JP2019159210A - Noise-reducing method and device - Google Patents

Abstract

To provide a noise-reducing method and device, effective in reducing noises generated in a closed space.SOLUTION: This invention relates to a noise-reducing method for reducing noises by generating sound waves having an inverse phase of noise to a noise source, from a sound wave-generator 10 arranged at a position where the noises of the noise source can be received. The sound wave-generator 10 includes DSP20 for generating waveforms of the sound wave having the inverse phase based on waveforms of the received noise, wherein the sound waves having the inverse phase, which are substantially synchronized with the sound waves of the noise, are generated from a loudspeaker 18.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a method and apparatus for reducing noise and vibration in an open space, and particularly paying attention to the fact that noise and vibration are waves, and a sound wave (wave) having an opposite phase to a sound wave (wave) that becomes noise (vibration). ) To cancel out the magnitude (amplitude) of the sound wave (wave), thereby reducing the noise (vibration).

  Sound is periodic vibration caused by minute pressure fluctuations through a medium such as air or glass, and is regarded as a kind of wave in physics. Although there are two types of waves, longitudinal waves and transverse waves, sounds that are longitudinal waves are often shown as transverse waves as shown in FIG. 8 in order to facilitate visual understanding. In FIG. 8, the horizontal axis indicates the pitch of the sound (frequency that is the length of the period of the horizontal wave), and the vertical axis indicates the magnitude of the sound (amplitude that is the amplitude of the horizontal wave).

  Noise is what causes discomfort by hearing sounds that should be hard to hear in the human audible range. As described above, the sound has a magnitude and a height, and there is a minimum necessary volume to hear a sound of a certain height. On the numerical values, the loudness (amplitude) of sound is expressed in dB (decibel), the pitch (frequency) of sound is expressed in Hz (hertz), and the human audible range is said to be 20 Hz to 20,000 Hz. FIG. 9 shows the relationship between the frequency and sound pressure in the audible range, and shows that lower sounds are harder to hear. This is also a metaphor that the main cause of noise is low frequency sound, suggesting that reducing low frequency sound will lead to a solution to the noise problem.

Yuichi Hirata, Masahiro Fukumoto, “Reduction of environmental noise using active noise control”, [online], Kochi University of Technology Department of Information Systems Engineering Graduation thesis 2012 [March 6, 2018 search], Internet “http: // www.kochi-tech.ac.jp/library/ron/2011/2011info/1110275.pdf " Hiroki Hashiku, Masahiro Fukumoto, “Noise Reduction Model for Road Noise”, [online], Kochi University of Technology, Graduate School of Informatics 2013 [Search March 6, 2018], Internet “http: / /www.kochi-tech.ac.jp/library/ron/2012/2012info/1130367.pdf "

  Non-Patent Document 1 describes an improved noise canceller that uses a noise removal filter to remove noise in a telephone call and extract only the speaker's sound in an environment where multiple sounds are mixed. ing. The effectiveness of this technology is limited to closed spaces where sounds such as pachinko parsons are likely to resonate, and there is no mention of noise reduction in open spaces such as noise from airplanes and wind power generation.

  Non-Patent Document 2 specifies the problem of a system with multiple input points and control points based on the conventional active noise control, and introduces a single input method that reduces the amount of computation and improves the follow-up performance. Thus, there is described a technology that can eliminate in-vehicle noise caused by running of the vehicle. In this technique, since the noise of the car is generated from the rotation of the tire, an input point can be provided only in the vicinity of the tire and is limited to a closed space inside the car. That is, as in Non-Patent Document 1, its effectiveness is limited to a closed space in the vehicle interior, and no mention is made of reducing noise in an open space such as airplane or wind power generation noise.

  The problem to be solved by the present invention is noise generated indoors and outdoors. There are various examples of noise sources. Noise occurs in various situations such as airplanes, traffic, windmills, and construction sites. From the above, it can be pointed out that low frequency sounds are often generated from large machines. In general, if you live on a daily basis in an environment of about 60 dB or higher, the blood pressure value increases due to the stress caused by noise, which may lead to serious diseases such as heart disease. The sound level of 60 dB is about the volume of a normal conversation voice in the office. Research has shown that as the noise level increases from 60dB to 10dB, the risk of heart disease increases by 3.5%. In addition to heart disease, noise is said to be a source of hearing loss, mental effects (such as depression), and concussion. The following table shows the standard noise level (dB).

In addition, the impact of noise on growing children is significant. Noise causes great damage to the growing brain and affects thought and hearing. As a result, the child's learning ability may be reduced and the quality of the learning environment may be reduced.

  In general, when a noise problem is considered as a physical phenomenon, a wave is emitted from the noise source to an infinitely large space, and in some cases, the noise source itself moves in many cases. "As a result, extinguishing the noise must be difficult in modern physics.

  In particular, the prior art documents (Non-Patent Documents 1 and 2) are designed to eliminate (reduce) noise in a so-called closed space under the assumption that noise spreads only in a finite space. There is no mention of noise reduction in an open space that extends infinitely like the noise generated by large wind turbines.

  In contrast, the inventor of the present invention considered as follows.

  By applying another sound to the noise and mixing (superimposing) the two kinds of sounds, the noise can be reduced. Even though the sound wave has the same amplitude and frequency, there are sound waves that differ only in “phase”. When a sound wave having a phase of -1 is applied to a sound wave having a phase of -1 at a certain point in time, the two sound waves are superimposed (overlapped), and the sound wave disappears (see FIG. 10). Such sound waves having opposite phases of + and − are referred to as opposite-phase sound waves. The inventor considered that the noise problem in the open space can be solved by using the sound wave having the opposite phase, that is, generating the sound having the opposite phase to the noise from the sound wave generator toward the noise generation source. .

  Then, the inventor conducted the following pseudo experiments 1 and 2 for verifying that the noise in the open space is reduced by superimposing the sound wave of the noise and the sound wave having a different “phase” from the sound wave. .

[Experimental Example 1]
That is, the noise of an aircraft just before landing near Narita Airport is recorded directly under the route, and the recorded sound is taken as the sound source 1 and, as shown in FIG. The recording was played at the same time. By reversing the connection between the speakers 4 and 6 and the amplifier 2, noise whose phase is reversed can be simultaneously output from one sound source 1. Two speakers 4 and 6 are directed in the same direction, and the original positive phase noise flows from one speaker 4 and the reverse phase noise flows from the other speaker 6 adjacent to each other. The noise reduction method was simulated. As a result, the noise from the speakers 4 and 6 overlapped, reducing the noise.

[Experiment 2]
In addition, an experiment was conducted in which a ventilation fan was regarded as a wind turbine for wind power generation, and a person listened to music wearing noise-cancelling headphones.

  Noise-canceling headphones create an anti-phase sound that cancels the noise from the external noise caught by the built-in microphone, and this anti-phase sound is played through the headphones along with the music sound, so that the music with no noise has disappeared. Only headphones that can be heard.

  In Experimental Example 2, it was confirmed that the noise generated by the motor and the fan of the ventilation fan, which is noise, is reduced and the music can be heard clearly only by a person wearing the noise canceling headphones.

  Needless to say, if the objective is not to eliminate the noise but to reduce the noise, the possibility of “solving” increases from the viewpoint of “solving” the physical problem. Furthermore, in order to have a noise reduction effect even in an infinitely wide space, infrastructure such as roads and buildings in the vicinity of the place where the noise source exists is used. For example, if the noise source is a moving body, the noise is reduced. This can be dealt with by installing a large number of anti-phase wave generators for reduction in the form of lines and planes (spots) with a predetermined interval along the moving path of the moving body set in advance.

  That is, when the noise source moves like an aircraft, if the route is fixed to a certain extent, the noise is generated in sequence from the anti-phase wave generator so as to follow the movement of the noise source. By doing so, noise can be reduced.

  The more complex the sound wave, the longer it takes to analyze it with the DSP and convert it into an electrical signal. Therefore, the object of the present invention is to reduce the analysis time and increase the noise reduction effect by limiting the noise source to aircraft and windmills.

  Furthermore, by reducing or reducing noise and vibration indoors and outdoors, if you can reduce the noise level (dB) even when you are outside a soundproof building, or if you can almost completely cancel the noise in the future, Therefore, it was thought that it would lead to the reduction of construction costs and noise damage for soundproofing equipment.

  The present invention has been made on the basis of the above-mentioned knowledge of the inventor, and an object thereof is to provide a noise reduction method and apparatus effective for reducing noise generated in an open space.

In order to achieve the above object, in the noise reduction method according to claim 1, a predetermined position where the first sound wave can be received with respect to the first sound wave that is noise generated from the first sound source that is a noise source. A second sound wave having a phase opposite to that of the first sound wave is generated toward the first sound source from a sound wave generator as a second sound source provided in the first sound source, and the amplitude of the first sound wave that becomes noise is reduced. A noise reduction method,
The sound wave generating device generates the waveform of the second sound wave having the same amplitude and frequency as the waveform of the first sound wave and having a reverse phase in which the phase is positive / negative inversion from the waveform of the first sound wave received. And a digital signal professor that generates the second sound wave that is substantially synchronized with the first sound wave.

The noise reduction device according to claim 2 is constituted by a sound wave generator as a second sound source provided at a predetermined position capable of receiving a first sound wave generated from the first sound source as a noise source, A noise reduction device that generates a second sound wave having a phase opposite to that of the first sound wave from the sound wave generation device toward the first sound source, and reduces an amplitude of the first sound wave that becomes noise,
The sound wave generating device generates the waveform of the second sound wave having the same amplitude and frequency as the waveform of the first sound wave and having a reverse phase in which the phase is positive / negative inversion from the waveform of the first sound wave received. And a digital signal professor that generates the second sound wave that is substantially synchronized with the first sound wave.

  (Operation) The first sound wave that overlaps the first sound wave that becomes noise and the second sound wave generated by the sound wave generator (the first sound wave and the sound wave having the same amplitude and frequency and opposite phase). Therefore, it is possible to reduce noise in an area where noise disturbance occurs around the noise source (hereinafter referred to as noise generation area).

  According to a third aspect of the present invention, in the noise reduction device according to the second aspect, the sound wave generator is configured to operate only when the amplitude of the received first sound wave is equal to or greater than a predetermined value that causes noise. May be.

  (Operation) Since the second sound wave generated from the sound wave generator has the same amplitude and frequency as the first sound wave, the second sound wave itself can also become noise, but the first sound source that is a noise source The sound wave generator does not operate except when the first sound wave generated from the sound becomes noise (when the noise level of the first sound wave is high), that is, the noise due to the second sound wave does not cause a problem.

According to a fourth aspect of the present invention, in the noise reduction device according to the third aspect, the first sound source that is a noise source is a moving body that moves along a predetermined movement path that is set in advance.
A plurality of the sound wave generators may be arranged at predetermined intervals along the movement path, and may be configured to sequentially operate following the movement of the first sound source.

  (Operation) With the movement of the noise source (first sound source), the noise generation area also moves along a predetermined movement path, but the noise source (first sound source) follows the movement of the noise source (first sound source). The sound wave generators arranged along the movement path of the first sound source operate sequentially. That is, since the second sound wave generation area moves following the movement of the noise generation area, noise in the noise generation area can be reliably reduced.

  In addition, since the noise generation area and the second sound wave generation area coincide with each other, the noise due to the second sound wave does not become a problem outside the noise generation area.

  Further, according to claim 5, in the noise reduction device according to claim 4, the first sound source that is a noise source is an aircraft, and the predetermined movement route is an intrusion route to the airport or from the airport. A plurality of the sound wave generators may be arranged at predetermined intervals along at least a length direction of the flight area in a flight area having a predetermined width and a predetermined length set on the ground corresponding to the intrusion route. .

  (Operation) The noise generation area moves in the flight area on the ground with the movement of the aircraft, and the sound wave generator arranged along the flight area follows the movement of the aircraft (movement of the noise generation area). Operates sequentially. That is, since the second sound wave generation area moves following the movement of the noise generation area, noise in the noise generation area can be reliably reduced.

  By arranging the sound wave generators at predetermined intervals along both outer sides in the width direction of the flight area, it is possible to cope with the noise of the aircraft moving in the flight area. However, since the width of the flight area is quite large, the actual intrusion route and the intrusion route of the aircraft may be greatly shifted in the width direction within the flight area. For this reason, if a plurality of sound wave generators are arranged at predetermined intervals also in the width direction of the flight area, the noise in the noise generation area can be reliably ensured even when the aircraft moves greatly in the width direction within the flight area. Can be reduced.

  According to a sixth aspect of the present invention, in the noise reduction device according to the second aspect, the first sound source as a noise source is a large windmill for wind power generation, and at least one of the sound wave generators is connected to the large windmill. You may arrange | position so that it may oppose.

  (Operation) One sound wave generator may be used. However, if a plurality of sound wave generators are arranged at equal intervals in the circumferential direction so as to surround the first sound source as a noise source, the effect of reducing noise (low frequency sound) is further increased. Go up.

  According to the noise reduction method and apparatus according to the present invention, the noise generated in the open space (first sound wave) is the same as the second sound wave generated in the sound wave generator (the first sound wave has the same amplitude and frequency). Since the amplitude of the noise (first sound wave) is reduced by superimposing the sound waves having opposite phases, the noise in the noise generation area can be reliably reduced.

It is a figure which shows the structure of the sound wave generator which is the principal part of the noise reduction apparatus which concerns on 1st Embodiment of this invention. It is a top view explaining the whole noise reduction apparatus. It is explanatory drawing explaining a mode that a predetermined sound wave generator operates following the movement of the aircraft which is a noise source. It is explanatory drawing explaining a mode that a predetermined sound wave generator operates following the movement of the aircraft which is a noise source. It is explanatory drawing explaining a mode that a predetermined sound wave generator operates following the movement of the aircraft which is a noise source. It is a figure which shows the noise reduction apparatus which concerns on 2nd Embodiment of this invention. It is a figure which shows the modification of the noise reduction apparatus which concerns on the 2nd Embodiment. It is a figure which shows the waveform of a sound as a transverse wave. It is a figure which shows a human audible range. It is a figure explaining that a pair of sound waves of a normal phase and an antiphase overlap and cancel each other. It is a figure which shows the experiment example which verifies that the noise (sound wave) of a positive phase and an antiphase cancels and noise reduces.

  1 and 2 show a first embodiment in which the noise reduction device according to the present invention is applied to noise reduction of an aircraft, and FIG. 1 is a diagram showing the configuration of a sound wave generator constituting the noise reduction device. Is a plan view of the entire noise reduction device provided in the flight area set on the ground corresponding to the route of the aircraft entering the airport, and FIGS. 3, 4 and 5 follow the movement of the noise source aircraft It is explanatory drawing explaining a mode that a predetermined sound wave generator operates.

  1 and 2, reference numeral 10 denotes a sound wave generator that constitutes a noise reduction device, and is arranged at a predetermined position where noise reaches the noise source.

  The sound wave generator 10 includes a microphone 12, an automatic switch 14, an A / D converter 16A, a DSP (Digital Signal Processor) 20, a D / A converter 16B, an amplifier 17, and a speaker 18. These are built in or attached to the main body case 11, and both the microphone 12 that picks up noise that is external sound and the speaker 18 that emits sound toward the outside can adjust the direction of the main body case 11. Note that the microphone 12 and the speaker 18 may be separated from the main body case 11 and installed at a predetermined position as necessary.

  An external sound (sound wave) S1, which is an analog signal, is always input to the automatic switch 14 via the microphone 12. The automatic switch 14 determines whether or not the amplitude of the sound wave that is the input signal is equal to or greater than a predetermined value (for example, 80 db). For example, the sound wave generator 10 has a function of holding the operation stopped.

  An A / D converter 16A is provided between the automatic switch 14 and the DSP 20, and the analog signal S1 is converted into a digital signal S2 and input to the DSP 20.

  The DSP 20 has a function of converting the digital signal S2 corresponding to the input sound waveform into the digital signal S3 corresponding to the antiphase sound waveform without changing the amplitude and frequency, that is, the function of inverting only the phase of the sound wave. is there.

  Specifically, the DSP 20 accesses a program memory 22 for storing a program used for data processing, a data memory 24 for storing information to be processed, a program in the program memory 22 and data in the data memory 24, and sets a numerical value. A calculation engine 26 for executing arithmetic processing is provided. The data memory 24 stores a digital signal S2 corresponding to the input sound waveform, which is processing information, and the program memory 22 reverses the digital signal corresponding to the sound waveform without changing the amplitude and frequency. A program for converting into a digital signal corresponding to the phase sound waveform, that is, inverting only the phase of the sound waveform is stored. Then, the calculation engine 26 accesses the program in the program memory 22 and the data in the data memory 24, and supports the digital signal S2 corresponding to the sound waveform to the sound waveform of the opposite phase without changing the amplitude and frequency. Is converted into a digital signal S3, that is, a numerical calculation process for inverting only the phase of the sound waveform is executed.

  In particular, several methods are conceivable as a program for inverting only the phase of a sound waveform, but with a simple arithmetic processing that applies "-1" to processing information (digital signal corresponding to the input sound waveform), When a program that can be converted into a digital signal corresponding to a waveform of a sound whose phase is inverted is used, the calculation processing speed is dramatically increased, and the cost of the DSP 20 is reduced because the built-in program is less expensive. .

  The digital signal S3 that is the output of the DSP is converted into an analog signal (sound wave) S4 by the D / A converter 16B, amplified by the amplifier 17, and as a sound (sound wave) having a phase opposite to that of the external sound (sound wave) picked up by the microphone 12. Are emitted from the speaker 18.

  That is, when the aircraft approaches the sound wave generation device 10 and the noise of the aircraft becomes a predetermined value or more (the amplitude of the sound wave constituting the noise is a predetermined value or more), the sound from the sound wave generation device 10 is in a phase opposite to the noise of the aircraft (sound wave ) Is generated, and when the aircraft moves away and the noise of the aircraft becomes less than a predetermined value (the amplitude of the sound waves constituting the noise is less than the predetermined value), the phase of the noise from the generated sound generator 10 is opposite to that of the aircraft Generation of sound (sound wave) is stopped.

  In this way, every time the aircraft passes over the sound wave generator 10, the sound wave generator 10 repeatedly generates a sound (sound wave) having a phase opposite to that of the aircraft.

  In FIG. 2, symbol A is a flight area of a predetermined width and a predetermined length set on the ground corresponding to the route of entry of the aircraft into the airport, and the airport runway (not shown) in the right direction in FIG. ) Shows a state in which the aircraft P enters (moves). A white arrow indicates the moving aircraft P. Symbol a is a noise generation area where the noise of the aircraft P that is a noise source reaches, and the noise generation area a moves together with the aircraft P.

  Near the outside in the width direction in the flight area A, the sound wave generators 10 as noise reduction devices are arranged at equal intervals (for example, at an interval of 500 m) along the longitudinal direction of the flight area A. Further, the sound wave generators 10 are arranged at regular intervals (for example, at an interval of 500 m) along the longitudinal direction of the flight area A at a substantially central position in the width direction of the flight area A, and the sound waves generated in the flight area A are generated. The intervals between the devices 10 are set to be substantially equal.

  In particular, when the aircraft P, which is a noise source, moves in the flight area A, even if the actual intrusion route of the aircraft P greatly deviates in the width direction in the flight area A, any one of the sound wave generators 10 generates noise. The distribution of the sound wave generator 10 in the flight area A is adjusted so as to be within the generation area a.

  Next, with reference to FIGS. 2, 3, 4, and 5, an operation for reducing noise generated when the sound wave generator 10 operates and the aircraft P moves in the flight area A will be described.

  In FIG. 2, reference signs P1, P2, and P3 indicate an aircraft P that is a moving noise source. Reference numerals a1, a2 and a3 indicate a noise generation area a formed around the aircraft P which is a moving noise source. 3, 4, and 5, a large number of sound wave generators 10 are arranged along the flight area A, and the sound wave generators 10 that are in the noise generation area a sequentially follow the movement of the aircraft P to generate sound waves. It is a figure which shows a mode that it takes out. 3, 4, and 5, the sound wave generator 10 is installed near a traffic signal in the town, and the microphone 12 is installed on the traffic signal.

  First, when the noise source (aircraft P) moves and the predetermined sound wave generator 10 is in the first noise generation area a1, as shown in FIGS. 2 and 3, the automatic switch 14 operates the sound wave generator 10. Make it possible. Then, the sound wave generator 10 generates a sound wave having an opposite phase from the noise (sound wave) of the aircraft P received via the microphone 12 and having the phase inverted, and the sound P has the same amplitude and frequency as the noise of the aircraft P. A phase sound (sound wave) is generated via the peaker 18 toward the sky (aircraft P1). In FIGS. 2 and 3, sound (sound waves) having a phase opposite to that of the aircraft P1 is generated from the two sound wave generators 10a1 and 10b1 in the noise generation area a1, and the noise of the aircraft P1 in the noise generation area a1 is generated. Is reduced. The sound wave generators 10a1 and 10b1 are in an operation stop state when the sound wave generators 10a1 and 10b1 are outside the noise generation area a1, so that the sound (sound wave) emitted from the sound wave generators 10a1 and 10b1 does not become noise.

  Next, when the noise source (aircraft P) further moves and the predetermined sound wave generator 10 is in the second and third noise generation areas a2 and a3 as shown in FIGS. Each automatic switch 14 makes the sound wave generator 10 operable. Then, as described above, the sound wave generator 10 generates sound waves having opposite phases from the noises (sound waves) of the aircrafts P2 and P3 received via the microphone 12, and the noises of the aircraft P are detected. A sound (sound wave) having the same amplitude and frequency and opposite phase is generated through the speaker 18 toward the sky (aircraft P). That is, in FIGS. 2 and 4, three sound wave generators 10a3, 10b2 and 10b3 in the noise generation area a2 are used, and in FIG. 2 and 5, three sound wave generators 10a5 and 10b4 in the noise generation area a3 are used. , 10b5 generate sounds (sound waves) having opposite phases to the noises of the aircrafts P2 and P3, respectively, and reduce the noises of the aircrafts P2 and P3 in the noise generation areas a2 and a3, respectively.

  In addition, since the automatic switch 14 detects the sound generation device 10 when it is outside the noise generation areas a1, a2, and a3, and the operation is stopped, the sound generation device 10 is outside the noise generation areas a1, a2, and a3. A certain sound wave generator 10 does not emit sound (sound wave) and does not generate noise.

  In this manner, noise from the aircraft P can be reliably reduced in the flight area A where noise disturbance is regarded as a problem.

  In the above-described embodiment, the noise reduction device according to the present invention is applied to reduce noise generated in the flight area set on the ground corresponding to the route of entry of the aircraft into the airport. You may apply to the reduction of the noise which generate | occur | produces in the flight area set on the ground corresponding to the invasion route from.

Further, when the flight route of the aircraft is determined in advance, it may be applied to the reduction of noise generated in a predetermined flight area set on the ground corresponding to the predetermined flight route.
Furthermore, the present invention can also be applied to a case where the noise source is not an aircraft but an automobile traveling on a highway or a Shinkansen vehicle traveling on a track.
For example, sound barriers for reducing noise disturbance to the surroundings are provided on both sides of a highway or a Shinkansen track so as to face a predetermined length along the road or the track. A plurality of sound wave generators 10, which are noise reduction devices, are arranged at predetermined intervals along the highway or the track on a soundproof wall provided so as to sandwich the highway or the track. Since the structure of the sound wave generator 10 is the same as the structure of the sound wave generator 10 constituting the vibration reducing apparatus of the first embodiment described above, a duplicate description thereof is omitted.
In a region where the noise exceeds a predetermined level, the sound wave generator 10 operates to generate a sound wave that cancels out the sound wave of the noise. To reduce. Since noise barriers are provided, the noise reduction effect around highways and Shinkansen tracks is high.
In addition, even in a place where no sound barrier is provided on the expressway or the Shinkansen track, the sound wave generator 10 that is a noise reduction device is placed at a predetermined interval along the expressway or the track so as to sandwich the expressway or the track. By arranging a plurality of vehicles in the vehicle, noise from automobiles traveling on highways and Shinkansen vehicles traveling on tracks can be reduced.

  6 and 7 are noise reduction devices according to the second embodiment of the present invention, which are devices for reducing the sound (low frequency sound) generated by the wind turbine (large wind turbine) 30 for wind power generation.

  FIG. 6 shows that two sound wave generators 10 are arranged so as to face the windmill 30, and FIG. 7 shows that six sound wave generators 10 are arranged at equal intervals in the circumferential direction so as to surround the windmill 30. Yes.

  In these drawings, since the structure of the sound wave generator 10 is the same as the structure of the sound wave generator 10 constituting the vibration reducing apparatus of the first embodiment described above, redundant description thereof is omitted.

  In FIG. 6, the two sound wave generators 10 are provided so as to face each other with respect to the windmill 30, but one sound wave generator 10 may be provided so as to face the windmill 30.

  Further, if the plurality of sound wave generators 10 are arranged at equal intervals in the circumferential direction so as to surround the wind turbine 30 that is a noise generation source, the noise (low frequency sound) reduction effect increases as the number increases.

  As countermeasures against the current noise problem, we are trying to reduce the noise by covering it with a soundproof wall indoors and shielding the sound outdoors with forests. However, sound barriers have limited space and the range of sound that can be shielded by forests is limited. Especially when it is cloudy, the noise is reflected by the clouds and the damage is increased. Although many measures for solving the noise problem have been implemented, they have not yet been fundamentally solved. Therefore, the present invention is understood to be a technique that can be widely used to reduce noise indoors and outdoors, particularly outdoor open spaces.

DESCRIPTION OF SYMBOLS 10 Sound wave generator 11 which comprises vibration reduction apparatus Main body case 12 Microphone 14 Automatic switch 14
16A A / D converter 16B D / A converter 17 Amplifier 18 Speaker 20 Digital signal professor 22 Program memory 22
24 Data memory 26 Calculation engine S1, S4 Analog signal S1
S2, S3 Digital signal P (P1, P2, P3) Aircraft 30 as noise source Windmill as noise source

Claims (6)

The first sound wave from the sound wave generator that is the second sound source provided at a predetermined position capable of receiving the first sound wave with respect to the first sound wave that is the noise generated from the first sound source that is the noise source. A noise reduction method for generating a second sound wave having an opposite phase to the first sound source and reducing the amplitude of the first sound wave as noise,
The sound wave generating device generates the waveform of the second sound wave having the same amplitude and frequency as the waveform of the first sound wave and having a reverse phase in which the phase is positive / negative inversion from the waveform of the first sound wave received. A noise reduction method comprising: generating a second sound wave that is substantially synchronized with the first sound wave. A sound wave generator that is a second sound source provided at a predetermined position capable of receiving a first sound wave generated from the first sound source that is a noise source, and has a phase opposite to that of the first sound wave from the sound wave generator. A noise reduction device that generates a second sound wave toward the first sound source and reduces the amplitude of the first sound wave that becomes noise,
The sound wave generating device generates the waveform of the second sound wave having the same amplitude and frequency as the waveform of the first sound wave and having a reverse phase in which the phase is positive / negative inversion from the waveform of the first sound wave received. A noise reduction apparatus comprising: a digital signal professor that generates the second sound wave substantially synchronized with the first sound wave.   The noise reduction device according to claim 2, wherein the sound wave generation device is configured to operate only when the amplitude of the received first sound wave is equal to or greater than a predetermined value that causes noise. The first sound source that is a noise source is a moving body that moves along a predetermined movement path that is set in advance,
4. The sound wave generator according to claim 3, wherein a plurality of the sound wave generators are arranged at predetermined intervals along the movement path, and are sequentially operated following the movement of the first sound source. The noise reduction device described.   The first sound source that is a noise source is an aircraft, and the predetermined movement path is set to a predetermined width and a predetermined length that are set on the ground corresponding to an intrusion path to the airport or an intrusion path from the airport. 5. The noise reduction device according to claim 4, wherein a plurality of the sound wave generation devices are arranged at predetermined intervals along at least a length direction of the flight area.   The first sound source as a noise source is a large windmill for wind power generation, and at least one of the sound wave generators is arranged so as to face the large windmill. Noise reduction device.