Acoustics - Determination of sound power levels of noise sources using pressure - Precision methods for anechoic and hemi-anechoic rooms
Some standard content:
ICS17.140
National Standard of the People's Republic of China
GB/T6882—2008/IS03745:2003
Replaces GB/T6882-1986
Acoustics-Determination of sound power levels ofnoise sources using pressure-Precision methodsfor anechoic and hemi-anechoic rooms(ISO3745:2003,IDT)
2008-07-02Issued
General Administration of Quality Supervision, Inspection and Quarantine of the People's Republic of ChinaStandardization Administration of the People's Republic of China
2009-02-01Implemented
Normative references
Terms and definitions
Measurement uncertainty
Requirements for test rooms
Requirements for suitability of test rooms
Requirements for background noise
Temperature requirements
Humidity correction
6.1 Overview
6.2 Calibration
7 Installation and operation of the sound source
Location of sound source
Installation of sound source
Auxiliary equipment
Operation of the sound source to be measured||tt ||8 Sound pressure level measurements for determining sound power levels 8.1 Measurement surface
Microphone position
Measurement conditions
Measurement data
8.6 Correction of background noise level
8.7 Calculation of surface pressure level
Single event acoustic level measurements for determining sound energy levels 10 Calculation of sound power level and sound energy level
10.1 Sound power level
10.2 Sound energy level
11 Contents of records
11.1 Overview
11.2 Sound source to be measured wwW.bzxz.Net
11.3 Sound environment
GB/T 6882—2008/ISO 3745:2003
GB/T 6882—2008/ISO 3745,200311.5 Acoustic data
12 Report content
Appendix A (Normative Appendix)
Appendix B (Normative Appendix)
Appendix C (Normative Appendix)
Appendix D (Normative Appendix)
Appendix E (Normative Appendix)
Appendix F (Normative Appendix)
Appendix G (Normative Appendix)
Appendix H (Normative Appendix)
Appendix I (Normative Appendix)
Appendix J (Informative Appendix)
Appendix K (Informative Excerpt)
References
General method for identifying anechoic and semi-anechoic chambersAnother identification method for determining the power level of a noise sourceArray of microphone positions in a free field...
Array of microphone positions in a free field above a reflecting surfaceCoaxial circular path of a microphone in a semi-free field·Meridian arc path of a microphone in a semi-free field·Spiral path of a microphone in a semi-free fieldCalculation of A-weighted sound power level from 1/3 octave band sound power levelCalculation of index and index factor
Measurement uncertainty
Guidelines for test room design
This standard is one of a series of standards for determining the sound power level of a noise source using the sound pressure method
GB/T 6882-2008/IS0 3745:2003 This standard is equivalent to ISO3745:2003 Acoustic sound pressure method for determining the sound power level of noise sources - Anechoic chamber and semi-anechoic chamber precision method, and revises GB/T 6882-1986. Compared with GB/T 6882-1986, this standard adds the following contents: strict restrictions on the identification of sound source directivity; determination of sound energy level: identification method of anechoic chamber and semi-anechoic chamber used for specific noise; additional measuring points for semi-anechoic chamber precision method; meridian path of microphone in half free field: helical path of microphone in half free field - calculation of A-weighted sound power level by 1/3 times the band sound power level; analysis of measurement uncertainty. Appendices A to I of this standard are normative appendices; Appendix J and Appendix K are informative appendices. This standard was proposed by the Chinese Academy of Sciences.
This standard is issued by the National Technical Committee for Acoustics Standardization (SAC/TC 17). The main drafting units of this standard are: Institute of Acoustics, Chinese Academy of Sciences, Nanjing University. The main drafters of this standard are: Zhang Ruwei, Sun Guangrong, Chang Yadong. The previous versions replaced by this standard are: -GB/T 6882-1986.
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GB/T6882-2008/1503745:2003
This standard is one of the series of standards of GB/T114367 on the determination of the sound power level of noise sources by sound pressure method. This series of standards specifies various methods for determining the sound power level of machines, equipment and their accessories. When using this series of standards, it is necessary to select the most appropriate method in the GB/T14367 series according to the test purpose and conditions. GB/T19052-2003 and G/T14367 provide guidance on how to choose the appropriate standard. The GB/T14367 series only gives the general principles for the operation and installation of the sound source. For a specific type of machine or equipment, if there are special requirements for its operation and installation conditions, if there are corresponding noise test specifications, the test can be carried out with reference to those specifications. This standard specifies the laboratory method for measuring the sound power radiated by the sound source in an anechoic room or semi-anechoic room with specific acoustic properties. The method specified in this standard is only applicable to indoor measurements in a specific laboratory. The laboratory method specified in this standard is not only used to measure the sound power level, but also the sound energy level of the sound source. For a single burst or instantaneous sound, the sound power cannot be determined, and the sound energy needs to be used to explain the emitted sound over such a time history. When other standards in the GB/T11367 series are not agreed, the application of the sound energy level will be considered. This standard takes meteorological conditions into consideration when measuring the sound power level or sound energy level. This is especially true for level 1 measurements. 1 Scope
GB/T 6882—2008/ISO 3745:2003 Acoustics Sound Pressure Method for Determining Sound Power Level of Noise Sources Anechoic Chamber and Semi-anechoic Chamber Precision Method
This standard specifies the measurement method for measuring the sound pressure level on the measuring surface of a noise source in an anechoic chamber or semi-anechoic chamber to determine the sound power level or sound energy level of the noise source. It gives the requirements for the test environment and the method for calculating the sound power level or sound energy level from the measured surface sound pressure level to ensure that the results obtained have Class 1 accuracy. The method specified in this standard is applicable to the measurement of all types of noise sources. The noise source can be equipment , machines, components or accessories. The maximum size of the measurable sound source depends on the radius of the imaginary sphere (or hemisphere) of the measurement envelope.
2 Normative references
The clauses in the following documents become the clauses of this standard through the reference of this standard. For any referenced document in Note 3, all subsequent amendments (excluding errata) or revisions are not applicable to this standard. However, parties to agreements based on this standard are encouraged to study whether the latest versions of these documents can be used. For any undated referenced document, the latest version applies to this standard. GB/T 32411998 Borrowed-band and fractional-octave filters (eq1EC61260:1995) GB/T3947--1996 Acoustic terminology
GB/T11573.1-1993 Acoustics Statistical methods for determining and verifying the noise radiation values specified for machinery and equipment Part 1: Overview and definitions (neqI507571-1:1985) GB/T14573.4-1993 Acoustics Statistical methods for determining and verifying the noise radiation values specified for machinery and equipment Part 4: Determination of label values for batch machines and test methods (neqISO7574-4:1985) GB/T17247.1-2000 Attenuation of outdoor sound propagation Part 1: Calculation of atmospheric sound absorption (eqVISO96131:1993)
JF1059-1999 Evaluation and expression of measurement uncertainty TEC609422003 Electroacoustic sound calibrator
IEC61672-1:2002 Electroacoustic sound level meter Part 1: Technical requirements 3 Terms and definitions
The following terms and definitions apply to this standard. 3.1
Instantaneous sound pressure instantaneoussoundpressurep(t)
The pulsating pressure value superimposed on the atmospheric static pressure at a certain time due to the presence of a sound at a certain point in space and a specified cheek strap.
Column: The unit is Pascal (Pa).
Sound pressure
The root mean square value of the instantaneous sound pressure over a period of time. Former: The unit is Pascal (Pa).
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GB/T 6882—2008/ISO 3745,20033.3
Sound pressure level
10 times the logarithm of the ratio of the square of the instantaneous sound pressure to the square of the quasi-sound pressure (p-2×10 -\Pa) to the base 10. L, = 101g
Note 1: The unit of sound pressure level is decibel (dB). Note 2: The frequency weighting or bandwidth and time weighting used should be specified. For example, the A-weighted sound pressure level with S (invasion) time weighting is L3, 3.3.1
Time-averaged sound pressure level time-averaged sound pressure level1
The average sound pressure level of a steady-state sound or a pulsating sound during the measurement time interval. That is, within the specified time interval T, the logarithm of the ratio of the time mean square of the instantaneous sound pressure to the square of the reference sound pressure is 10 times the base 10, the unit is dBLT
= 10lgl
Note: The subscripts *Q" and \ are usually omitted, because the time-averaged sound pressure level needs to be determined within a certain measurement time interval. 3.3.2
Measurement time interval
measurementttmeinterval
The time interval used to determine the time-averaged sound pressure level. 3.4
Measurement surface
measurement surface
An imaginary surface with an area of $, which encloses the sound line and arranges the measurement points on it. Note, in a semi-anechoic chamber, the terminal of the measurement surface is located on the reflecting plane. 3.5
Surface sound pressure level
strface sound pressure levelL.
The energy average of the time-averaged sound pressure level after being normalized by background noise (3.18) at all the transmitter positions on the measurement surface. L = 101g(
Where:
Lt—surface sound pressure level, in decibels (dB) 100 1
Lt—sound pressure level at the microphone position after being normalized by background noise; Lt—number of microphone positions.
Note: The unit is decibels (dB).
Sound power sound pawer
The air sound energy radiated by the sound source per unit time Note: The unit is watts (W).
Sound power
tsound power level
The logarithm to the base 10 of the ratio of the sound power radiated by the sound source to the fundamental sound power W, (W.=10-12 W) [0 times. 2
...( 3)
Note 1: The unit is decibel (dB).
Law = 10lg w.
Note 2: The frequency weighting or bandwidth should be specified. For example, the A-weighted sound power level is Lw. Single-event sound pressure level
single-event sound pressure levelLE
The sound pressure level of a single burst or instantaneous sound is given by formula (5): L
Where:
Sound pressure in seconds, in Pascals (Pa),
p——reference sound pressure, = 20 μ Pa;
GB/T 6882—2008/ISO3745:2003(4)
A time interval long enough to include all the meaningful sounds in the event; T.=l s.
Note 1: The unit is decibel (dB).
Note 2: In other standards, this quantity is called "sound exposure level". 3.9
Sound energy soundenersy
The sound energy E of a single burst or instantaneous sound radiated by a sound source
Note: The unit is joule (J).
sonnd energy level
Sound energy level
W(t)dt
+（6)
10 times the logarithm to the base 10 of the ratio of the sound energy E (joule) radiated by the sound source under test to the reference sound energy F, [E1PJ(10-12J)I.
Note 1: The unit is decibel (dB).
Note 2: The frequency weighting or bandwidth used should be specified. 3. 11
free fieldfree field
L, - 101s
A sound field in a homogeneous isotropic medium in which the effects of other boundaries are negligible. Note: In practical applications, the free field refers to the sound field in which the boundary reflections can be neglected within the frequency range to be considered. 3.12
anechoic roamanechoic roam
A sound field obtained from the experience.
free field over a reflecting planefree field over a reflecting planehemi-free fieldhemi-free ficld
A sound field in a homogeneous isotropic medium in the half space above an infinite rigid plane in which the effects of other boundaries are negligible. KAOrKAca
GB/T 6882—2008/ISO 3745:20033.14
hemi-anechoic room
room where the sound can be obtained from above the reflecting surface. 3.15
freqocncy range of interest
frequency range covered by 1/3 octave bands with a center frequency from 100 Hz to 10 000 Hz. Note: For special spheres, the frequency range can be extended or reduced at both ends. In this case, the accuracy of the test room and instrument provided should meet the expanded or reduced frequency range.
?measurement radius
radius of the spherical or hemispherical measurement surface. 3.17
background noise
noise from all other sources other than the sound source being measured. Note: Background noise may include airborne sound, structure-borne sound and electrical sound from instruments. 3.18 Background noise correction Ke The correction term for the effect of background noise on the measurement results at each microphone position. Note: K is related to the frequency and is expressed in dB. 3.19 Directivity factor Directivity factor (5.417 in GB/T 3947 1996) The ratio of the square of the sound pressure of a certain frequency radiated by the emitting transducer at a certain point far away on its main axis to the square of the sound pressure generated at the same point after a point source with the same sound power and the same frequency replaces the transducer. b) The ratio of the square of the electromotive force generated by the receiving transducer due to a sound wave of a certain frequency propagating along the main axis of the transducer to the square of the electromotive force generated by the same frequency and the same root mean square sound pressure: Note: The far distance in the definition refers to the place where the divergence of the spherical surface is full. 3.20
Directivity index
[GB/T 397-1996 5.42]
10 times the logarithm of the directivity factor with the base 10. Note: The unit is decibel (dB).
4 Measurement uncertainty
If the sound power level of a given noise source is measured in accordance with this standard in several different laboratories, the results will show discreteness, and the standard deviation of the measured power level can be calculated (see the example of B2.1 in GB/T14573.4-1993), which varies with the frequency. These standard deviations will not usually exceed the values in Table 1, except in some special cases. The values given in Table 1 are the reproducibility standard deviations defined in GB/T 14573.1, which take into account the cumulative effect of measurement uncertainty when applying this standard method, but do not include changes in power output caused by changes in operating conditions (such as 4
rotation speed, supply voltage) or installation conditions. GB/T 6882-2008/ISO 3745:2003Unless otherwise specified by the laboratory undertaking the measurement or in the noise test specification for a particular series of noise sources, the expanded measurement uncertainty for determining the sound power level or sound energy level at a confidence level of 95% (coverage factor = 2) shall be taken as twice the reproducibility standard deviation as defined in JJF1059-1999.
Upper limit of the estimated value of the reproducibility standard deviation for the sound power level and sound energy level determined in accordance with this standard1/3 times the rated range center frequency/Hz
100~630
800~5000
6300-10000
12500~200005
Anechoic chamber
Upper limit of reproducibility standard deviation/dB
Half-acoustic case
Note 1: The standard deviation in Table 1 is related to the test conditions and the method defined in this standard, and has nothing to do with the noise itself : The standard deviation is partly due to variations between measurable laboratories, such as the geometry (dimensions) of the test room, the acoustic properties of the reflecting surfaces, the absorption of the test room boundaries, the background noise, and the type and calibration of the instrument. Another part is due to variations in the experimental technique, including the size of the full disk area, the location and number of microphone points, the location of the sound source and the integration time. The uncertainty in the near field of the sound source also causes the standard deviation. This uncertainty depends on the nature of the sound source and increases when the measuring distance is small and the frequency is low (below 250 Hz). NOTE 2: For some sources, the reproducibility standard deviation may be less than the values listed in Table 1. Therefore, when the test results between appropriate laboratories can be demonstrated to be valid, the noise test specification prepared in accordance with this standard for a given type of machine or equipment can be shown to have a standard deviation less than the estimated values listed in Table 1. 7 If the sound is qualified according to the method in Chapter 5, b If only the instrument is allowed and the atmospheric sound absorption correction has been made. The reproducibility standard deviation listed in Table 1 includes the variation between repeated measurements of the opposite sound source under the same conditions (see GB/T14573.1-1993 for the repeatability standard deviation). This uncertainty is usually much smaller than the uncertainty of the difference between laboratories. However, if it is difficult to maintain stable operating and installation conditions for a specific sound source, its repeatability standard deviation will not be less than the value given in Table 1. At this time, the fact that it is difficult to obtain repeatable sound power level data for the sound source should be recorded and explained in the test report. Note that the reproducibility standard deviation given in Table 1 is obtained from the comparison test of different laboratories. The information about the measurement uncertainty provided by this method does not meet the requirements of JF10591999. When this standard was formulated, there was no sufficient information to demonstrate compliance with the requirements of JF1059-1999. However, Appendix 1 gives an explanation that includes this information. 5 Requirements for test rooms
5.1 Overview
The test room used for measurements in accordance with this standard is one of the following: a) A room that provides a free field or a free field above a reflecting plane, which meets Appendix A in the measurement frequency range. b) A room that provides a free field or a free field above a reflecting plane for the purpose of determining the sound power level of a noise source, which meets Appendix B in the measurement frequency range.
The requirements of this standard should be met at least in the test frequency range. If these requirements are only met in a more limited frequency range, this should be clearly stated in the report and a statement should be made that the instrument is in accordance with "GB/T6882" only in these limited frequency ranges. 5.2 Requirements for suitability of test rooms
Appendix A and the appendix introduce the method for determining the deviation range of the test room from the ideal free field condition or the ideal semi-free field condition, and give the requirements for evaluating the suitability of the test room. For the identification method of the test room, see Appendix A or Appendix B. Note: If it is necessary to carry out the base in a space where the false difference value required by the inverse square law exceeds the value in Appendix A and B, see GB/T3767, GB/T3768, GB/T16404.CB/T 15401.2 or GB/T 16404.3.5
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GB/T 6882-2008/1SO 3745:20035.3 Background noise requirements
In each frequency band at all microphone positions on the measurement surface and within the test frequency range, the background noise level should be at least 10 dI3 lower than the vocal level when the sound source is working. If it is assumed that the A-weighted background noise level obtained by adding these bands is 10dB or more lower than the A-weighted sound pressure level obtained by adding all frequency bands, it is not required that all frequencies meet the above requirements when the A-weighted sound power is determined. 5.4 Temperature requirements
The air temperature range during measurement is 15 ℃ to 30 ℃. Note: The temperature range is limited to ensure that the deviation is less than 0.2 dB when applying formula (15) to noise sources with different noise generation mechanisms. 5.5 Humidity correction
In the air temperature range of 15 ℃ to 30 ℃, the maximum humidity correction is approximately 0.04 dB and can be ignored. 6 Receiver
6.1 Overview
The acoustic instrument system including microphone and cable shall meet the requirements of Class 1 instrument specified in IEC61672-1:2002, and the filter shall meet the requirements of Class 1 instrument specified in GH/T3241-1998. The microphone shall be oriented in the direction when calibrated. According to the test conditions, a more appropriate orientation may be selected according to the manufacturer's instructions or the requirements of the specific test specifications. In the absence of instructions or test specifications, the microphone shall be perpendicular to the measured surface at the point on the measured surface closest to the sensor. The uncertainty of the instrument for determining atmospheric pressure is equal to or less than 2%. The uncertainty of the instrument for determining temperature is equal to or less than 1. The uncertainty of the instrument for determining relative humidity is equal to or better than 10%. 6.2 Calibration
Before each series of measurements, the microphone shall be calibrated using a sound calibrator with Class 1 accuracy as specified in IEC60942:2003. The entire system shall be calibrated at one or more frequencies within the frequency range of the measurement. The calibrator shall be calibrated and the instrument system shall be calibrated periodically in accordance with the requirements of IEC61672-1:2002. The specific calibration method may be specified in the relevant standard.
7 Installation and operation of the sound source under test
7.1 General
The installation and operation of the sound source under test have an important influence on the sound power radiated by the sound source. The installation and operation conditions of the sound source under test specified in this chapter are those that minimize the change in sound power output. If the installation and operation conditions of the sound source under test are specified in its noise test specification, they shall be followed.
7.2 Source Location
When placing the source in the test chamber, there should be enough space to allow the measurement surface to envelop the source under test in accordance with the requirements of 8.2. The details of the mounting conditions and microphone array arrangement should be based on the general requirements of this standard and the specific noise test specification for the source type. 7.3 Source Mounting
7.3.1 General
In many cases, the sound power emission is related to the support or mounting conditions of the source under test. Whenever typical mounting conditions exist for the equipment under test, such conditions should be used or simulated.
If a specific test specification specifies the support or mounting conditions for the source under test, these conditions should be used. If the specific conditions specified in the test specification do not exist, but the prevailing or typical conditions of support or mounting exist, these prevailing or typical conditions should be used. In all these cases, care should be taken to avoid changes in the sound emission of the source caused by the mounting system used for the test. Measures should be taken to reduce any sound radiation from the mounting structure of the source under test.
Note: Many small sound sources, although they are not strong radiators themselves, radiate more low-frequency sound due to improper installation, which causes their kinetic energy to be transmitted to a large enough surface to make them effective low-frequency radiators. 6
7.3.2 Handheld noise sources
GB/T 6882—2008/ISO 3745:2003 Handheld noise sources are held or controlled by hand. If the sound source under test needs to be supported for operational reasons, the support structure should be small and considered as part of the sound source under test. This should be stated in the machine test specification. 7.3.3 Foundation-mounted and wall-mounted noise sources Foundation-mounted and wall-mounted noise sources should be located on a reflective acoustically "hard" surface (floor and wall). Tabletop equipment should be placed on the floor unless the equipment is placed on a table or stand when operating according to its test specification. In this case, the equipment should be located in the center of the test table.
7.4 Auxiliary Equipment
Ensure that any air supply ducts, cables, arm wires, and other ducts connected to the sound source under test do not radiate significant sound energy from the test room. All auxiliary equipment that is not part of the sound source must be located outside the test room if possible. 7.5 Operation of the measured sound source During the measurement, for a specific type of machine and equipment, if the operating conditions are specified in the relevant test specifications, they shall be operated under the conditions specified in the relevant test specifications. If there are no test specifications, the sound source shall be operated in a typical normal use mode, if possible. In this case, one or more of the following operating conditions shall be selected: a) specified load and operating parts; b) full load (if different from the above conditions); c) no load (speed); d) operating conditions corresponding to the maximum sound generation in normal use; simulated load operation under carefully specified conditions; f) operating conditions with a specific working interval. The sound power of the sound source can be determined with any required set of operating conditions (i.e. load, equipment speed, temperature). These test conditions are pre-selected and kept constant during the test. The sound source shall be operated under the required conditions before any noise measurement. If the noise emission is related to minor operating parameters, such as the type of material being processed or the type of tool used, the parameters that cause the least change and are typical operating conditions should be selected as far as possible. The acoustic test specification for a particular series of machines shall specify the tools and materials used for the test. For a particular purpose, one or more operating conditions shall be specified so as to give a high degree of reproducibility of the noise emitted by the same series of sources and to cover the most common and typical operating conditions for the series of sources. These operating conditions shall be specified in the specific test specification. If simulated operating conditions are used, those conditions shall be selected which give sound power levels representative of those normally used by the source. If appropriate, the test results of several independent operating conditions, each lasting a certain period of time, may be combined by averaging to obtain a composite result for the total operation. The operating conditions of the source during the acoustic measurements shall be fully described in the test report. 8 Sound pressure level measurements for the determination of sound power levels 8.1 General
An anechoic chamber provides the preferred measurement environment with the smallest uncertainty, but reasonable accuracy can be obtained in a semi-anechoic chamber provided that the precautions specified in this standard are observed. 8.2 Measurement Surface
8.2.1 Measurement Sphere (Anechoic Chamber Measurement)
When measuring in an anechoic chamber, the center of the spherical surface used to measure the sound pressure level is preferably located at the acoustic center of the sound source. Since the location of the acoustic center is usually unknown, the assumed acoustic center (e.g., the geometric center of the sound source) should be clearly stated in the test report. The radius of the test sphere should be equal to or greater than all of the following requirements; a) twice the maximum dimension of the sound source;
b) a/4 of the lowest frequency measured;
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