Sound level meter

Abstract

To provide a technology for reducing the influence of atmospheric pressure in measurement.SOLUTION: Arithmetic processing executed by a signal processing part 32 with time T as a period first specifies a correction amount h to an output value of the current atmospheric pressure sensor 24 on the basis of information related to a correction amount corresponding to an atmospheric pressure characteristic unique to the model of a microphone 12 stored in a correction information storage part 34 in advance (S110). Next, it applies each filter of frequency weighting characteristics A, C, and Z to an individual input signal sampled during the time T (S120), corrects each evaluation value before and after dB conversion by using the correction amount h (S140) after calculating a prescribed evaluation value required to evaluate a sound pressure level on the basis of an output of each filter (S130), and outputs each corrected evaluation value. In this manner, a noise meter 100 can reduce the influence of atmospheric pressure in measurement because of outputting an evaluation value corrected on the basis of the atmospheric pressure characteristic unique to the model of the microphone 12.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a sound level meter used for measuring sound pressure levels indoors and outdoors.

Background Art

[0002] Sound level meters (sound pressure level meters) are widely used in various fields for measuring sound pressure levels indoors and outdoors, such as environmental noise measurement and sound insulation performance measurement of buildings. In the standards for sound level meters (JIS C 1509-1 and IEC 61672-1, hereinafter collectively referred to as "standards"), two types, class 1 and class 2, are defined according to performance. Class 1 has a wider measurement frequency range compared to class 2, and stricter regulations are imposed on stability due to environmental variations, and is used for more precise acoustic measurements. Also, in the standards, atmospheric pressure (static pressure) is defined as one of the environmental variation parameters, and stability of the indicated value against static pressure variation is required, and the acceptance limit values of the deviation of the indicated value are defined for each class. The stability of the indicated value against static pressure variation largely depends on the static pressure characteristics of the microphone used in the sound level meter.

Prior Art Documents

Non-Patent Documents

[0003]

Non-Patent Document 1

Non-Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] Incidentally, it is not uncommon for environmental noise measurements to be conducted continuously over long periods. For example, in the measurement of aircraft noise, measurements may be taken for a week continuously during the hours when aircraft are flying, or, in the case of locations near airports, during the operating hours of the airport. Such measurements may be conducted up to four times a year. In the measurement of road traffic noise, 24-hour measurements may be taken for a week continuously, or sound level meters may be permanently installed for continuous measurement.

[0005] During such measurement periods, atmospheric pressure can fluctuate significantly due to changes in weather and climate. Furthermore, atmospheric pressure naturally differs depending on the altitude of the measurement location. In contrast, microphone sensitivity depends on atmospheric pressure. Moreover, the degree to which sensitivity depends on atmospheric pressure varies with frequency, and is particularly noticeable at high frequencies above 1 kHz. Therefore, due to these differences in the measurement environment, the sound level meter, i.e., the microphone, may be affected by atmospheric pressure, and even if the measured sound pressure level is physically the same, the reading of the sound level meter may differ, potentially compromising the reliability of the measurement.

[0006] Therefore, the present invention aims to provide a technology for reducing the influence of atmospheric pressure on measurements. [Means for solving the problem]

[0007] To solve the above problems, the present invention employs the following sound level meter. Note that the following statements in parentheses are merely examples, and the present invention is not limited thereto.

[0008] In other words, the sound level meter of the present invention comprises a microphone that converts sound into an electrical signal, a preamplifier that converts the electrical signal into an impedance, a pressure sensor that detects atmospheric pressure, and a signal processing unit that calculates a predetermined evaluation value based on the output signal of the preamplifier and the output value of the pressure sensor.

[0009] Since microphone sensitivity depends on atmospheric pressure, when using a general sound level meter to take measurements in different environments such as different weather conditions or altitudes, the measured sound pressure level may be physically the same, but the resulting evaluation values ​​may differ.

[0010] In contrast, the sound level meter of the above embodiment is equipped with a pressure sensor, and calculates an evaluation value based on the output value of the pressure sensor. Therefore, with this embodiment of the sound level meter, the influence of atmospheric pressure on the measurement can be reduced, and it becomes possible to perform highly accurate and stable measurements.

[0011] Furthermore, the sound level meter according to the above embodiment is further equipped with a correction information storage unit that stores in advance pressure characteristic information relating to the correction of the amount of variation in the sensitivity level with respect to atmospheric pressure (hereinafter referred to as "pressure characteristic") which is specific to the microphone model, and the signal processing unit uses the pressure characteristic information to identify a correction amount corresponding to the output value of the pressure sensor, and calculates a predetermined evaluation value based on the output signal of the preamplifier and the identified correction amount.

[0012] According to this embodiment of the sound level meter, information regarding the correction of the pressure characteristics of the microphone mounted on the sound level meter can be used to identify a correction amount corresponding to the pressure at the time of measurement, and an evaluation value can be calculated based on this correction amount. As a result, a more accurate evaluation value can be shown, and measurements can be performed with higher precision and stability.

[0013] More preferably, the correction information storage unit of the sound level meter in the above embodiment stores in advance a calculation formula for determining the correction amount with atmospheric pressure as a variable.

[0014] According to this embodiment of the sound level meter, when the microphone has good linear characteristics with respect to atmospheric pressure, the correction amount can be identified with high resolution, and the evaluation value can be calculated accurately based on this correction amount.

[0015] Alternatively, the correction information storage unit of the sound level meter in the above embodiment stores information in advance that defines the correspondence between atmospheric pressure and the correction amount.

[0016] According to the noise meter of this aspect, even when the microphone does not have linearity with respect to air pressure (has complex air pressure characteristics), the evaluation value can be accurately calculated based on this correction amount.

[0017] Also, preferably, in the noise meter of any of the above aspects, the correction information storage unit stores in advance frequency characteristic information regarding the correction of the amount of variation (frequency characteristics) of the sensitivity level of the microphone with respect to atmospheric pressure according to frequency, and the signal processing unit uses the frequency characteristic information to identify correction information corresponding to the output value of the air pressure sensor, and applies the correction information in the process of calculating a predetermined evaluation value based on the output signal of the preamplifier to correct the amount of variation according to frequency.

[0018] The dependence of the sensitivity of the microphone on air pressure varies depending on frequency. According to the noise meter of this aspect, when calculating the evaluation value, information regarding the correction of the frequency characteristics according to the air pressure at the time of measurement can be applied to correct the frequency characteristics, so that a more accurate evaluation value can be shown and a more accurate measurement can be performed.

[0019] More preferably, in the noise meter of any of the above-described aspects, it further includes a housing that houses the components of the noise meter, and the housing has a hole that communicates the space that houses the microphone and the space outside thereof.

[0020] According to the noise meter of this aspect, since the air pressure in the space where the microphone is housed and the air pressure in the external space are kept substantially equal, the influence of the air pressure difference on the measurement can be reduced.

Effect of the Invention

[0021] As described above, according to the present invention, the influence of atmospheric pressure in measurement can be reduced.

Brief Description of the Drawings

[0022] [Figure 1] It is a front view showing the appearance of the noise meter 100 of one embodiment. [Figure 2]It is a block diagram showing the main configuration of the noise meter 100. [Figure 3] It is a flowchart showing an example of the procedure of arithmetic processing. [Figure 4] It is a diagram showing the air pressure characteristics of a microphone of a certain model at 250 Hz and the characteristics after correction. [Figure 5] It is a block diagram showing the main configuration of the noise meter 100' as a comparative example. [Figure 6] It is a flowchart showing an example of the procedure of arithmetic processing in the comparative example. [Figure 7] It is a flowchart showing an example of the procedure of arithmetic processing in Modification 1. [Figure 8] It is a flowchart showing an example of the procedure of arithmetic processing in Modification 2.

Mode for Carrying Out the Invention

[0023] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the following embodiments are preferred examples, and the present invention is not limited to this example.

[0024] FIG. 1 is a front view showing the appearance of the noise meter 100 according to one embodiment. The noise meter 100 includes, for example, a microphone unit 10 in which a microphone is arranged, a preamplifier unit 20 in which a preamplifier is arranged, and a main body unit 30 in which various components related to measurement are arranged. Further, outside the main body unit 30, a display unit 40 for displaying measurement results and an operation unit 50 having various operation buttons for the noise meter 100 are arranged.

[0025] Note that the appearance shown in FIG. 1 is merely an example and is not limited thereto. In the present embodiment, the part where the microphone is arranged (microphone unit 10) and the part where the preamplifier is arranged (preamplifier unit 20) are provided separately from the main body unit 30, but both the microphone and the preamplifier may be arranged in one part, or the preamplifier may be arranged in the main body unit 30.

[0026] Figure 2 is a functional block diagram showing the main components of the sound level meter 100. As shown in Figure 2, the sound level meter 100 has functional components such as a microphone 12, a preamplifier 22, a pressure sensor 24, a signal processing unit 32, a correction information storage unit 34, a display unit 40, and an operation unit 50, and is powered by a battery or an external power supply.

[0027] The microphone 12 detects sound, converts it into an electrical signal, and outputs it. The preamplifier 22 converts the output signal from the microphone 12 to an impedance and outputs it. The output signal from the preamplifier 22 is converted into a digital signal by an A / D conversion unit (not shown) and then input to the signal processing unit 32. The pressure sensor 24 detects atmospheric pressure and outputs a value corresponding to its magnitude. In this embodiment, a small pressure sensor using semiconductor technology is employed, which is mounted on a printed circuit board and incorporated, for example, inside the preamplifier unit 20.

[0028] The correction information storage unit 34 stores information regarding correction amounts and correction coefficients corresponding to the fluctuation amount of the sensitivity level to atmospheric pressure specific to the microphone 12 model, and the fluctuation amount of the sensitivity level with respect to frequency (hereinafter referred to as "frequency characteristics"). The signal processing unit 32 calculates a predetermined evaluation value based on the sampled input signal, and further calculates a correction amount based on the output value of the pressure sensor 24 and the information stored in the correction information storage unit 34, thereby outputting an evaluation value corrected for the pressure characteristics of the microphone 12 to the display unit 40. The specific details of the processing performed by the signal processing unit 32 will be described in detail later with reference to another drawing. The signal processing unit 32 can be implemented, for example, by a DSP (Digital Signal Processor).

[0029] The display unit 40 displays various information related to the measurement, including the evaluation value output from the signal processing unit 32. The operation unit 50 receives operations on the sound level meter 100 and, via a control unit (not shown), causes each functional unit to execute processing corresponding to the received operation. Although not shown, the sound level meter 100 can also continuously store measurement results in a storage medium such as internal memory or an SD card, or in another device connected by a cable (hereinafter collectively referred to as the "data storage unit").

[0030] Incidentally, although not shown in the diagram, a small hole (hereinafter referred to as the "pressure adjustment hole") is provided near the area where the rear of the diaphragm of the microphone 12 is located in the microphone unit 10. Through the pressure adjustment hole, the pressure between the inside and outside of the microphone unit 10 (the inside and outside of the housing in which the microphone 12 is located) can be adjusted, making it possible to obtain good frequency characteristics for the microphone 12. If the microphone is to be permanently installed, the pressure adjustment hole may be provided at the connection point between the microphone unit 10 and the preamplifier unit 20. This allows the pressure between the inside and outside of the microphone unit 10 to be adjusted through the preamplifier unit 20.

[0031] Furthermore, if the sound level meter 100 is to be waterproof, for example, the space between the rear of the diaphragm of the microphone 12 and the preamplifier 22 is made to be sealed from the outside. In such a sound level meter 100, if the pressure sensor 24 is placed inside the preamplifier section 20, a hole (hereinafter referred to as a "communication hole") is provided to connect the internal spaces of the microphone section 10, the preamplifier section 20, and the main body section 30, while maintaining the sealed structure between the rear of the diaphragm of the microphone 12 and the preamplifier 22 as described above. In addition, the main body section 30 is provided with a small hole sealed with a material that allows air to pass through but does not allow water to pass through (for example, Gore-Tex®). With this structure, the air pressure inside the main body section 30 can be adjusted to match the outside air pressure, and even if the temperature inside the main body section 30 rises during measurement, heat can be released to the outside to prevent an increase in internal pressure. As a result, the internal pressure of the microphone 10 and the preamplifier section 20 can be kept approximately equal to the outside air pressure through the communication hole.

[0032] In this embodiment, the pressure sensor 24 is built into the preamplifier unit 20, but its location is not limited to this. It may also be built into the main unit 30, or into the microphone unit 10 if constraints regarding electrical connections and space permit.

[0033] [Calculation processing] Figure 3 is a flowchart showing an example of the calculation process. The calculation process refers to the process in which the signal processing unit 32 calculates and outputs a predetermined evaluation value once every time T (for example, 10 minutes) has elapsed. During time T, the signals input to the signal processing unit 32 are sampled at a constant interval, and these input signals are the subject of the calculation process. For the sake of explanation, in the following explanation, each input signal sampled during time T will be represented as "x(t)". ​​The following explanation will follow an example procedure.

[0034] Step S110: The signal processing unit 32 performs correction amount identification processing. As described above, the correction information storage unit 34 has in advance information regarding the correction amount corresponding to the atmospheric pressure characteristics specific to the model of the microphone 12. Examples of information regarding the correction amount include calculation formulas that use atmospheric pressure as a parameter, and correction amount tables that define correction amounts according to atmospheric pressure. This information is set according to the atmospheric pressure characteristics of a predetermined frequency (e.g., 250 Hz). In the correction amount identification processing, the signal processing unit 32 obtains the current output value P(t) of the atmospheric pressure sensor 24 and identifies the correction amount h corresponding to the value P(t) using, for example, a calculation formula that has been in advance stored in the correction information storage unit 34.

[0035] Step S120: The signal processing unit 32 performs weighted filtering. In this process, the signal processing unit 32 applies the frequency weighting characteristics A, C, and Z filters defined in the standard to each input signal x(t) sampled over time T to correct the frequency. The output of each filter is conveniently represented as "α(t)".

[0036] Step S130: The signal processing unit 32 performs the evaluation value calculation process. In this process, the signal processing unit 32 calculates the evaluation value of the sound pressure level based on the output α(t) of each filter using the following formula.

[0037]

number

[0038] The signal processing unit 32 calculates the squared value of the output α(t) of each filter using equation (1) to obtain β(t), and then performs the statistical operations shown in equations (2) to (4) to calculate three types of evaluation values ​​specified by standards and laws. Specifically, it finds the square root of the maximum value of β(t) using equation (2), calculates the equivalent noise level (square root of the mean squared value over time T) using equation (3), and calculates the time-weighted RMS value using equation (4). In the above equations, "a" represents the time constant in seconds according to the time weighting characteristics. The reverse of the value It is a number, and the time-weighted characteristic F is 8 ( = The reciprocal of the time constant 0.125 s ), the time-weighted characteristic S is 1 ( = The reciprocal of the time constant 1.0 s The following are used respectively. For convenience, each calculated evaluation value is represented as "V(t)".

[0039] The signal processing unit 32 further converts each evaluation value V(t) calculated using the above formulas (2) to (4) into dB units using the following formula.

[0040]

number

[0041] In the above formula, "V dB "(t)" represents each evaluation value V(t) in dB units, and "Vr" is the reference sound pressure of 0 dB, i.e., 2 × 10 -5 It is Pa (=20 μPa).

[0042] Step S140: The signal processing unit 32 performs pressure characteristic correction processing. In this process, the correction amount h identified in step S110 is used to correct each evaluation value before and after dB conversion calculated in step S130 using the following formula.

[0043]

number

[0044] In the above formula, "O L(t) is the value obtained by correcting the evaluation value expressed as a linear value before dB conversion, "O dB (t) is the value obtained by correcting the evaluation value after dB conversion.

[0045] Upon completion of the above procedure, the signal processing unit 32 outputs each corrected evaluation value, that is, each evaluation value that takes into account the atmospheric pressure characteristics specific to the microphone model 12, in both dB and linear values. The evaluation value (dB value) obtained by formula (7) is mainly used for displaying the measurement results on the display unit 40. On the other hand, the evaluation value (linear value) obtained by formula (6) is stored in the data storage unit (not shown) described above and used for subsequent analysis processing, etc.

[0046] In the above example procedure, the output value P(t) of the pressure sensor 24 at the time of execution in step S110 is used directly. However, instead, a moving average over time T may be used as P(t). In this case, the moving average is calculated using the following formula.

[0047]

number

[0048] In the above formula, "t" is a discrete time point, and "p(i)" is the output value of the pressure sensor 24 sampled at each time point.

[0049] [Microphone pressure characteristics] Figure 4 shows an example of the atmospheric pressure characteristics of a certain microphone model at 250 Hz, and an example of its corrected characteristics. In the graph shown in Figure 4, the three gray dashed lines represent the atmospheric pressure characteristics of three microphones of the same model, No. 1 to No. 3, and the gray solid line represents the average value of these atmospheric pressure characteristics. The three black dashed lines represent the characteristics of the three microphones after correcting their atmospheric pressure characteristics based on the atmospheric pressure characteristics of this model, and the black solid line represents the average value of the corrected characteristics. The dotted line represents the acceptable limit of deviation of the indicated value specified in the standard for Class 1 sound level meters, and the double dotted line represents the acceptable limit of deviation of the indicated value specified for Class 2 level meters.

[0050] The standard specifies the acceptable limit for deviation of the sound level indication value from the reference static pressure (101.325 kPa) at one frequency between 160 Hz and 1250 Hz, as follows: "The deviation of the sound level reading from the reference static pressure reading in the static pressure range of 85 kPa or higher and 108 kPa or lower shall not exceed ±0.4 dB for Class 1 sound level meters and ±0.7 dB for Class 2 sound level meters." "The deviation of the sound level reading from the reference static pressure reading in the static pressure range of 65 kPa or higher but less than 85 kPa shall not exceed ±0.9 dB for Class 1 sound level meters and ±1.6 dB for Class 2 sound level meters."

[0051] Thus, the standard requires stable measurements with minimal fluctuation in indicated values ​​over a wide static pressure range of 65kPa to 108kPa. Furthermore, stricter acceptance limits (tolerance ranges) are specified for deviations from indicated values ​​compared to Class 1. For this reason, expensive microphones that are highly precise and have low static pressure dependence are generally used in Class 1 sound level meters.

[0052] As shown in Figure 4, the uncorrected responses of the three microphones No. 1 to No. 3, based on the readings at a reference static pressure (101.325 kPa), fall within the Class 2 tolerance range across the entire specified static pressure range (65 kPa to 108 kPa). However, they exceed the Class 1 tolerance range in the 65 kPa to approximately 78 kPa and 85 kPa to approximately 91 kPa ranges. This indicates that this microphone does not conform to the Class 1 standard but conforms to the Class 2 standard, meaning it has pressure characteristics equivalent to Class 2. Such microphones are often less expensive than microphones used in Class 1 sound level meters.

[0053] Incidentally, as mentioned above, atmospheric pressure can fluctuate significantly during the measurement period. For example, in 2020, the maximum daily pressure fluctuation at the Japan Meteorological Agency's Tokyo Observatory was approximately 2.7 kPa, and the maximum daily pressure fluctuation throughout the year was approximately 4 kPa. Considering the pressure characteristics shown in Figure 4, when observing noise levels seasonally throughout the year using a sound level meter equipped with the above-mentioned microphone (hereinafter referred to as "measurement case 1"), even if the noise level is physically the same, if the reading at 101 kPa is 80 dB, the reading at 97 kPa, which is 4 kPa lower, may be 80.2 dB. Furthermore, when measuring the same physically occurring noise level at measurement points with different altitudes, for example, at an altitude of 0 m (e.g., 101.325 kPa) and at the summit of Mt. Fuji (e.g., 65 kPa) (hereinafter referred to as "measurement case 2"), if the reading at 0 m is 80 dB, the reading at the summit of Mt. Fuji may be 81.4 dB.

[0054] From the graph in Figure 4, it can be seen that this microphone model has good linear characteristics with respect to atmospheric pressure (its atmospheric pressure characteristics can be sufficiently approximated by a linear equation). In such cases, it is possible to determine the correction amount h according to the atmospheric pressure using a linear equation. Focusing on the corrected characteristics of the three units, that is, the value obtained by subtracting the correction amount determined by the linear equation from the response before correction, in all cases the slope is smaller than before correction, and the response is well within the acceptable range for Class 1 across the entire specified static pressure range. Therefore, the difference in each indicated value due to the difference in atmospheric pressure that may occur in the above measurement cases 1 and 2 will become very small (almost nonexistent) if corrected using the determined correction amount h.

[0055] As shown above, the corrected response falls well within the acceptable range of Class 1, as well as Class 2, with ample margin. This indicates that even microphones that meet the Class 2 standard but not the Class 1 standard in their uncorrected state can be made to meet the Class 1 standard by appropriately correcting them based on their atmospheric pressure characteristics. Furthermore, it is possible to reduce (significantly reduce) the difference in evaluation values ​​caused by differences in atmospheric pressure when measuring sounds at physically the same sound pressure level.

[0056] If the microphone 12 mounted on the sound level meter 100 has good linear characteristics with respect to atmospheric pressure, as shown in Figure 4, the correction amount h for the output value P(t) of the atmospheric pressure sensor 24 can be determined using a linear equation (h=γP(t)) with atmospheric pressure as the variable. On the other hand, if the microphone 12 does not have linearity with respect to atmospheric pressure and the atmospheric pressure characteristics have a more complex shape, the correction amount h for the output value P(t) of the atmospheric pressure sensor 24 can be determined from the correction amount table by pre-defining the correspondence between atmospheric pressure and the correction amount in the correction amount table.

[0057] In this embodiment, the above-mentioned calculation formulas and correction amount tables derived based on the atmospheric pressure characteristics specific to the microphone 12 model are pre-stored in the correction information storage unit 34. Therefore, by subtracting the correction amount h, which is specified according to the atmospheric pressure at the time of measurement, from the calculated evaluation value, the evaluation value can be corrected with high accuracy. As a result, it is possible to use an inexpensive microphone with performance sufficient to satisfy the acceptable limit of deviation of the indicated value for Class 2 (atmospheric pressure characteristics equivalent to Class 2) to satisfy the acceptable limit of deviation of the indicated value for Class 1, and to manufacture a sound level meter that conforms to the Class 1 standard at a low cost.

[0058] [Comparative Example] Figure 5 is a block diagram showing the main configuration of a conventional general sound level meter 100' as a comparative example. The comparative sound level meter 100' differs from the sound level meter 100 of the embodiment described above in that it does not have a pressure sensor and a correction information storage unit.

[0059] Figure 6 is a flowchart showing an example of the calculation process in sound level meter 100' as a comparative example. In Figure 6, steps common to the calculation process in the embodiment shown in Figure 3 are denoted by the same reference numerals. The calculation process of the comparative example consists of steps S120 and S130, and the correction amount identification process and the pressure characteristic correction process (steps S110 and S140 in Figure 3) are not performed.

[0060] In other words, the comparative example sound level meter 100' does not have a pressure sensor or a correction information storage unit, and the signal processing unit 32' calculates and outputs the evaluation value without considering the pressure characteristics specific to the microphone model mounted on the sound level meter 100'. Therefore, the sound level meter 100' cannot cope with the influence of atmospheric pressure due to differences in the measurement environment (weather, altitude, etc.), and may display different evaluation values ​​even if the measured sound pressure level is physically the same.

[0061] [Advantages of the present invention] In contrast, the sound level meter 100 of the above-described embodiment has a pressure sensor 24 and a correction information storage unit 34. Using information on the pressure characteristics specific to the model of the microphone 12 that is stored in advance in the correction information storage unit 34, it can identify a correction amount corresponding to the output value of the pressure sensor 24, and calculate and output an evaluation value based on this correction amount.

[0062] Therefore, according to the sound level meter 100 of this embodiment, the influence of atmospheric pressure on the microphone 12 during sound pressure level measurement can be reduced, enabling highly accurate and stable measurements. Furthermore, according to the sound level meter 100 of this embodiment, a sound level meter having Class 1 atmospheric pressure characteristics can be realized using an inexpensive microphone having Class 2 equivalent atmospheric pressure characteristics, thereby reducing the manufacturing cost of a sound level meter that conforms to the Class 1 standard.

[0063] Incidentally, the pressure dependence of a microphone's sensitivity varies with frequency. Generally, microphones mounted on sound level meters can be considered to have roughly constant pressure dependence regardless of frequency within the standard static pressure range (160Hz to 1250Hz) and below. In contrast, at frequencies higher than the standard range, the pressure dependence differs depending on the frequency, resulting in fluctuations in the frequency characteristics. In particular, when performing frequency analysis of sound, this can affect the reliability of the measurement results.

[0064] Therefore, in addition to the correction based on the fluctuation in the microphone's sensitivity due to atmospheric pressure (atmospheric pressure characteristics) as described above, performing a correction based on the fluctuation in the microphone's frequency characteristics due to atmospheric pressure (hereinafter sometimes referred to as "frequency correction") makes it possible to perform measurements with even greater accuracy. Below, a modified example in which frequency correction is performed according to the output value of the atmospheric pressure sensor 24 will be described.

[0065] [Variation 1] Figure 7 is a flowchart showing an example of the calculation process in Modification 1. In Figure 7, the same reference numerals are used for the same steps as in the embodiment shown in Figure 3.

[0066] The calculation process in Modification 1 differs from the embodiment described above in that it includes additional steps related to frequency correction according to the output value of the pressure sensor 24 (steps S112 and S114, described later). The following will be explained according to an example of the procedure, but explanations of points that are the same as in the embodiment will be omitted as appropriate.

[0067] Step S110: The signal processing unit 32 performs a correction amount identification process and, for example, uses a calculation formula pre-stored in the correction information storage unit 34 to identify a correction amount h corresponding to the current output value P(t) of the pressure sensor 24.

[0068] Step S112: The signal processing unit 32 performs a correction coefficient identification process. The correction information storage unit 34 has information regarding frequency characteristic correction specific to the microphone model 12 stored in advance. Information regarding frequency characteristic correction includes, for example, a correction amount table that defines correction amounts for output values ​​for each bandwidth such as octave and 1 / 3 octave, correction amounts for each spectrum for the results of spectral analysis represented by Fourier transform, a frequency characteristic correction coefficient table that defines correction coefficients according to atmospheric pressure, and a calculation formula for a correction coefficient with atmospheric pressure as a parameter. This information is set according to the frequency characteristics associated with atmospheric pressure based on a predetermined frequency (e.g., 250 Hz). In the correction coefficient identification process, the signal processing unit 32 uses, for example, the frequency characteristic correction coefficient table to determine the correction coefficient a corresponding to the value P(t). n ,b n Identify the following: Here, "n" is Subscripts to distinguish coefficients That is the case.

[0069] Step S114: The signal processing unit 32 performs frequency correction filtering. In this process, the signal processing unit 32 applies a frequency correction filter to each input signal x(t) sampled during time T using the following formula to correct the frequency.

[0070]

number

[0071] Step S120: The signal processing unit performs weighted filtering and applies the above frequency weighting characteristics A, C, and Z filters to the output y(t) of the above frequency correction filter to correct the frequency.

[0072] Step S130: The signal processing unit 32 performs an evaluation value calculation process and calculates a predetermined evaluation value based on the output α(t) of each filter applied in step S120.

[0073] Step S140: The signal processing unit 32 performs pressure characteristic correction processing and corrects the evaluation value calculated in step S130 using the correction amount h identified in step S110.

[0074] Thus, in the calculation process of the modified example 1, a frequency correction filter is applied to the input signal x(t) to correct the frequency characteristics (steps S112, S114), and the evaluation value calculated after weighted filtering (step S120) and evaluation value calculation (step S130) is corrected based on the atmospheric pressure characteristics (step S140).

[0075] [Variation 2] Figure 8 is a flowchart showing an example of the calculation procedure in Modification Example 2.

[0076] The calculation process in Modification 2 includes an additional step (step S240, described later) to perform frequency analysis on the output of the weighted filter process. This significantly differs from the embodiment described above in that it calculates and corrects evaluation values ​​for each target segmented by the frequency analysis. The differences from the embodiment will be explained below, following an example procedure.

[0077] Step S210: The signal processing unit 32 performs a correction amount identification process and, for example, uses a calculation formula pre-stored in the correction information storage unit 34 to identify a correction amount h corresponding to the current output value P(t) of the pressure sensor 24.

[0078] Step S220: The signal processing unit 32 performs a correction coefficient identification process and, for example, uses a formula for calculating a correction coefficient that uses atmospheric pressure as a parameter, which is pre-stored in the correction information storage unit 34, to identify the correction coefficient c for the frequency characteristics of the output value P(t).

[0079] Step S230: The signal processing unit 32 performs weighted filtering and applies the above-mentioned frequency weighting characteristics A, C, and Z filters to each input signal x(t) sampled during time T to correct the frequency.

[0080] Step S240: The signal processing unit 32 performs frequency analysis. In this process, the signal processing unit 32 performs frequency analysis on the output α(t) of each of the filters described above and divides the output into multiple parts. The signal processing unit 32 may perform octave analysis or 1 / 3 octave analysis as the frequency analysis and divide the output into multiple frequency bands, or it may perform spectral analysis using Fourier transform or the like and divide the output into multiple spectra. For convenience, the output of the frequency analysis process is represented as "ξ(s,t)". Here, "s" is a numerical value that indicates the divided frequency band or spectrum.

[0081] Step S250: The signal processing unit 32 executes the evaluation value calculation process and calculates a predetermined evaluation value V(s,t) based on the output ξ(s,t) of the frequency analysis process using the following formula.

[0082]

number

[0083] Specifically, the signal processing unit 32 calculates the squared value of the output ξ(s,t) of the frequency analysis process using equation (11) and sets it as β(s,t). Then, it finds the square root of its maximum value using equation (12), calculates the equivalent noise level (square root of the mean squared value over time T) using equation (13), and calculates the time-weighted RMS value using equation (14). The constant a used in each equation is the same as in the embodiment described above (and so on).

[0084] The signal processing unit 32 further converts each evaluation value V(s,t) calculated using the above formulas (12) to (14) into dB units using the following formula.

[0085]

number

[0086] Step S260: The signal processing unit 32 performs pressure characteristic and frequency characteristic correction processing. In this process, the signal processing unit 32 first uses the frequency characteristic correction coefficient c identified in step S210 to determine the frequency characteristic correction amount k for the divided frequency band or spectrum. Then, using the pressure characteristic correction amount h identified in step S220 and the frequency characteristic correction amount k, it corrects each evaluation value before and after dB conversion calculated in step S250 using the following formula.

[0087]

number

[0088] In formulas (16) and (17) above, the evaluation value is corrected by subtracting the sum of the pressure characteristic correction amount h and the frequency characteristic correction amount k (h+k). Alternatively, the correction amounts h and k could be subtracted one by one from the evaluation value.

[0089] Thus, in the calculation process of Modified Example 2, a weighted filter is applied to the input signal x(t) (step S230), then a frequency analysis is performed (step S240), an evaluation value is calculated for each frequency band or spectrum divided by the frequency analysis (step S240), and the calculated evaluation value is corrected based on the atmospheric pressure characteristics and frequency characteristics (step S250). Modified Example 2 is mainly used when the output of the results of the frequency analysis of sound is required.

[0090] In the above example procedure, the correction amount h for atmospheric pressure characteristics and the correction amount k for frequency characteristics are identified separately (information used to identify correction amount h and information used to identify correction amount k are stored separately), and the evaluation value is corrected using correction amounts h and k. However, if it is possible to define information (correction amount table or calculation formula) for identifying a correction amount w that takes into account both atmospheric pressure characteristics and frequency characteristics, that information may be stored in the correction information storage unit 34 in advance, and the correction amount w identified using that information may be used to correct the evaluation value.

[0091] As described above, the following effects can be obtained with the noise meter 100 of the above-described embodiment and its modified form.

[0092] (1) According to the sound level meter 100, information regarding the pressure characteristics specific to the microphone 12 model is pre-stored in the correction information storage unit 34. Using this information, a correction amount h corresponding to the output value of the pressure sensor 24 at the time of measurement can be identified. Therefore, by subtracting the correction amount h from the calculated evaluation value, the evaluation value can be corrected with high accuracy.

[0093] (2) According to the sound level meter 100, information regarding the frequency characteristics associated with atmospheric pressure specific to the microphone 12 model is pre-stored in the correction information storage unit 34. This information can be used to identify correction information corresponding to the output value of the atmospheric pressure sensor 24 at the time of measurement. By calculating the evaluation value based on this correction information, a highly accurate evaluation value can be output.

[0094] (3) According to the sound level meter 100, small holes (communication holes) are provided in appropriate positions according to its structure, so that the air pressure between the space in which the microphone 12 is placed and the outside of the sound level meter 100 can be adjusted, and the influence of the air pressure difference on the measurement can be reduced.

[0095] (4) According to the sound level meter 100, a communication hole is provided at an appropriate position according to its structure, which allows for adjustment of the air pressure between the space in which the pressure sensor is located and the outside of the sound level meter, enabling accurate correction.

[0096] (5) According to the sound level meter 100, the evaluation value is calculated based on the atmospheric pressure characteristics specific to the microphone 12 model and the frequency characteristics associated with atmospheric pressure. Therefore, the influence of atmospheric pressure on the microphone 12 during noise level measurement can be reduced, enabling highly accurate and stable measurements.

[0097] (6) According to the sound level meter 100, the influence of atmospheric pressure on the microphone 12 during measurement can be reduced by correcting for the pressure characteristics and frequency characteristics specific to the model of microphone 12. Therefore, a sound level meter conforming to the Class 1 standard can be realized using an inexpensive microphone with pressure characteristics equivalent to Class 2, and the manufacturing cost of a sound level meter conforming to the Class 1 standard can be reduced.

[0098] The present invention can be implemented in various ways without being limited to the embodiments and modifications described above.

[0099] In the calculation process of the embodiment described above (Figure 3), the atmospheric pressure characteristics are corrected, and in the modified examples described above (Figures 7 and 8), both the atmospheric pressure characteristics and the frequency characteristics are corrected. However, as a further modification, a configuration in which only the frequency characteristics are corrected may also be used.

[0100] In the embodiment described above, a pressure sensor 24 is built in, but a temperature sensor may also be built in to calculate the evaluation value taking into account the influence of temperature in addition to atmospheric pressure.

[0101] In the above-described embodiment, an evaluation value is calculated by statistical calculation during the calculation process, which is performed with time T as the calculation period (step S130 in Figure 3), and this evaluation value is corrected based on the atmospheric pressure characteristics (step S140 in Figure 3). However, instead, a process equivalent to correction amount identification (step S110 in Figure 3) and filtering (step S120 in Figure 3) may be performed when sampling the input signal, the correction amount is subtracted in real time from the result, and after time T has elapsed, statistical calculations are performed on the corrected sampled data to calculate the evaluation value.

[0102] In the embodiment described above, the output signal of the preamplifier 22 is A / D converted before being input to the signal processing unit 32. However, it is also possible to configure the system to perform subsequent processing on the analog signal without A / D conversion.

[0103] In the embodiment described above, the microphone unit 10, the preamplifier unit 20, and the main unit 30 are connected to form an integrated sound level meter 100. However, instead, the sound level meter can also be implemented by mounting each functional unit (signal processing unit 32, correction information storage unit 34, display unit 40, and operation unit 50) located in the main unit 30 onto a general-purpose computer equipped with a CPU, RAM, HDD, monitor, etc., and connecting the microphone unit 10 and the preamplifier unit 20 to this computer via cables or the like.

[0104] Furthermore, the configurations and numerical values ​​mentioned in the explanation of the sound level meter 100 are merely examples, and it goes without saying that they can be modified as appropriate when implementing the present invention. [Explanation of symbols]

[0105] 10 Microphone section 12 Microphones 20 Preamplifier Section 22 Preamplifier 24 barometric pressure sensor 30 Main body 32 Signal Processing Unit 34 Correction Information Storage Unit 40 Display section 50 Control section 100 Sound level meter

Claims

1. A microphone that converts sound into electrical signals, A preamplifier that performs impedance conversion on the aforementioned electrical signal, A pressure sensor that detects atmospheric pressure, A correction information storage unit that pre-stores pressure characteristic information related to the correction of fluctuations in the sensitivity level of the microphone with respect to atmospheric pressure, A signal processing unit that uses the aforementioned pressure characteristic information to identify a correction amount corresponding to the output value of the pressure sensor, and calculates a predetermined evaluation value based on the output signal of the preamplifier and the identified correction amount. A sound level meter is included.

2. In the sound level meter according to claim 1, The correction information storage unit is, As the aforementioned atmospheric pressure characteristic information, a calculation formula for determining a correction amount using atmospheric pressure as a variable is stored in advance. A sound level meter characterized by the following features.

3. In the sound level meter according to claim 1, The correction information storage unit is, The aforementioned pressure characteristic information includes pre-stored information defining the correspondence between pressure and correction amount. A sound level meter characterized by the following features.

4. In the sound level meter according to any one of claims 1 to 3, The correction information storage unit is, The frequency characteristic information relating to the correction of the frequency variation in the sensitivity level of the microphone with respect to atmospheric pressure is stored in advance. The signal processing unit, The frequency characteristic information is used to identify correction information corresponding to the output value of the pressure sensor, and the amount of variation due to frequency is corrected by applying the correction information in the process of calculating the predetermined evaluation value based on the output signal of the preamplifier. A sound level meter characterized by the following features.

5. In the sound level meter according to any one of claims 1 to 4, The sound level meter further comprises a housing for housing its components, The aforementioned enclosure is A sound level meter characterized by having a hole that connects the space for housing the microphone with the space outside of it.

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