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GB/T 20441.2-2018 English PDF

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GB/T 20441.2-2018: Electroacoustics -- Measurement microphones -- Part 2: Primary method for pressure calibration of laboratory standard microphones by the reciprocity technique
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GB/T 20441.2-2018644 Add to Cart 3 days Electroacoustics -- Measurement microphones -- Part 2: Primary method for pressure calibration of laboratory standard microphones by the reciprocity technique Valid

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Basic data

Standard ID: GB/T 20441.2-2018 (GB/T20441.2-2018)
Description (Translated English): Electroacoustics -- Measurement microphones -- Part 2: Primary method for pressure calibration of laboratory standard microphones by the reciprocity technique
Sector / Industry: National Standard (Recommended)
Classification of Chinese Standard: A59
Classification of International Standard: 17.140.50
Word Count Estimation: 34,375
Date of Issue: 2018-06-07
Date of Implementation: 2019-01-01
Issuing agency(ies): State Administration for Market Regulation, China National Standardization Administration

GB/T 20441.2-2018: Electroacoustics -- Measurement microphones -- Part 2: Primary method for pressure calibration of laboratory standard microphones by the reciprocity technique


---This is a DRAFT version for illustration, not a final translation. Full copy of true-PDF in English version (including equations, symbols, images, flow-chart, tables, and figures etc.) will be manually/carefully translated upon your order.
Electroacoustics--Measurement microphones--Part 2. Primary method for pressure calibration of labor standard microphones by the reciprocity technique ICS 17.140.50 A59 National Standards of People's Republic of China Electroacoustic measuring microphone Part 2. Using reciprocal technology to the laboratory Primary method for sound pressure calibration of standard microphones Part 2.Primarymethodforpressurecalibrationof (IEC 61094-2.2009, Measurementmicrophones- Part 2.Primarymethodforpressurecalibrationof 2018-06-07 released.2019-01-01 implementation State market supervision and administration China National Standardization Administration issued

Content

Foreword III 1 Scope 1 2 Normative references 1 3 Terms and Definitions 1 4 Reference environmental conditions 2 5 Principle of reciprocal sound pressure calibration 2 5.1 Principle Overview 2 5.1.1 Overview 2 5.1.2 Overview of the principle of the three-microphone method 2 5.1.3 Overview of the principle of two microphones and an auxiliary sound source method 2 5.2 Basic Expression 2 5.3 Insertion Voltage Technology 3 5.4 Calculation of acoustic transfer impedance 3 5.5 Heat conduction correction 5 5.6 Capillary correction 5 5.7 Final expression of sound pressure sensitivity 5 5.7.1 Three-microphone method 5 5.7.2 Two microphones and one auxiliary source 6 6 Factors affecting sound pressure sensitivity 6 6.1 Overview 6 6.2 Polarization voltage 6 6.3 Grounding Shield Reference Structure 6 6.4 Sound pressure distribution on the surface of the diaphragm 6 6.5 Relationship with environmental conditions 7 6.5.1 Static pressure 7 6.5.2 Temperature 7 6.5.3 Humidity 7 6.5.4 Transition to reference environmental conditions 7 7 Calibration uncertainty component 7 7.1 Overview 7 7.2 Electrical Transfer Impedance 7 7.3 Acoustic transfer impedance 8 7.3.1 Overview 8 7.3.2 Coupling cavity 8 7.3.3 Microphone parameters 8 7.4 Theoretical imperfections 9 7.5 Uncertainty of sound pressure sensitivity level 9 Appendix A (Normative) Heat transfer and viscous losses in closed chambers 12 Appendix B (Normative Appendix) Acoustic Impedance of Capillary 15 Appendix C (informative) Example 18 of a cylindrical coupling cavity for microphone calibration Appendix D (informative) Impact of the environment on the sensitivity of the microphone 21 Appendix E (informative) Method for determining microphone parameters 23 Appendix F (informative) Physical properties of humid air 25 Reference 29

Foreword

GB/T 20441 "Electrical Acoustic Measurement Microphone" is divided into 8 parts. --- Part 1. Specification for laboratory standard microphones; --- Part 2. The primary method of using the reciprocity technology to calibrate the sound pressure of the laboratory standard microphone; --- Part 3. The primary method of free field calibration of laboratory standard microphones using reciprocity technology; --- Part 4. Working standard microphone specifications; --- Part 5. Comparison of sound pressure calibration of working standard microphones; ---Part 6. Electrostatic exciters for determining the frequency response; --- Part 7. Difference between free field sensitivity and sound pressure sensitivity of laboratory standard microphones; --- Part 8. Comparison method for determining the free field sensitivity of working standard microphones. This part is the second part of GB/T 20441. This part is drafted in accordance with the rules given in GB/T 1.1-2009. This part uses the translation method equivalent to IEC 61094-2.2009 "Measurement microphones Part 2. Using reciprocity technology for laboratory standards The original method of sound pressure calibration of quasi-microphones. This section also made the following editorial changes. --- In line with the series of national standard names, the title of this section adds "electroacoustics"; --- Because the original text is wrong, the voltage value in 6.2 is changed to "200.0V". Please note that some of the contents of this document may involve patents. The issuing organization of this document is not responsible for identifying these patents. This part was proposed by the Ministry of Industry and Information Technology of the People's Republic of China. This part is under the jurisdiction of the National Electroacoustic Standardization Technical Committee (SAC/TC23). This section drafted by. China Institute of Metrology, China Electronics Technology Group Corporation Third Institute, Beijing 797 audio unit Co., Ltd., Changzhou Chenguang Electronic Instrument Factory. The main drafters of this section. He Longbiao, Niu Feng, Xu Huan, Han Jie, Zhao Jing, Song Ming, Deng Gancheng. Electroacoustic measuring microphone Part 2. Using reciprocal technology to the laboratory Primary method for sound pressure calibration of standard microphones

1 Scope

This part of GB/T 20441 specifies the primary method for determining the complex sound pressure sensitivity of the laboratory standard microphone, which is built for sound pressure measurement. Establish an accurate basis for reproducibility. This section applies to laboratory standard microphones that meet the requirements of GB/T 20441.1-2010 and other types of electricity of the same size Rong microphone. All quantities in this section are expressed in SI units.

2 Normative references

The following documents are indispensable for the application of this document. For dated references, only dated versions apply to this article. Pieces. For undated references, the latest edition (including all amendments) applies to this document. GB/T 20441.1-2010 Electroacoustic measuring microphones - Part 1. Specification for laboratory standard microphones (IEC 61094-1. 2000, IDT) ISO /IEC Guide 98-3 Measurement uncertainty - Part 3. Guidance for the expression of uncertainty in measurement [Uncerntaityof measurement-Part 3. Guidetotheexpressionofuncertaintyinmeasurement(GUM1995)1)]

3 Terms and definitions

The following terms and definitions as defined in GB/T 20441.1-2010, ISO /IEC Guide 98-3 apply to this document. 3.1 Reciprocal microphone reciprocalmicrophone A linear passive microphone with equal amplitudes of the forward and reverse transfer impedances of the open circuit. 3.2 The phase angle of the sound pressure sensitivity of the microphone phaseangleofpressuresensitivityofmicrophone The phase angle between the open circuit voltage of the microphone at a given frequency and the sound pressure uniformly applied to the diaphragm. Note. The phase angle is expressed in degrees or radians [(°) or rad]. 3.3 Electrical transfer impedance electricaltransferimpedance For two acoustically coupled microphone systems, the open circuit voltage used as the receiving microphone and the electrical input input for the microphone used as the transmitter The ratio of the flow. Note 1. The electrical transfer impedance is expressed in ohms (Ω). Note 2. This definition only applies to the grounded shield structure given in 7.2 of GB/T 20441.1-2010. 1) ISO /IEC Guide 98-3.2008 is a reprint of the.1995 Guide to Expression of Uncertainty in Measurement. 3.4 Acoustic transfer impedance acoustictransferimpedance For two acoustically coupled microphone systems, the sound pressure acting on the receiving microphone diaphragm and the shortness produced by the microphone used for the emission The quotient of the road volume speed. Note. The acoustic transfer impedance is expressed in pascals per cubic meter (Pa·s/m3). 3.5 Coupled cavity coupler The acoustic coupling unit between the microphones, after the microphone is installed, forms a cavity that is predictable in shape and size.

4 Reference environmental conditions

The reference environmental conditions are. ---Air temperature. 23.0 ° C; --- Static pressure. 101.325kPa; --- Relative humidity. 50%.

5 Principle of reciprocal sound pressure calibration

5.1 Principle Overview 5.1.1 Overview The reciprocal calibration of the microphone can be done with three microphones, two of which should be reciprocal microphones, or one auxiliary source and two The microphones are completed and one of them should be reciprocal. Note. Non-reciprocal microphones can only be used as acoustic receivers. 5.1.2 Overview of the principle of the three-microphone method The two microphones are acoustically coupled with a coupling cavity, one as a sound source and the other as an acoustic receiver, measuring its electrical transfer impedance. When the acoustic transfer impedance of the system is known, the sound pressure sensitivity product of the two coupled microphones can be determined. Microphone (1), microphone (2), the microphone (3) paired two pairs, can get three independent products, can derive the sound pressure sensitivity expression of each microphone. 5.1.3 Overview of the principle of two microphones and an auxiliary sound source method First, the two microphones are acoustically coupled with the coupling cavity to determine the sound pressure sensitivity product of the two microphones, see 5.1.2. Then, The sound source radiates the same sound pressure to the two microphones, and the ratio of the output voltage is equal to the sound pressure sensitivity ratio. According to the spirit of two microphones The ratio of the sensitivity product to the sound pressure sensitivity can be used to derive the sound pressure sensitivity expression for each microphone. Note. In order to obtain the ratio of sound pressure sensitivity, direct comparison method can be used. The auxiliary sound source can be the third microphone, and its mechanical and acoustic characteristics are mediated. The sounder can be different. 5.2 basic expression Laboratory standard microphones and similar microphones have reciprocity, so the two-port equation of the microphone can be written as equation (1). Z11i z12q=U Z21i z22q=p (1) In the formula. p --- sound pressure uniformly acting on the sound end (membrane) of the microphone, the unit is Pa (Pa); U --- the signal voltage of the microphone terminal, in volts (V); q --- Through the volume of the sound end of the microphone (diaphragm), the unit is cubic meters per second (m3/s); i --- the current flowing through the electric terminal of the microphone, the unit is Am (A); Z11=Ze --- The electrical impedance of the microphone when the diaphragm is blocked, the unit is ohm (Ω); Z22=Za --- The acoustic impedance of the microphone when the electric terminal is open, in units of Pascals per cubic meter (Pa·s/m3); Z12=z21=MpZa --- Forward and reverse transfer impedance in volt-seconds per cubic meter (V·s/m3), Mp is the sound of the microphone Pressure sensitivity in volts per kPa (V/Pa). Note. The underline of the symbol indicates the complex quantity. Equation (1) can also be written as. Zei MpZaq=U MpZai Zaq=p (2) Equation (2) is the reciprocity equation of the microphone. The two microphones (1) and the microphone (2) with sound pressure sensitivity of Mp, 1 and Mp, respectively are acoustically coupled by a coupling cavity, and the equation (2) can be It can be seen that the current i1 at the electrical end of the microphone (1) produces a short-circuit volume velocity Mp, 1i1 (p=0 at the diaphragm), and the sound pressure at the sound end of the microphone (2) P2 = Za, 12Mp, 1i1, where Za, 12 is the transfer impedance of the system. The open circuit voltage of the microphone (2) is. U2=Mp, 2p2=Mp, 1Mp, 2Za, 12i1 The product of sound pressure sensitivity is given by equation (3). Mp, 1Mp, 2= Za, 12 U2 I1 (3) 5.3 Insertion voltage technology The insertion voltage technique is used to determine the open circuit voltage of a microphone with an electrical load. A load impedance is connected to the microphone having the measured open circuit voltage and internal impedance. In order to measure the open circuit voltage, one will be much smaller than The impedance of the load impedance is connected in series with the microphone and a calibration voltage is applied to it. Alternately apply sound pressure and calibration voltage of the same frequency, adjust the calibration voltage to make the voltage drop generated on the load and act on the microphone The voltage drop produced by the sound pressure is equal. At this time, the magnitude of the calibration voltage is the open circuit voltage. 5.4 Calculation of acoustic transfer impedance The acoustic transfer impedance Za, 12 = p2/(Mp, 1, i1) can be calculated by the equivalent circuit shown in Figure 1, where Za, 1 and Za, 2 are microphones, respectively. (1) Sound impedance of the microphone (2). Description. 1---Coupling cavity. Figure 1 is the equivalent circuit for calculating the acoustic transfer impedance Za,12 In certain cases, Za, 12 can be calculated theoretically. When the physical size of the coupling cavity is much smaller than the wavelength of the acoustic wave, it is assumed that the acoustic sound in the coupling cavity The pressure is equal, the gas in the cavity is equivalent to pure sound, and the equivalent circuit is shown in Figure 2. It is assumed that the compression and expansion process of the gas is adiabatic, Za, 12 It can be given by Z'a,12, and the expression is shown in equation (4). Z'a, 12= Za, V Za,1 Za, 2=jω Κps Ve, 1 Κrps,r Ve, 2 Κrps,r ÷ (4) In the formula. The total geometric volume of the V --- coupling cavity in cubic meters (m3); Ve, 1 --- The equivalent volume of the microphone (1), in cubic meters (m3); Ve, 2 --- The equivalent volume of the microphone (2), in cubic meters (m3); Za, V= Κps jωV ---The acoustic impedance of the gas in the closed coupling cavity, in units of Pascals per cubic meter (Pa·s/m3); ω --- angular frequency in radians per second (rad/s); Ps --- static pressure, the unit is Pa (Pa); Ps, r --- static pressure under reference conditions, the unit is Pa (Pa); κ --- specific heat capacity ratio under measurement conditions; Κr --- κ value under reference conditions. The value of κ can be derived from the formula given in Appendix F. Figure 2 Calculating the equivalent circuit of Z'a, 12 when the coupling cavity size is smaller than the wavelength of the acoustic wave When the frequency is high and the coupling cavity size is much smaller than the wavelength, the calculation of Za, 12 becomes more complicated. If the shape of the coupling cavity The shape is cylindrical and the diameter is the same as the diaphragm of the microphone. Assuming that the sound wave propagates in the plane wave at the current frequency, the whole system can be considered Is a uniform transmission line (see Figure 3); assuming that the gas compression and expansion process is adiabatic, Za, 12 can be expressed as Z'a, 12 as equation (5). Z'a, 12= Za,0 Za,0 Za,1 Za,0 Za, 2 ÷coshγl0 1 Za,0 Za,1 Za,0 Za, 2 ÷sinhγl0 ú (5) In the formula. Za,0 --- The acoustic impedance of the plane wave in the coupled cavity. If the loss of the coupling cavity is neglected, there is Za,0=ρc/S0; ρ --- the density of the enclosed gas in kilograms per cubic meter (kg/m3); c --- the speed of sound in free space gas in meters per second (m/s); S0 --- the cross-sectional area of the coupling cavity, in square meters (m2); L0 --- the length of the coupling cavity, that is, the distance between the two diaphragms, the unit is meters (m); γ=α jβ---complex transmission coefficient in units of meters (m-1). The values of ρ and c in humid air can be derived from the formula given in Appendix F. The real part of γ represents the viscous loss and heat conduction of the cylindrical surface, and the imaginary part represents the angular wave number. When equation (5) is used, let α = 0, β = ω/c, and γ can be approximated. The volume of air in the microphone that is not enclosed by the coupling cavity and the two diaphragms should be considered (see 7.3.3.1). Figure 3 assumes the equivalent circuit for calculating Z'a,12 for the plane wave transmission in the coupling cavity. 5.5 Heat conduction correction Calculating Z'a in 5.4, it is assumed that the coupling cavity is adiabatic. In fact, the heat conduction of the cavity wall will deviate from the ideal adiabatic process. Don't be in a small coupling cavity and low frequency. At low frequencies, it can be considered that the sound pressure in the cavity is equal, satisfying the assumption that the temperature of the cavity wall remains unchanged, and the heat conduction loss can be compared with the equation (3). The complex correction factor ΔH of the medium geometric volume V indicates that the expression of ΔH is given in Appendix A. At high frequencies, there will be fluctuations in the cavity and the sound pressure will no longer be equal everywhere. For a right-angled cylinder coupling cavity, the transmission line theory in 5.4 can be used. The overall effect of heat conduction and viscous losses on the surface of a cylindrical cavity can be represented by the complex propagation coefficient and the acoustic impedance of the plane wave propagation. The end face of the cavity, i.e., the portion of the diaphragm of the microphone, can be corrected for heat transfer by adding other components to the acoustic impedance of the microphone. 5.6 Capillary correction The coupling chamber is usually equipped with a capillary to equalize the static pressure inside and outside the chamber, or it can discharge air through two capillaries and charge other gases. The acoustic input impedance of the open capillary is given by equation (6). Za, C=Za, tanhγlC (6) In the formula. Za, t---the complex acoustic impedance in an infinitely long thin tube, in units of pascals per cubic meter (Pa·s/m3); lC --- The length of the tube in meters (m). Considering the shunting effect of the capillary, the acoustic transfer impedance given in equations (4) and (5) is repaired by introducing a complex correction factor ΔC. Positive, see equation (7). ΔC, 12=1 n Z′′a,12 Za, C (7) In the formula. n --- the number of identical capillaries used; Z′′a, 12 --- The acoustic transfer impedance after heat conduction correction of 5.5 pairs of Z'a, 12, in units of Pas per cubic meter (Pa·s/m 3 ). The expression of the acoustic input impedance Za, C of the open capillary is given in Appendix B. 5.7 Final expression of sound pressure sensitivity 5.7.1 Three-microphone method With Ze, 12 is the electrical transfer impedance U2/i1 (see 5.2), and the remaining microphone combinations are similar. Considering the corrections of 5.5 and 5.6, the final expression of the sound pressure sensitivity mode of the microphone (1) is equation (8). |Mp,1|= Ze, 12Ze, 31 Ze, 23 Z′′a, 23 Z′′a, 12Z′′a, 31 ΔC, 12ΔC, 31 ΔC, 23{ } (8) The expression of the microphone (2) and the microphone (3) are similar. The phase angle of the sound pressure sensitivity of the microphone is determined according to the phase angle of each of the equations. Note. When the complex quantity is expressed by the mode and phase angle, the range of the phase angle is (0π~2π) rad or 0°~360°. 5.7.2 Two microphones and one auxiliary source If only two microphones and one auxiliary source are used, the final expression of the sound pressure sensitivity mode is equation (9). |Mp,1|= Mp, 1 Mp, 2 Ze, 12 Z′′a,12 ΔC{ } (9) The ratio of the two sound pressure sensitivities......
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