident on the sensor microphone 18 Find a function φ <Mi> xy (τ).
[0068]
And a sine wave x (t) of frequency f Hz (for example, if the main frequency band is 1/3 octave
band center frequency 250 Hz, f = 250 Hz) included in the main frequency band of noise from
the noise source Si (t) is determined by convolution integration with the cross correlation
function φ <Mi> xy (τ) as shown in the following equation (13).
[0069]
[0070]
Then, as shown in FIG. 6, with the sine wave (M9) starting from the earliest time as a reference
(Δts = 0 delay time zero), the phase difference Δtsi of the noise incident on each speaker
proximity microphone 38 is determined.
09-05-2019
18
[0071]
Then, the information of Δtsi is added to Δ of the above-described equation for calculating the
delay time as a delay due to the phase.
That is, it is expressed by the following equation (14).
[0072]
Δi = ((R <2> + Di <2>) <1/2> -R) / c + Δtsi (14)
[0073]
Next, the operation of the noise reduction system 10 according to the first embodiment will be
described.
First, the noise emitted from the noise source is collected by the sensor microphone 18, the
acoustic signal is amplified by the microphone amplifier 20, and is input to the inverse filter DSP
22.
Then, the inverse filter 28 of the inverse filter DSP 22 performs digital filtering processing using
the digital signal input from the A / D converter 26 and the set filter coefficient.
[0074]
At this time, by passing the reverse filter 28, the waveform of the signal is shaped and moved in
time, and a reduced signal in which the input signal is in reverse phase is generated, so the
speaker 12 emits noise based on the reduced signal. A sound reduction effect can be obtained by
the control sound.
[0075]
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19
The reduced signal subjected to the filtering process by the inverse filter 28 is input to each
delay circuit 30, and each delay circuit 30 delays the signal by a delay time set in accordance
with the arrangement order of the corresponding speakers 12.
The delayed signal is input to the D / A converter 34, D / A converted, and output to the speaker
unit 14 through the power amplifier 36.
Then, sound waves corresponding to the filtered signal, that is, sound waves of all frequency
bands below the maximum frequency in the frequency band of noise to be reduced which is the
reverse phase wave of noise, are control sound, and each speaker of speaker unit 14 It is emitted
from 12 to the control point.
[0076]
When the noise from the noise source has directivity, the directivity of the noise from the noise
source is calculated by the signal processing unit 40 based on the sound wave information of the
sensor microphone 18 and the speaker proximity microphone 38 According to the directivity, the
directivity correction coefficient is calculated for each speaker 12, the directivity correction
coefficient is set in each delay circuit 30, and the magnitude of the control sound is corrected
according to the directivity correction coefficient. Correct the amplitude of the reduction signal.
[0077]
When the noise from the noise source has a phase difference, the signal processing unit 40
calculates the phase difference of the noise from the noise source based on the sound wave
information of the sensor microphone 18 and the speaker proximity microphone 38 and
calculates the phase difference. The delay time set in each delay circuit 30 is calculated for each
speaker 12 in accordance with the phase difference, and the delay time set in each delay circuit
30 is changed to the calculated delay time.
[0078]
Then, the reduced signal subjected to the filtering process by the inverse filter 28 is delayed by
the delay time corrected by each delay circuit 30, and the noise is transmitted from each speaker
12 of the speaker unit 14 based on the delayed signal. Sound waves in all frequency bands below
the maximum frequency in the frequency band of noise to be reduced, which is a reverse phase
wave, are emitted as control sounds toward the control point.
09-05-2019
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[0079]
When the noise from the noise source has directivity, the directivity of the control sound emitted
from each speaker 12 is the same as the directivity of the noise.
Also, when there is a phase difference in noise from the noise source, the control sound is
delayed according to the phase difference of the noise, so the control sound corresponding to the
noise diffused with the phase difference is emitted from the noise source. The control sound
emitted from each speaker 12 is synthesized, and the envelope surface of the wave front of the
synthesized sound wave corresponds to the wave front of the noise, and the control sound has
the opposite phase of the noise.
[0080]
Here, the practical meaning of the fact that the directivity of the control sound emitted from each
speaker 12 is the same as the directivity of the noise will be clarified.
When there is directivity (or phase difference) of a noise source, here, consider the case where
the cause of directivity is reflection from the outer wall of three buildings A, B, and C of factory
buildings as shown in FIG. .
[0081]
First, when the frequency characteristics of the noise generated by the noise source to be
controlled and the sound pressure level are steady, the directivity (or phase difference) indicated
by the arrow in the upper right diagonal direction and the ellipse in FIG. It is constant, that is, it
does not change from moment to moment, and is constant.
At this time, the directivity (or phase difference) of the noise source is determined by the mutual
relationship between the noise x (t) generated from the noise source collected by the sensor
microphone 18 and the noise y (t) incident on each speaker proximity microphone 38 It is
obtained from the inverse Fourier transform xy xy (τ) of the correlation function, but x (t) and y
(t) include components of "all frequency bands below the maximum frequency in the frequency
09-05-2019
21
band of noise to be controlled" There is.
[0082]
Therefore, although the directivity (or phase difference) to be calculated depends on the
frequency characteristic of noise in this frequency band, the distance d of each speaker proximity
microphone 38 is set to 1/2 of the wavelength corresponding to the maximum frequency to be
controlled. The directivity (or phase difference) is determined using information of xy xy (τ) of
“the entire band of frequencies below the maximum frequency in the frequency band of the
noise to be controlled” as equal to or less than the corresponding length.
That is, it is considered that the directivity (or phase difference) of the noise source is required in
a method which is not perfect but in an engineering optimum.
[0083]
As described above, when the control sound is controlled so that the directivity (or phase
difference) of the control sound emitted from the plurality of speakers is the same as the
directivity (or phase difference) of the noise from the noise source. As described above, the
directivity (or phase difference) of the noise source is calculated by an engineeringally optimal
method, and the directivity (or phase difference) of the control sound emitted from the plurality
of speakers is calculated. This means that the magnitude of the control sound is controlled so
that the directivity (or phase difference) of the noise source is the same.
[0084]
In addition, when the frequency characteristics of the noise generated by the noise source to be
controlled and the sound pressure level are non-stationary, the directivity (or phase difference)
changes every moment, so the directivity ( Or, control may be made to follow the phase
difference correction.
[0085]
Therefore, even if the noise from the noise source has directivity and there is a phase difference,
the noise from the noise source is canceled by the control sound from the speaker 12 in a wide
range including the control point.
09-05-2019
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Further, as shown in FIG. 8, the same is true even when there are two sound sources, and it is
shown that the speaker 12 works as two arcs.
When there are two noise sources, as shown in FIG. 9, sensor microphones 18A and 18B,
microphone amplifiers 20A and 20B, inverse filters DSPs 22A and 22B, and delay circuits 30A
and 30B are provided for each noise source. There is.
Further, the output from each of the delay circuits 30A and 30B for each of the plurality of noise
sources is output to each D / A converter 34 having an addition function, and the speaker 12 of
the speaker unit 14 via each power amplifier 36. Control sound is emitted from.
[0086]
As described above, according to the noise reduction system according to the first embodiment,
the directivity of the control sound emitted from the plurality of speakers and the directivity of
the noise are based on the directivity of the noise source. While correcting the magnitude of the
control sound so as to be the same, input to each speaker so that the envelope surface of the
control sound emitted from the plurality of speakers based on the reduction signal corresponds
to the wave front of noise By reducing the delay signal and emitting the control sound from each
speaker, the noise diffused from the noise source can be reduced in a wide range even if the
noise from the noise source has directivity. can do.
[0087]
Also, based on the phase difference of the noise from the noise source, the noise is corrected by
correcting the time for delaying the reduction signal so that the envelope surface of the control
sound emitted from the speaker corresponds to the wave front of the noise. Even when the noise
from the source has a phase difference, the noise diffused from the noise source can be reduced
in a wide range.
[0088]
Further, even when there are a plurality of noise sources, noise diffused from the noise sources
can be reduced in a wide range.
[0089]
09-05-2019
23
In addition, active control can be performed even for free sound fields, that is, even when there is
no sound barrier, and noise can be reduced.
[0090]
In the above embodiment, although the case where the plurality of speakers are linearly arranged
is described as an example, the present invention is not limited to this, and the speakers may be
arranged in an arc.
Also in this case, for each speaker, the delay time is determined based on the distance between
the noise source and the speaker, and set in the delay circuit so that the virtual sound source of
the speaker is disposed on the arc relative to the noise source. do it.
[0091]
Next, a noise reduction system according to a second embodiment will be described.
In addition, about the part which becomes the structure similar to 1st Embodiment, the same
code | symbol is attached | subjected and description is abbreviate | omitted.
[0092]
The second embodiment is different from the first embodiment in that only one speaker
proximity microphone is provided.
[0093]
As shown in FIG. 10, in the noise reduction system 210 according to the second embodiment, the
wire 240 is provided along the arrangement direction of the plurality of speakers 12 of the
speaker unit 14 and the speaker proximity microphone 238 is hung on the wire Enables the
speaker proximity microphone to be moved.
[0094]
When the position of the noise source is specified, the noise from the noise source is collected
09-05-2019
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while moving the speaker proximity microphone 238 to a predetermined position close to each
of the plurality of speakers 12, and the sound corresponding to the collected noise The signal is
output to the signal processing unit 40.
[0095]
Thus, since only one speaker proximity microphone is required, the noise reduction system can
be configured at low cost.
[0096]
Next, a noise reduction system according to a third embodiment will be described.
In addition, about the part which becomes the structure similar to 1st Embodiment, the same
code | symbol is attached | subjected and description is abbreviate | omitted.
[0097]
As shown in FIG. 11, in the noise reduction system according to the third embodiment, a
soundproof wall 350 is provided, and a plurality of speakers 12 of the speaker unit 14 are
installed on the soundproof wall 350.
[0098]
As described above, even when the sound barrier is provided, the noise diffused from the noise
source can be reduced in a wide range.
Also, even if the noise from the noise source has directivity and the noise has a phase difference,
the size of the control sound set in each delay circuit without moving the speaker on the
soundproof wall. By correcting the delay time and the delay time, the noise diffused from the
noise source can be reduced in a wide range.
[0099]
09-05-2019
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In the first to third embodiments, the sensor microphone is used to collect noise from the noise
source, and an acoustic signal corresponding to the collected noise is transmitted through the
microphone amplifier. Although the case of outputting to the inverse filter DSP has been
described as an example, a vibration detector for detecting the vibration of the noise source may
be used.
In this case, a vibration detector is used to detect the vibration of the noise source, and a
vibration signal corresponding to the detected vibration is output to the reverse filter DSP via the
microphone amplifier, and the reverse filter DSP converts it into a vibration signal. Inverse
filtering may be applied to generate a reduced signal.
[0100]
Next, a noise reduction system according to a fourth embodiment will be described.
In addition, about the part which becomes the structure similar to 1st Embodiment, the same
code | symbol is attached | subjected and description is abbreviate | omitted.
[0101]
As shown in FIG. 12, in the noise reduction system according to the fourth embodiment, a
soundproof wall 450 bent at an angle θ is provided, and the plurality of speakers 12 of the
speaker unit 14 are on the soundproof wall 450. Installed in
[0102]
As described above, even when the sound barrier is bent, the noise diffused from the noise
source can be reduced in a wide range.
Also, even if the noise from the noise source has directivity and the noise has a phase difference,
the size of the control sound set in each delay circuit without moving the speaker on the
soundproof wall. By correcting the delay time and the delay time, the noise diffused from the
noise source can be reduced in a wide range.
09-05-2019
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[0103]
Next, a noise reduction system according to the fifth embodiment will be described.
In addition, about the part which becomes the structure similar to 1st Embodiment, the same
code | symbol is attached | subjected and description is abbreviate | omitted.
[0104]
As shown in FIG. 13, the noise reduction system according to the fifth embodiment is provided
with a soundproof wall 550 extending in two straight lines, and the plurality of speakers 12 of
the speaker unit 14 are: It is installed on the soundproof wall 550.
[0105]
As described above, even in the case where the sound barriers are formed in two straight lines,
the noise diffused from the noise source can be reduced in a wide range.
Also, even if the noise from the noise source has directivity and the noise has a phase difference,
the size of the control sound set in each delay circuit without moving the speaker on the
soundproof wall. By correcting the delay time and the delay time, the noise diffused from the
noise source can be reduced in a wide range.
[0106]
The soundproof wall on which the speaker is disposed on the wall may be curved around the
opposite side of the noise source.
Also in this case, the noise diffused from the noise source can be reduced in a wide range by
delaying the reduction signal.
09-05-2019
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[0107]
Further, although the case where the soundproof wall is provided is described as an example,
even in the free sound field without the soundproof wall, as described above, without moving the
plurality of speakers not arranged in a straight line, The noise from the noise source has
directivity by correcting the magnitude and delay time of the control sound set in the delay
circuit, and the noise diffused from the noise source even if the noise has a phase difference Can
be reduced in a wide range.
For example, when the site boundary is not linear, even if speakers are arranged along the site
boundary, noise diffused from the noise source can be reduced in a wide range.
[0108]
It is a schematic diagram showing composition of a noise reduction system concerning a 1st
embodiment of the present invention.
It is the schematic which shows the structure of the rail for moving a speaker, and a trolley |
bogie. It is an image figure showing the directionality of a noise source, and the case where a
center speaker is determined. It is an image figure which shows the case where delay time is
determined. It is a graph which shows the cross correlation function obtained when a noise
source has directivity. It is a graph which shows Si (t) obtained by the convolution integral of a
sine wave and a cross correlation function in case a noise source has directivity and has a phase
difference. It is a figure for demonstrating the directivity of the directivity of a noise source, and
the directivity of a control sound. It is an image figure which shows arrangement | positioning of
the virtual sound source in, when there are multiple noise sources. It is a schematic diagram
showing composition of a noise reduction system corresponding to a plurality of noise sources. It
is the schematic which shows the structure of the noise reduction system which concerns on the
2nd Embodiment of this invention. It is the schematic which shows the soundproof wall and
speaker of the noise reduction system which concern on the 3rd Embodiment of this invention. It
is the schematic which shows the soundproof wall and speaker of the noise reduction system
which concern on the 4th Embodiment of this invention. It is the schematic which shows the
soundproof wall and speaker of the noise reduction system which concern on the 5th
Embodiment of this invention.
09-05-2019
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Explanation of sign
[0109]
10, 210 Noise reduction system 12 Speaker 14 Speaker unit 16 Control block 18 Sensor
microphone 20 Microphone amplifier 22 Inverse filter DSP 26 A / D converter 28 Inverse filter
30 Delay circuit 34 D / A converter 36 Power amplifier 38, 238 Speaker proximity Microphone
40 signal processing unit 240 wire 350, 450, 550 soundproof wall
09-05-2019
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