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DESCRIPTION JP2007024619

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DESCRIPTION JP2007024619
PROBLEM TO BE SOLVED: To provide a noise measurement device having a relatively small
microphone array capable of changing the direction of directivity characteristics to a
predetermined angle while maintaining sharp directivity characteristics and freely changing the
directivity characteristics by post-processing. SOLUTION: A microphone array 1 in which a
plurality of microphones M1, M2, ..., MN are arranged, an A / D conversion unit 2 digitizing an
output signal from the microphone array 1, and digitization by the A / D conversion unit 2 The
data recorder 3 stores the output signal from the microphone array 1 for a predetermined time,
and the personal computer 4 inputs and processes the output signal of the data recorder 3. The
personal computer 4 has directivity characteristics of the microphone array 1 A plurality of
signal processing means for generating variously, an arithmetic processing means for
arithmetically processing various directional characteristics generated by these signal processing
means, and a setting for setting the signal processing means and the arithmetic processing
means at predetermined angles A means was provided. [Selected figure] Figure 1
Noise measurement device
[0001]
The present invention relates to a noise measurement apparatus having a sharp directivity and
being able to change the directivity as compared to the directivity determined by the base line
length of a microphone array.
[0002]
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1
In order to change the directivity of the microphone array, it is known to physically change the
orientation of the microphone array.
Also, as a method of changing the direction of the directional characteristics by electrical
processing without physically changing the direction of the microphone array, as shown in FIG.
7, a plurality of microphones M1, M2,. , MN (hereinafter referred to as “linear arrangement
microphone array”), the delay amounts of the appropriate delay amounts d1, d2,..., DN are
changed by the delay unit 100, and the sum of the outputs of these delay units is calculated by
the adder 101. It is known to make it happen. Reference numeral 103 denotes a display unit.
[0003]
However, when the orientation of the microphone array is physically changed, in order to
perform measurement in all directions, only one direction can be measured in one measurement,
and therefore, it is necessary to measure many times for each angle. There is. In addition, simply
summing up the output from each microphone by changing the delay amount causes the
apparent baseline length of the microphone array to be shortened at angles other than the front,
so that the directivity characteristic becomes dull and the accuracy becomes worse There is a
problem of In order to obtain sufficient accuracy, the baseline length of the microphone must be
long.
[0004]
The present invention has been made in view of such problems in the prior art, and the object of
the present invention is to change the direction of the directivity at a predetermined angle while
maintaining the sharp directivity, Another object of the present invention is to provide a noise
measurement device having a relatively compact microphone array whose directivity
characteristics can be freely changed by post-processing.
[0005]
In order to solve the above-mentioned problems, the invention according to claim 1 comprises a
microphone array in which a plurality of microphones are arranged, an AD conversion unit for
digitizing an output signal from the microphone array, and the above digitized by the AD
conversion unit. A memory unit for storing an output signal from the microphone array for a
predetermined time, a plurality of signal processing means for generating various directional
characteristics of the microphone array, and arithmetic processing on various directional
characteristics generated by these signal processing means An arithmetic processing means, and
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2
a setting means for setting the signal processing means and the arithmetic processing means at
predetermined angles.
[0006]
The invention according to claim 2 comprises a microphone array in which a plurality of
microphones are arranged, an AD converter for digitizing an output signal from the microphone
array, and an output signal from the microphone array digitized by the AD converter. Of the
microphone array for the predetermined time, first signal processing means for generating
directivity characteristics in which the gain in the target direction is maximum for the
microphone array, the gain in the target direction for the microphone array is minimized, and the
side lobe is Second signal processing means for generating directivity characteristics similar to
the directivity characteristics by the first signal processing means, directivity characteristics
generated by the second signal processing means, and directivity characteristics generated by
the first signal processing means Arithmetic processing means for calculating the difference
between the first signal processing means, the first signal processing means, the second signal
processing means, and the arithmetic processing means Those having a setting means for setting
every predetermined angle.
[0007]
The invention according to claim 3 is the noise measurement device according to claim 2,
wherein a baseline length of the microphone array is 1 m or more and 3 m or less.
[0008]
According to the first aspect of the present invention, sharp directivity can be realized by the
signal processing means for changing the directivity, without unnecessarily increasing the base
length of the microphone array without increasing the number of microphones.
Therefore, the directivity can be made sharper than the baseline length, so that deterioration of
the directivity can be suppressed even if the baseline length of the microphone array is
shortened.
This effect can be used for analysis of a moving sound source because measurements can be
made with sharp directivity characteristics for all directions at a predetermined angle in one
measurement without moving the microphone array.
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Furthermore, since the contribution rate according to the direction of arrival can be known, the
superior sound source direction can be specified.
For example, it can be used for efficient measures by estimating which part of a moving train is
making a loud noise.
[0009]
According to the second aspect of the present invention, the output signal of the first signal
processing means having the maximum gain in the target direction, the second gain having the
minimum gain in the target direction and the side lobe similar to the first signal processing
means By obtaining the difference of the signal processing means, it is possible to suppress the
side lobe component and sharpen the main lobe. Thereby, sharp directivity can be realized
without unnecessarily increasing the base length of the microphone array without increasing the
number of microphones. Therefore, the directivity can be made sharper than the baseline length,
so that deterioration of the directivity can be suppressed even if the baseline length of the
microphone array is shortened. This effect can be used for analysis of a moving sound source
because measurements can be made with sharp directivity characteristics for all directions at a
predetermined angle in one measurement without moving the microphone array. Furthermore,
since the contribution rate according to the direction of arrival can be known, the superior sound
source direction can be specified. For example, it can be used for efficient measures by
estimating which part of a moving train is making a loud noise.
[0010]
According to the third aspect of the present invention, the base length of the microphone array,
which has been about 5 m in the prior art, can be set to about 2 m.
[0011]
Embodiments of the present invention will be described below based on the attached drawings.
Here, FIG. 1 is a block diagram of the noise measuring apparatus according to the present
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invention, FIG. 2 is a block diagram of the main parts of the same, FIG. 3 is a directivity
characteristic diagram, and FIGS. 4 to 6 are display examples of measurement results.
[0012]
The noise measuring apparatus according to the present invention is, as shown in FIG. 1, a
microphone array 1 in which N microphones M1, M2,..., MN are arranged, and output signals of
the microphones M1, M2,. , A data recorder 3 for storing output signals from the A / D converter
2, and a personal computer 4 for receiving and processing output signals from the data recorder
3.
[0013]
Further, as shown in FIG. 2, the personal computer 4 is provided with an arithmetic processing
block 20 for each frequency band and for each angle, that is, the number obtained by multiplying
the number of frequency bands by the number of angles to be measured. Each block 20 is
provided with setting means 21.
Reference numeral 22 denotes a display unit for displaying the final calculation result.
[0014]
The arithmetic processing block 20 generates a predetermined directivity characteristic of the
signal received from the data recorder 3 and processes it, and the directivity characteristic
different from the first signal processing unit 5 with respect to the signal received from the data
recorder 3 A second signal processing means 6 for generating and processing the signal, a phase
shifter 7 for shifting the phase of the output signal of the first signal processing means 5 by .pi. /
2, and a coefficient k to the output signal of the second signal processing means 6 The difference
between the output signal of the phase shifter 7 and the output signal of the multiplier 8 is
calculated. The multiplier 8 to be multiplied, the first signal processing means 5, the control unit
9 for controlling the second signal processing means 6, and the multiplier 8 An arithmetic
processing means 10 is provided.
[0015]
The setting unit 21 sets the first signal processing unit 5, the second signal processing unit 6,
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and the arithmetic processing unit 10 at predetermined angles.
The signal processing means for generating a predetermined directivity characteristic is not
limited to the first signal processing means 5 and the second signal processing means 6, and
three or more may be provided. Then, those output signals may be arithmetically processed by
the arithmetic processing means 10.
[0016]
The first signal processing means 5 comprises N digital filters Fa (1), Fa (2),..., Fa (N) and N digital
filters Fa (1), Fa (2),. It comprises the adder 11 which adds and outputs the output signal of N).
The digital filters Fa (1), Fa (2),..., Fa (N) have a function to divide a frequency band according to
the purpose, such as an octave, 1/2 octave, 1/3 octave, etc., and a spatial filter function .
[0017]
The second signal processing means 6 also includes N digital filters Fb (1), Fb (2),..., Fb (N) and N
digital filters Fb (1), Fb (2),. It consists of an adder 12 which adds and outputs the output signal
of Fb (N). Digital filters Fb (1), Fb (2), ..., Fb (N) divide the frequency band according to the
purpose, such as 1 octave, 1/2 octave, 1/3 octave, etc., and spatial filter function. Have.
[0018]
The control unit 9 sets parameters of the digital filters Fa (1), Fa (2),..., Fa (N) and the digital
filters Fb (1), Fb (2),. Further, the control unit 9 indicates an appropriate coefficient k that the
multiplier 8 should not multiply. Although the phase shifter 7 is provided at the subsequent stage
of the adder 11, the π / 2 phase shift function can be applied to the digital filters Fa (1), Fa (2),...,
Fa (N) without providing the phase shifter 7. It is also possible to incorporate. The multiplier 8
optimizes the magnitude of the signal input to the arithmetic processing means 10 by
multiplying the output signal of the second signal processing means 6 by an appropriate
coefficient k. In the multiplier 8, a table of coefficients k is created and set in advance.
[0019]
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The operation of the noise measurement device according to the present invention configured as
described above will be described. First, the sound pressure signal acquired by the microphone
array 1 is converted to a digital signal by the A / D converter 2. Then, the signal digitized by the
A / D converter 2 is stored in the data recorder 3 for a predetermined time. The signal stored in
the data recorder 3 is transferred from the data recorder 3 to the personal computer 4. The
signal transferred to the personal computer 4 is supplied to the first signal processing means 5
and the second signal processing means 6.
[0020]
In the first signal processing means 5, the digital filters Fa (1), Fa (2),..., Fa (N) divide the
frequency of the digital signal every 1/3 octave, and process each signal by the spatial filter.
Similarly, in the second signal processing means 6, the digital filters Fb (1), Fb (2),..., Fb (N) divide
the frequency of the digital signal every 1/3 octave, and each signal is divided by the spatial
filter. To process.
[0021]
The frequency band can be divided into one octave, one half octave, etc. according to the
purpose. Also, by using a spatial filter, the directivity can be varied by setting the zero and pole.
Also, the combination of microphones to be used is selected according to the frequency band to
be processed. The control unit 9 changes setting of parameters of the digital filters Fa (1), Fa
(2),..., Fa (N) and the digital filters Fb (1), Fb (2),. Then, the signal to be input to the adders 11 and
12 can be selected.
[0022]
In the first signal processing means 5, a spatial filter is set so as to obtain a directivity
characteristic in which the gain in the target direction is maximized. Further, in the second signal
processing means 6, the spatial filter is set such that the gain in the target direction is minimized
and the side lobes are similar to the first signal processing means 5.
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[0023]
Next, the output signals of the digital filters Fa (1), Fa (2),..., Fa (N) are added by the adder 11,
and the digital filters Fb (1), Fb (2),. The output signals of are added by the adder 12. Further, the
phase shifter 7 shifts the phase of the output signal of the adder 11 by π / 2, and the multiplier
8 multiplies the output signal of the adder 12 by an appropriate coefficient k to be input to the
arithmetic processing means 10 Optimize the size. The waveform A shown in FIG. 3 represents
the output signal of the phase shifter 7, and the waveform B represents the output signal of the
multiplier 8.
[0024]
Next, in the arithmetic processing means 10, the difference between the output signal of the
phase shifter 7 and the output signal of the multiplier 8 is calculated. Then, since the side lobe
components are similar, they decrease, and the main lobe component does not have a
suppressing effect on the components in the target direction, so the output signal of the
arithmetic processing means 10 has the target direction as shown in waveform C in FIG. In
contrast, it has sharp characteristics.
[0025]
Next, the data recorder 3 is determined in each of the arithmetic processing blocks 20
determined for each 1/3 octave band by the first signal processing means 5 and the second
signal processing means 6 and determined for each angle by the setting means 21. By processing
the signal from, it is possible to analyze for frequency, direction, level and time. The analysis
result is displayed on the display unit 22 as shown in FIG. 4, FIG. 5, and FIG. 6 in accordance with
the purpose. The result to be displayed can be selected by the user's operation. Using one
measurement data, multiple octave bands and directivity in all angular directions can be obtained
with one button operation, and contribution rates can be easily determined for each frequency
and for each direction.
[0026]
The direction can be changed without increasing the baseline length of the microphone array
while maintaining the sharpness of the directional characteristics, and directivity in multiple
octave bands and all angular directions can be obtained in one measurement, for each frequency,
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direction Since the contribution rate can be easily obtained for each case, it is expected to be
used for investigating the cause of noise from moving sound sources such as trains.
[0027]
The block diagram of the noise measurement apparatus according to the present invention The
block diagram of the main part The directional characteristic diagram Display example of level
change with respect to time of three frequency bands at a predetermined angle (+ 30 °) Three
examples at a predetermined frequency (800 Hz) Display example of level change against time of
angle Display example of contribution analysis of noise coming from each direction at a time
Example block diagram of a sound level meter having a conventional microphone array
Explanation of sign
[0028]
DESCRIPTION OF SYMBOLS 1 ... Microphone array, 2 ... A / D converter, 3 ... Data recorder, 4 ...
Personal computer, 5 ... First signal processing means, 6 ... Second signal processing means, 7 ...
Phase shifter, 8 ... Multiplier, DESCRIPTION OF SYMBOLS 9 ... Control part, 10 ... Arithmetic
processing means, 11, 12 ... Adder, 20 ... Arithmetic processing block, 21 ... Setting means, 22 ...
Display part, Fa (1), Fa (2), ..., Fa (N) , Fb (1), Fb (2),..., Fb (N)... Digital filters, M1, M2,.
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