JP2014240761A - Sound calibrator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sound calibrator which performs accurate calibration by generating sound which has a fixed sound pressure and has a signal waveform less distorted, without being affected by variation in atmospheric pressure.SOLUTION: A sound calibrator 10 includes: a coupler 21 to which a microphone 31 is to be inserted; a speaker 11 which outputs sound into the coupler 21; a gauge pressure sensor 12 which measures a sound pressure in accordance with a difference between an air pressure in the coupler 21 to which the sound is outputted by the speaker 11, and an atmospheric pressure; analysis means 17 which analyzes distortion of a signal waveform on the basis of the sound pressure measured by the gauge pressure sensor 12; distortion correction means 18 which corrects the distortion of the signal waveform of the sound outputted by the speaker 11 on the basis of analysis in the analysis means 17; and control means 13 which performs correction using the distortion correction means 18 to control an output to the speaker 11 so that the sound pressure measured by the gauge pressure sensor 12 becomes a fixed sound pressure and the distortion of the signal waveform is reduced.

Description

  The present invention relates to an acoustic calibrator.

Conventionally, in the measurement for measuring the sound level, the adjustment in the environment at the time of measurement is performed by the generated sound pressure level of the speaker of the acoustic calibrator. Usually, the sound pressure generated by a speaker or the like varies depending on environmental factors such as atmospheric pressure, temperature, and humidity. For this reason, the change in atmospheric pressure is corrected and adjusted based on the reference atmospheric pressure (1.01325 × 10 ⁵ Pa) based on the atmospheric pressure measured using the barometer and the correction table. Yes. In addition, a speaker or the like having a good temperature characteristic with respect to a change in temperature (a variation in generated sound pressure with respect to the temperature is small) is selected and used. Further, a speaker or the like that does not distort the sound pressure waveform is selected so as not to lower the calibration accuracy.

Patent Documents 1 to 3 are known as techniques for compensating for these adjustments.
Patent Document 1 discloses an acoustic calibrator that performs acoustic calibration efficiently without worrying about changes in atmospheric pressure. This acoustic calibrator is an acoustic calibrator in which a pressure microphone is inserted into a coupler, a sound pressure is generated by an electromagnetic earphone in the coupler, and the sound pressure is supplied to the pressure microphone. The electromagnetic earphone is controlled so that the inside of the coupler has a predetermined sound pressure corresponding to the detected value of the atmospheric pressure sensor to be detected.

  Patent Document 2 discloses an acoustic calibration that can automatically adjust the output and sensitivity following the ambient temperature change without complicating the structure of the microphone, and maintain a highly accurate output against environmental changes. Disclose the vessel. This sound calibrator has a built-in sound generator, and an output monitoring microphone is arranged in the vicinity of the sound generator, and the output of the output monitoring microphone is constantly monitored and controlled to always generate a constant calibration sound pressure. And an acoustic calibrator for calibrating the sensitivity of the object to be inspected, including a microphone unit or a sound level meter, in the vicinity of the sound calibrator by a temperature detection sensor. The output monitoring microphone output is corrected based on the detection result of the temperature detection sensor.

  Patent Document 3 discloses an easy-to-use acoustic calibrator by reducing the height and reducing the calibration accuracy to a shape that is stable during calibration work. This acoustic calibrator includes a coupler into which a pressure microphone is inserted, and an electromagnetic earphone that is smaller than a speaker in the coupler. The acoustic calibrator uses the waveform data obtained by superimposing the harmonic component on the sine wave to measure the sound pressure distortion in the coupler using a distortion meter, and the sound pressure distortion is detected for each superimposed harmonic component. The minimum amplitude and phase are found, and waveform data obtained by superimposing the found harmonic components is supplied to the electromagnetic earphone so that the waveform distortion of the calibration sound generated by the electromagnetic earphone is minimized.

JP 2001-349773 A JP 2008-256433 A JP 2001-352598 A

  However, the acoustic calibrator of Patent Document 1 is provided with a communication hole through which the cavity in the coupler communicates with the outside air so that the pressure in the coupler is equal to the atmospheric pressure, and according to the detection value by the atmospheric pressure sensor, The output of the electromagnetic earphone is controlled so that the inside has a predetermined sound pressure. For this reason, if the amount of leakage from the communication hole changes, or if leakage from other sources occurs, or if the pressure in the coupler immediately after the microphone to be calibrated is not equal to the atmospheric pressure, the volume in the coupler will change. In such a case, there is a possibility that the sound pressure in the coupler does not become a predetermined sound pressure. Moreover, the technique of patent document 2 is a technique for maintaining a highly accurate output with respect to a temperature change among environmental changes. Furthermore, the technique of Patent Document 3 needs to find the optimum waveform data for a speaker or an electromagnetic earphone for each environment at the time of measurement. As described above, none of the techniques is sufficient as a technique for accurately calibrating changes in the environment at the time of measurement.

  An object of the present invention is to provide an acoustic calibrator for accurately calibrating by generating sound having a constant sound pressure and little distortion of a signal waveform without being affected by changes in atmospheric pressure. To do.

The present invention provides the following solutions.
(1) An acoustic calibrator having a coupler for inserting a microphone, an acoustic output means for outputting sound into the coupler, an atmospheric pressure in the coupler to which sound is output by the acoustic output means, and an atmospheric pressure Based on the analysis by the analysis means, the sound pressure measurement means for measuring the sound pressure by the difference between, the analysis means for analyzing the distortion of the signal waveform based on the sound pressure measured by the sound pressure measurement means, Distortion correcting means for correcting distortion of the acoustic signal waveform output by the acoustic output means, and the sound pressure measured by the sound pressure measuring means becomes a constant sound pressure, and the distortion of the signal waveform is reduced. And a control unit that corrects the distortion using the distortion correction unit and controls the output to the sound output unit.

  According to the configuration of (1), the acoustic calibrator according to the present invention outputs sound in the coupler, measures the sound pressure by the difference between the atmospheric pressure and the atmospheric pressure in the coupler from which the sound is output, and measures the sound pressure. Analyzes the distortion of the signal waveform based on the sound pressure, corrects the distortion of the signal waveform of the output sound based on the analysis, reduces the measured waveform to a constant sound pressure, and reduces the distortion of the signal waveform And the output to the sound output means is controlled.

That is, the acoustic calibrator according to the present invention measures the sound pressure generated in the coupler by the difference between the atmospheric pressure in the coupler and the atmospheric pressure, the measured sound pressure becomes a constant sound pressure, and the signal waveform The output to the sound output means is controlled so that the distortion of the sound is reduced.
Therefore, the sound calibrator according to the present invention can generate a sound having a constant sound pressure and a small distortion of the signal waveform without being affected by a change in the atmospheric pressure, thereby enabling accurate calibration. it can.

  (2) The sound pressure measuring means has a difference between the atmospheric pressure in the coupler and the atmospheric pressure in which the sound is output by the acoustic output means in a state where one end communicates with the coupler and the other end is opened to the atmospheric pressure. The sound calibrator according to (1), wherein the sound pressure is measured by:

  Therefore, the acoustic calibrator according to (2) can calibrate more accurately by reliably generating a sound with a constant sound pressure and less distortion of the signal waveform without being affected by the change in atmospheric pressure. Can be.

  (3) Computation means for performing computation for extracting the sound pressure level of the frequency of the generated sound pressure signal from the sound pressure measured by the sound pressure measurement means is further provided, and the control means is computed by the computation means. The acoustic calibrator according to (1) or (2), wherein the output to the acoustic output means is controlled using the obtained value.

  Therefore, the sound calibrator according to (3) uses the sound pressure level to reliably generate sound that is constant sound pressure and has little distortion in the signal waveform without being affected by changes in atmospheric pressure. It is possible to calibrate with higher accuracy.

  (4) The acoustic calibrator according to (3), wherein the calculation unit performs an FFT or DFT calculation, and the control unit performs feedback using a value of the FFT or the DFT calculation.

  Therefore, the acoustic calibrator according to (4) feeds back the calculation result of the sound pressure level to ensure that the sound has a constant sound pressure and little distortion of the signal waveform without being affected by changes in atmospheric pressure. Can be calibrated and more accurately calibrated.

  (5) The sound pressure measured by the sound pressure measuring means based on the temperature measuring means arranged along the sound pressure measuring means and measuring the temperature of the gas and the temperature measured by the temperature measuring means. The acoustic calibrator according to any one of (1) to (4), further comprising temperature correction means for correcting.

  Therefore, the sound calibrator according to the present invention corrects the temperature of the measured sound pressure to ensure that the sound has a constant sound pressure and little distortion of the signal waveform without being affected by changes in atmospheric pressure and temperature. Can be calibrated and more accurately calibrated.

According to the present invention, it is possible to provide an acoustic calibrator for generating a sound that has a constant sound pressure and little distortion of a signal waveform without being affected by changes in atmospheric pressure, and calibrates with high accuracy. it can.
Furthermore, according to the present invention, there is no need to separately perform signal waveform distortion correction, atmospheric pressure correction, coupler volume correction, and temperature correction, and the generated sound pressure can be kept constant and signal waveform distortion can be automatically performed. Fewer acoustic calibrators can be provided. It is possible to provide an acoustic calibrator in which the influence of the self-noise and offset of the sensor used for automatically performing these corrections is reduced.

It is a block diagram which shows the structure of the acoustic calibrator which concerns on one Embodiment of this invention. It is a flowchart which shows the processing content of the acoustic calibrator which concerns on one Embodiment of this invention. It is a flowchart following FIG. It is a flowchart following FIG. It is a flowchart following FIG. It is a flowchart following FIG. It is a figure which shows the example of the signal which the acoustic calibrator which concerns on one Embodiment of this invention outputs.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a block diagram showing a configuration of an acoustic calibrator 10 according to an embodiment of the present invention. The acoustic calibrator 10 includes a speaker 11 as an acoustic output unit, a gauge pressure sensor 12 as a sound pressure measuring unit, a control unit 13, a calculating unit 14, a temperature sensor 15 as a temperature measuring unit, and a temperature correcting unit. 16, analysis means 17, and distortion correction means 18. The acoustic calibrator 10 is operated by, for example, a battery including a battery detector 136 and a DC-DC converter 137, and the power is controlled by the control unit 13. Hereinafter, each part is explained in full detail.

The speaker 11 outputs sound into the coupler 21. Specifically, the speaker 11 is attached to the coupler 21 and generates a sound pressure in the coupler 21. The coupler 21 includes, for example, an opening 211 so that a microphone 31 as a calibration target can be inserted. When the microphone 31 is inserted into the opening 211, the coupler 21 becomes a sealed space.
The speaker 11 is controlled by current drive. For example, a diaphragm (diaphragm) vibrates according to a sine wave electric signal, and radiates sound waves. Assuming that a sine wave is emitted from the speaker 11 as a sound wave, the change in the atmospheric pressure in the coupler 21 is a sine wave centered on the atmospheric pressure. Even if the moving amount of the diaphragm (diaphragm) of the speaker 11 is the same, the atmospheric pressure in the coupler changes due to the atmospheric pressure. That is, in order to keep the sound pressure generated by the speaker 11 constant, it is necessary to change the amplitude of a sine wave electric signal to the speaker 11.

The gauge pressure sensor 12 has a first end 121 communicating with the coupler 21 and a second end 122 opened to the atmospheric pressure. Measure the pressure.
That is, the gauge pressure sensor 12 is connected to the coupler 21 so that the gauge pressure in the coupler 21 of the acoustic calibrator 10 (pressure at which atmospheric pressure is 0 Pa) can be measured. It arrange | positions so that the atmospheric | air release opening | mouth of the end 122 may become out of the coupler 21. FIG.
Since the pressure in the coupler is a positive / negative pressure with the atmospheric pressure set to 0 Pa, it is desirable to use a continuous gauge pressure sensor that can measure the positive / negative pressure as the gauge pressure sensor 12.

Adjustment of the gauge pressure sensor 12 is performed as follows.
First, zero adjustment of the gauge pressure sensor 12 is performed in a state where the microphone 31 is not inserted into the coupler 21, that is, in a state where the atmospheric pressure is released. Thereafter, the microphone 31 is inserted into the coupler 21 to generate a sine wave sound from the speaker 11. The sound pressure generated by the speaker 11 is changed until the value indicated by the gauge pressure sensor 12 reaches 10 Pa. At this time, the positive and negative gauge pressures are measured so that the effective value (1 / √2 times the maximum value) is 10 Pa. When 114 dB is generated, the pressure is adjusted to 10 Pa. When 94 dB is generated, the pressure is adjusted to 1 Pa.
With such a method, the sound pressure in the coupler 21 can be adjusted according to the atmospheric pressure at the time of calibration.
In addition, when using the sound pressure frequency component of the FFT calculation mentioned later, zero adjustment does not need to be performed.

  By using the gauge pressure sensor 12, the gauge pressure sensor 12 can measure the amount of change in the sound pressure generated by the speaker 11 in real time. Since the sound pressure fluctuates plus / minus with respect to the atmospheric pressure, the signal of the gauge pressure sensor 12 can be handled as an AC signal. The gauge pressure sensor 12 may measure the relative pressure with respect to the atmospheric pressure using a differential pressure sensor in addition to the gauge pressure sensor 12.

The measurement by the gauge pressure sensor 12 at the time of calibration will be described.
In the initial state of inserting the microphone 31 into the coupler 21, since the speaker 11 is not operating, the coupler 21 is the volume V ₀ at the same pressure P ₀ and atmospheric pressure. When a sine wave is supplied to the speaker 11 using the amplifier 135, the diaphragm moves, the coupler 21 is not in an open state, so the volume changes by ΔV, and the pressure also changes according to the volume change ΔV.
That is, pressure change amount ΔPv (Pa) is V ₀ ; volume (mm ³ ), ΔV; volume change amount by speaker 11 (mm ³ ), P ₀ ; reference atmospheric pressure (kPa), ΔP ₀ ; Change in atmospheric pressure (kPa), γ: Specific heat ratio of air
ΔPv = (ΔV / V ₀ × (P ₀ + ΔP ₀ ) × 1000) γ.
The gauge pressure sensor 12 measures ΔPv.

  The analysis means 17 analyzes the distortion of the signal waveform based on the sound pressure measured by the gauge pressure sensor 12. Specifically, the analysis means 17 performs an FFT (Fast Fourier Transform) analysis based on the measured sound pressure. Harmonics are obtained by the analysis means 17.

The distortion correction unit 18 corrects the distortion of the acoustic signal waveform output from the speaker 11 based on the analysis by the analysis unit 17.
The fundamental wave is set to 0 dBVrms (effective value), and each harmonic is leveled. That is, 0 dBVrms is set with reference to the FFT result at a sound pressure of 1 kHz. Calculation of how small a harmonic is with respect to a reference is called leveling, and the amount of distortion is calculated. Since the signal component level is simply obtained from the FFT result, the fundamental wave signal level-harmonic signal level is calculated as the distortion with respect to the fundamental wave.

Table 1 shows OVERALL of the FFT operation, that is, the total power (overall) up to the analysis frequency range. In the case of an ideal sine wave, the level of the fundamental wave and the overall match, and the overall is equal to the mean square value of the input time signal.
For example, when the distortion is large, if the fundamental wave level is adjusted to 10 Pa as in the case where there is no distortion at all, the actual generated sound pressure increases as the distortion increases. Actually, it is considered that there is no effect if the distortion is 30 dB or more and is small with respect to the fundamental wave. In the case of 30 dB, there is an influence of 0.004 dB.

In the above case, when the secondary harmonic is reduced, a coefficient 40 dB smaller than the fundamental wave coefficient is used. For example, the second harmonic coefficient (k2) is 0. 0 of the fundamental wave coefficient k. 01 times (k2 = 0.01k).
The distortion correction means 18 obtains the phase at which the harmonic distortion is minimized while shifting the phase of each harmonic from 0 to 359 °. When the distortion correction unit 18 obtains the phase at which the harmonic distortion is minimized, the distortion correction unit 18 obtains a level at which the distortion is further reduced by reducing the coefficient.

The control means 13 controls the output to the speaker 11 so that the sound pressure measured by the gauge pressure sensor 12 becomes a constant sound pressure and the distortion of the signal waveform is reduced. Specifically, the control means 13 drives the speaker 11 with a fundamental sine wave based on the sine wave table 133 to generate sound pressure in the coupler 21, and the generated sound pressure is measured by the gauge pressure sensor 12. The measured data is converted into a digital value via the amplifier 131 and the delta-sigma A / D converter 132, and sound pressure data is obtained.
Next, the control means 13 determines the coefficient k for the fundamental sine wave based on the sound pressure data and the prescribed value so that the sound pressure is constant, and the coefficient and phase obtained by the distortion correction means 18. Is output through a delta-sigma D / A converter 134 and an amplifier 135 to drive the speaker 11.
That is, the control means 13 calculates the fundamental harmonic sine wave multiplied by the coefficient k + the second harmonic sine wave multiplied by the coefficient k2 + the third harmonic sine wave + multiplied by the coefficient k3. Actually, infinite processing is not possible, so the fifth harmonic is used in the flowcharts (FIGS. 2 to 6 described later). The harmonics added to the fundamental sine wave are synchronized and added to the fundamental sine wave in accordance with the phase of each harmonic obtained by the distortion correction means 18.
The sine wave table 133 stores data constituting the fundamental wave and the harmonic sine wave corresponding to the frequency.

  The value V output to the speaker 11 is V = fundamental sine wave multiplied by a coefficient k + phase corrected sine wave multiplied by a coefficient kx (that is, k × sin (ωt) + kx × sin (ωt + φx The range of the coefficient k is 1> k> 0, φn is an integer and 359> φn> 0, the phase φx is 2π × φn / 360 (rad), and the default of k may be appropriately selected.

  Further, the calculation means 14 performs a calculation for extracting the frequency level of the generated sound pressure signal from the sound pressure measured by the gauge pressure sensor 12. The control unit 13 controls the output to the speaker 11 using the value calculated by the calculation unit 14.

The calculation means 14 extracts only the frequency of the generated sound pressure signal generated from the speaker 11 by performing FFT (Fast Fourier Transform) or DFT (Discrete Fourier Transform) on the sound pressure data as an AC signal. (Level) is calculated. The influence of the sensor self-noise and offset can be reduced by FFT or DFT calculation, and the sound pressure accuracy of the generated frequency can be increased.
The control means 13 performs feedback based on the calculated value (for example, the value of FFT or DFT calculation), for example, changes the amplitude of the fundamental sine wave so that the adjustment value becomes 10 Pa, and vibrates the speaker 11. Control is performed by increasing or decreasing ΔV by moving the plate.

  For example, since the sound pressure of 114 dB is a pressure change of 10 Pa, the amplifier 11 is varied to control the speaker 11 so that the calculation result of the generated frequency becomes 10 Pa. Thus, it is not necessary to know the characteristics of the speaker 11 in advance. Further, not only a fixed frequency but also a sound pressure of 114 dB can be generated from the speaker 11, and the response of the gauge pressure sensor 12 is a calculation condition (requires a response more than twice the generated frequency, for example, 1 kHz If it is desired to obtain up to the 5th harmonic, a response speed exceeding 10 kHz is required), and calibration can be performed at an arbitrary frequency. However, since the distortion increases when the sound pressure (volume) generated by the speaker 11 is increased, it is possible to monitor the harmonics by performing the FFT operation and generate the sound pressure while controlling (in this case, Response more than twice that of harmonics is required).

The temperature sensor 15 is disposed along the gauge pressure sensor 12 and measures the temperature of the gas. Specifically, the temperature sensor 15 is disposed along the gauge pressure sensor 12 and installed so as to measure the temperature of the gas.
The temperature correction unit 16 corrects the sound pressure measured by the gauge pressure sensor 12 based on the temperature measured by the temperature sensor 15. For example, it is assumed that the temperature characteristic of the gauge pressure sensor 12 is constant from 0 degrees to 50 degrees, but changes when the temperature characteristics are 0 degrees or less or 50 degrees or more. Based on the temperature characteristics of the gauge pressure sensor 12, the temperature correction unit 16 corrects the measured sound pressure based on the temperature measured by the temperature sensor 15.

  As described above, the temperature sensor 15 is used to correct the measurement value of the gauge pressure sensor 12, and the operating temperature range of the acoustic calibrator 10 (for example, in JIS C 1515, -10 ° C to 50 ° C is specified). If the temperature range of the gauge pressure sensor 12 is sufficiently wide and no correction is required, it can be omitted. That is, the temperature correction coefficient of the gauge pressure sensor 12 is determined by the specification of the gauge pressure sensor 12, and the correction is used when necessary.

  2-6 is a flowchart which shows the processing content of the acoustic calibrator 10 which concerns on one Embodiment of this invention. The acoustic calibrator 10 includes hardware included in a computer and its peripheral devices and software that controls the hardware, and the following processing is executed by a control unit (for example, CPU) of the acoustic calibrator 10 according to predetermined software. It is processing to do.

  In step S101, the CPU sets the frequency of the generated sound pressure (for example, the sound pressure is 114.0 dB). More specifically, the CPU sets the frequency of the generated sound pressure to an initial value of 1 kHz. Further, the CPU sets an initial value of the coefficient k (for example, 0.5), an initial value of the distortion (for example, 0%), an initial value of the minimum distortion (for example, 100%), and an initial value of the start address (for example, , 0 degrees). Thereafter, the CPU moves the process to step S102.

  In step S102, the CPU determines whether to change the frequency setting. More specifically, the CPU determines whether or not an instruction for changing the frequency setting is given (for example, a switch indicating a change in frequency is pressed). If this determination is YES, the CPU moves the process to step S103, and if this determination is NO, the CPU moves the process to step S106.

  In step S103, the CPU sets a frequency. More specifically, the CPU inputs the frequency when an instruction for changing the frequency setting is given and stores it in the storage unit. Thereafter, the CPU moves the process to step S104.

  In step S104, the CPU calculates the thinning amount. More specifically, the CPU calculates the digital value of the fundamental sine wave corresponding to the input frequency based on the sine wave table 133 in which the frequency is associated with the digital value of the sine wave of the fundamental wave and the harmonic wave. Calculate the decimation amount when converting from to analog value. Thereafter, the CPU moves the process to step S105.

  In step S105, the CPU sets a sample clock. More specifically, the CPU sets a sample clock corresponding to the frequency of the fundamental sine wave to be generated. Thereafter, the CPU moves the process to step S106.

  In step S106, the CPU reads the fundamental sine wave. More specifically, the CPU reads from the sine wave table 133 the digital value of the fundamental sine wave corresponding to the frequency set according to the thinning amount calculated in step S104 based on the sine wave table 133. Thereafter, the CPU moves the process to step S107.

  In step S107, the CPU stores the read sine wave data in the fundamental wave table. More specifically, the CPU stores the read sine wave data in the fundamental wave table. Thereafter, the CPU moves the process to step S108.

  In step S108, the CPU multiplies the stored fundamental sine wave by a coefficient k. More specifically, the CPU multiplies the fundamental wave table data stored in step S107 by a coefficient k (1> k> 0). Output V = table value × k, that is, k × sin (ωt) is calculated. Thereafter, the CPU moves the process to step S109.

  In step S109, the CPU initially sets the harmonic order x to 2 in order to perform processing from the second harmonic to the fifth harmonic. Thereafter, the CPU moves the process to step S110.

  In step S110, the CPU determines whether correction of the x-order harmonic is necessary. More specifically, the CPU determines whether or not there is an x-order harmonic component stored in the x-order harmonic table created in steps S144 to S146 described later. If this determination is YES, the CPU moves the process to step S111, and if this determination is NO, the CPU moves the process to step S115.

  In step S111, the CPU determines whether or not the phase is 2π (rad) or more. More specifically, the CPU has detected the phase with the smallest x-order harmonic component in the range of 0 to 2π (rad), and has repeated it to the range of 2π (rad) for storing in step S148 described later. Judge whether or not. If this determination is YES, the CPU moves the process to step S117, and if this determination is NO, the CPU moves the process to step S112.

  In step S112, the CPU delays the start address of the x-order harmonic table by Φx (rad). Thereafter, the CPU moves the process to step S113.

  In step S113, the CPU multiplies the x-order harmonic component by a coefficient kx. More specifically, the CPU calculates kx × sin (ωt−Φx). Thereafter, the CPU moves the process to step S114.

  In step S114, the CPU stores the x-order harmonic component. More specifically, the CPU stores the calculated value of the x-order harmonic component kx × sin (ωt−Φx) in the x-order component table. Thereafter, the CPU moves the process to step S115.

  In step S115, the CPU determines whether it is a fifth harmonic. More specifically, the CPU determines whether or not the harmonic order x is 5 or more. If this determination is YES, the CPU moves the process to step S120, and if this determination is NO, the CPU moves the process to step S116.

  In step S116, the CPU increases the harmonic order x by 1, and the process proceeds to step S110. That is, the CPU executes steps S110 to S114 from the second harmonic to the fifth harmonic.

  In step S117, the CPU loads the x-order harmonic component from the minimum phase table storing the x-order harmonic component. More specifically, the CPU loads the x-order harmonic component from the minimum phase table stored in step S149 described later. Thereafter, the CPU moves the process to step S118.

  In step S118, the CPU determines whether or not the x-order harmonic coefficient kx is smaller than a predetermined value. More specifically, the CPU determines whether or not the x-order harmonic coefficient kx is smaller than the attenuation amount of 10 dB. If this determination is YES, the CPU moves the process to step S119, and if this determination is NO, the CPU moves the process to step S113. The minimum value of attenuation may be adjusted as appropriate.

  In step S119, the CPU decreases the x-order harmonic coefficient kx by a predetermined value. More specifically, the CPU subtracts 0.1 dB from the x-order harmonic coefficient kx. Thereafter, the CPU moves the process to step S113.

  In step S120, the CPU adds the stored x-order harmonic component to the fundamental sine wave. More specifically, the CPU adds the data of the x-order harmonic table stored in step S114 to the data of the fundamental table stored in step S107. That is, the following formula 1 is calculated. Thereafter, the CPU moves the process to step S121.

  In step S <b> 121, the CPU converts the digital value into an analog value for driving the speaker 11 and drives the speaker 11. More specifically, the CPU uses the delta sigma D / A converter 134 (for example, the ΔΣ16Bit D / A converter) to convert the digital value added in step S120 into an analog value, and the speaker 11 through the amplifier 135. Output to. Thereafter, the CPU moves the process to step S122.

  In step S122, the CPU measures the generated sound pressure in the coupler 21. More specifically, the CPU uses the gauge pressure sensor 12 to measure the difference between the atmospheric pressure and the atmospheric pressure in the coupler 21 as the sound pressure generated in the coupler 21. Thereafter, the CPU moves the process to step S123.

  In step S123, the CPU measures the gas temperature. More specifically, the CPU measures the temperature of the gas using a temperature sensor disposed along the gauge pressure sensor 12. Thereafter, the CPU moves the process to step S124.

  In step S124, the CPU converts the measured generated sound pressure and gas temperature into digital values. More specifically, the CPU converts the analog values of the generated sound pressure and the gas temperature into digital values using a delta sigma A / D converter 132 (for example, a ΔΣ16Bit A / D converter) via the amplifier 131. Thereafter, the CPU moves the process to step S125.

  In step S125, the CPU calculates the temperature correction value and the generated sound pressure. More specifically, the CPU calculates a temperature correction value of the gauge pressure sensor 12 corresponding to the measured gas temperature based on the temperature characteristic of the gauge pressure sensor 12. Next, the CPU performs an FFT operation or a DFT operation on the generated sound pressure ΔPv to calculate a sound pressure calculation value. Thereafter, the CPU moves the process to step S126.

  In step S126, the CPU determines whether or not to correct the sensor temperature. More specifically, the CPU determines whether or not the calculated temperature correction value exceeds a predetermined range value. If this determination is YES, the CPU moves the process to step S127, and if this determination is NO, the CPU moves the process to step S128.

  In step S127, the CPU corrects the temperature. More specifically, the CPU corrects the generated sound pressure ΔPv with the calculated temperature correction value. Thereafter, the CPU moves the process to step S128.

  In step S128, the CPU determines whether the sound pressure calculation value is within a range between a predetermined maximum value and a minimum value. More specifically, the CPU determines whether or not the sound pressure calculation value is within a range between a predetermined maximum value (for example, 10.31 Pa) and a predetermined minimum value (for example, 9.74 Pa). If this determination is YES, the CPU moves the process to step S129, and if this determination is NO, the CPU moves the process to step S130.

  In step S129, the CPU maintains the correction coefficient k for the fundamental sine wave, and proceeds to step S134.

  In step S130, the CPU determines whether the sound pressure calculation value is equal to or greater than a predetermined maximum value. More specifically, the CPU determines whether or not the sound pressure calculation value is equal to or greater than a predetermined maximum value (for example, 10.31 Pa). If this determination is YES, the CPU moves the process to step S131, and if this determination is NO, the CPU moves the process to step S132.

  In step S131, the CPU decreases the correction coefficient k for the fundamental sine wave. More specifically, the CPU subtracts a predetermined value (for example, 0.01) from the correction coefficient k to reduce the correction coefficient k. Thereafter, the CPU moves the process to step S134.

  In step S132, the CPU increases the correction coefficient k for the fundamental sine wave. More specifically, the CPU adds a predetermined value (for example, 0.01) to the correction coefficient k to increase the correction coefficient k. Thereafter, the CPU moves the process to step S133.

  In step S133, the CPU determines whether or not the correction coefficient k has exceeded a specified value. If this determination is YES, the CPU moves the process to step S152, and if this determination is NO, the CPU moves the process to step S134.

  In step S134, the CPU determines whether distortion correction is complete. More specifically, the CPU determines whether the distortion is smaller than 0.25% (−52 dB) or the phase difference is performed up to 2π (rad) and the x-order harmonic coefficient kx is attenuated by 10 dB. Judging. If this determination is YES, the CPU moves the process to step S108, and if this determination is NO, the CPU moves the process to step S135.

  In step S135, in order to perform processing from the second harmonic to the fifth harmonic, the CPU initially sets the harmonic order x to 2 and moves the process to step S136.

  In step S136, the CPU reads the level of the x-order harmonic component. More specifically, the CPU reads the leveled value of the x-order harmonic component. Thereafter, the CPU moves the process to step S137.

  In step S137, the CPU determines whether or not the phase is 0 (rad). More specifically, the CPU determines whether the phase of the x-order harmonic component is 0 (rad). If this determination is YES, the CPU moves the process to step S138, and if this determination is NO, the CPU moves the process to step S139.

  In step S138, an initial x-order harmonic coefficient kx in a state where correction is not performed is calculated. More specifically, the CPU sets 0 dBVrms, for example, based on the FFT result at a sound pressure of 1 kHz. Calculate how small the harmonics are relative to the reference (eg, calculate the harmonic signal level minus the fundamental signal level). This value can be treated as a relative attenuation. This level is used in the calculation formula of step S113 as the coefficient kx of the x-order harmonic. Thereafter, the CPU moves the process to step S139.

  In step S139, the CPU calculates the distortion factor of the x-order harmonic component. More specifically, the CPU calculates a level difference (distortion rate) between the level of the x-order harmonic component and the level of the fundamental component from the calculation result of step S125. Thereafter, the CPU moves the process to step S140. Note that the fundamental wave FFT result level is set to 0 dB, and how much the x-order harmonic FFT result level is attenuated with respect to the fundamental wave FFT result level is calculated, and this value becomes the distortion factor.

  In step S140, the CPU stores the distortion factor of the x-order harmonic component. More specifically, the CPU stores the calculated distortion factor of the x-order harmonic component in association with the harmonic order. Thereafter, the CPU moves the process to step S141.

  In step S141, the CPU compares the distortion factor of the x-order harmonic component with the minimum distortion factor. More specifically, the CPU compares the stored distortion factor of the x-order harmonic component with the minimum distortion factor of the x-order harmonic component (default is 100%). Thereafter, the CPU moves the process to step S142.

  In step S142, the CPU determines whether or not the distortion factor of the x-order harmonic component is smaller than the minimum distortion factor. If this determination is YES, the CPU moves the process to step S143, and if this determination is NO, the CPU moves the process to step S150.

  In step S143, the CPU determines whether an x-order component table has been created. If this determination is YES, the CPU moves the process to step S144, and if this determination is NO, the CPU moves the process to step S147.

  In step S144, the CPU determines whether or not the distortion factor of the x-order harmonic correction is larger than a predetermined value. More specifically, the CPU determines whether or not the distortion factor of the x-order harmonic component stored in step S140 is greater than 0.25% (−52 dB). If this determination is YES, the CPU moves the process to step S145, and if this determination is NO, the CPU moves the process to step S147.

  In step S145, the CPU reads the x-order harmonic component. More specifically, the CPU reads out the sine wave data of the x-order harmonic component from the sine wave table. Thereafter, the CPU moves the process to step S146.

  In step S146, the CPU stores the read x-order harmonic component. More specifically, the CPU stores the read x-order harmonic component in the x-order harmonic table. Thereafter, the CPU moves the process to step S147.

  In step S147, the CPU stores the distortion factor of the x-order harmonic component as the minimum distortion factor of the x-order harmonic component. That is, the distortion rate obtained in step S139 for the delay phase φx is stored. Thereafter, the CPU moves the process to step S148.

  In step S148, the CPU stores the x-order harmonic coefficient kx and the phase Φx. Thereafter, the CPU moves the process to step S149.

  In step S149, the CPU stores the x-order harmonic component in the x-order harmonic table as the minimum distortion phase in association with the harmonic order. Thereafter, the CPU moves the process to step S150.

  In step S150, the CPU determines whether it is a fifth harmonic. More specifically, the CPU determines whether or not the harmonic order x is 5 or more. If this determination is YES, the CPU moves the process to step S108, and if this determination is NO, the CPU moves the process to step S151.

  In step S151, the CPU increases the harmonic order x by 1, and the process proceeds to step S136. That is, the CPU executes steps S136 to S149 from the second harmonic to the fifth harmonic.

  In step S152, the CPU determines that the microphone 31 is not inserted and turns off the power of the acoustic calibrator 10. Thereafter, the CPU ends the process.

  FIG. 7 is a diagram illustrating an example of a signal output from the acoustic calibrator 10 according to the embodiment of the present invention. The example shown in FIG. 7 is an example of a synthesized signal to which harmonic components are added so as to reduce distortion of the acoustic signal waveform output from the speaker 11 based on the basic signal.

According to the present embodiment, the acoustic calibrator 10 outputs sound into the coupler 21 by the speaker 11, measures the sound pressure based on the difference between the atmospheric pressure in the coupler 21 to which the sound is output, and the atmospheric pressure, and measures the sound pressure. Analyzing the distortion of the signal waveform based on the measured sound pressure, correcting the distortion of the signal waveform of the output sound based on the analysis, the measured sound pressure becomes a constant sound pressure, and the distortion of the signal waveform Correction is made to decrease, and the output to the speaker 11 is controlled. In other words, the acoustic calibrator 10 performs an FFT operation on the measured generated sound pressure, and drives the speaker 11 with a signal obtained by adjusting and adding the phase and gain in order to cancel generated harmonics.
Furthermore, the acoustic calibrator 10 is connected to the atmospheric pressure in the coupler 21 to which the sound is output by the speaker 11 in a state where one end thereof is passed into the coupler 21 by the gauge pressure sensor 12 and the other end is opened to the atmospheric pressure. The sound pressure is measured by the difference from the atmospheric pressure, the FFT or DFT calculation is performed to extract the sound pressure level of the frequency of the generated sound pressure signal from the measured sound pressure, and based on the temperature measured by the temperature sensor 15, The sound pressure measured by the gauge pressure sensor 12 is corrected.
Therefore, the acoustic calibrator 10 can generate a sound having a constant sound pressure and a small distortion of the signal waveform without being affected by a change in atmospheric pressure, and can calibrate with high accuracy. Furthermore, the generated sound pressure is kept constant regardless of the frequency characteristics and temperature characteristics of the speaker 11, and sound with little distortion of the signal waveform is generated so that calibration can be performed with high accuracy. Furthermore, the acoustic calibrator 10 can increase the accuracy without being affected by sensor offset or noise by performing FFT or DFT calculation on the frequency of the generated sound pressure.
Further, as in step S152, the acoustic calibrator 10 can determine whether or not the microphone 31 is inserted in the coupler 21, and can turn off the acoustic calibrator 10 itself. It is also possible to control to automatically turn off the power without turning off the power when the microphone 31 is removed from the power supply.

  As mentioned above, although embodiment of this invention was described, this invention is not restricted to embodiment mentioned above. The effects described in the embodiments of the present invention are only the most preferable effects resulting from the present invention, and the effects of the present invention are limited to those described in the embodiments of the present invention. is not.

DESCRIPTION OF SYMBOLS 10 Acoustic calibrator 11 Speaker 12 Gauge pressure sensor 13 Control means 14 Calculation means 15 Temperature sensor 16 Temperature correction means 17 Analysis means 18 Distortion correction means 21 Coupler 31 Microphone

Claims (5)

An acoustic calibrator having a coupler for inserting a microphone,
Sound output means for outputting sound in the coupler;
A sound pressure measuring means for measuring the sound pressure by the difference between the atmospheric pressure in the coupler to which the sound is output by the acoustic output means and the atmospheric pressure;
Analyzing means for analyzing the distortion of the signal waveform based on the sound pressure measured by the sound pressure measuring means;
Distortion correction means for correcting distortion of the acoustic signal waveform output by the sound output means based on the analysis by the analysis means;
The sound pressure measured by the sound pressure measuring means becomes a constant sound pressure and is corrected using the distortion correcting means so that the distortion of the signal waveform is reduced, and the output to the sound output means is controlled. Control means;
An acoustic calibrator comprising:   The sound pressure measuring means has one end communicating with the coupler and the other end opened to the atmospheric pressure, and the sound pressure is calculated by the difference between the atmospheric pressure in the coupler to which the sound is output by the acoustic output means and the atmospheric pressure. The sound calibrator according to claim 1, wherein A calculation means for performing calculation for extracting the sound pressure level of the frequency of the generated sound pressure signal from the sound pressure measured by the sound pressure measurement means;
The acoustic calibrator according to claim 1, wherein the control unit controls output to the acoustic output unit using a value calculated by the calculation unit. The calculation means performs an FFT or DFT calculation,
The control means performs feedback using the value of the FFT or the DFT operation.
The acoustic calibrator according to claim 3. A temperature measuring means arranged along the sound pressure measuring means for measuring the temperature of the gas;
Temperature correction means for correcting the sound pressure measured by the sound pressure measurement means based on the temperature measured by the temperature measurement means;
The acoustic calibrator according to claim 1, further comprising:

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