JP6199926B2 - Low frequency sound measurement system and wind noise reduction expansion method - Google Patents

Description

The present invention relates to a low-frequency sound measuring unit and wind noise reduction enhancement method for measuring low-frequency noise generated from such wind farms.

  Low frequency sound (less than 100Hz) or very low frequency sound (less than 20Hz) generated from facilities and equipment such as wind power generation facilities and eco-cutes are insensitive to hearing, but may cause insomnia and tinnitus due to human exposure. It has become a big problem in recent years by bringing about health damage. These evaluations and causal investigations require accurate measurements such as low-frequency sounds. Therefore, a low-frequency sound measuring device for measuring low-frequency sound (low-range noise) generated from a wind power generation facility or the like has been proposed.

  The low-frequency sound measuring device, for example, a microphone arranged on a metal disk installed on the ground surface, a low-frequency windshield formed in a substantially hemispherical shape and covering the microphone, and an electric signal generated by the microphone is processed. And a controller that extracts the measurement target sound from which wind noise has been removed.

  As a low-frequency windshield for a microphone, there is one having a main windshield mounted on a microphone and a secondary windshield formed in a substantially hemispherical shape and covering the microphone and the main windshield. A spherical windshield may be used for the main windshield, and a two-layer structure may be used for the secondary windshield. The secondary windshield having a two-layer structure includes, for example, an outer side made of a cloth and an aluminum foil fiber material and an inner side made of an aluminum foil fiber material as the windproof layer. Moreover, as a wind-proof layer, there exist some comprised by combining the fluorine sheet and the thick metal fiber sheet, and one layer.

  In addition, since the measurement is generally performed outdoors and the influence of wind on the microphone, that is, wind noise (wind noise), becomes a problem, it is usually a hemispherical type using a porous material according to JIS C1400-11: 2005. A windshield is used. As a noise measuring device, a noise measuring device that can measure only noise generated by a measurement object without being influenced by external noise has been proposed (see Patent Document 1).

JP 2000-275095 A

  In the conventional low frequency sound measuring device, the wind noise reduction effect on the microphone installed in the windshield is about 20 to 25 dB at most, which is not sufficient.

  Further, the conventional windshield or windscreen has the following problems.

  (1) The effect of reducing wind noise is at most 25 dBA, and is particularly insufficient in the low range. In other words, noise generated from wind power generation equipment is low-frequency sound or very low-frequency sound, so even under strong winds, noise is masked by wind noise, even if a windshield with a low wind noise reduction effect is used. It is impossible to measure and observe small noise in the low frequency range.

  (2) If a large wind noise effect is to be realized at low frequencies only by a physical method, the size of the windshield increases, and handling and portability become very poor. In physical correspondence, the material of the windbreak layer is generally a dense material having a high surface density. As a result, the flow resistance due to the porous layer inside increases, and the insertion loss in the high sound range cannot be ignored. That is, the sound permeability is hindered. As a result, even if the wind noise is reduced, the frequency characteristics for the measurement target sound / sound are inaccurate.

  (3) In order to estimate wind noise from an anemometer or the like, the influence of wind direction and turbulent flow must be taken into account, and analysis processing and a large-scale measuring device for specifying the wind direction are required. In addition, there is a limit to predicting wind noise corresponding to wind speed and wind direction that changes every moment in real time. That is, it is difficult to accurately predict the residual wind noise remaining in the microphone inside the windshield from only the wind speed.

  (4) In relation to (2) above, the outermost windbreak layer (in the case of JIS etc., “2 Although the next screen (secondary windshield) corresponds to this), a large windbreak effect is exhibited, but on the inner side, the wind speed falls almost to zero. Furthermore, the outermost windbreak layer does not lead to expansion of effective wind noise reduction because the individual sound induced by the wind circulates inside through the disk.

The present invention has been made in view of the above-described problems of the prior art, and an object thereof is to provide a low-frequency sound measurement unit and a wind noise reduction and expansion method that can further reduce wind noise.

In order to achieve the above object, the present invention provides a microphone that outputs an electrical signal in response to vibration of air, and a microphone disposed on a ground surface or a metal disk installed on the ground surface to cover the microphone. A low-frequency windshield, a controller that calculates an effective true value indicating a square effective value of the sound to be measured based on the output signal of the microphone, and a sound source that generates the sound to be measured and the low-frequency windshield A wind noise reduction and extension method comprising: a wind noise reduction and extension method, wherein the wind noise reduction and extension unit has an aperture ratio of 70% or more, transmits wind from the sound source side, and transmits from the sound source. Of the generated sound to be measured, it is composed of a ventilation member that transmits an acoustic signal in an audio band at 90% or more in each frequency band, and is perpendicular to the ground surface on the ground surface. Based on the direct axis, said characterized in that it is disposed inclined to the low frequency windshield side of the sound source.

  According to the present invention, wind noise can be further reduced.

It is a block diagram which shows 1st Example of a low frequency sound measuring device. It is a block diagram of a management table. It is a block diagram which shows 2nd Example of a low frequency sound measuring device. It is a block diagram which shows 3rd Example of a low frequency sound measuring device. It is a block diagram which shows 4th Example of a low frequency sound measuring device. It is a block diagram which shows 5th Example of a low frequency sound measuring device. It is a characteristic view for explaining a wind noise reduction effect. It is a block diagram which shows 1st Example of the low frequency sound measuring system to which the wind noise reduction expansion method was applied, Comprising: (a) is a front view, (b) is a top view. It is a block diagram which shows 2nd Example of the low frequency sound measuring system to which the wind noise reduction expansion method was applied, Comprising: (a) is a front view, (b) is a top view. It is a block diagram which shows 3rd Example of the low frequency sound measuring system to which the wind noise reduction expansion method was applied, Comprising: (a) is a front view, (b) is a top view, (c) is a reduced perspective view. FIG. It is a block diagram which shows 4th Example of the low frequency sound measuring system to which the wind noise reduction expansion method was applied, Comprising: (a) is a front view, (b) is a top view, (c) is a reduced perspective view. FIG. It is a block diagram which shows 5th Example of the low frequency sound measurement system to which the wind noise reduction expansion method was applied, Comprising: (a) is a front view, (b) is a top view, (c) is a reduced perspective view. FIG. It is a characteristic view for demonstrating the wind noise reduction effect of an independent net | network.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

(First embodiment)
In this embodiment, microphones are arranged inside and outside the low-frequency windshield, and the output signal of each microphone is processed by the controller. At this time, the controller compares the management table in which the measurement values measured under the condition where the measurement target sound does not exist with the measurement values measured under the condition where the measurement target sound exists, and the comparison result. Based on the above, the measurement target sound from which wind noise has been removed is obtained.

  FIG. 1 is a block diagram showing a first embodiment of a low frequency sound measuring apparatus. In FIG. 1, the low-frequency sound measuring device includes a low-frequency windshield 10 configured in a substantially hemispherical shape, and an outer microphone (hereinafter sometimes referred to as an outer microphone) 12 disposed outside the low-frequency windshield 10. , And an internal microphone (hereinafter also referred to as an internal microphone) 14 disposed inside the low-frequency windshield 10 and a controller 16.

  The low-frequency windshield 10 is disposed on a metal disk 18 installed on the ground surface. In addition, the low frequency windshield 10 can also be arrange | positioned directly on the ground surface.

  The inner microphone 12 and the outer microphone 14 are each configured as a sensor that outputs an electrical signal in response to vibration of air (sound wave), and are separated from each other along the central axis (virtual central axis) 20 of the low-frequency windshield 10. Arranged. The outer microphone 12 is disposed on the top of the low-frequency windshield 10 such that a diaphragm (not shown) built in the outer microphone 12 is flush with the surface of the low-frequency windshield 10. The inner microphone 14 is installed at a position 1 mm to several mm away from the surface of the metal disk 18.

  The outer microphone 12 and the inner microphone 14 are each non-directional and are installed along the central axis 20 of the low-frequency windshield 10, and therefore depend on the wind direction when processing or correcting the output signal of each microphone. There is nothing.

  Further, since the outer microphone 12 and the inner microphone 14 are installed along the central axis 20 of the low-frequency windshield 10, wind noise corresponding to the wind speed of the portion where the outer microphone 12 is installed is detected by each microphone. It will be. Further, since the inner microphone 14 is installed close to the surface of the metal disk 18, it can collect accurate surface sound pressure.

  The controller 16 includes head amplifiers 22 and 24, a sound card 26, and a personal computer 28.

  The head amplifier 22 is connected to the outer microphone 12, amplifies the electric signal output from the outer microphone 12, and outputs the amplified signal to the sound card 26.

  The head amplifier 24 is connected to the inner microphone 14, amplifies the electric signal output from the inner microphone 14, and outputs the amplified signal to the sound card 26.

  The sound card 26 is configured as an analog-to-digital converter that converts an analog signal into a digital signal. The sound card 26 converts an electrical signal output from the head amplifiers 22 and 24 into a digital signal, and converts the converted digital signal into a personal computer 28. Output to.

  The personal computer 28 is configured as a computer device having a CPU (Central Processing Unit), a RAM (Random Access Memory), a ROM (Read Only Memory), a memory, an input / output interface (all not shown), and the like. Stores a control program, a management table, and the like.

  The CPU executes various arithmetic processes based on the control program and management table stored in the memory, and is the square of the measurement target sound that is not affected by the wind noise based on the output signals of the outer microphone 12 and the inner microphone 14. A process for obtaining an effective value (true value) and wind speed is executed.

  In addition, when the measurement target sound is measured, the output of the outer microphone 12 and the output of the inner microphone 14 are different due to the insertion loss due to the low-frequency windshield 10 or the difference between the types of the outer microphone 12 and the inner microphone 14. Performs processing for frequency correction for each frequency band.

  Hereinafter, a specific processing procedure of the CPU will be described.

  Here, in this embodiment, the wind speed is estimated based on the output signals of the outer microphone 12 and the inner microphone 14 on the assumption that the wind noise corresponds to the wind speed v on a one-to-one basis. Is calculated as a square effective value of the wind noise remaining in the inner microphone 14, and the calculated value is corrected. Based on the corrected calculated value, the sound of the measurement target sound is calculated. The square root-mean-square value is estimated accurately.

  Specifically, based on the output signals of the outer microphone 12 and the inner microphone 14, the sound pressure of the measurement target sound detected by the outer microphone 12 and the inner microphone 14, respectively, and the outer microphone 12 and the inner microphone 14, respectively. The square effective value of the output signal including the sound pressure of the wind noise is calculated. At this time, the square effective value of the output signal of the inner microphone 14 and the square effective value of the output signal of the outer microphone 12 are calculated based on the following equations.

  Here, considering that there is a difference in the output signal between the inner microphone 14 and the outer microphone 12, frequency correction processing (equalizing) is performed using the frequency correction coefficient a for each frequency band, and both effective The value output is made equal to the true wind noise effective value.

That is, the CPU executes the following processing.

Thereafter, processing for multiplying the output signal of the outer microphone 12 by the frequency correction coefficient a is executed. At this time, due to the wind noise reduction effect of the low-frequency windshield 10, the effective square noise value of the wind noise detected by the inner microphone 14 is lower than the effective square noise value of the wind noise detected by the outer microphone 12 by 1 / q. Assuming that

When the calculation of the above expression (2) × a− (1) is performed using the expressions (6) and (1) as shown below, from the expression (5), each microphone 12, The influence of noise / sound entering 14 is canceled, and only the wind noise term on the right side of equation (7) remains.

  On the other hand, prior to actual measurement, the inside microphone 14 and the outside under various wind speeds (v (m / s)) under a quiet indoor place (silent outdoors), that is, under conditions where there is no sound to be measured. The square root mean square value of wind noise detected by the microphone 12 is measured for each frequency band, for example, in the range of 1 Hz to 20 kHz for every 1/3 octave, and the measurement results are shown in FIG. In addition, the calculation of the right side of the equation (7) that is an argument is performed for each frequency band, and each calculation result is recorded in the management table 30 in association with the measurement value of the anemometer.

  At this time, the squared effective value of the residual noise remaining in the inner microphone 14 includes self noise of the inner microphone 14, electrical noise of the preamplifier 24, background noise of the measurement site, and the like as components other than the residual noise. When the wind speed is low, these components are processed as a square effective value of residual noise remaining in the inner microphone 14.

  In actual measurement, under the condition that the sound to be measured exists, the calculation of the expressions (1) to (7) is performed based on the output signals of the outer microphone 12 and the inner microphone 14, and the right side of the expression (7) The management table 30 is referred to based on the value of this argument (calculated value) as an argument. At this time, if the value of the argument is 92.19, for example, 80.12 can be obtained as the squared effective value of the residual wind noise corresponding to the value of this argument, and the value of this argument can be handled. A wind speed of 0.10 m / s can be obtained as the wind speed.

Next, the square effective value of the sound to be measured to be obtained is obtained from the following equation (8).

  In the equation (8), the second term of the integration becomes zero due to the integration of the product of the orthogonal functions, and the third and fourth terms of the integral are the squared root mean square values of the wind noise and are essentially equal. Because there is, it becomes zero in the process of integration.

  As described above, the calculation of the expressions (1) to (7) is performed based on the output signals of the inner microphone 14 and the outer microphone 12, and the calculated value on the right side of the expression (7) is used as an argument. By referring to the management table 30 on the basis, the square effective value of the residual wind noise remaining in the inner microphone 14 and the wind speed can be obtained. Furthermore, by calculating the difference between the square effective value of the output signal of the inner microphone 14 and the square effective value of the residual wind noise remaining in the inner microphone 14 by the equation (8), it is not affected by the wind noise. The square effective value (true value) of the measurement target sound can be obtained.

  According to the present embodiment, since the influence of the residual wind noise remaining on the inner microphone 14 is minimized, the wind noise reduction of 40 dB or more is combined with the wind noise reduction effect (about 20 dB) of the low-frequency windshield 10. The effect can be obtained, and a high speed and omnidirectional anemometer can be constructed.

  Moreover, according to the present Example, the following effects can be acquired.

  (1) Since it is independent of the physical wind noise reduction means and performs processing for reducing wind noise using an electrical signal processing means, the effect of the physical wind noise reduction means And a high wind noise reduction effect can be obtained by combining the effects of the electrical signal processing means.

  (2) Since the inner microphone 14 and the outer microphone 12 are used for estimating the wind speed, the responsiveness is high, and the uncertainty that may exist between the microphones is higher than the method of estimating the wind noise from the anemometer output. It is hard to be affected by. Further, when the low frequency sound measuring device is configured as an anemometer, if an omnidirectional microphone is used for the inner microphone 14 and the outer microphone 12, an anemometer can be manufactured at high speed regardless of the wind direction.

  (3) Since the directivity central axes of the inner microphone 14 and the outer microphone 12 coincide with the target axis (the central axis 20) of the low-frequency windshield 10 that is a circular object, the wind noise does not depend on the wind direction. ) The square root mean square value of the wind noise due to the output of the inner microphone 14 can be obtained with a high stability corresponding to the square root mean square value of the wind noise due to the output of the outer microphone 10.

  (4) Further, in actual measurement, noise / sound to be measured exists, so that the effective square value of the residual wind noise remaining in the inner microphone 14 from only the effective squared value of the wind noise due to the output of the outer microphone 12. In the method of estimating the noise, it is not possible to estimate the correct square root effective value of the residual wind noise due to the influence of noise and sound.

  On the other hand, in this embodiment, the difference between the square root effective value of the wind noise due to the output of the outer microphone 12 and the square root effective value of the residual wind noise due to the output of the inner microphone 14, that is, the value on the right side of the equation (7). Is used as an argument, and the effective square value of residual wind noise remaining in the inner microphone 14 is obtained by referring to the management table 30. Therefore, the influence of noise and sound is canceled between the microphones, and the correct square of residual wind noise is obtained. The effective value can be estimated.

  (5) The square effective value of the residual wind noise remaining in the inner microphone 14 includes all noise components other than the effective square value of the sound to be measured, such as self noise of the inner microphone 14 and electrical noise of the preamplifier 24. However, these noise components are also removed as a part of the squared effective value of the residual wind noise. Furthermore, when there is a background noise source that cannot be avoided at the measurement site, the effect of the background noise source can be avoided by recording the squared effective value of the residual wind noise in the management table 30 under the condition of the background noise source. Can do.

  (6) Even if the wind noise is not excessively reduced with only the physical low-frequency windshield 10 used in combination, a high wind noise reduction effect can be realized even in a low frequency range by using a small low-frequency sound measuring device. Moreover, since the low-frequency windshield 10 can use a light windshield layer (good air permeability = low flow resistance, non-solid resistance = low aperture ratio), it has high sound permeability and wide area. Insertion loss can be minimized.

  Next, FIG. 3 shows a second embodiment in which a condenser microphone is used as a microphone.

  In FIG. 3, the inner microphone 14 is composed of an omnidirectional condenser microphone with a built-in preamplifier, and is arranged along the central axis 20 of the low-frequency windshield 10 so that the tip side is suspended toward the metal disk 18. The At this time, the inner microphone 14 is arranged so that the diaphragm surface on the tip side thereof is close to the metal disk 18 and does not touch the metal disk 18. In this case, by setting the gap between the inner microphone 14 and the metal disk 18 to about 1 m to 5 mm, the inner microphone 14 collects accurate ground surface sound pressure in the audio frequency range (1 Hz to 20 kHz). be able to.

  On the other hand, the outer microphone 12 is composed of an omnidirectional condenser microphone with a built-in preamplifier, and is disposed along the central axis 20 of the low-frequency windshield 10. At this time, the outer microphone 12 is installed upward or outward so that the diaphragm surface protrudes out of the low-frequency windshield 10 by about 1 mm so that the diaphragm surface substantially coincides with the surface of the low-frequency windshield 10. Thereby, the outer microphone 12 can effectively collect wind noise caused by wind passing through the surface of the low-frequency windshield 10.

  The inner microphone 14 and the outer microphone 12 are each non-directional and are disposed along the central axis 20 of the low-frequency windshield 10, so that the wind noise collecting effect and the wind noise reducing effect are independent of the wind direction. Is constant.

  Incidentally, wind noise is mainly due to negative pressure fluctuations to the diaphragm due to the passage of wind, so even if the diaphragm of the outer microphone 12 is installed flush with the surface of the low-frequency windshield 10, Wind noise is rarely stopped or reduced.

  Further, since the noise / low frequency sound that is the measurement target sound arrives from a distance (relative to the wavelength) as a plane wave, substantially the same components are output from the inner microphone 14 and the outer microphone 12. The difference between the microphones is only the magnitude of the wind noise, that is, the square root mean square value of the wind noise due to the output of the outer microphone 12 and the square root mean square value of the residual wind noise due to the output of the inner microphone 14. . For this reason, the wind noise square effective value from the output of the outer microphone 12 and the residual wind noise square effective value remaining in the inner microphone 14 are measured without wind, and each measured value is managed in association with the wind speed. By recording on the table 30, the effective square value of the residual wind noise and the wind speed remaining in the inner microphone 14 can be obtained.

  The controller 16 can also be configured as a sound level meter or a low frequency sound pressure meter. Further, the inner microphone 14 can be inserted into the main windshield 32 and the inner microphone 14 can be covered with the main windshield 32.

  Further, as the low-frequency windshield 10, a structure in which a semicircular protective net 34 including a porous sheet is fixed to a plurality of metal frames 36 arranged radially from the top of the low-frequency windshield 10 is used. Can do. As the metal disk 18, a circular aluminum base can be used.

  Next, FIG. 4 shows a third embodiment in which a silicon microphone is used for the outer microphone and a condenser microphone is used for the inner microphone.

  In FIG. 4, the inner microphone 14 is composed of a non-directional condenser microphone with a built-in preamplifier, and is disposed along the central axis 20 of the low-frequency windshield 10. The inner microphone 14 is substantially covered with the main windshield 32, and a part thereof is exposed from the main windshield 32. At this time, the gap between the diaphragm of the inner microphone 14 and the metal disk 18 is set to about 1 mm. For this reason, the inner microphone 14 can collect accurate ground surface sound pressure in the audio frequency range (1 Hz to 20 kHz).

  On the other hand, the outer microphone 12 is composed of an omnidirectional silicon microphone with a built-in preamplifier, and is disposed along the central axis 20 of the low-frequency windshield 10. At this time, the outer microphone 12 has a thickness of about 1 mm and is fixed in a state where it is exposed at the top of the low-frequency windshield 10.

  FIG. 5 shows a fourth embodiment in which a silicon microphone is used for the outer microphone, an electret condenser microphone is used for the inner microphone, and a spherical windshield for measuring the sound pressure in the air is used for the windshield.

  In FIG. 5, the inner microphone 14 is formed of a non-directional electret condenser microphone with a built-in preamplifier, and is disposed along the central axis 42 of the spherical windshield 40. The tip side of the inner microphone 14 is covered with a protective metal net 50 including a waterproof stainless fiber sheet. The protective metal net 50 is formed in a substantially cylindrical shape as a main windshield, and is attached to the distal end side of the cylindrical metal holder 52. A cylindrical airtight rubber packing 54 is attached between the cylindrical metal holder 52 and the inner microphone 14.

  At this time, since the cylindrical metal holder 52 is disposed in the air and supported by a support device (not shown), the inner microphone 14 collects accurate air sound pressure in the audio frequency range (1 Hz to 20 kHz). Can sound.

  On the other hand, the outer microphone 12 is composed of a non-directional silicon microphone with a built-in preamplifier, and is disposed along the central axis 42 of the spherical windshield 40. At this time, the outer microphone 12 has a thickness of about 1 mm and a length of about 50 mm to 200 mm, and is fixed in a state of being exposed at the top of the spherical windshield 40.

  The spherical windshield 40 is configured by a hollow structure or a filling structure in which a porous material, for example, a metal net 44 of 0.5 mm square or less and a metal net 46 of 2 to 4 mm square are combined.

  FIG. 6 shows a fifth embodiment in which a silicon microphone is used for the outer microphone, a silicon microphone is used for the inner microphone, and a cylindrical windshield for measuring the surface sound pressure is used for the windshield.

  In FIG. 6, the inner microphone 14 is configured by an omnidirectional condenser microphone and is disposed along the central axis 62 of the cylindrical windshield 60. At this time, the inner microphone 14 is arranged on the surface of the measurement object 64 such as the body or the vehicle body. For this reason, the inner microphone 14 can accurately collect the surface sound pressure of the measurement object 64 in the audio frequency range (1 Hz to 20 kHz).

  On the other hand, the outer microphone 12 is composed of an omnidirectional silicon microphone and is disposed along the central axis 62 of the cylindrical windshield 60. At this time, the outer microphone 12 is fixed in a state of being exposed at the top of the cylindrical windshield 60.

  The cylindrical windshield 60 is formed in a substantially cylindrical shape, and is installed on a measurement object 64 such as a body or a vehicle body. The cylindrical windshield 60 is configured in a cylindrical shape for the purpose of measuring the surface sound pressure, and the inner microphone 14 and the outer microphone 12 are silicon microphones that are small in size.

  As for the cylindrical windshield 60, the basic structure of the windbreak layer may be a hollow structure made of a porous material or a filled structure, as with the spherical windshield 40.

  In the second to fifth embodiments, the same effects as in the first embodiment can be obtained.

  Next, FIG. 7 shows a characteristic diagram for explaining the wind noise reduction effect.

  In FIG. 7, characteristic curves 200, 202, and 204 are measurement results when the low-frequency sound measurement apparatus 10 measures the wind from the blower.

  The wind noise of the outer microphone 12 corresponding to the absence of the windshield is a squared effective value of the wind noise included in the output signal of the outer microphone 12, and is represented by a characteristic curve 200.

  On the other hand, since the wind noise of the inner microphone 14 can obtain the effect of reducing the wind noise by the low-frequency windshield 10, the output signal of the outer microphone 12 and the output signal of the inner microphone 14 are expressed as When the processing is not performed by the controller 16 on the basis of the expression), the characteristic curve 202 indicates that the processing is reduced as compared with the outer microphone 12. However, the effect of reducing the residual wind noise remaining in the inner microphone 14 is about 20 dB, which is not sufficient.

  On the other hand, when the output signal of the outer microphone 12 and the output signal of the inner microphone 14 are processed by the controller 16 based on the equations (1) to (7), the residual wind noise is represented by a characteristic curve 204. In this case, it can be seen that the residual wind noise remaining in the inner microphone 14 is further reduced by 10 to 15 dB in addition to the effect of reducing the wind noise by the low-frequency windshield 10.

(Low frequency sound measurement system)
FIG. 8 is a block diagram showing a first embodiment of a low-frequency sound measurement system to which the wind noise reduction and expansion method according to the present invention is applied.

  In FIG. 8, the low-frequency sound measurement system includes a microphone 100, a main windshield 102 covering the microphone, a secondary windshield 104 covering the microphone 100 and the main windshield 102, and a low-frequency sound measurement device having a metal disk 106. And a net 110.

  The microphone 100, the main windshield 102, and the secondary windshield 104 are disposed on a metal disk 108 installed on the ground surface. The microphone 100 has the same function as the inner microphone 14 and is connected to a controller (not shown) having the same configuration as the controller 16 of FIG.

  This controller is configured using, for example, a personal computer, and can process an electrical signal generated by the output of the microphone 100 to extract a measurement target sound from which wind noise has been removed.

  The secondary windshield 104 is formed of, for example, a hemisphere, and the opening side of the hemisphere is disposed on the metal disk 106. At this time, the microphone 100 is disposed along the central axis 108 of the secondary windshield 104.

  The independent net 110 is a low-frequency windshield including the main windshield 102 and the secondary windshield 104 (JIS C 1400-11: 2005 and IEC61400-11; 2002) for the purpose of further expanding the degree of wind noise reduction. In order to satisfy the following conditions, it is outside of the low-frequency windshield between the sound source that generates the measurement target sound and the low-frequency windshield. The wind noise reduction expansion unit that is installed and has air permeability and wind permeability is configured using metal or a material other than metal.

  Specifically, the independent net 110 is higher in height from the ground surface than the low-frequency windshield, wider than the low-frequency windshield, and has a flat frame 112 and a net material fixed to the frame 112. 114 and configured to satisfy the conditions defined in the following items.

  (1) Opening ratio is 70% or more, air permeability, audio bandwidth (20Hz ~ 20kHz), sound transmission is 90% or more, insertion loss is within ± 2dB, metal Or it is comprised using materials other than a metal.

  (2) The shape of the existing windshield defined by JIS or the like, for example, a hemispherical shape, is basically different.

  (3) The metal disk 108 is directly installed on the ground surface so as to be cut off by vibration. Note that the independent net 106 can be installed at a position different from the metal disk 108 through the vibration isolating means.

  (4) The surface facing the sound source that generates the measurement target sound or the surface facing the wind generating source is slightly inclined toward the low-frequency windshield side with respect to the vertical axis perpendicular to the ground surface, for example, θ = 1 Installed at a tilt of ~ 5 degrees.

  Next, the second to fifth embodiments of the low-frequency sound measurement system are shown in FIGS.

  In FIG. 9, the independent net 120 is formed in a rectangular shape, is higher from the ground surface than the low-frequency windshield, and wider than the low-frequency windshield, and is defined by the items (1) to (4) above. Configured as a net that satisfies the specified conditions. At this time, the independent net 120 includes a rectangular frame 122 and a net material 124 fixed to the frame 122, and is bent with respect to a virtual center line 126 to be formed in a “<” shape. .

  In FIG. 10, the independent net 130 is formed in a substantially conical shape, is formed in a rectangular shape, is higher from the ground surface than the low-frequency windshield, and is wider than the low-frequency windshield. It is configured as a net that satisfies the conditions specified in item (4).

  At this time, in the independent net 130, a plurality of bird guards 132 are combined to form a substantially conical frame, and the net material 134 is fixed to the frame.

  In FIG. 11, the independent net 140 is formed in a substantially cylindrical shape, is higher from the ground surface than the low-frequency windshield, is wider than the low-frequency windshield, and has the above items (1) to (4). It is configured as a net that satisfies the specified conditions.

  At this time, the net material 146 is fixed around the circular frames 142 and 144 arranged above and below the independent net 140. Of the net material 146, the net material 146 which is disposed between the circular frame 142 and the circular frame 144 and forms a slope is attached to be openable and closable along the slope.

  In FIG. 12, the independent net 150 is formed in a substantially hemispherical shape and is configured as a net that satisfies the conditions defined in the items (1) to (4) above.

  At this time, in the independent net 150, the net material 154 is fixed around the frame 152 formed in a substantially hemispherical shape.

  Each of the independent nets 110, 120, 130, 140, 150 can be configured as a wind noise reduction expansion unit so that it can be folded so as not to be bulky during transportation. At this time, the independent nets 130, 140, and 150 can be configured like a straw umbrella or a folding umbrella.

  Moreover, as each independent net | network 130-150, it can also be set as the structure which uses a waterproof material for the net materials 134, 146, and 154, and water does not permeate the internal secondary windshield 104, the microphone 100, etc. FIG. Further, the net materials 134, 146 and 154 may be made of a metal net-like material, a metal fiber board or a sheet so as to have an electromagnetic circumferential effect simultaneously with the windshield effect.

  According to the independent nets 110, 120, 130, 140, 150, the following effects can be obtained.

  (1) Unlike the existing windshield (low-frequency windshield) structure of the windshield layer in terms of shape, form, etc., the existing windshield is installed as a vibration edge, so each functions independently of the windshield. The wind noise reduction degree can be improved effectively.

  (2) Because it is an air-permeable independent net that passes almost all the wind, it does not induce a new air vortex flow and effectively reduces only the speed of the wind entering the outermost windbreak layer of the existing windshield. Reduction of wind noise of the entire system can be realized.

  (3) At the same time, since the independent net is made of a material having a very high aperture ratio, it is not only air permeable, but there is almost no concern of impairing sound transmission.

  (4) Since the independent ventilation net is installed outside the existing windshield, there is a tendency to increase the size of the independent net. However, since it can be folded like an umbrella, for example, there is almost no hindrance to transportation.

  In addition, when comprising a low frequency sound measuring system, it is any one of the low frequency sound measuring devices (low frequency sound measuring devices shown in FIGS. 1 and 3 to 6) of the first to fifth embodiments. One low-frequency sound measuring device and any one of the independent nets 110, 120, 130, 140, and 150 can be combined.

  Next, FIG. 13 is a characteristic diagram for explaining that wind noise changes depending on the presence / absence of an independent net.

  In the measurement for obtaining the characteristic diagram shown in FIG. 13, when the independent net 140 or the like is not used, a blower is arranged at a position several m away from the existing windshield, and the wind speed is 7 m from the blower toward the existing windshield. The wind noise was measured with the inner microphone 14 and the outer microphone 12, and the measurement result was recorded.

  On the other hand, when the independent net 140 or the like is used, a blower is arranged at a position 1 m away from the independent net 140 or the like, and a wind speed of 7 m / s is sent from the blower toward the independent net 140 or the like. Wind noise was measured with the outer microphone 12, and the measurement results were recorded.

  In FIG. 13, a characteristic curve 300 is a characteristic curve of wind noise output from the outer microphone 12 when an existing windshield is used as a windshield in the absence of the independent net 140 or the like. A characteristic curve 302 is a characteristic curve of wind noise output from the outer microphone 12 when an existing windshield is used as a windshield in the presence of the independent net 140 or the like. A characteristic curve 304 is a characteristic curve of wind noise output from the outer microphone 12 when 50 mm thick glass wool (fiber glass) is added inside the independent net 140 or the like and an existing windshield is used as the windshield. . It can be seen from the characteristic curves 300, 302, and 304 that in the absence of the independent net 140 or the like, a sufficient wind noise reduction effect cannot be obtained even if the windshield is used.

  On the other hand, the characteristic curve 400 is a characteristic curve of wind noise output from the inner microphone 14 when an existing windshield is used as a windshield without the independent net 140 or the like.

  A characteristic curve 402 is a characteristic curve of wind noise output from the inner microphone 14 when an existing windshield is used as a windshield in the presence of the independent net 140 or the like. In this case, it can be seen that the wind noise is reduced by 10 to 15 dB in the entire frequency band than when there is no independent net 160, and the wind noise is reduced by about 35 dB even at 10 Hz.

  A characteristic curve 404 is a characteristic curve of wind noise output from the inner microphone 14 when 50 mm thick glass wool (fiber glass) is added to the inside of the independent net 140 or the like and an existing windshield is used as the windshield. . In this case, wind noise is reduced by 10 to 15 dB in the entire frequency band, compared to when there is no independent net 140 or the like. However, the insertion loss is worse than in the configuration in which the characteristic 402 is obtained, and wind noise increases at 4 Hz or higher. The characteristic curve 406 is a fan noise characteristic of the blower.

  From the measurement results shown in FIG. 13, when configuring the independent net 140 or the like, the validity of the configuration using a net material having air permeability is shown. Naturally, since the aperture ratio of the independent net 140 or the like is high, there is almost no influence on the sound transmission. In other words, the insertion loss of the independent net 140 or the like is substantially zero.

  Note that any one of the independent nets 110, 120, 130, 140, and 150, and any one of the low-frequency sound measurement devices of the first to fifth embodiments are low-frequency sound measurement devices. 8 to 12, as shown in FIGS. 8 to 12, any one of the independent nets 110, 120, 130, 140, and 150 and an existing low-frequency sound measurement device (for example, FIG. 8). Even when combined with the low-frequency sound measurement apparatus shown in FIG. 12), wind noise can be reduced as compared with a device without an independent net.

  10 low-frequency windshield, 12 outer microphone, 14 inner microphone, 16 controller, 18 disc, 102 main windshield 104 secondary windshield, 110, 120, 130, 140, 150 independent net.

Claims (2)

A microphone that outputs an electrical signal in response to vibration of air, a low-frequency windshield that is disposed on the ground surface or a metal disk installed on the ground surface and covers the microphone, and an output signal of the microphone And a wind noise reduction / expansion unit disposed between a sound source that generates the measurement target sound and the low-frequency windshield. A noise reduction extension method comprising:
The wind noise reduction expansion unit has an aperture ratio of 70% or more, transmits wind from the sound source side, and transmits an acoustic signal in the audio band of the measurement target sound generated from the sound source by 90% in each frequency band. A wind noise reduction and expansion method comprising the above-described air-permeable member and arranged on the ground surface with an inclination to the low-frequency windshield side with respect to the sound source on the basis of a vertical axis perpendicular to the ground surface . A microphone,
A windshield covering the microphone;
A controller that extracts the measurement target sound from which wind noise has been removed, and processes an electrical signal from the output of the microphone;
A frame provided around the windshield and fixed with a net material;
With
The net material is composed of a ventilation member having an aperture ratio of 70% or more and an acoustic transmission of 90% or more in the audio band ,
The frame is
A substantially hemispherical head,
Formed in a substantially cylindrical shape, having a body covering the windshield,
The net material is fixed to the head and the main body,
One end of the main body in the axial direction is opened,
A low frequency sound measurement system in which the other axial end of the main body is closed by the head .

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