JPH0454420Y2 - - Google Patents

Description

[Detailed Description of the Invention] Industrial Application Field The present invention relates to a sound intensity measuring device for various sounding bodies.

BACKGROUND ART Conventionally, as a sensor in a device for measuring the acoustic intensity of various sounding bodies, a pair of microphones consisting of two microphones with matching characteristics arranged before and after the sounding body is known. The sound intensity is calculated based on the cross power spectrum obtained by Fourier transform (FFT) the outputs of this pair of microphones.

In other words, the cross power spectrum Gba() obtained by the above FFT process is: Gba()=SbSa ^* (1) where, Sb: Fourier transform spectrum of the output of one microphone Sa ^* : Fourier transform spectrum of the other microphone This cross power spectrum Gba() is the complex conjugate spectrum of
Based on the sound intensity I from frequency ₁ to ₂
( _{1-2 )} can be found as follows.

I( ₁ ~ ₂ )=-1/2πρΔγ∫ ^f2 _f1 Im{Gba(
)}/d(2) Here, Im{Gba()}: Imaginary part of the one-sided cross spectrum of the cross power spectrum Gba ρ: Density of the medium: Frequency Δγ: Distance between both microphones However, this holds true only when This is the case when the two microphones used have the same phase and amplitude characteristics.

However, it is difficult to manufacture two microphones with exactly the same characteristics as described above, and generally two microphones with relatively similar characteristics are selected from among the many manufactured microphones. In this case as well, the characteristics do not match at all, so the difference in characteristics appears as a measurement error.

To solve this problem, the difference in characteristics between the two microphones and the reference microphone is stored in the memory as a function of frequency, and the measurement data is corrected according to this stored content to improve measurement accuracy. This was proposed as Utility Model Application No. 61-108934.

As shown in FIG. 3, two microphones 12a and
It consists of a pair of microphones 12 (12b) and a measuring device 13 into which the output thereof is introduced. This measuring device 1
3 is an FFT calculation section 14, a calculation section 15, which is similar to the conventional one.
It is equipped with a display section 16 and further includes a correction calculation section 2.
1 is added, which causes the cross power spectrum obtained by the FFT processing unit 14 to be stored in the ROM.
22 is corrected in accordance with a correction coefficient corresponding to the characteristic difference between the paired microphones 12, and outputted to the calculation section 15. This ROM22
The characteristic difference stored in is a characteristic difference between the two microphones 12a and 12b constituting the pair microphone 12 and a reference microphone (not shown), which is stored in advance as a function of frequency before actual measurement. It is. That is, the amplitude ratio and phase difference of the microphone 12a with respect to the reference microphone are determined by installing the reference microphone and the microphone 12a at the same sound field position in the calibrator, and inputting the outputs of these two microphones to the FFT calculation section 14. The transfer function H is obtained by calculating the transfer function H=S _R ^* S _a /S _R ^* S _R = S _a /S _R (3) S _R : Fourier transform of the output of the reference microphone Spectrum Sa: Fourier transform spectrum of the output of the microphone 12a S _R ^* : Conjugate complex spectrum of S _R. In this case, since S _R and Sa are both complex numbers, the solution H is also a complex number. Therefore, by performing polar coordinate transformation, a correction coefficient Ka for correcting the amplitude ratio and phase difference of the microphone 12a with respect to the reference microphone is obtained.
Similarly, the correction coefficient Kb of the microphone 12b with respect to the reference microphone is obtained, and the difference in characteristics between these two microphones 12a, 12b and the reference microphone is stored in the ROM 22.

Problems that the invention aims to solve By the way, the reliability of data is ensured by calibrating microphones each time a measurement is made, but in the past, the memory section of the correction calculation section was
The ROM is used to store the characteristic differences between each microphone and the reference microphone, which have been calibrated in advance, and to hold these values thereafter. That is, this does not take into account calibration at the measurement location. For example, even if calibration is performed to check for changes in characteristics over time, there is a problem in that it is difficult to write the results to ROM at the measurement site. In addition, the calibrator for calibration requires a closed space large enough to insert at least a speaker, a reference microphone, and a microphone to be calibrated, which poses the problem of increasing the overall size and making it inconvenient to carry to the measurement location. be.

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention is configured such that the storage section of the correction calculation section is composed of a writable and readable storage means, and the calibrator of the measurement microphone calibration system is installed in a closed space. The calibrator is a small device having a space for inserting a speaker and a microphone to be calibrated, and the storage means is capable of storing, when necessary, the relative characteristic difference between the two measurement microphones to be calibrated by the calibrator. . That is, the present invention includes two measurement microphones arranged before and after the sound source, a storage section that stores the characteristic difference between the two measurement microphones measured by a calibrator, and a storage section that stores the outputs of the two measurement microphones. In the sound intensity measurement device, the sound intensity measuring device includes a converting section that performs Fourier transform, and a correction calculating section that corrects and calculates the sound intensity according to the output of the converting section and the storage contents of the storage section, wherein the storage section is of a writable and readable type. The above calibrator has a speaker in a closed space,
The calibrator shall have a space for inserting the microphone to be calibrated, and the speaker of the calibrator is connected to the generated sound pressure control signal generator, and the calibrator is calculated based on the generated sound pressure control signal and the Fourier transform spectrum of the output of each microphone to be calibrated. The present invention is characterized in that the difference in characteristics between the two microphones is written in the write/read storage section. In this case, in addition to the predetermined sound pressure of the calibrated sound field of the calibrator, the storage section stores the relative characteristics obtained by calibrating the two microphones when necessary when there is a possibility of a difference in characteristics. You will remember the difference. Therefore, when performing calibration to determine this relative difference in characteristics, it is not necessary to determine the characteristics of the reference microphone as is; instead, the sound pressure control signal generated by the speaker, which has a linear relationship with the characteristics, is used as the output signal of the reference microphone. In the end, the calibrator no longer requires a reference microphone, since it can be used instead.

Function In the above, first, we will explain the calibration that calculates the characteristic difference between both microphones, which is stored in the storage section of the correction calculation section.One of the measurement microphones is attached to the calibrator, and the microphone output is
Obtain the Fourier transform spectrum by performing FFT calculation. At the same time, the Fourier transform spectrum of the generated sound pressure control signal introduced into the calibrator speaker is determined, and the transfer function between these two signals is determined.
Next, replace the microphone in the calibrator with another one, and similarly find the transfer function between this and the generated sound pressure control signal. Subsequently, the ratio of both of the obtained transfer functions is calculated, and the result is written into the storage section. The above is the writing of the calibration value.

Next, regarding the actual measurement, the sound generated by the sounding body is measured by two measurement microphones.
The output is Fourier transformed by FFT operation.
Next, this Fourier-transformed data is corrected in the correction calculation section using the transfer function ratio of both microphones stored in the storage section, and converted into data equivalent to that obtained when the characteristics of both microphones are the same. be done. This correction data is then sent to the arithmetic section, and after the sound intensity is calculated based on the above equation (2), the result is displayed on the display section.

Embodiment In FIG. 1, a pair of microphones 12 consisting of microphones 12a and 12b with the same numbers as in FIG. 3, an FFT calculation section 14, a calculation section 15, and a display section 1
Each element of 6 is similar to that in Figure 3,
works similarly. 23 and 24 are elements that characterize the present invention, and 23 is the FFT calculation unit 14.
A correction calculation section 24 into which the output of is introduced is a RAM that constitutes a storage section of the correction calculation section.

FIG. 2 shows a calibration system for measuring the difference in characteristics between the microphones 12a and 12b stored in the RAM 24, and includes a calibrator 30 that forms a calibration sound field with a speaker 31 installed inside a closed space, and the speaker 31 a generator 32 for generating sound pressure control signals;
An FFT calculation unit 14 (the one with the same number in FIG. 1 can be used) performs Fourier transform of the output of the microphone to be calibrated 12a (or 12b) placed in the calibration sound field of the calibrator 30 and the generated sound pressure control signal. (This is used in this example.)
It consists of a calibration value calculation unit 17 that calculates the characteristic difference between both microphones based on the output of the FFT calculation unit and writes the result to the RAM 24.

For calibration, sound pressure is generated from the speaker 31 by the output of the signal generator 32, and the output of the microphone 12a inserted therein is extracted and introduced into the FFT calculation unit 14. At the same time, the output of the signal generation section 32 is also introduced into the FFT calculation section 14, and both of these outputs are subjected to Fourier transformation. Then, the transfer function Ha of the two outputs is determined using the Fourier transform spectrum in the calibration value calculating section 17.

That is, Ha=Sr ^* Sa/Sr ^* Sr=Sa/Sr (4) where, Sr: Fourier transform spectrum of the output of the signal generator 32 Sa: Fourier transform spectrum of the output of the microphone 12a Sr ^* : Conjugate complex spectrum of Sr In this case, since both Sr and Sa are complex numbers, the amplitude ratio and phase difference of the microphone 12a with respect to the output of the signal generating section 32 are calculated by polar coordinate transformation.

Next, the microphone inserted into the calibrator 30 is replaced with the other microphone 12b, and the transfer function Hb between the output of the signal generator 32 and the output of the microphone 12b is determined in the same manner as described above. That is, Hb=Sr ^* Sb/Sr ^* Sr=Sb/Sr (5) Here, Sb: Fourier transform spectrum of the output of the microphone 12b Next, using these transfer functions Ha and Hb, the characteristic difference Hc of the microphone 12b with respect to the microphone 12a is calculated. is calculated using the following formula.

Hc＝Hb／Ha＝Sb／Sa ＝Be ^j( 〓 ^t+ 〓 ^b) ／Ae ^j( 〓 ^t+ 〓 ^a) ＝B／Ae ^j( 〓 ^b- 〓 ^a) (6) Here, ω: Angular frequency ( B/A): Output of microphone 12a and 12b
Amplitude ratio of output (φb − φa): Output of microphone 12a and output of microphone 12b
Then, this amplitude ratio and phase difference are written into the RAM 24. In addition, microphones 12a and 12b
The sound pressure sensitivity value of
It can be calculated using the sound pressure of the calibration sound field,
The value of one for the other can be calculated based on B/A. The above is the calibration, and this calibration is performed as needed.

In actual measurement, the sound pressure generated from the sounding body 11 is measured by the paired microphone 12, and its output is
The signal is input to the FFT calculation unit 14 and subjected to Fourier transformation. This Fourier-transformed data includes an error caused by the difference in characteristics between the microphones 12a and 12b, and data containing the error is input to the correction calculation section 23. Correction calculation unit 23
Now, based on the amplitude ratio B/A and the phase difference φb-φa stored in the RAM 24, the Fourier-transformed data is corrected. This corrects the difference in characteristics between the microphones 12a and 12b, and when the characteristics of both microphones are the same, equivalent true Fourier transform values are obtained, and this true Fourier transform value is The sound intensity I( ₁ to ₂ ) from frequencies ₁ to ₂ is calculated from the cross power spectrum Gba(), and the result of the calculation is displayed on the display unit 16.

In the above embodiment, the storage section is RAM2.
4, the memory contents will be erased when the device power is turned off, but the correction value of the pair microphone 12 can be easily obtained prior to measurement.
No problem. Furthermore, the RAM 24 may be equipped with a battery backup so that data can be written only when necessary.

Effects of the invention As described above, according to this invention, two inexpensive microphones with mismatched characteristics can be used as a pair of microphones, and the difference in characteristics of the paired microphones can be measured and corrected prior to measurement. , the reliability of the measured values is improved. Furthermore, since the calibrator is also made smaller and lighter, it can be attached to the measuring device at all times, and calibration can be easily performed. Therefore, the correction value of the pair of microphones can be obtained at any time not only at room temperature but also in a wider range of environments, thereby expanding the range of sound intensity measurement.

[Brief explanation of the drawing]

Fig. 1 is a block diagram showing the circuit configuration of an embodiment of this invention, and Fig. 2 is an embodiment of the calibration system of this invention. Figure 1 is used for conversion.
A block diagram showing an example of using the FFT calculation unit 14,
FIG. 3 is a block diagram showing a conventional sound intensity measuring device. 12a, 12b...Microphone, 14...
FFT calculation section, 15... calculation section, 16... display section,
17... Calibration value calculation section, 23... Correction calculation section, 2
4...RAM, 32... Generated sound pressure control signal generator.

Claims (1)

[Scope of utility model registration request] Two measurement microphones placed before and after the sound source, a storage unit that stores the characteristic difference between the two measurement microphones measured by a calibrator, and a conversion unit that performs Fourier transform on the outputs of the two measurement microphones. and a correction calculation section that corrects the sound intensity according to the output of the conversion section and the storage contents of the storage section, wherein the storage section is of a writable and readable type, and the calibrator has a speaker in a closed space,
The calibrator shall have a space for inserting the microphone to be calibrated, and the speaker of the calibrator is connected to the generated sound pressure control signal generator, and the calibrator is calculated based on the generated sound pressure control signal and the Fourier transform spectrum of the output of each microphone to be calibrated. A sound intensity measuring device characterized in that a characteristic difference between both microphones is written in the write/readable storage section.