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JPH09222893

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DESCRIPTION JPH09222893
[0001]
BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a
noise reduction device that reduces the level of noise dissipated from a noise source to the
surrounding space using an active noise reduction method, and more particularly to a feedback
system using only a power amplifier without phase correction. The present invention relates to
an analog noise reduction device that constitutes
[0002]
2. Description of the Related Art As a noise source, for example, an industrial generator emits
large noises, so it is disposed in a casing constituting a compartment for the purpose of reducing
the level of the noises emitted, but it is still noise outside the casing. The level is big.
[0003]
An active noise reduction system is known as a measure for reducing the level of noise dissipated
from such a noise source to the surrounding space.
This active noise reduction method is basically a method of emitting the sound of the phase
opposite to the noise emitted by the noise source collected by the microphone serving as the
noise detection means from the speaker toward the noise source, but changes in air flow and
temperature changes Since the propagation state of the sound changes due to the above, etc.,
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when the arrangement distance between the microphone and the speaker is long, phase
correction in consideration of environmental conditions is required in the feedback system.
[0004]
This phase correction is usually performed by digital processing, but if equivalent processing is
to be performed by analog processing, the configuration between the microphone and the
speaker can be ignored because changes in environmental conditions can be ignored because the
configuration becomes very complex and difficult to realize. An analog noise reduction device has
been proposed in which the feedback system is made up of only a power amplifier in close
proximity (see, for example, U.S. Pat. No. 4,455,675). According to this method, the noise
reduction device can be configured inexpensively and simply.
[0005]
On the other hand, the noise source generates sounds of various frequencies ranging from low
frequency to high frequency, but if the frequency of the noise in question is a high frequency of
400 Hz or more, which strongly senses human hearing, the speaker is a noise source. It is
supposed that they should be placed close to each other, and if the static area with reduced noise
level is to be formed over a wide angular range by the same noise control method as in the low
frequency case, the relationship with the wavelength It is known that noise control in multiple
sound fields is necessary, that is, it is necessary to arrange a large number of speakers at 1/4
wavelength intervals, making practical noise control difficult (Japanese Acoustical Society
Journal) 47: 9: 688 (1991), Materials of the Acoustical Society of Japan (1994), etc.).
[0006]
However, in the above-described conventionally proposed analog system, it is necessary to place
the microphone and the speaker close to each other, so the situation of the existing space of the
noise source to be silenced When it becomes difficult to arrange the microphone and the speaker
close to each other, the noise reduction effect may not be obtained.
[0007]
In particular, in the case where the frequency of the noise in question is a high frequency of 400
Hz or more, which strongly senses human hearing, it is not only necessary to arrange a large
number of loudspeakers as described above in the related art. There is a restriction called an
interval, so control may not be possible depending on the frequency (refer to the aforementioned
Acoustical Society of Japan, 47, 9 and 688 (1991)).
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[0008]
The present invention was created to solve such conventional problems, and its object is to
obtain a predetermined noise reduction effect even under the situation where the noise detection
means and the speaker can not be arranged close to each other, and An object of the present
invention is to provide an analog noise reduction device which enables noise control of a target
frequency with a simple configuration even at a high frequency of 400 Hz or more.
[0009]
SUMMARY OF THE INVENTION In order to achieve the above object, the noise reduction device
of the present invention has the following construction.
The noise reduction device according to claim 1 emits from the speaker a noise having a phase
opposite to that of the noise generated by the noise source detected by the noise detection means
toward the noise source to reduce the noise level radiated from the noise source. In the noise
reduction device, the noise detection means measures and sets a spatial position at which a
sound of a specific frequency can be detected at a level higher than that of any other frequency,
and a speaker is a height above a wall giving a maximum sound field. It is characterized in that
the position is measured and set.
[0010]
The noise reduction device according to claim 2 is characterized in that in the noise reduction
device according to claim 1, the wall surface on which the speaker is disposed is one wall surface
of a housing surrounding the periphery of the noise source.
The noise reduction device according to claim 3 is the noise reduction device according to claim
1, wherein the wall surface on which the speaker is disposed is a wall surface of one substantially
flat partition arranged in the vicinity of the noise source. It is characterized by
[0011]
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Next, the operation of the noise reduction apparatus of the present invention configured as
described above will be described.
In the noise reduction device of the present invention, the noise source does not generate sound
of all frequencies from low frequency to high frequency with uniform intensity, but generates
particularly strong sound of specific frequency among them. Focusing on the characteristic of the
noise source which is often said, it is intended to reduce the noise level of a particular high
frequency of that level, thereby reducing the overall noise level.
[0012]
That is, the noise reduction device according to claim 1 detects the sound of a specific frequency
at a level higher than that of any other frequency, and the noise source from the position giving
the maximum sound field the sound in the reverse phase of the detected noise. Send towards.
Therefore, at least on the back side of the speaker, the noise of the specific frequency can be
muted, so that a static area with a reduced noise level is generally formed. The static area that
can be formed is a specific narrow angle range, but since the sound of the target frequency can
be controlled with at least one speaker, noise of any frequency can be generated with a simple
configuration even at high frequencies that were conventionally considered difficult It is possible
to reduce the level.
[0013]
Specifically, when the noise source is in the housing, the arrangement position of the speaker is,
like the noise reduction device according to claim 2, one wall surface of the housing facing the
area side where the static area is to be formed. If the noise source is not enclosed, as in the noise
reduction device according to claim 3, the noise source is disposed close to the noise source
between the area where the static area is to be formed and the noise source. It may be a wall
surface of a substantially flat partition.
[0014]
BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be
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described below with reference to the drawings.
FIG. 1 is a block diagram of a noise reduction device according to a first embodiment of the
present invention. In FIG. 1, an engine 2 as a noise source is disposed in a housing 1. The engine
2 is provided with a fan 3, a radiator 4 and an exhaust tail pipe 5 or the like. That is, the first
embodiment is an application example to the industrial generator described above.
[0015]
In contrast to the engine (hereinafter referred to as “noise source”) 2 that is a noise source, the
noise reduction device of the present invention comprises a noise detection unit 6 provided at a
spatial position in the housing 1 and one wall surface of the housing 1 , And a power amplifier 8
provided between them. Here, the noise detection means 6 measures a spatial position at which a
sound of a specific frequency can be detected at a level higher than that of any other frequency,
and is suspended from the ceiling of the housing 1 or supports the camera with three legs It is
fixed to a stand placed on the floor of the housing 1 in the same way as it is made to be, and it is
set to the measured spatial position. A microphone, a piezoelectric element or the like is used for
the noise detection means 6.
[0016]
In addition, the speaker 7 measures the intensity distribution of the sound field on one wall
surface of the housing 1 one by one, and measures the height position on the wall surface of the
housing 1 giving the maximum sound field. It is set to face. The power amplifier 8 reversely
amplifies the noise detected by the noise detection means 6, for example, and causes the speaker
7 to transmit the noise at a high level.
[0017]
Next, the specific setting method of the noise detection means 6 and the speaker 7 is
demonstrated with reference to FIG.2 and FIG.3. First, FIG. 2 is an explanatory view of a method
of determining the position of the noise detection means. In FIG. 2, the sound generated by the
noise source 2 in the housing 1 spans from low frequency to high frequency of 2 kHz or more,
but the noise detection means 6 is supported at a spatial position near the noise source 2 and its
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output signal To the frequency analyzer and measuring the relationship between the noise
frequency and the level is repeated while changing the position of the noise detection means 6,
and the sound of the specific frequency (400 Hz in the example shown) is the sound of any other
frequency A spatial position which can be detected at a higher level (level difference 19.8 dB in
the illustrated example) is searched for, and the position is determined as the set position of the
noise detection means 6.
[0018]
That is, the noise source 2 in the first embodiment has the characteristic of generating the noise
of 400 Hz most strongly. FIG. 3 is an explanatory diagram of a method of determining the
speaker position. In FIG. 3, the “+” mark in the drawing is a measurement point, and the
numerical value below each measurement point “+” is a measurement value (dB).
Measurement points “+” are set in a grid point shape at intervals of 20 cm, for example, on
wall surfaces of a predetermined range facing noise source 2 on one wall surface of housing 1
and sound pressure level (dB in each measurement point “+” ) Is measured by an appropriate
sensor (for example, a microphone, a piezoelectric element, etc.) and a frequency analyzer, and
an isoacoustic line is drawn to search for an area giving the maximum sound field.
[0019]
In the illustrated example, there is a region giving the maximum sound field around the 78.9 dB
measurement point “+” (hatched circle portion), so the center point position of that region is,
for example, 78.9 dB measurement point “ Obtained from the position of “+”, it is defined as
the height position on the wall surface giving the maximum sound field, and the speaker 7 is set
at that position. In this case, the distance between the speaker 7 and the noise source 2 is defined
exclusively by the distance between the wall surface of the housing 1 and the noise source 2, but
since the distance between the wall surface of the housing 1 and the noise source 2 is usually
narrow, The noise reduction requirements in the case of high frequency mentioned above are
satisfied.
[0020]
FIG. 4 is a measurement diagram of the noise level behind the speaker 6 when the noise
detection means 6 and the speaker 7 are set as described above. In FIG. 4, the horizontal axis is
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frequency (Hz), and is scaled at 200 Hz intervals. The vertical axis is the noise level, which is
scaled at 10 dB intervals. The measurement position is a position 7 m behind the speaker 6.
[0021]
The frequency ranges from 60 Hz to 1 kHz or more, but does not activate the noise detection
means 6 and the speaker 7, as shown by the dotted line in the case of the active muffling OFF,
exceeds 10 dB more than the noise levels of other frequencies at 400 Hz. A loud noise is
generated. With respect to such a noise source 2, the noise is detected by the noise detection
means 6, and inverted and amplified by the power amplifier 8, and the output of the power
amplifier 8 is manually adjusted to an output that does not cause howling. In the case of the
active muffling, as indicated by the solid line, the noise level of 400 Hz is reduced by almost 10
dB, and the noise levels at other frequencies are also reduced slightly.
[0022]
Thus, it has been shown that the noise level as a whole is reduced, and it is shown that a quiet
area with a reduced noise level can be formed behind the loudspeaker 7. Next, FIG. 5 is a block
diagram of a noise reduction device according to a second embodiment of the present invention.
The second embodiment shows a noise reduction method in the case where the noise source 21
is not surrounded, that is, in the case where there is no wall provided with a speaker as in the
case 1 in the first embodiment.
[0023]
In FIG. 5, between the noise source 21 and the area where the static area 27 is desired to be
formed, a substantially flat partition 22 is disposed close to the noise source 21 and the noise
detection means 23 supported by the stand 24 is It is disposed near the noise source 21, and the
speakers 25 are set on the wall surface of the partition 22. The setting positions of the noise
detection means 23 and the speaker 25 are determined in the same manner as in the first
embodiment.
[0024]
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Even in this case, it is apparent that the static area 27 with reduced noise level is formed on the
back side of the speaker 25 as in the first embodiment. Even if partition 22 is set, the sound on
the back side is attenuated to some extent, and in the past, in order to attenuate the sound
propagating to the back side through partition 22, a thick wall is used for partition 22, sound
absorption processing Measures have been taken to However, even if such measures are taken,
the noise coming around from the top and the side of partition 22 can not be reduced.
[0025]
In the present invention, the sound propagating to the rear side through the partition 22 is
attenuated only by setting the speaker 25 without taking measures such as using a thick
partition for the partition 22 or performing sound absorption processing. It is possible to reduce
noise coming around from the top and the side.
[0026]
When it is desired to improve the detection characteristics of the noise detection means, for
example, a method of combining in an array arrangement, a method of using super directivity, or
the like may be adopted.
Moreover, although a power amplifier usually uses an inverting amplifier, when using an inphase amplifier, it may be sent out by inverting the phase on the speaker side.
[0027]
As described above, the noise reduction device according to claim 1 detects a sound of a specific
frequency at a level higher than that of any sound of other frequencies, and generates a sound in
reverse phase to the detected noise. Since the sound is sent from the position giving the
maximum sound field to the noise source, a static area with reduced noise level can be formed at
least behind the speaker.
[0028]
In particular, since noise of a specific frequency is targeted for noise reduction, noise can be
reduced even at high frequencies above 400 Hz, which are highly sensitive to human hearing,
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which has been considered extremely difficult in the past, and noise control of specific
frequencies is selectively performed. It becomes possible.
The arrangement position of the speaker can be determined according to the condition of the
space where the noise source is present, irrespective of the arrangement position with the noise
detection means as in the noise reduction device according to claim 2 or 3.
[0029]
Therefore, the layout design of the speaker and the noise detection means becomes easy, and the
distance between the speaker and the noise detection means and the noise source can be made
wider than before, so that the degree of deterioration due to heat or foreign matter can be
reduced. As described above, according to the present invention, an analog system suitable for
forming a static area with a reduced noise level in at least a specific narrow angle range with an
inexpensive configuration in which one noise detection means and one speaker are addressed to
each one. Noise reduction device can be provided.
[0030]
Brief description of the drawings
[0031]
1 is a block diagram of the noise reduction device of the first embodiment of the present
invention.
[0032]
2 is an explanatory view of a method of determining the position of the noise detection means.
[0033]
3 is an explanatory view of a method of determining the position of the speaker.
[0034]
4 is a measurement diagram of the noise level.
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[0035]
5 is a block diagram of the noise reduction device of the second embodiment of the present
invention.
[0036]
Explanation of sign
[0037]
DESCRIPTION OF SYMBOLS 1 Case 2 engine (noise source) 6, 23 noise detection means 7, 25
speaker 8, 26 power amplifier 21 noise source 22 partition
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