JP5818575B2 - Standing wave noise reduction method - Google Patents

Description

  The present invention relates to a standing wave noise reduction method for reducing a noise standing wave generated based on noise emitted from a noise source by using an active silencer unit.

  Today, wind power generators are attracting attention for the purpose of effectively using natural energy. However, since the installation location is limited by weather conditions, for example, a hilly area near a general house is also a target of the installation location. However, the wind power generation apparatus has a problem of noise, in particular, a problem that disturbs sleep at night by neighboring residents due to low frequency noise. Since this low-frequency noise continues in the wind turbine generator, some residents have to move with the installation of the wind turbine generator.

  A wind turbine noise reduction system that reduces the noise of a wind turbine generator is described in Patent Document 1. The system includes a nacelle to which a plurality of wings that rotate under the force of wind are attached, and a columnar tower that supports the wings and the nacelle, and the rotation axis direction of the wings is determined according to the direction of the wind. In order to reduce the noise from the wind power generator to be changed, a speaker arranged outside the wing to emit control sound, and arranged outside the wing and corresponding to the speaker at a position on the wing side from the speaker And a microphone that outputs an acoustic signal corresponding to the noise collected from the wind power generator or the device, and a reduction signal for reducing the noise from the acoustic signal to the speaker according to the rotational axis direction of the wing. The generating unit includes a generating unit and an input unit that inputs a reduction signal generated by the generating unit to a speaker. A control sound is emitted from the speaker by inputting the reduction signal to the speaker. Thereby, noise can be reduced by active control. However, with active silencing systems, it is difficult to significantly reduce noise in large open spaces that are well-winded and not sufficient to convince residents affected by low-frequency noise. is there.

  In particular, when low-frequency noise enters a house, a standing wave may be generated in a room partitioned in the house. The noise reduction of this low-frequency standing wave is more difficult for active noise reduction than the noise reduction in the pipeline. Patent Document 2 describes a silencing unit that silences such a difficult low-frequency standing wave in a closed space. This silencer unit silences mechanical noise emitted from the noise source device.It surrounds the noise source device, and the horizontal distance from the noise source position is in front, back, left, and right. Equally, a sound-absorbing wall standing in parallel with each other and a control sound whose phase is inverted by 180 degrees with respect to a standing wave generated by reflection of the noise on the sound-absorbing wall are emitted. Further, the horizontal distance between the front and rear, left and right from the sound source position of the control sound to the sound deadening wall and the horizontal distance between the front and rear, left and right from the sound source position of the noise to the noise deadening wall are equal to each other. A muffler is disposed in the space. In this silencing unit, noise is prevented from spreading to the surroundings by setting up a silencing wall that is parallel to the front, back, left, and right of the device that is a noise source. Further, by surrounding the noise source device in front, back, left, and right with a noise reduction wall, a noise reduction device that emits a control sound whose phase is inverted by 180 degrees with respect to a standing wave generated by reflection of noise on the noise reduction wall is provided. By arranging it in the space surrounded by the sound deadening wall so that the horizontal distance of each of the front and rear left and right from the sound source position to the sound deadening wall is equal to the horizontal distance of each front and rear left and right from the sound source position of the noise to the noise deadening wall, The standing wave and the control sound are matched in phase to mute the standing wave. However, in this silencer unit, a noise source device is first surrounded by a silencer wall, and an active silencer device is placed in it, and it comes from a noise source outside the house and is generated in the room of the house. It is difficult to apply to the reduction of standing noise.

  Furthermore, in Technical Document 3, in order to reduce low-frequency noise of 100 Hz or less, noise generated from a noise generation source is detected by a first noise detection means arranged at a first position, and the first position and Are detected by second noise detection means arranged at different second positions, and are based on first noise information detected by the first noise detection means and second noise information detected by the second noise detection means. An active silencer technique is described in which a control sound is generated from a secondary sound source and silenced at least at the second position. In this technique, for noise generated from the noise generation source in a three-dimensional open space, a first step for obtaining a high sound pressure level frequency that is a high sound pressure level in a low frequency region, and a high sound obtained in the first step. With respect to the sound of the pressure level frequency, the acoustic state when the sound of the high sound pressure level frequency is generated from the noise generation source in the three-dimensional closed space with the noise generation source arranged is obtained by wave acoustic analysis. Performing the second step, and in the obtained acoustic state of the three-dimensional closed space, a position where the sound pressure level of the three-dimensional closed space is higher than the average sound pressure level in the space at the abdomen of the standing wave It is set as the 2nd position which arranges a secondary sound source or the 2nd noise detection means. However, this active noise reduction technology is also intended for a space having a noise source inside, and it is difficult to apply it to the reduction of standing wave noise generated in the room of a house due to noise entering from outside. is there.

JP 2010-216309 A (paragraph number [0008-0012], FIG. 1) JP 2011-43585 A (paragraph number [0006-0019], FIG. 1) JP 2011-107673 A (paragraph number [0001-0021], FIGS. 1 and 2)

  In view of the above circumstances, an object of the present invention is to provide a standing wave noise reduction technique for reducing a noise standing wave generated in a house based on noise emitted from an external noise source using an active silencer unit. Is to provide.

In order to reduce the noise standing wave generated in the room of the house based on the noise emitted from the noise source using the active silencer unit, the standing wave noise reducing method according to the present invention is:
Obtaining a loud volume position as a basic position from a rough planar distribution measurement in which noise volume measurement in the room is performed around the interior of the room; calculating a main frequency of the high volume noise; and wavelength of the main frequency Setting a measurement grid point with the basic position as a base point with 1/4 or 1/8 of the unit length as a unit length, and a plane volume indicating a volume value at the measurement grid point through volume measurement at the measurement grid point A step of obtaining a distribution, a step of calculating the measurement grid point indicating the maximum volume from the planar volume distribution as a maximum volume point, and a speaker that emits a control sound for silencing the active silencer unit at the maximum volume point a step, a step of calculating a specific loudness point measurement points shown near ion amount in the maximum volume at average volume or more of the measurement grid points, the specific Comprising a step of arranging the noise detecting microphone of the active silencer unit amount point.

In this method, a position where an antinode of a standing wave generated in a room is likely to exist, that is, a position where the volume is larger than other positions is estimated through rough planar coarse distribution measurement, and the position is set as a basic position. By setting a measurement grid with 1/4 or 1/8 of the wavelength of the noise main frequency at this basic position as a unit length, two or more measurement points in the abdominal region are effectively included in this measurement grid point. Can be included. Therefore, since the maximum volume in the planar volume distribution generated from the measurement results at all measurement grid points is estimated to be the antinode portion of the noise standing wave, a speaker is arranged at the measurement grid point indicating the maximum volume. . Further, a noise detection microphone as a reference microphone is arranged at a measurement point having a volume similar to the maximum volume. This makes it possible for the speaker driven by the mute control signal generated based on the noise detection signal obtained at the antinode of the standing wave to reduce the active noise against the noise standing wave at the antinode of the standing wave. And effective noise reduction can be obtained.

If it is considered that the antinodes of standing waves generated in the room tend to be generated in the corner of the room (including the contact portion between the floor and the vertical wall surface), the planar coarse distribution measurement is performed inside the room. It is effective to be performed for the surroundings .

As the unit length of the measurement grid is shorter, a more precise planar sound volume distribution can be generated, but the processing burden increases. Considering that the standing wave has a form like a sine wave, in order to obtain a good plane volume distribution, the unit length is 1 / n of the wavelength of the main frequency (n is 4 or more). It is effective to be an integer). Considering that the measurement work is performed by a human and the room size of a general house is taken into consideration, it is preferable to set 1/4 or 1/8 of the wavelength of the main frequency as the unit length of the measurement grating.

  In order to perform active mute control accurately, it is preferable to incorporate feedback control, particularly adaptive control. Accordingly, in one preferred embodiment of the present invention, the evaluation microphone of the active silencer unit is arranged at a specific volume point other than the specific volume point where the noise detection microphone is arranged. This evaluation microphone is used as a so-called error microphone.

It is a schematic diagram illustrating the setup process of the active silencer unit according to the present invention. It is a sound pressure distribution diagram showing a sound pressure measurement result in a room, (a) shows a sound pressure distribution table showing sound pressure values at measurement grid points, and (b) shows a sound pressure distribution. A sound pressure distribution diagram is shown in which is smoothed. It is a functional block diagram of an active silencer unit according to the present invention. It is a diagram which shows an example of the frequency characteristic of noise. It is a diagram which shows an example of the frequency characteristic of the sound pressure measurement data in the room where the standing wave has generate | occur | produced. It is a diagram which shows an example of the frequency characteristic of the sound pressure measurement data in the room where the standing wave has generate | occur | produced.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. First, a method for reducing a low-frequency standing wave (hereinafter simply referred to as a standing wave) generated in one room in a house that receives noise from a wind power plant or the like as a noise source will be described. FIG. 1 illustrates the setup process of an active silencer unit for reducing noise standing waves generated in a substantially rectangular room.

First, the noise volume around the interior of the room that is the target of standing wave noise reduction is measured. Here, sound pressure is measured at each corner position in this room (# 01). In FIG. 1, four corner positions indicated by Pa, Pb, Pc, and Pd are measurement points for sound pressure measurement. Here, since the measured noise volume is represented by sound pressure, the volume and the sound pressure are used with substantially the same meaning.
From the measurement result at each measurement point, the position indicating the maximum volume is set as the basic position (# 02). In FIG. 1, since the measurement position: Pc indicates the maximum sound pressure (dB), the basic position is Pc.
Next, the temporal measurement data (sound pressure variation data) of the sound pressure at the basic position Pc is subjected to Fourier transform processing to calculate its frequency characteristic, and the frequency band indicating the maximum sound pressure is calculated as the main frequency (# 03). In FIG. 1, 60 Hz is the main frequency.
The base position determined in step # 02 is used as a base point, and it is 1/4 or less of the wavelength of the main frequency, preferably 1 / n of the wavelength of the main frequency (n is an integer of 4 or more). A measurement lattice point is set with 1/8 of the wavelength as a unit length (# 04). If the speed of sound is 340 m / s, the unit length is
340 ÷ 60 ÷ 8 = 0 .71 (m)
It becomes. Therefore, 0 .71 (m) square measuring grating is set in the room.
Next, the sound pressure is measured at the set lattice point (measurement lattice point) of the measurement lattice to obtain a plane sound pressure distribution (# 05). FIG. 2A shows a sound pressure distribution table showing the sound pressure values at the measurement grid points, and FIG. 2B shows a sound pressure distribution chart in which the sound pressure distribution is smoothed. It is shown. From the two sound pressure distributions in FIG. 2, it can be seen that a region with low sound pressure is generated so as to cut through the center of the room, and regions with high sound pressure are generated at both left and right ends. Thereby, it can be estimated that a standing wave of 60 Hz is generated in the direction crossing the room (the horizontal direction in the drawing) (# 06).

In the above process, a standing wave of 60 Hz has been generated in this room, and the approximate positions of the antinodes and nodes of the standing wave have been confirmed. Reduce the standing wave used.
First, the measurement point indicating the maximum volume in the planar sound pressure distribution (see FIG. 2) obtained in step # 05 is set as the maximum volume point, and the active silencer unit is configured to emit the mute control sound toward the maximum volume point. A speaker is arranged (# 07). Here, the measurement point: Pc, which is also the basic position, is set as the maximum volume point, and the speaker is arranged so that the mute control sound is sent out here.
Further, a measurement point that is equal to or higher than the average volume of the measurement grid point and that is close to the maximum volume is set as a specific volume point, and a noise detection microphone (reference microphone) of the active silencer unit is disposed at the specific volume point. Here, measurement points: Pa and Pd are set as one or more specific volume points. A noise detection microphone is arranged at one measurement point: Pa. If the active silencer unit is an adaptive control type feedback control type, an evaluation microphone (error microphone) for noise reduction evaluation is arranged at the measurement point Pd (# 08). These noise detection microphones and evaluation microphones are preferably non-directional.

  When the active silencer unit is set up, the noise reduction operation of the well-known active silencer unit is executed, and the standing wave is canceled by canceling the antinode of the standing wave with the wave of the opposite phase from the speaker. Reduce sound pressure.

An example of the active silencer unit used in the standing wave noise reduction method according to the present invention will be described with reference to the functional block diagram of FIG.
The active silencer unit 1 includes a sound pressure measurement module 10 and an active silencer control module 20. As described with reference to FIG. 1, the sound pressure measurement module 10 performs sound pressure measurement of noise in a room and frequency analysis of noise, and planar sound pressure distribution for confirming the generation of a noise standing wave in the room. Is generated. The active mute control module 20 detects noise generated by a noise source with a microphone, and emits sound having a phase opposite to that of the detection signal from the speaker to reduce noise.

  The sound pressure measurement module 10 includes a sound pressure calculation unit 11, an FFT calculation unit 12, and a data visualization unit 13. The sound pressure calculation unit 11 calculates the sound pressure from the noise detection signal of the noise detection microphone 2. The FFT operation unit 12 calculates the frequency characteristics of noise from the temporal variation of the noise detection signal using a fast Fourier transform (FFT) algorithm. The sound pressure calculation unit 11 also has a function of calculating a sound pressure limited to the main frequency band obtained based on the frequency characteristic calculated by the FFT calculation unit 12. The data visualization unit 13 is a plane sound pressure distribution diagram or a three-dimensional sound pressure distribution diagram based on a sound pressure signal at a two-dimensional measurement point or a three-dimensional measurement point obtained from the sound pressure calculation unit 11, and an FFT calculation unit. A frequency characteristic diagram showing the frequency characteristic calculated in 12 is created. The data visualization data generated by the data visualization unit 13 can be printed out by the printer 14 and can be displayed on the monitor 15.

  The active silence control module 20 includes a preprocessing unit 21 including a preamplifier and an A / D converter, a noise control filter unit 22, a low-pass filter 23, and a driving unit 24 including a D / A converter and an amplifier. The preprocessing unit 21 processes and outputs the detection signal of the noise detection microphone 2 used in cooperation with the sound pressure measurement module 10 in a form suitable for subsequent processing. That is, in the active mute control module 20, the noise detection microphone 2 is used as a reference microphone. The noise control filter unit 22 generates a control waveform having a phase opposite to that of the noise waveform (standing wave waveform) based on the detection signal from the noise detection microphone 2 so that the volume of the noise detected by the noise detection microphone 2 is reduced. The control signal shown is generated. The drive unit 24 drives the speaker 3 based on the control signal from the noise control filter unit 22, and outputs a control waveform that cancels out the noise waveform from the speaker 3. Since the muffling target is a low-frequency standing wave, when a high frequency is output from the speaker 3, there is a possibility that the noise will increase conversely. In order to avoid this, the noise control filter unit 22, the drive unit 24, A low-pass filter 23 is interposed between the two.

  This active silencing control module 20 can be configured to output a control waveform from a speaker simply by feedforward control. In this embodiment, in order to obtain a more accurate silencing effect, Adaptive control using feedback is adopted. Accordingly, the evaluation microphone 4 functioning as an error microphone is prepared, and the active silencing control module 20 performs an inverse filter calculation for adjusting the filter coefficient of the noise control filter unit 22 based on the evaluation noise signal from the evaluation microphone 4. Part 25 is included.

  The acoustic model used in the adaptive control of the active silencer control module 20 includes a primary path from the noise detection microphone (reference microphone) 2 to the evaluation microphone (error microphone) 4 and the speaker (silenced sound source) 3 to the evaluation microphone (error microphone). ) Modeled with a transfer function by a secondary path to 4 and a feedback path from the speaker (silenced sound source) 3 to the noise detection microphone (reference microphone) 2. As a detailed description of such mute adaptive control, reference can be made to JP 2011-107673 A by the same applicant.

  The active silencing unit 1 of the present invention is a target for silencing low-frequency standing waves, but the position of a noise detection microphone (reference microphone) 2, the position of a speaker (silenced sound source) 3, and an evaluation microphone (error microphone) 4. It has been experimentally confirmed that when a standing wave node is present at the position of, the error signal cannot be sufficiently detected and sufficient silencing cannot be performed. For this reason, it is important to arrange the noise detection microphone 2, the speaker 3, and the evaluation microphone 4 while avoiding standing wave nodes.

A specific procedure for disposing the noise detection microphone 2, the speaker 3, and the evaluation microphone 4 while avoiding the standing wave node generated in the room is as follows. The room shape is a simple rectangle.
(1) In the corner area of the room, the sound pressure of the noise is measured using a position that is about 10 to 30 cm away from the floor or wall as a measurement point.
(2) The main frequency governing the noise is determined from the frequency characteristic calculated from the measurement data. Here, the main frequency is assumed to be 60 Hz.
(3) Starting from the measurement point at which the highest sound pressure was measured, 10/8 above the floor as a unit length (grid length) of 1/8 (0.7 m) of the wavelength of the main frequency in this room. A plane grid is set at a distance of 30 cm.
(4) Similarly, a vertical grating is set above the planar grating with the unit length (grating height) being 1/8 (0.7 m) of the wavelength of the main frequency.
(5) A three-dimensional grid is set in this room based on the plane grid and the vertical grid, and the sound pressure of noise is measured using the grid point (lattice intersection) as a measurement point.
(6) Generate a plurality of planar sound pressure distributions by height, that is, a three-dimensional sound pressure distribution, from the sound pressure measurement results.
(7) From the generated three-dimensional sound distribution, assuming the form of standing waves existing in the room, the antinode region and the nodal region are determined.
(8) The noise detection microphone 2, the speaker 3, and the evaluation microphone 4 are arranged in the determined abdominal region, and the active silencing control module 20 is operated.
Note that a three-dimensional sound pressure distribution is generated by a plurality of plane sound pressure distributions by height, but it is also possible to assume a standing wave form that exists in a room with only one plane sound pressure distribution of a specific height. In the present invention, it is only necessary to generate a plane sound pressure distribution having at least one specific height.

  The generation of standing waves depends on the shape of the room, the sound absorption coefficient of the wall that bounds the room, and other acoustic characteristics. Therefore, it is necessary to determine whether a standing wave that causes noise that cannot be ignored is generated for each room. FIG. 4 shows the frequency characteristics of a noise source having a main frequency of 60 Hz. FIG. 5 shows the frequency characteristics of noise measured in the room A when the noise sound source of FIG. 4 is placed outside. FIG. 6 shows frequency characteristics of noise measured in the room B when the noise sound source of FIG. 4 is placed outside. From FIG. 5, it can be assumed that the sound pressure is increased in the 60 Hz band in the room A, and a standing wave resonating with the room space is generated in the 60 Hz band. Conversely, from FIG. 6, the sound pressure in the room B is relatively low in the 60 Hz band, and there is no frequency band that protrudes and shows a high sound pressure. It can be assumed that it has not occurred.

As described above, the possibility of standing waves varies depending on the acoustic characteristics of the room. It is necessary to investigate and mute the noise. For the inspection of the occurrence state of the low-frequency standing wave for each room, the above-described method for generating the three-dimensional sound pressure distribution or the planar sound pressure distribution from (1) to (6) can be used as it is. . When a three-dimensional sound pressure distribution or a plane sound pressure distribution at a specific frequency in a room of interest is generated, a standing wave to be muffled is generated through evaluation of the high sound pressure region and low sound pressure region in the sound pressure distribution. Determine whether or not. This evaluation is performed in both the spatial domain and the temporal domain. In particular, the determination of whether or not a standing wave is occurring is based on the point that the sound pressure changes greatly with respect to the average sound pressure (antinode) and the sound pressure is almost equal to the average sound pressure. Judgment can be made based on whether or not the remaining zero point (node) is spatially determined.
If a standing wave to be silenced is generated, the noise detection microphone 2, the speaker 3, and the evaluation microphone 4 are arranged at different antinode positions of the standing wave, and active silencing of the standing wave is performed. Do.
[Another embodiment]
(1) In the above embodiment, low-frequency external noise such as wind power generation is taken up as noise and is located outside the house, but the noise source may of course be a facility other than wind power generation. Furthermore, the noise source may be installed in a house, or may be a moving noise source that regularly approaches the house.
(2) The number of speakers 3 is not limited to one, but may be plural. A plurality of evaluation microphones 4 may be used.
(3) Although only such a standing wave noise reduction method is described in the scope of claims at the time of filing as an object of the invention, a standing wave generation confirmation method using the standing wave noise reduction method The standing wave noise reduction device is also included in the present invention.

  The present invention can be applied to the field of active noise reduction technology for confirming the presence of a standing noise wave generated in a room of a house based on noise emitted from a noise source and reducing the noise.

1: Active silencer unit 2: Noise detection microphone 3: Speaker 4: Evaluation microphone 10: Sound pressure measurement module 11: Sound pressure calculator 12: FFT calculator 13: Data visualization unit 20: Active silencer control module 21: Pre-processing unit 22: noise control filter unit 23: low-pass filter 24: drive unit 25: inverse filter calculation unit

Claims (2)

In the standing wave noise reduction method of reducing the noise standing wave generated in the room of the house based on the noise emitted from the noise source using the active silencer unit,
Obtaining a position of a loud volume as a basic position from a plane coarse distribution measurement in which the measurement of the noise volume in the room is performed around the interior of the room ;
Calculating a main frequency of loud noise;
Setting a measurement grid point using the basic position as a base point with a unit length of 1/4 or 1/8 of the wavelength of the main frequency;
Obtaining a planar volume distribution indicating a volume value at the measurement grid point through volume measurement at the measurement grid point ;
Calculating the measurement grid point indicating the maximum volume from the planar volume distribution as a maximum volume point;
Disposing a speaker that emits a control sound for silencing the active silencer unit at the maximum volume point;
Calculating a measurement point indicating a volume close to the maximum volume above the average volume of the measurement grid point as a specific volume point;
Placing a noise detection microphone of the active silencer unit at the specific volume point;
A standing wave noise reduction method comprising: A standing wave noise reduction method according to claim 1 to place the evaluation microphone of the active silencer unit specific loudness point other than the specific loudness point the noise detecting microphone is arranged.