This standard specifies the acoustic performance requirements of standard sound sources: 1. Short-term stability and repeatability of sound power output; 2. Spectral characteristics; 3. Directivity index. This standard applies to standard sound sources. GB/T 4129-2003 Acoustics Performance and calibration requirements for standard sound sources used for sound power level determination GB/T4129-2003 Standard download decompression password: www.bzxz.net
This standard specifies the acoustic performance requirements of standard sound sources: 1. Short-term stability and repeatability of sound power output; 2. Spectral characteristics; 3. Directivity index. This standard applies to standard sound sources.

GB/T 4129—2003/1SO 6926:1999 This standard adopts the international standard 1S06926:1999 "Performance and calibration requirements of standard sound sources used for sound power level determination in acoustics".
This standard specifies the performance and calibration requirements of standard sound sources used for sound power level determination of noise sources. This standard replaces GB/T4129.1995 from the date of implementation.
Compared with GB/T4129-1995, the important technical changes of this standard include: 1) the frequency range is broadened (50Hz~20000Hz), and more stringent requirements are put forward for the performance of standard sound sources (such as short-term stability and repeatability of sound power output, spectrum characteristics, directivity index, recalibration, etc.); 2) the calibration method of standard sound sources is divided into two parts: semi-anechoic chamber calibration and reverberation chamber calibration, and more detailed and specific requirements are given for the test environment, microphone characteristics, microphone position and integral measurement time of each microphone position (such as adding the meridian diameter to the microphone position in the semi-anechoic chamber calibration); 3) This standard also adds content for air absorption correction when the measurement frequency is higher than 10000Hz. This standard, when equivalent to the international standard ISO6926:1999, replaces some ISO standards in its normative references and references with the corresponding national standards currently being implemented in my country, adds GB/T3102.71993 "Acoustic Quantities and Units" and GB/T39471996 "Acoustic Terminology" to the normative references, and gives the definitions of terms such as sound power level, near field and far field, mixed time, and standard sound source in accordance with CB/T3947-1996. This standard is proposed by the Chinese Academy of Sciences.
This standard is under the jurisdiction of the National Technical Committee for Acoustic Standardization. The drafting units of this standard are: Institute of Acoustics, Chinese Academy of Sciences, China Institute of Metrology. The main drafters of this standard are: Lv Yadong, Yu Bo, Zhang Ruxi, and Xu Xin. GB/T 4129-—2003/IS0 6926: 1999 Introduction
Standard sound sources are widely used in the "comparison method" to determine the noise emission of fixed sound sources. A standard sound source with known sound power output is used to establish the numerical relationship between the sound power level of the noise source at a given location and in a given acoustic environment and the spatial and temporal average sound pressure level of a series of microphone positions. Then, the sound power level of the "unknown sound source" can be determined by directly measuring the average sound pressure level of the "unknown sound source". This standard specifies the important physical performance characteristics of the standard sound source and its calibration method for determining the sound power level of the noise source. This standard is a supplement to the GB/T14367 series of standards, which specifies various methods for determining the sound power level of machines and equipment and acoustic measurement requirements applicable to different test environments. There are six standards in the GB/T14367 series of standards that involve test methods that use standard sound sources. These six standards are GB/T 6881.1, GB/T 6881.2, GB/T 6881.3, GB/T 3767, GB/T 3768, GB/T 16538. GB/T 14367 provides guidelines for the use of the series of standards.
It is worth noting that the sound power output of the standard sound source, especially the low-frequency sound power output, will change with the distance from the sound source to the adjacent reflecting surface. The sound power value of the standard sound source is only valid for the position used during calibration. In addition to the comparison method for determining the sound power level, the standard sound source can also be used for the acceptance test of the acoustic environment and for estimating the impact of the acoustic environment on the sound pressure level generated by one or more sound sources placed in the environment. For standard examples of standard sound sources and their application, see ISO/TR11690-3 and ISO14257. There are also some requirements in these examples that are different from this standard. V
1 Scope
GB/T 4129-—2003/ISO 6926: 1999 Acoustics Performance and calibration requirements for standard sound sources used for sound power level determination
This standard specifies the acoustic performance requirements for standard sound sources. - Short-term stability and repeatability of the sound power output, - Spectral characteristics:
Directivity index;
The stability of the sound power output and the directivity index of a directional sound source can usually only be determined by evaluating the radiation directivity diagram of a standard sound source. Due to directivity measurements (exceptions in 5.5), the evaluation of the radiation directivity diagram can only be carried out in a semi-anechoic chamber environment. For routine verification measurements, only the band sound power level is usually determined. In this case, the measurement can be carried out under semi-anechoic or reverberation chamber conditions. This standard also specifies the calibration method of the sound source used as a standard sound source, the calibration method of expressing the sound power level of the standard sound source in octave bands and 1/3 octave bands and A weighting under standard conditions (characteristic impedance of air PC equal to 400Pas/m), and specifies different methods for evaluating and verifying the radiation pattern.
Note: Standard sound sources can also be used for 1/2 borrowing frequency band measurements, such as SO9295, but in this case, the stability and reproducibility restrictions stated in this standard no longer apply.
This standard specifies not only the calibration method of a standard sound source in a free field above a reflecting surface, but also the calibration method of a standard sound source in a reverberation chamber at different distances from the interface. For the position of the standard source on a reflecting surface, the two different test environments mentioned above are considered equivalent in the frequency band greater than or equal to 100 Hz. Below 100 Hz, the measurement uncertainty of the two different test environments will be significantly different (see Table 1).
This standard applies to standard sound sources. The sound source can be placed directly on the floor or mounted on a bracket at a certain height above the floor. For floor-mounted sound sources, this standard only applies to sound sources with a maximum dimension less than 0.5 m in the height direction and less than 0.8 m in the horizontal direction. According to this standard, only floor-mounted standard sound sources can be used when measuring on the measurement surface. There is no maximum size restriction for standard sound sources used or calibrated under reverberation chamber conditions. 2 Normative references
The provisions of the following documents become provisions of this standard through reference in this standard. For any dated referenced document, all subsequent amendments (excluding errata) or revisions are not applicable to this standard. However, parties to an agreement based on this standard are encouraged to investigate whether the latest versions of these documents can be used. For any undated referenced document, the latest version applies to this standard. GB/T 3102.7-1993 Acoustic quantities and units eqV ISO 31-7:1992) GB/T3767-1996 Acoustics - Determination of sound power level of noise source by sound pressure method - Engineering method for approximate free field above reflecting surface (eqvISO3744:1994)
GB/T3947-1996 Acoustics - Terminology
GB/T6881.1-2002 Acoustics - Determination of sound power level of noise source by sound pressure method - Precision method in reverberation chamber (idtISO3741:1999) GB/T6882--1986 Acoustics - Determination of sound power level of noise source by sound pressure method - Engineering method for approximate free field above reflecting surface (eqvISO3744:1994)
GB/T6881.1-2002 Acoustics - Determination of sound power level of noise source by sound pressure method - Precision method in reverberation chamber (idtISO3741:1999) Power level determination - Anechoic chamber and semi-anechoic chamber precision method (neqISO37451977)
GB/T14573.4-1993 Acoustics - Statistical method for determining and verifying the noise radiation values ​​specified for machinery and equipment - Part 4: Method for determining and verifying the plate values ​​of batch machines (neqISO7574-4:1985) GB/T17247.1-2000 Acoustics - Attenuation of outdoor sound propagation - Part 1 - Calculation of atmospheric sound absorption (eqvISO9613GB/T 4129--2003/IS0 6926:19991:1993)
GB/T17312-1998 Calibration of random incident and diffuse fields of sound level meters (eqvIEC61183:1994) ISO3745:1977 Acoustic noise sources Determination of sound power levels of anechoic and semi-anechoic chambers Precision method ISO5725-1 Accuracy (true value and precision) of measurement methods and measurement results Part 1: General principles and definitions 3 Terms and definitions
The following terms and definitions apply to this standard. 3.1
Free field over a reflecting plane Sound field of a uniform, isotropic medium in half space above an infinite rigid plane on which a sound source is placed. 3.2
Semi-anechoic room
Anechoic room with a reflecting floor to simulate a room in half free space. Note: A test room with a reflecting plane (hard floor) that meets the requirements of GB/T 6882. 3.3
Surface sound pressure level Lpr surface sound pressure level is the energy average of the time-averaged sound pressure level at all microphone positions on the measurement surface plus background noise correction and environmental correction, dB. 3.4
Sound power level Lwsound power levelThe logarithm to the base 10 of the ratio of the sound power radiated by the sound source to the reference sound power, in bels, B. However, dB is usually used as the unit. The reference sound power must be specified.
Note: The reference sound power is 1 pW.
Measurement surface
measuremeat surface
The hypothetical surface that envelops the sound source, on which each measuring point is located. Note: The measurement surface specified in this standard is a hemispherical surface or a spherical surface that ends at the reflecting surface. 3.6
Far fieldfar[sound]field
In a free field, the sound field in which the instantaneous sound pressure and the instantaneous particle velocity are in phase at a distance from the sound source. Note: In the far field, the sound waves diverge spherically, that is, the sound pressure generated by the sound source at a certain point is inversely proportional to the distance from the point to the sound center of the sound source. 3.7
Near fieldnear 「sound field
In a free field, the sound field in which the instantaneous sound pressure and instantaneous particle velocity near the sound source are out of phase. 3.8
Dridirectivity indexDridirectivity indexThe degree to which a sound source radiates sound in a certain direction Note 1: The directivity index of direction i is measured in a semi-anechoic room or an anechoic room and calculated using formula (1): D = Lμ — Lpf
Where:
The sound pressure level on the measurement surface of the sound source along the specific direction in which D is to be measured, (dB); Lef -
The surface sound pressure level averaged on the measurement surface at the same distance. (1)
If you want to place the standard sound source directly on the ground, the measurement surface is a hemispherical surface. If you want to place the standard sound source above the ground, the measurement surface is a spherical surface.
GB/T 4129—2003/IS0 6926:1999 Note 2: Because the standard sound source is a free-field sound source above a reflecting surface, rather than a sound source in the free field, this definition is different from the definition given in GB/T6882.
Reverberation room
A room with a long reverberation time that makes the sound field as diffuse as possible. Note: A test room that meets GB/T6881.1. 3.10
Frequency range of interest Usually the octave band with a center frequency from 125Hz to 8000Hz or the 1/3 octave band with a center frequency from 100Hz to 10000Hz.
Note: If the requirements of this standard can be met, the frequency range can be extended to an upper limit of 20000Hz and a lower limit of 50Hz3. 11
Comparison method method
A method of calculating the sound power level of the sound source being measured by comparing the sound pressure level of the sound source being measured in a certain environment with the sound pressure level of a standard sound source with known sound power output in the same environment. 3.12
Reverberation time The time required for the average sound energy density to decay from the original value to one millionth of its original value (60dB) after the sound source is stopped after the sound has reached a steady state. The unit is seconds, s.
Note 1: When measuring, the time required for the initial sound pressure level decay of 5dB to 35dB to decay to 60dB is often extrapolated. Note 2: If the reverberation time is calculated by initially decaying the sound energy density by 10dB or 15dB, it is expressed as Tlo or Tis respectively. 3.13
RSS reference sound Source is a sound source with stable sound power output and broadband spectrum, and it shall meet the requirements of this standard in terms of short-term stability and repeatability of sound power output, spectrum characteristics, directivity index, calibration, etc. (see Chapter 5). It is generally a movable sound-generating device such as an electric source, a pneumatic source or a mechanical source.
Repeatability
The consistency between the results obtained by continuous multiple measurements of the same measured quantity under the same measurement conditions. When any method of this standard is used for measurement, it shall comply with the provisions of ISO5725-1. 4 Measurement uncertainty
The single value of the sound power level of the standard sound source measured according to the method of this standard is likely to be different from the true value within the measurement uncertainty range. The uncertainty of the sound power level measurement is caused by several factors that affect the measurement results. Some factors are related to the environmental conditions of the measurement laboratory, and others are related to the experimental method. If a specific sound source is transported to different laboratories and the sound power of the sound source is measured in each laboratory according to the provisions of this standard, the results will be discrete. The standard deviation of the measured value can be calculated (as shown in Appendix B of GB/T14573.4-1993) and the standard deviation will vary with frequency. These standard deviations should not exceed the values ​​listed in Table 1. The values ​​given in Table 1 are the reproducibility standard deviations GR defined in accordance with ISO5725-1. The values ​​in Table 1 take into account the cumulative effect of the measurement uncertainty generated by the measurement method of this standard, but do not include the changes in sound power output caused by changes in operating conditions (such as speed, voltage) or installation conditions.
The measurement uncertainty depends on the reproducibility standard deviation listed in Table 1 and the expected confidence level. For example, for the normal distribution of sound power level, with a 95% confidence level, the true value of the sound power level of the sound source is within ±1.96gk of the measured value. For further examples, see GB/T14573.4. 3
GB/T4129-2003/IS06926:1999Table 1
Estimated upper limit of standard deviation of reproducibility of sound power level of standard sound source determined according to this standardSound source on the ground in semi-anechoic room
Center of octave band
Frequency/Hz
250～2000
4 000~-8 000
Center of 1/3 octave band
Frequency/Hz
100～160
200～3 150
4 000-~10 000
12 500~20 000
A-weighted
Reproducibility standard deviation"
Meridian path
or spiral path
values ​​do not include variations in the sound source output and are confirmed by experiments. bA-weighted values ​​calculated from 1/3 octave band values. 20 discrete positions or
coaxial circular path
sound sources in reverberation chambers,
Reproducibility standard deviation
Note 1: The measurement uncertainty in Table 1 applies only to the specific standard sound source being calibrated. Unless statistical data on the additional uncertainty caused by product variations can be obtained, the calibration of a specific standard sound source is not applicable to other standard sound sources using the same design and manufacturing process. Note 2: The measurement uncertainty in Table 1 does not include the systematic deviation caused by measuring the sound power level in two different test environments. This deviation is not important in the range above 100 Hz. However, in the range of 100 Hz and below, this deviation is larger. For a 200m2 reverberation chamber, this deviation is generally less than or equal to 1.5 dB.
5 Performance requirements
5.1 Overview
The manufacturer shall indicate whether the standard sound source complies with this standard. 5.2 Short-term stability and repeatability of sound power output The design and manufacture of the standard sound source shall ensure that under repeated conditions, the sound power level of each 1/3 octave band remains constant over time, as shown in Table 2. Table 2 Maximum standard deviation of the sound power level of the standard sound source under repeated conditions in accordance with this standard Frequency range/Hz
100～160
200～20 000
Note 1: Standard sound sources used for special purposes may have more restricted frequency ranges. Standard Deviation/dB
The manufacturer of the standard sound source shall indicate the range of variation of the electrical power or mechanical power (such as the supply voltage) to ensure that the sound power level in any 1/3 octave band within the test frequency range does not vary by more than ±0.3dB. The manufacturer shall provide a method for adjusting the sound power level produced by the standard sound source in the case of a large range of changes in the supply voltage or mechanical power. Note 2: The sound power level of the standard sound source is related to the atmospheric pressure and air temperature. For the use of the standard sound source under different temperature and altitude conditions, the manufacturer shall provide appropriate correction data and uncertainty to take into account the influence of air temperature and atmospheric pressure on the sound power level. 5.3 Total Sound Power Level
There are no specific requirements for the total sound power level produced by the standard sound source. However, if the total sound power level is given in the report, the corresponding frequency range should also be reported.
5.4 Spectral characteristics
The standard sound source shall at least be able to generate broadband steady-state sound within the frequency range used, within the range of 100Hz to 10000Hz of the center frequency of the 1/3 octave band. Within this frequency range, the difference between the sound power levels of all 1/3 octave bands measured in accordance with Chapter 7 and Chapter 8 of this standard shall be within 12dB. Under the same measurement conditions and within the same frequency range, the difference between the sound power levels of two adjacent 1/3 octave bands shall be less than 3dB. If the frequency range is extended beyond 100Hz to 10000Hz, the difference between the sound power levels of all 1/3 octave bands and the difference between the sound power levels of two adjacent 1/3 octave bands within the extended frequency range shall be less than 16dB and 4dB respectively. For special sound sources, it is hoped that these criteria can be met within a more limited frequency range or with different spectral shapes. If the standard sound source does not meet the requirements of this standard within the frequency range of 100 Hz to 10,000 Hz, the manufacturer shall indicate that the frequency response of the standard sound source does not comply with this standard. 5.5 Directivity Index
When measured in a semi-anechoic chamber according to Chapter 7, the maximum value of the directivity index of a sound source in any 1/3 octave band with a center frequency in the range of 100 Hz to 10,000 Hz shall not exceed 6 dB. For mobile microphones, the maximum sound pressure level measured by the time weighting S for each 1/3 octave band during the movement shall be recorded and used to calculate the directivity index; for fixed microphone positions, the maximum sound pressure level in each frequency band at any of the 20 positions shall be used for calculation. If the standard sound source is only used in a reverberation room that meets the requirements of GB/T6881.1, the above requirements no longer apply. However, in this case, the standard sound source shall be marked "only used as a standard sound source in a qualified reverberation room". If the standard sound source is designed to be used on a bracket above the ground, the above requirements apply to the free field and the directivity measurement should be carried out in an anechoic chamber in accordance with GB/T6882.
5.6 Recalibration
The manufacturer should recommend the maximum time interval between two consecutive calibrations. During this interval, the sound power change of the standard sound source should not exceed the limits shown in Table 2. When any mechanical damage occurs to the standard sound source, it should be recalibrated. In order to determine whether the standard sound source needs to be recalibrated during the recommended maximum time interval, the 1/3 octave band sound pressure level at one or more fixed reference points (i.e., the manufacturer's recommended position) should be measured in the specified test environment and under the condition that the sound source is operating at the specified position. If the test value is unstable, the measured sound pressure level can be adjusted to a stable state using the method specified by the manufacturer. After adjustment, if the sound pressure level of any 1/3 octave band changes by more than 2.83 times the value in Table 2, the standard sound source should be recalibrated (see ISO5725-1). 6 Installation and operation of standard sound sources in calibration Www.bzxZ.net
6.1 General
The sound source shall be operated in accordance with the manufacturer's instructions. Record the basic characteristics of the mechanical or electrical power source (i.e. voltage and frequency) and the relevant operating parameters of the standard sound source (rotational speed for pneumatic sound sources). Note: It may be necessary to use auxiliary equipment to measure the relevant operating parameters (e.g. stroboscope to measure rotational speed). The standard sound source shall be in stable operating condition before measurement (acoustic characteristics or operating parameter measurement). 6.2 Position of standard sound source
6.2.1 Standard sound source located on a reflecting surface and away from the walls In a semi-anechoic chamber, place the sound source to be calibrated on a reflecting surface in the same direction as it is normally used. In a reverberant chamber, place the sound source on the ground asymmetrically with respect to the walls and at least 1.5 m from the nearest wall. Use four such positions with a distance of at least 2 m between them.
6.2.2 The standard sound source is located above the ground or close to the wall If the standard sound source is not calibrated in the position of 6.2.1, the calibration should be carried out in a reverberation room. If the standard sound source is located more than 0.5m from the reflecting surface or close to the wall, the calibration cannot be carried out in a semi-anechoic room. 7 Calibration method for semi-anechoic room
7.1 Test environment
The test environment should be a semi-anechoic room that meets the acceptance requirements of Appendix A of GB/T6882 within the test frequency range. The ground should be at least 1m larger than the projection of the measurement surface on the ground in all horizontal directions. 7.2 Microphone
For the conventional test frequency range, a microphone with a flat frequency response in normal incidence (towards the center of the measuring hemisphere) with the diaphragm plane or a microphone with a flat frequency response in grazing incidence (90° to the diaphragm plane, toward the center of the measuring hemisphere) with the diaphragm plane is used. After the microphone response is calibrated, it should be able to give a flat frequency response within the test frequency range under normal incidence or grazing incidence conditions within the 0.1dB range. If the frequency range is extended to 1/3 octave bands above 10000Hz, only microphones with a nominal flat frequency response under grazing incidence conditions are used.
7.3 Microphone positions
7.3.1 General
Use a hemispherical measurement surface with a radius R of 2 m, with the geometric center of the projection of the upper surface of the standard sound source on the reflecting surface as the center, and use a series of microphone positions given in 7.3.2, 7.3.3, 7.3.4 or 7.3.5. At the same time, confirm that the mechanical device for fixing or moving the microphone will not affect the measurement results.
7.3.2 Meridian path
For rotationally symmetrical sound sources, use three displacement mechanisms spaced 120° around the vertical axis of the measurement surface (see Figure F4 in Annex F of ISO3745:1977); for other sound sources, at least 8 displacement mechanisms should be used, and the displacement mechanisms should be manufactured to have a constant angular velocity. Use a sine potentiometer (or electrical, mechanical or mathematical equivalent) to obtain the surface area weighting related to the time required for the microphone to move along a given arc length. If the displacement mechanism is operated so that the microphone moves at a constant vertical velocity (i.e. the angular velocity is inversely proportional to the sine of the angle between the microphone's angular position and the axis perpendicular to the measurement surface), no area weighting is applied. NOTE When a sine potentiometer is used, the angular velocity at the vertex of the hemisphere is infinite. In practice, this problem can be solved by stopping the integration before the term is reached.
7.3.3 Spiral path
A spiral path around the axis perpendicular to the measurement surface is formed by using a displacement mechanism along a meridian path as shown in 7.3.2 and by moving the microphone slowly through a path that is an integer multiple of at least five circular paths. Conversely, a spiral path can also be formed by slowly rotating the standard sound source at a constant speed through at least five full revolutions while moving the microphone along a meridian path. If area weighting as shown in 7.3.2 is required, use 3 displacement mechanisms (120° apart around the axis perpendicular to the measurement surface) for each of the above methods. 7.3.4 Fixed point array
Use 20 fixed point microphone positions distributed on the surface of a hemisphere with a radius of 2m. These fixed points are evenly distributed along the height from the ground and there is one microphone position at each height. The 20 heights are 0.025R0.075R··0.975R. For each height, the azimuth position is moved 60° from the previous position to obtain a spiral template. If the sound source is not rotationally symmetrical in the horizontal plane, the second set of measurements is obtained by rotating the first set of measurements 180° and averaging the results of the first set of measurements. 7.3.5 Coaxial circular path
Use 20 circular displacement mechanisms on the 2m hemisphere around the vertical axis passing through the center of the standard sound source. The circular displacement mechanism should be located at the 20 height positions given in 7.3.4 and represent the same area on the hemisphere. The circular path can be achieved by slowly rotating the microphone or standard sound source uniformly along the 360° direction. The period of circular scanning rotation should be at least 60S. If a rotating table is used to rotate the standard sound source, the surface of the rotating table should be flush with the reflecting surface. 7.4 Measurement
The integration time for measuring the 1/3 octave band sound pressure level in accordance with GB/T6882 should be at least 200 seconds for each quarter-circle displacement of the meridian path and at least 600 seconds for the spiral path. For discrete microphone positions, the integration time is 30 seconds for each microphone position. For coaxial circular paths, the integration time should correspond to an integer multiple of the microphone or sound source rotation period. Note: The octave band and A-weighted sound pressure levels can be directly measured or calculated from the 1/3 octave band data according to the principle of mean square sound pressure. 7.5 Air absorption
If the measurement frequency is higher than 10000Hz, air absorption correction should be made in accordance with GB/T17247.1. 7.6 Calculation
According to GB/T6882, the sound power level is calculated from the surface sound pressure level in the 1/3 octave band using formula (2), [+cdB
Lw Lp + 10lg
Where:
Surface sound pressure level of the measurement surface, dB (reference sound pressure:20 μPa); the area of ​​a measured surface;
C——correction factor considering the influence of temperature (℃) and atmospheric pressure B (Pa); So=1 m2. The value of
C is calculated according to formula (3):
GB/T4129-—2003/ISO6926:1999[_273]BdB
C = 251g
L400V(273+e)B.
Where: B. =105 Pa.
Note 1: Formula (2) obtains the sound power level under standard conditions pc=400 Pa·s/m. According to the actual meteorological conditions B and 8 at the measurement location, the correction term C can be calculated. The ratio 423/400 can be obtained according to 6=0℃ and B. =105Pa, the difference between the actual characteristic impedance pc of the propagation medium and the reference characteristic impedance (pc)ret=400Pa·s/m is adjusted. Since the actual acoustic impedance pc of the air at the measurement location is included here, the sound power level obtained by the same machine under significantly different meteorological conditions will be slightly different. The reason for the difference is that the difference in air βc under different meteorological conditions will change the effective sound radiation of the sound source, and the maximum value of the sound source directivity index of each 1/3 octave band is calculated. Note 2: The octave band and A-weighted sound source directivity index can also be calculated accordingly. 8 Reverberation chamber calibration method
8.1 Test environment
The test environment should meet the requirements of GB/T6881.1 and the additional requirement that the minimum size of the reverberation chamber should be greater than 4m. Note: The reproducibility measurement uncertainty of this standard is based on the measurement results of seven reverberation chambers with different volumes ranging from 197m2 to 238m. 8.2 Microphones
The microphones shall be of random incidence type and calibrated to give diffuse field flat frequency response in accordance with GB/T17312. 8.3 Microphone positions
Usually 6 microphone positions or mobile microphones in accordance with GB/T6881.1 are used. If the frequency range is above the 1/3 octave band of 10000 Hz, only fixed microphone positions with random orientation may be used indoors. 8.4 Measurements
The integration time for measuring the sound pressure level in the 1/3 octave band in accordance with GB/T6881.1 for each microphone position shall be at least 64 s. The reverberation time T shall be measured using at least 3 sound source positions and 6 microphone positions. At least 3 attenuation curves shall be measured for each combination, using 10 dB or 15 dB attenuation depending on the equipment used and calculating T1o or Tis from the average of T or from the overall average. 8.5 Calculation
Calculate the 1/3 octave band sound power level in accordance with GB/T6881.1. Calculate the average sound power level from the 4 specified sound source positions. The octave band and A-weighted sound pressure levels can be obtained from the 1/3 octave band data based on the principle of mean square sound pressure. 9 Recording content
The recording content should be carried out in accordance with Chapter 9 of GB/T6882-1986 or Chapter 9 of GB/T6881.1-2002. The recorded measured and calculated values ​​should be rounded to the nearest 0.1 dB. 10 Reporting content
The reporting content should be carried out in accordance with Chapter 10 of GB/T6882-1986 or Chapter 10 of GB/T6881.1-2002. Report the following:
a) Whether the calibration performed fully complies with the requirements of this standard method and report the deviation. 7
GB/T4129—2003/IS06926:1999b) Whether the calibration is carried out in a semi-anechoic chamber or a reverberation chamber. If semi-anechoic chamber conditions are used, the microphone position should be indicated. If an elevated sound source position is used in a reverberation chamber, the bracket or support should be detailed (size, material). Reverberation chamber volume or lower cut-off frequency of the semi-anechoic chamber. c) The sound power level in the
frequency band should be rounded to the nearest 0.1 dB and the sound power level should be stated as the reference condition (pc=400Pa·s/m) d)
decibel value (reference sound power: 1pW).
Note: Since the reference condition pc=400 Pa·s/m was not used in the previous version of this standard, during the transition period, not only the sound power level under the reference condition but also the sound power level under the actual measurement conditions should be reported. Measurement uncertainty (see Table 1).
Temperature, relative humidity and atmospheric pressure during calibration, the value of the constant C (see 7.6) or other adjustments f)
for specified ambient conditions (if any) (see 5.2 and 7.6) and the method of determination. Basic characteristics of the electrical or mechanical power sound source and relevant operating parameters of the reference sound source (see 5.1). If calibration is part of the tests necessary to verify all the requirements specified in this standard, the following additional h)
information should be reported:
Whether the degree of spectral consistency, temporal stability, sound power output, spectral characteristics and directivity index meet the requirements of Chapter 5.
References
GB/T4129—2003/IS06926:1999
［17GB/T6881.2—2002 Acoustics - Determination of sound power level of noise source by sound pressure method - Small and medium-sized movable sound sources in reverberation field - Engineering method - Part 1 - Hard-wall test chamber comparison method (idtISO3743-1:1994)［2]GB/T6881.3—2002 Acoustics - Determination of sound power level of noise source by sound pressure method - Small and medium-sized movable sound sources in reverberation field - Engineering method - Part 2 - Special reverberation chamber method (idtISO3743-2:1994)［3GB/T3768--1996 Acoustics - Determination of sound power level of noise source by sound pressure method - Simple method using envelope measuring surface above reflecting surface (eqv ISO 3746 :1995)
［4]GB/T14367-1993 Basic standards for the determination of sound power levels of acoustic noise sources and criteria for the formulation of noise test specifications (neg ISO 3740:1980)
［5］GB/T14573.1—1993 Acoustics—Statistical method for determining and verifying the specified noise radiation values ​​of machinery and equipment—Part 1: Overview and definitions (neqISO7574-1:1985)[6]GB/T14573.2—1993 Acoustics—Statistical method for determining and verifying the specified noise radiation values ​​of machinery and equipment—Part 2: Method for determining and verifying the plate value of a single machine (neqISO7574-2:1985)[[7]GB/T14573.3—1993 Acoustics—Statistical method for determining and verifying the specified noise radiation values ​​of machinery and equipment—Part 3: Simple (transitional) method for determining and verifying the plate value of a batch of machines (neqISO7574-3:1985)[8J ISO 3747:2000, Acoustics—Determination of sound power levels of noise sources using sound pressure—Comparison method in situ[9] ISO 5725-2,Accuracy (trueness and precision) of measurement methods and results—Part 2: Basicmethod for the determination of repeatability and reproducibility of a standard measurement method.
[1oJ ISO 9295, Acoustics-Measurement of high-frequency noise emitted by computer and business equipment
[11J ISO/TR 11690-3, Acoustics—Recommended practice for the design of low- Noise workplaces containing machinery--Part 3: Sound propagation and noise prediction in workrooms.[12J ISO 14257, Acoustics-Measurement and parametric description of spatial sound distributioncurves in workrooms for evaluation of their acoustical performance.[13] VORLANDER M. and RAABE G. ,Calibration of reference sound sources, Acustica,81,1995,pp.247-263.
[14] CAMPANELLA AJ ,Calibration of reference sound sources,a US perspective, Noise-CON 96 Proceedings,1996,pp.931-936.[15] NOBILE M, A. ,Calibration of reference sound sources according to ANSI S12. 5 and ISO/DIS6926,Noise-Con 96 Proceedings,1996,pp. 937- 942.[16J HUBNER G. and JIANG Wu, National round-robin test determining the sound power by soundpressure measurements—Further results, Internoise 94, Proceedings, 1994, pp. 1769-1774.
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