JP5235120B2 - Sound level meter and noise measurement program - Google Patents

Description

  The present invention relates to a sound level meter that can be used for outdoor noise measurement, and a noise measurement program.

  In recent years, the importance of living a comfortable life in a favorable environment has become more conscious. In particular, noise as well as air and water pollution should be widely taken as a cause of various problems from the past as so-called pollution. Therefore, wherever there are noise sources, it is necessary to evaluate the noise when developing countermeasures. For example, permanent noise includes noise from airplanes and bullet trains, noise from viaducts such as expressways, and noise from dam discharges. There is noise and noise from concert halls and stadiums.

As a measuring instrument for measuring these noises, a sound level meter is widely used. FIG. 8 is a schematic diagram showing a conventional sound level meter for measuring noise. The sound level meter 1 is a measuring instrument including a microphone 2 and a calculation processing unit 3 that calculates and evaluates an output from the microphone 2 and a display device 4 that displays the calculation and evaluation results. The microphone 2 is transmitted by the vibration film 5 that detects the vibration of the air caused by the sound source, that is, the change in atmospheric pressure (sound pressure), the transmission member 6 that transmits the vibration of the vibration film 5, and the transmission member 6. It consists of a ceramic vibrator 7 that converts vibrations into electrical signals. An electric signal (voltage) generated by the ceramic vibrator 7 is detected by a preamplifier (not shown) and used for calculation by the calculation processing unit 3.
The sound level meter 1 can measure noise by directing the microphone 2 toward the measurement target sound source. Further, the main body portion and the microphone 2 can be separated via the connection portion 8, and the microphone 2 can be fixed to a tripod. In this case, it is necessary to connect the main body of the sound level meter 1 and the microphone with a cable.

  Here, what is common to the noises mentioned above is that these noises are all acoustic propagation outdoors. Therefore, sound level meters often need to be used outdoors.

  However, the use of a sound level meter outdoors is affected by weather conditions. In particular, in the measurement of low-frequency noise, it is known that pressure fluctuations due to wind turbulence components act on the microphone. This is called wind noise. In this case, the measurement value of the sound level meter is a value obtained by adding wind noise to the measurement target sound. Wind noise is generated to a considerable extent even when the wind speed is low. When the wind speed exceeds 5 m / sec, the influence of wind noise cannot be ignored, and measurement must be stopped according to ISO regulation. Therefore, the use of the sound level meter outdoors has to be performed by selecting a time when there is no wind, and there is a problem that the noise measurement depends on the weather conditions and cannot be measured for a considerably long period depending on the season.

In order to solve these problems, there is a technique in which wind is not directly applied to the microphone by disposing a windproof member around the microphone so that the microphone is not affected by the wind (Patent Document 1).
However, there is a problem that the windproof member cannot completely remove the influence of wind. Furthermore, since the windproof member also blocks a part of the measurement target sound, there is a problem that accurate measurement of the measurement target sound is hindered.

Focusing on the fact that wind noise is mainly composed of low-frequency components, focusing on the technology that removes wind noise components with a high-pass filter and the effect of wind noise on a pair of microphones has low correlation. There is a technology that removes wind noise components by using (Patent Document 2).
However, even in these cases, the measurement object sound is removed because it does not evaluate the influence of the wind itself, but uses the characteristics and correlations found in the noise measurement results affected by the wind noise. This cannot be completely prevented.
JP 2001-91351 A JP 2001-124621 A

Therefore, an object of the present patent invention is to realize a high-accuracy sound level meter that is not affected by weather conditions, that is, can be used in a normal usage mode even when wind is blowing.
The claims in the next stage and the next stage refer to the claims at the time of filing.

The sound level meter according to claim 1 of the present invention obtains a pressure value from an output signal of a microphone, an anemometer, and an anemometer that measures the sound pressure value of the sound to be measured, and the sound pressure value and the pressure value. And an arithmetic processing unit for processing the above.
The sound level meter according to claim 2 of the present invention is characterized in that, in the sound level meter according to claim 1, the processing of the calculation unit subtracts the effective value of the pressure value from the effective value of the sound pressure value.
The sound level meter according to claim 3 of the present invention is the sound level meter according to claim 1, based on the output signal of the anemometer, in the arithmetic processing unit,
(Cw: coefficient, ρ: air density, u: fluctuating wind speed)
The pressure value Pwind is obtained by performing the above calculation.
The sound level meter according to claim 4 of the present invention is the sound level meter according to claim 1, characterized in that the anemometer is located in front of the microphone.
The sound level meter according to claim 5 of the present invention is the sound level meter according to claim 1, wherein the distance between the microphone and the anemometer is 10 to 150 mm.
The noise measurement program according to claim 6 of the present invention includes a step of inputting the output Pout of the microphone, a step of inputting the output U of the anemometer, a step of obtaining the pressure value Pwind from the output U of the anemometer, Subtracting the effective value of Pwind from the effective value of Pout.

According to the first aspect of the present invention, noise can be measured even when the wind is blowing, and the effect that noise measurement work independent of weather conditions is possible can be achieved. Further, since the influence of the wind itself is evaluated as the pressure value acting on the microphone, the effect that the target sound can be measured more accurately is exhibited.
According to the second, third, and sixth aspects of the present invention, the effect that the measurement target sound can be accurately evaluated by a simple calculation is exhibited.
According to the present invention described in claims 4 and 5, it is possible to measure the sound pressure and the wind speed without the microphone and the anemometer interfering with each other.

First, the principle of the present invention will be described.
The governing equations of the compressible flow field include the elastic behavior of the fluid in addition to the fluid advection-diffusion phenomenon, so the compressible Navier-Stokes equation also represents the acoustic wave propagation phenomenon, where the velocity field and The compression field is a physical quantity related to each other. The relationship between the wind pressure (pressure value) acting on the microphone and the wind speed can be expressed as equation (1).
(1)
Here, Pwind is the fluctuating pressure value that the wind gives to the microphone, ρ is the air density, and u is the fluctuating wind speed that is a fluctuation component of the wind speed. Further, the fluctuating wind speed u can be obtained by subtracting the average wind speed value u ₀ from the measured wind speed value U measured by the anemometer as shown in the equation (2). The average wind speed value u ₀ can be calculated by averaging measured wind speed values U for a certain period of time.
(2)
In this way, the fluctuation component of the pressure is generated by the fluctuation component of the wind speed. The correction coefficient Cw is a coefficient depending on the shape of the microphone and the response mechanism of the microphone to the wind (the sensitivity of the microphone, the flow field around the microphone, the incident angle of the wind, the frequency component of the wind, and the wind speed).

On the other hand, the sound pressure (value) acting on the microphone can be expressed as in equation (3).
(3)
Here, V is the vibration velocity of fluid particles (air), and c is the speed of sound.

If the phase of sound and wind is random, the effective value of Pound (rms) and the effective value of Pwind (r. m.s.) can be added.



(4)
Here, Pout is a sound pressure value (measured value) measured by a microphone of a sound level meter.

If Cw is known, Pound can be obtained by measuring Pout and U. In other words, if the relationship between Cw and U and other variables constituting Cw is obtained in advance through a wind tunnel experiment and a sound level meter incorporating a specific Cw value is used, the measured noise value outdoors will be The effect of wind can be corrected. Specifically, when the sound level meter Pout is measured outdoors and the wind speed U is measured with an anemometer, the accurate sound pressure of the sound to be measured can be obtained.
Examples of the sound level meter of the present invention are shown below.

Example 1
FIG. 1 is a schematic configuration diagram of a sound level meter according to an embodiment of the present invention. In FIG. 1, reference numeral 10 denotes a sound level meter main body, and the sound level meter 10 includes a microphone 11 and an anemometer 12 as detection units, and an arithmetic processing unit 13 that receives and processes electrical signals from these, and an arithmetic processing unit 13. And a display device 14 for displaying calculation results. Further, although the microphone 11 and the anemometer 12 are configured integrally, the anemometer 12 is provided so as to be rotatable around the microphone 11. Moreover, the anemometer 12 is provided so as to protrude forward from the microphone 11. The microphone 11 and the anemometer 12 are configured so as to be separable by a connecting portion 15 made of a screw. When separated, the microphone 11 and the anemometer 12 are used by being connected to the sound level meter 10 by a cable (not shown).

  The microphone 11 and the anemometer 12 are installed at a distance of 10 mm or more in order to avoid mutual interference. In order to measure the wind speed near the microphone, an anemometer may be installed within 150 mm from the microphone. Preferably, when installed within a range of 40 mm to 50 mm, there is little interference with each other and the wind speed near the microphone can be measured.

  FIG. 3 is an enlarged cross-sectional view of an essential part of the microphone 11. The microphone 11 has the same configuration as a microphone mounted on a conventional sound level meter. The microphone 11 detects vibrations of air caused by a sound source, that is, a vibration film 21 that detects a change in atmospheric pressure (sound pressure), a transmission member 22 that transmits vibrations of the vibration film 21, and vibrations transmitted by the transmission member 22. It comprises a ceramic vibrator 23 that converts it into an electrical signal. An electric signal (voltage) generated by the ceramic vibrator 23 is detected by a preamplifier (not shown) and is used for calculation by the calculation processing unit 13.

  FIG. 4 is an enlarged view in which the main part of the tip of the anemometer 12 is enlarged. As the anemometer 12, a general-purpose hot-wire anemometer probe can be used. The anemometer 12 includes a filament 31 made of tungsten, a support member 32 that supports the filament 31, and a protection member 33, and the fragment 31 is provided so as to protrude from the opening 34 of the protection member 33. The support member 32 is made of a conductor, and the filament 31 is energized and heated via the support member 32.

The operation principle of the anemometer 12 will be described. When the wind hits the heated filament 31, the filament 31 is cooled by the wind. In order to keep the filament 31 at a constant temperature, the energization amount may be increased. However, since this current amount depends on the wind speed value, if these relationships are obtained in advance and the amount of current that keeps the filament 31 at a constant temperature is measured. The wind speed can be obtained.
In addition to the standard linear probe that is a one-dimensional filament as shown in FIG. 4, an X-type probe that can handle various wind directions and other three-dimensional probes can be used to obtain a more accurate wind speed that does not depend on the wind direction. it can.

  FIG. 5 is a block diagram of the arithmetic processing unit 13. The outputs of the microphone 11 and the anemometer 12 are amplified by the preamplifier 41, converted into a digital signal by the A / D converter 42, and input to the CPU 43. The CPU 43 performs an operation according to a program stored in the storage device 44 and outputs the result to the display unit 14.

  As will be described later, the calculation performed by the CPU 43 performs calculation for removing the influence of wind noise from the result measured by the microphone 11, and the calculation result is subjected to octave analysis, 1/3 octave analysis, FFT (fast Fourier transform). ) Analysis is performed, and the result is output to the display unit, or the wind speed is obtained by calculation from the output of the anemometer 12, and the wind speed is output to the display unit. In addition, as the output of the sound level meter, the equivalent noise level (Leq), the maximum level value (Lmax), the time series level (LP), the low frequency characteristics (LG) are calculated, and the output of the anemometer is averaged. Calculations are also performed to determine the wind speed, wind turbulence intensity, maximum wind speed, and time series waveform.

  About the sound level meter which has the above structure, the usage method is demonstrated. The main body of the sound level meter 10 is a handy type that is convenient to carry, and the measurer can start the measurement by pointing the microphone 11 and the anemometer 12 in the direction of the measurement target sound and pressing the measurement start button. Further, as shown in FIG. 2, the microphone 11 and the anemometer 12 may be separated at the connection portion 15 and fixed to a tripod or the like. This is suitable for more precise measurement because it does not pick up noise caused by camera shake.

  Furthermore, especially in the case of low-frequency noise, the sound source cannot be specified, or the noise is often not generated from a certain point, such as noise from a highway viaduct, so the directivity is the same around it. If the microphone 11 and the anemometer 12 are installed in the vertical direction as shown in FIG. 2 using a microphone, noise from any direction can be measured. Moreover, since the shape of the microphone 11 with respect to the wind is constant regardless of the direction from which the wind blows, the influence of the wind does not depend on the wind direction, and the number of types of Cw to be obtained in advance through wind tunnel experiments can be reduced. . Therefore, in such a case, it is desirable to install the microphone 11 and the anemometer in the vertical direction as shown in FIG.

  When the microphone 11 and the anemometer 12 are used while being fixed in the vertical direction as shown in FIG. To receive as much as possible. Further, since the anemometer 12 is provided so as to protrude forward (upward in this case) from the microphone 11, the anemometer can measure an accurate wind speed without being interfered by the microphone 11. .

  Next, the operation of the sound level meter 10 during noise measurement will be described with reference to FIG. FIG. 6 is a flowchart illustrating the operation of the sound level meter. Such an operation is realized by expanding and executing a program stored in the storage device 44.

  As shown in FIG. 2, the user of the sound level meter fixes the microphone 11 and the anemometer 12 with a tripod in the vertical direction, presses a measurement start button (not shown), and starts noise measurement (S1).

  The sound pressure Pout of the measurement target sound source measured by the microphone 11 is converted into an electric signal and input to the CPU 43. Here, as described above, the measured sound pressure Pout is a value that is influenced by the wind, and is not an accurate sound pressure value generated from the measurement target sound source. On the other hand, the wind speed U measured by the anemometer 12 is similarly converted into an electrical signal and input to the CPU 43 (S2).

The CPU 43 develops a program stored in advance in the storage device 44 from the input sound pressure Pout of the measurement target sound source and the measured wind speed U, and obtains an accurate sound pressure of the measurement target sound source according to this program.
First, by using the equation (2), an average wind speed value u ₀ measured for a predetermined time is subtracted from the measured wind speed U to obtain a fluctuating wind speed u. Further, using this u, the influence of the wind on the microphone 11 is obtained as a pressure value Pwind using the equation (1) (S3).
Here, ρ is stored in advance in the storage device 44 as a constant. Cw is also stored in the storage device 44 in advance by a wind tunnel experiment, and is used by calling it.

  Next, the accurate sound pressure Psound of the target sound source is obtained from the measured effective value of the sound pressure Pout of the sound source to be measured and the effective value of Pwind using the equation (4) (S4).

Psound is obtained from the calculation result, and the sound pressure of the measurement target sound is converted into a value such as dB (decibel) and displayed on the display device 14 (S5). Further, according to the command input by the measurer, the CPU 43 follows the program stored in the storage device in advance, and the equivalent noise level (Leq), the maximum level value (Lmax), the time series level (LP), and the low frequency characteristic (LG). ), Octave analysis, 1/3 octave analysis, FFT (Fast Fourier Transform) analysis, and the analysis result can be displayed on the display device 14.
Further, the average wind speed, the wind turbulence intensity, the maximum wind speed, and the time series waveform can be obtained from the output of the anemometer 12 and displayed on the display device 14 in accordance with the instructions of the measurer.

  The correction coefficient Cw is a coefficient depending on the shape of the microphone and the response mechanism of the microphone to the wind (the sensitivity of the microphone, the flow field around the microphone, the incident angle of the wind, the frequency component of the wind, the wind speed), and the like. Therefore, these values may be detected and the corresponding Cw may be called and used. For example, the incident angle of the wind can be measured with an anemometer, and the speed of wind and laminar turbulence can be measured with an anemometer, and the corresponding Cw can be called up based on this.

  In this embodiment, the value obtained by subtracting the effective value of Pwind from the effective value of Pout is used as it is as Psound, but this does not exclude further performing other necessary calculations.

(Example 2)
FIG. 7 is a configuration diagram showing the configuration of the sound level meter 70 of the second embodiment. The sound level meter of the second embodiment is provided with an anemometer in addition to the configuration of the sound level meter of the first embodiment, and the number of wind information channels is increased to two channels of wind speed and wind direction. In other words, in addition to the microphone 71 and the anemometer 72, the anemometer 73 is attached to the casing in which the microphone 71 is provided. The anemometer 73 is composed of a single blade portion 75 standing in a vertical direction by a shaft 74 and an angle detection device (not shown) provided at the other end of the shaft 74. And the wing | blade part 75 rotates centering on the axis | shaft 74 according to a wind direction, and an angle detection apparatus detects the rotation angle.

  About the sound level meter which has the above structure, the usage method is demonstrated. As shown in FIG. 7, the microphone 11 and the anemometer 12 are separated, and are used by being fixed horizontally on a tripod or the like so that the microphone faces the direction of the noise source. Such a method of use is suitable for noise measurement when a noise source is specified as in a construction site or a baseball stadium, and the direction of noise generation is also specified. However, the shape of the microphone 71 with respect to the wind is not constant depending on the wind direction, and as a result, the influence of the wind on the microphone 71 is different. Therefore, it is necessary to obtain the relationship between the incident angle of the wind and Cw in advance through wind tunnel experiments and mount it. is there. When measuring the noise, the wind speed is measured by the anemometer 72 and the wind direction is measured by the anemometer 73 to call Cw corresponding to these wind speeds and wind directions, and the target sound source is processed in the same manner as in the first embodiment. Is obtained as an accurate sound pressure Psound.

  The anemometer 72 may be provided so as to be rotatable around the microphone 71 as in the first embodiment, but it may be fixed instead of being rotatable.

  The anemometer uses a configuration in which the wings rotate according to the wind direction. Instead of this, the anemometer includes the function of the anemometer by using an X-type probe or a multidimensional probe. be able to.

  The sound level meter of the present invention can be used for any type of sound level meter such as a handy type and a fixed type. The measurement target sound is not limited to noise, and can be used for sound measurement in general, such as acoustic measurement at an outdoor concert venue.

Configuration diagram of the sound level meter of the present invention Explanatory drawing showing the mode of use of the sound level meter of the present invention Sectional drawing of the principal part of the microphone mounted in the sound level meter of the present invention Configuration diagram of an anemometer mounted on the sound level meter of the present invention Configuration diagram of arithmetic processing unit mounted on sound level meter of the present invention Flow chart showing the operation of the sound level meter of the present invention The block diagram of the sound level meter which is another Example of this invention Configuration diagram of conventional sound level meter

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Sound level meter 11 Microphone 12 Anemometer 13 Arithmetic processing part 14 Display apparatus 15 Connection part

Claims (5)

Includes a microphone that measures the sound pressure value of the measurement target sound, and anemometer, together determine the pressure value from the output signal of the anemometer, the arithmetic processing unit for processing said pressure value and the sound pressure value,
The processing of the arithmetic unit is based on the output signal of the anemometer.
(Cw: coefficient depending on the shape of the microphone and the response mechanism of the microphone to the wind, ρ: air density, u: fluctuating wind speed)
A sound level meter that calculates the pressure value by subtracting the effective value of the pressure value from the effective value of the sound pressure value.   The sound level meter according to claim 1, wherein a distance between the microphone and the anemometer is 10 mm or more.   The sound level meter according to claim 1, wherein low-frequency noise can be measured.   The sound level meter according to claim 1, wherein the anemometer is provided so as to be rotatable around the microphone. A step of inputting the output Pout of the microphone, the method comprising: inputting the output U of the anemometer, and determining a pressure value Pwind from the output U of the anemometer, the effective value of the output Pout of the microphone of the pressure value Pwind A program for noise measurement comprising a step of subtracting an effective value ;
In the step of obtaining the Pwind,
(Cw: coefficient depending on the shape of the microphone and the response mechanism of the microphone to the wind, ρ: air density, u: fluctuating wind speed)
A noise measurement program characterized by performing the above calculation.