Acoustics—Determination of sound power levels of noise sources using sound pressure—Engineering merthod in an essentially free field over a reflecting plane
Some standard content:
GB/T3767—1996
This standard is a revision of GB 3767-83 based on the international standard ISO3744:1994 "Acoustics - Determination of sound power level of noise source by sound pressure method - Engineering method for approximate free field above reflecting surface". This standard is equivalent to the international standard in terms of technical content. This makes the measurement results of sound power level of noise source comparable internationally, which is conducive to the import and export trade and technical exchanges of my country's mechanical products.
When revising GB 3767-83 based on the international standard, the engineering method and quasi-engineering method in the original standard are merged into the engineering method. The applicable noise types include various types of noise including impulse noise. The measurement environment is changed from allowing only one reflecting plane to allow the sound source to be measured close to multiple reflecting planes, and the corresponding measurement point layout diagram is given for each situation; the measurement uncertainty is expressed by the reproducibility standard deviation. This standard replaces GB3767-83 from the date of entry into force. Appendix A, Appendix B and Appendix C of this standard are all standard appendices. Appendix D, Appendix E and Appendix F of this standard are all informative appendices. This standard was proposed and coordinated by the National Technical Committee on Acoustic Standardization. The drafting unit of this standard is China Institute of Metrology. The main drafters of this standard are Zhang Mei'e, Chen Jianlin and Shen Yang. This standard was first issued on June 23, 1983. This standard is entrusted to the National Technical Committee on Acoustic Standardization for interpretation. GB/T 3767—1996
ISO Foreword
ISO (International Organization for Standardization) is a world alliance of national standards organizations (ISO member states). The formulation of international standards is carried out through ISO technical committees. Each member country has the right to send representatives to participate in the committee when it is interested in the topic established by the technical committee. International organizations associated with ISO, both official and non-official, can participate in this work. The draft international standard adopted by the technical committee shall be circulated to the member states for voting. As an international standard publication, at least 75% of the member states must vote in favor.
International Standard ISO3744 was prepared by Technical Committee SC1 Noise, Technical Committee on Acoustics, ISO/TC43. This second edition replaces the first edition (ISO3744:1981) on the basis of technical revision of the first edition. Annexes A, B and C form an integral part of this International Standard. Annexes D, E and F are for information only. 8
GB/T 3767-- 1996
This standard is one of a series of standards for determining the sound power level of noise sources. This series of standards specifies different methods for determining the sound power level of machinery and equipment or their combinations. When selecting these standards, the best choice should be made according to the general guidelines given in GB/T14367 based on the purpose and conditions of noise measurement. The above series of standards only give general principles for the installation and working conditions of machinery and equipment. For a specific type of machinery and equipment, the technical requirements for its installation and working conditions need to refer to the corresponding noise test specifications. This standard specifies a method for measuring the sound pressure level on the measurement surface of an envelope sound source to calculate the sound power level. The envelope surface method is applicable to all three accuracy levels (see Table 0.1). The accuracy level of this standard is level 2. When using this standard, it is required to meet the identification standards listed in Table 0.1. If the corresponding standard cannot be met, it is recommended to use other basic standards with different requirements for the environment (see Table 0.1 and GB/T14367 and ISO9614). Specific to a machine or equipment, its noise test specifications should be based on the series of standards for the determination of the sound power level of the noise source or ISO9614, and there should be no contradictions.
In a typical machine room where the sound source is placed, free field conditions are generally not met. When measuring under such conditions, corrections need to be made for background noise or unwanted sound reflections.
The method specified in this standard allows the determination of A-weighted sound power levels and band sound power levels. The A-weighted sound power level calculated from the band data may not be exactly the same as the sound power level determined by measuring the A-weighted sound pressure level.
The calculation of sound power levels from measured sound pressure levels in this standard is based on the premise that the sound power output of a sound source is proportional to the mean square sound pressure averaged over time and space.
Table 0.1 Determination of sound power level of noise source on reflecting surface using envelope surface method List of national standards with different accuracy levels GB6882
Test environment
Test environment suitability evaluation criteria\)
Sound source volume
Noise characteristics
Limitation on background noise!)
Number of measuring points
Precision method
Semi-anechoic room
K≤0.5dB
Preferably less than 0.5% of the volume of the test
room
GB3767
Engineering method·
Outdoor or indoor
K2≤2 dB
Unrestricted
Limited only by effective test environment
All types of noise (broadband, narrowband, discrete frequency, steady-state, non-steady-state, pulse) AL≥10 dB
(If possible, greater than 15dB)
K,≤0.4dB
AL≥6dB
(If possible, greater than 15dB)
K,≤1.3dB
GB3768
Simplified method
Outdoor or indoor
K,≤7 dB
Unrestricted
Limited only by effective test environment
AL≥3 dB
Ki≤3dB
≥42)
GB/T3767-1996
Instrument:
Sound level meter at least meets
GB6882
Precision method
Table 0.1 (end)
8) Type 1
Integrating sound level meter specified in GB3785 at least meets b) Type 1 bandpass filter specified in IEC804 at least meets c) Accuracy of LwA determination method specified in GB3241 Accuracy is expressed by
standard deviation of reproducibility
GB3767
Engineering method
a) Type 1 specified in GB3785
b) Type 1 specified in GB3785
c) Regulations of GB3241
GB3768
Simplified method
a) Type 2 specified in GB3785
b) Type 2 specified in IEC804
When K2<5dB,
5 dB≤K2≤7 dB,
When discrete pure tones account for the main components
d increases by 1 dB
1) When measuring the sound power spectrum, K, and K should meet the requirements in each color band within the tested frequency range. When measuring the A-weighted sound power level, the above values of KiA and K2A should also be used.
2) Under given conditions, the number of measuring points may be reduced by 10
1 Scope
1.1 General
National Standard of the People's Republic of China
Acoustics-Determination of sound power levels of noise sources using sound pressure--Engineering method in anessentially free field over a reflecting planeGB/T3767—1996
eqyISo3744-1994
Replaces GB3767—83
This standard specifies the method for measuring the sound pressure level on the measurement surface of the enveloping sound source under the condition of approximate free field near one or more reflecting surfaces to calculate the sound power level of the noise source. At the same time, the requirements for the test environment and measuring instruments as well as the calculation methods of the surface sound pressure level and sound power level are given. The accuracy level of the sound power level measurement result is Class 2. It is very important to develop and use special noise test specifications for various types of equipment in accordance with this standard. The noise test specifications should give detailed instructions on the installation, load, working conditions, measurement surface and microphone array selection of the sound source to be measured. Note 1: For special types of equipment, the noise test specifications should give detailed information on the specific measurement surface selected, because the use of measurement surfaces of different shapes will result in different evaluations of the sound power level of the sound source. 1.2 Types and sources of noise
The methods specified in this standard are applicable to the measurement of various types of noise. Note 2: For noise classification (steady-state, non-steady-state, quasi-steady-state, pulse, etc.), see GB/T14529. This standard is applicable to various types and sizes of sound sources (equipment, machines, components, assemblies, etc.). This standard does not apply to extremely high or extremely long sound sources, such as smoke halogens, pipelines, conveying machinery, industrial equipment with multiple sound sources, etc. 1.3 Test environment
This standard is applicable to the test environment of an approximate free field near one or more reflecting surfaces indoors or outdoors. 1.4 Measurement uncertainty
Except for individual cases, the reproducibility standard deviation of the A-weighted sound power level of the results measured in accordance with this standard is equal to or less than 1.5 dB (see Table 1).
There is a high probability that there is a difference between the single value of the sound power level of a noise source measured in accordance with this standard and its true value that is within the uncertainty range. The uncertainty of the sound power level measurement comes from the combined influence of the environmental conditions and experimental techniques of the measurement laboratory. If a specific noise source is measured in different laboratories according to this standard, the measurement results will show discreteness. The calculation of the standard deviation of the measurement results is shown in GB/T14573.4 and is related to the frequency. Except for individual cases, the above standard deviation does not exceed the value in Table 1. The reproducibility standard deviation aR given in Table 1 takes into account the cumulative effect of uncertainty in the measurement process, but does not include changes in sound power output caused by changes in working conditions (speed, power supply, voltage) or installation conditions. The measurement uncertainty is not only related to the reproducibility standard deviation, but also to the required confidence level. For example, for a normally distributed sound power level, when the confidence level is 90%, the true value of the sound power level of the sound source is within the range of ±1.645gk of the measured value, and when the confidence level is 95%, the true value is within the range of ±1.960gR of the measured value. For details, see GB/T14573 series and ISO9296. Table 1 Estimated values of standard deviation of sound power level reproducibility determined according to this standard Octave band center frequency
500～4 000
A weighting
1/3 Octave band center frequency
100～160
200～~315
400～5000
6300~10000
1) Generally applicable to outdoor measurements, many rooms cannot meet this frequency band. 2) Applicable to sound sources with relatively "flat" radiated noise spectra in the range of 100 to 10,000 Hz. Note: Reproducibility standard deviation 0R The standard deviations listed in Table 1 are the combined effects of the measurement conditions and methods specified in this standard, and do not include the influence of the sound source itself. They are caused by the following three aspects: changes between measurement locations, including outdoor environment and climatic conditions, indoor room geometry and boundary sound absorption, acoustic properties of reflecting surfaces, and calibration form of background noise instruments; and changes in experimental techniques, including the shape and size of the measurement surface, the number of measurement points and microphone positioning, sound source location, integration time, and determination of environmental corrections (if any). The standard deviation is also affected by the error caused by near-field measurement. This error is related to the characteristics of the sound source. When the measurement distance is small and the cheek frequency is low (250 Hz and below), the error generally increases. 4 If several laboratories use similar instruments and equipment, the consistency of the sound power level results measured by these laboratories for a given sound source may be better than the consistency reflected by the standard deviation in Table 1.
5 For a specific type of sound source with similar size, similar sound power spectrum and similar operating conditions, the reproducibility standard deviation may be smaller than the value in Table 1. When formulating noise test specifications with reference to this standard, a smaller standard deviation than the value in Table 1 may be marked in the noise test specifications if it is proven feasible through appropriate laboratory verification.
6 The reproducibility standard deviation in Table 1 includes the uncertainty of repeated measurements of the same noise source under the same conditions (standard deviation of repeatability), which is generally larger than the uncertainty caused by changing laboratories. The standard deviation is much smaller. For special sound sources, if it is difficult to maintain stable working conditions and installation conditions, the repeatability and standard deviation may not be smaller than the values given in Table 1. In this case, it is difficult to obtain reproducible sound power levels, which should be recorded and explained in the test report.
7 The methods of this standard and the standard deviations given in Table 1 are applicable to the measurement of a single machine. For batch-phase type machines, the characteristic representation of the sound power level involves random sampling techniques with specified confidence intervals, and the results are expressed as statistical upper limits. When applying these techniques, the total uncertainty must be known or estimated, including the product standard deviation defined in GB/T 14573.2, which is the deviation in sound power output between individual machines in a batch of machines. The statistical methods for machine batch characteristics can be found in GB/T14573.4.2 Cited standards
The clauses contained in the following standards constitute the clauses recommended by this standard through reference in this standard. At the time of publication of this standard, the versions shown are valid. All standards will be revised, and parties using this standard should explore the possibility of using the latest versions of the following standards. GB3241-82 1/1 and 1/3 octave filters for sound and vibration analysis (negIEC225:1966) GB3785--83 Electrical and acoustic properties and test methods of sound level meters (negIEC651:1979) GB3947—83 Acoustic terminology
GB6882-86 Determination of sound power level of acoustic noise sources - Precision method for anechoic chambers and semi-anechoic chambers (neqISO3745 :1977) GB3102.7--93 Acoustic quantities and units (negISO31-7:1992) GB/T14259-93 Acoustics Guide to standards for the measurement of airborne noise and the evaluation of its impact on people (neqISO2204:1979)
GB/T3767-1996
GB/T14573.1-93 Acoustics Statistical methods for determining and verifying specified noise radiation values of machinery and equipment Part - Overview and definitions (neqISO7574-1:1985) GB/T14573.4-93
Acoustics Statistical methods for determining and verifying specified noise radiation values of machinery and equipment Part 4: Methods for determining and verifying the label values of batch machines. (neqISO7574-4:1985) GB/T14574-93 Acoustics - Noise labels for machines and equipment (neqISO4871:1984) GB/T15173-94 Sound calibrator (eqvIEC942:1988) GBJ47-83 Reverberation chamber method - Measurement specification for sound absorption coefficient IEC804--85 Integrating average sound level meter
GB/T16538-1996 Acoustics - Determination of sound power level of noise source by sound pressure method - Simple method using standard sound source (neqISO3747:1987)
GB/T4129-1995 Acoustics - Determination of sound power level of noise source - Performance requirements and calibration of standard sound sources (eqvISO6926:1990)
3 Definitions
This standard adopts the following definitions. Other acoustic terms, quantities and units shall comply with the provisions of GB3947 and GB3102.7. 3.1 Time-averaged sound pressure level Lpeq.T time-averaged sound pressure level Lpea The sound pressure level of a continuous steady-state sound. In the measurement time interval T, it has the same mean square sound pressure as the measured sound that changes with time. It is also called equivalent continuous sound pressure level.
Leg.(dB) -101g[[100-2,dt
T(t)dt
=10lg[]. P
Note 8: The time-averaged sound pressure level is generally A-weighted and is expressed as LAg.r. (1)
3.2 Single-event sound pressure level Lp1 single-event sound pressure level Lp1. The time-integrated sound pressure level of an independent single event over a specified time interval T (or specified measurement time T), T. Normalized to 1s. The formula is as follows:
lrptdt
Lp.s(dB) =10lg[J. P
= Lpea, + 10lg[
3. 3 Surface sound pressure level L, surface sound pressure level Z, (2)
The energy average of the time-averaged sound pressure level at all microphone positions on the measurement surface plus the background noise correction K, and the environmental correction K, dB.
3.4 Measuring surface messurement surface An imaginary geometric surface with area S that envelops the sound source and on which the measuring points are located. The measuring surface terminates on one or more reflecting surfaces. 3.5 Free field free field
A sound field in a homogeneous, isotropic medium in which the effects of boundaries are negligible. A practical free field is a sound field in which the boundary reflections are negligible within the frequency range of the test.
3.6 Free field over a reflecting plane The sound field in a homogeneous, isotropic medium in half space above an infinitely large, hard, flat surface. The sound source to be measured is located on this surface.
3.7 Frequency range of interest In general, the frequency range of interest includes an octave band with a centre frequency of 125 to 8000 Hz. NOTE 9: For special purposes, it is permissible to extend or reduce the frequency range of interest at both ends. As long as the test environment and instrument accuracy can meet the requirements within the extended or reduced frequency range. For sound sources dominated by high (or low) frequency sounds, in order to obtain the best test method, it is allowed to extend or reduce the test frequency range.
3.8 Reference box
The smallest rectangular parallelepiped imaginary surface that just envelops the sound source and ends on one or more reflecting surfaces. 3.9 Characteristic source dimension d. Half the length of the diagonal of the box formed by the reference box and its virtual image in the adjacent reflecting surface. 3.10 Measurement distance d The vertical distance between the reference box and the box-shaped measurement surface. 3.11 Measurement radius r Measurement radius r The radius of the hemispherical measurement surface.
3.12 Background noise Background noise from all other sound sources other than the sound source being measured. Note 10: Background noise includes airborne sound, structurally transmitted vibration, electrical noise of instruments, etc. 3.13 Background noise correction K, a correction term introduced by the effect of background noise on the surface pressure level, dB. K, is related to frequency. In the case of A-weighting, it is expressed as KIA.
3.14 Environmental correction K, environmental correction Kz, a correction term introduced by the effect of sound reflection or sound absorption on the surface sound pressure level, dB. K, is related to frequency. In the case of A-weighting, it is expressed as K2A.
3.15 Impulsive noise index (impuisiveness) A quantity used to characterize the "impulse" of the noise radiated by the sound source, dB. 3.16 Directivity index The degree to which the sound source radiates sound mainly in a certain direction, dB. 4 Acoustic environment
4.1 The test environment applicable to this standard is: a) a laboratory that provides a free field above a reflecting surface; b) an outdoor flat open space that meets the requirements of 4.2 and Appendix A (Appendix of the standard); c) a room where the effect of the reverberation field on the sound pressure on the measurement surface is less than that of the sound source directly reaching the sound field. Note 11: The condition of c) can generally be met in a very large room or a room that is not very large but has sufficient sound absorbing materials on the walls and ceiling. 4.2 Criteria for judging the suitability of the test environment
The test environment should have no other reflectors except the reflecting surface, so that the sound source can radiate into the free space above the reflecting surface. Appendix A (Appendix of the standard) gives the method for determining the environmental correction K. This standard requires that the environmental correction K2A is less than or equal to 2 dB. When measuring the spectrum, K is less than or equal to 2 dB in each frequency band within the test frequency range.
Note 12: If it is necessary to measure in an environment where K2A exceeds 2dB, refer to Table 0.1 and 8.4 or ISO3746 and ISO96144.3 background noise standards.
The average background noise level at the microphone position should be at least 6dB lower than the measured sound pressure level, and preferably 15dB lower. Note 13: If the difference between the background noise and the sound source noise sound pressure level is less than 6dB, refer to Table 0.1 and 8.3 or ISO3746. Minimize the influence of wind during measurement to avoid increasing background noise.
5 Measuring instruments
5.1 General
GB/T 3767--1996
The instrument system including microphones and cables shall meet the requirements of Type I in GB3785. If an integrating sound level meter is used, it shall meet the requirements of Type I in IEC804. The filters used shall meet the requirements of GB3241. 5.2 Calibration
Before and after each measurement, the entire measurement system shall be calibrated at one or more frequency points within the frequency range of the test using a sound calibrator with an accuracy better than ±0.3 dB. The sound calibrator and the measurement system shall be qualified by metrological verification every year. 5.3 Microphone wind shield
When measuring outdoors, it is recommended to use a wind shield to ensure that the accuracy of the instrument is not affected by wind. 6 Installation and operating conditions of the sound source under test
6.1 General
The installation and operating conditions of the sound source under test can have a great influence on the sound power radiation of the sound source. This chapter specifies the conditions to minimize the changes in the sound power level caused by installation and operation. If the sound source under test has noise test specifications, the relevant regulations shall be followed. Especially for large sound sources, the noise test specifications are more important. It lists in detail the components, assemblies, auxiliary equipment, power sources, etc. included in the reference body.
6.2 Location of the sound source
The sound source under test shall be installed at one or more locations on the reflecting surface according to normal use conditions. If several possibilities exist, or the typical installation conditions are unknown, special treatment should be given and stated in the test report. When positioning the sound source in the test environment, sufficient space should be left so that the measurement surface meets the requirements of 7.1. The sound source to be measured should be kept at a sufficient distance from the reflecting wall, ceiling or reflector so that the measurement surface meets the requirements of Appendix A (Annex to the standard).
For some sound sources, the typical installation conditions involve two or more reflecting surfaces (for example, a wall-mounted device in Figures C7 and C8) or an opening in free space (such as an elevator) or other reflecting surface (and therefore may radiate to both sides of the vertical plane). For such sound sources, the details of the installation conditions and the microphone array pattern should be determined based on the general requirements of this standard and the corresponding noise test specifications. The sound source is close to two when this situation does represent the normal use of the sound source. or multiple reflecting surfaces. 6.3 Sound source installation
In many cases, the radiation of sound power is related to the support and installation conditions of the sound source under test. When the equipment under test has typical installation conditions, this condition should be used or simulated if feasible. If typical installation conditions are not available or cannot be used for testing, care should be taken to avoid changes in the sound power output of the sound source due to the installation system used for the test. And take measures to try to reduce the sound radiation of the equipment installation structure. Note 14: Many small sound sources, although they radiate little low-frequency sound themselves, after installation, their vibration energy is transferred to a sufficiently large surface. At this time, more low-frequency sound may be radiated by the surface. If possible, an elastic support should be added between the device under test and its base surface to minimize the transmission of vibration to the base and the reaction force of the sound source. In this case, the mounting base should have a sufficiently high mechanical impedance to prevent additional sound radiation due to vibration.
When the typical installation condition of the sound source under test is not elastic mounting, the above method should not be used. Note 15: Coupling conditions (for example, between the prime mover and the driven machine) may also have a significant effect on the sound radiation of the sound source under test. 6.3.1 Handheld mechanical equipment
This mechanical equipment should be suspended or handheld. So that the structure-borne sound does not pass through any part that is not the sound source under test. Accessory delivery. If the source under test requires a support for operation, the structure of this support should be small enough to be considered as part of the source and described in the noise test specification.
6.3.2 Floor-mounted and wall-mounted machinery Such machinery should be placed on a reflecting surface (floor, wall). When referring to machinery installed on the floor in front of a wall, the machinery should be installed on the floor in front of the wall. Table equipment should be placed on the floor, at least 1.5m away from any wall in the room, unless a workbench is required according to the test specification of the device under test, in which case the equipment should be placed in the center of the test table. 15
6.4 Auxiliary equipment
GB/T 3767-1996
Any cable duct, air pipe joint, etc. connected to the sound source under test should not have obvious sound radiation to the test environment. All auxiliary equipment required for the operation of the sound source under test but not part of the sound source should be located outside the test environment. Otherwise, the auxiliary equipment should be included in the reference body and its working conditions should be described in the test report. 6.5 Working conditions of the sound source during measurement
During the measurement, if the mechanical equipment has noise test specifications, the working conditions specified in the test specifications should be used, otherwise, the sound source works in a typical mode of normal use. At this time, the following working conditions should be selected: under the specified load and working conditions;
-full load;
-no load (idle);
--under the working conditions corresponding to the maximum noise output during normal use;-with a simulated load working under the set conditions; under the conditions where the characteristic working cycle is available.
The sound power level of the source can also be determined under any desired operating conditions (i.e. load, speed, temperature, etc.). The test conditions should be preselected and kept constant during the test. Before any measurements are made, the source should be in the required operating conditions. If the noise emission is related to secondary operating parameters, such as the type of material being processed or the type of tool used, appropriate parameters should be selected as far as possible to minimize the change in the noise emission and to be in typical operating conditions. The tools and materials used in the test should be specified in the special test specifications for machinery. For special purpose tests, one or more operating conditions can be appropriately set. It can provide a high reproducibility of the noise emission of the same machine and it is the most common and typical for the type of machinery involved. Such operating conditions should be specified in the specific noise test specifications.
If simulated operating conditions are used, they should be selected so that the source under test is in normal use and the radiated sound power is maximized. In the case of several operating conditions, each condition lasts for a set time interval if appropriate, and the results of the entire operating sequence are combined by energy averaging.
The operating conditions of the sound source during the acoustic measurement should be described in detail in the test report. 7 Measurement of sound pressure level
7.1 Selection of measurement surface
In order to facilitate the positioning of the microphone position on the measurement surface, a reference body should be set. When setting the reference body, units that protrude from the sound source but do not radiate significant sound energy can be ignored. For different types of equipment, the protruding units should be noted in the specific noise test specifications. The position of the sound source under test, the measurement surface and the microphone position are defined by a coordinate system. The X-axis and Y-axis of the coordinate system are located on the ground and are parallel to the length and width of the reference body, with a specific sound source size d. As shown in Figure 1. The measurement surface can use the following two shapes: a) hemispherical or partially hemispherical surface;
b) a rectangular parallelepiped surface with each side parallel to the corresponding reference body. 16
GB/T 3767-1996
Reference body on one reflecting plane
dg—V/2)2+(t2/2)2+
b) Reference body on two reflecting planes
d= V1/2)2+12+13
Reference body on three reflecting planes
do= ++3
Figure 1 Reference body and characteristic sound source size d. Example of relationship with the origin Q of the coordinate system For sound sources located in rooms or spaces with unfavorable acoustic conditions (e.g. many reflectors, high background noise), a smaller measurement distance can be selected. Generally, a parallelepiped measurement surface is specified. For sound sources that are often installed or tested in large outdoor spaces with satisfactory acoustic conditions, a larger measurement distance is generally selected. A hemispherical measurement surface is preferred. Directivity measurements require a hemispherical or partially hemispherical measurement surface. Note 16: For detailed information, refer to the special noise test specification for the sound source being studied. The composition of the reference body, the shape and size of the measuring surface and the measuring distance d or the hemispherical radius shall be described in the test report.
7.2 Hemispherical measuring surface
The center of the hemisphere is located at the center of the box formed by the reference body and its virtual image in the adjacent reflecting surface (origin Q in Figure 1). The radius r of the hemispherical measuring surface shall be greater than or equal to twice the size d of the characteristic sound source and not less than 1 m. Note 17: The hemispherical radius shall be one of the following values (m): 1, 2, 4, 6.8, 10, 12, 14, 16. Some radii are too large and it is difficult to meet the environmental conditions of Appendix A (Appendix to the standard). These radii should not be used. 7.2.1 Area of hemispherical measurement surface and basic microphone positions When there is only one reflecting surface, the area of the imaginary hemispherical surface where the microphone position is located is S=2 yuan 2. When the sound source to be measured is located in front of a wall, S=r2. If it is located at a corner of a wall, S=0.5 yuan r2. The microphone positions on the hemispherical surface are shown in Figures B1 and B2 of Appendix B (Standard Appendix). Figure B1 shows 10 basic microphone positions, which are connected with equal areas on the hemispherical surface with a radius of r. The hemispherical array selected in Figures B1 and B2 minimizes the error caused by interference between the direct sound wave and the reflected wave of the reflecting surface. If the sound source is placed close to more than one reflecting surface, refer to Figure B3 of Appendix B (Standard Appendix) to set the appropriate measurement surface and microphone position.
In special cases (i.e. for special types of machines, such as construction equipment or earth-moving machinery, which are measured in motion or in a driven mode) different numbers of microphones and arrays may be used, provided that preliminary investigations have demonstrated that the sound power level values deviate by less than 1 dB from those determined using the array given in this standard.
7.2.2 Additional microphone positions on the hemispherical measurement surface Additional microphone positions are required on the measurement surface in the following cases: a) the range of sound pressure level values measured at the basic microphone positions (i.e. the dB difference between the highest and lowest sound pressure levels) exceeds the number of basic measurement points,
b) the noise radiated by the sound source is highly directional; c) a loud source whose noise is radiated outwards only through a small local part of the sound source, such as an opening in a machine that is enclosed around it.
For a) the additional 10 measurement points are obtained by rotating the original array of Figure B1 by 180° about the Z axis (see Table B1 and Figure B2). Note that the vertex of the new array on the Z axis coincides with the vertex of the original array, so the total number of microphone positions increases from 10 to 19. For b) or c), additional microphone positions should be used in the high noise radiation area of the measurement surface (see 7.4.1). 7.3 Parallelepiped measurement surface
The measurement distance d is preferably 1m, at least 0.25m. Note 18: d should be one of the following values (m): 0.25, 0.5, 1, 2, 4, 8 The measurement distance of the sound source should be greater than 1m. When selecting d, the environmental requirements given in Appendix A (Standard Appendix) should be met first. 7.3.1 Area and microphone positions of parallelepiped measurement surface The measurement surface where the microphone positions are located is an imaginary surface with an area S, enveloping the sound source, with each side parallel to the side of the reference body, and a distance d (measurement distance) from the reference body. The microphone positions on the parallelepiped measurement surface
are shown in Figures C1 to C8 of Appendix C (Standard Appendix). According to Figures C1 to C6, the area S of the measurement surface is given by formula (3):
S = 4(ab + ac + bc)
a=0.5l+d;
b=0. 512+d;
c=ls+d;
where: 11, 12, l3 are the length, width and height of the reference body respectively. (3)
If the sound source is placed close to more than one reflecting surface, an appropriate measurement surface should be set with reference to Figures C7 and C8 of Appendix C (Standard Appendix). In this case, the calculation of the measurement surface area S is given in the respective figures. The microphone positions are arranged according to Figures C1 to C6. 7.3.2 Additional microphone positions on the parallelepiped measurement surface Additional microphone positions are required on the parallelepiped measurement surface in the following cases: a) The range of sound pressure level values (dB difference between the highest and lowest sound pressure levels) measured at the basic microphone positions exceeds the number of measurement points;5 Working conditions of the sound source during measurement
During the measurement, if the mechanical equipment has a noise test specification, the working conditions specified in the test specification shall be used, otherwise the sound source shall work in a typical manner in normal use. In this case, the following working conditions should be selected: under the specified load and working conditions;
- full load;
- no load (idle);
- working conditions corresponding to the maximum noise output in normal use; - working under the set conditions with a simulated load; under the conditions where the characteristic working cycle is available.
The sound power level of the sound source can also be determined under any desired working conditions (i.e. load, speed, temperature, etc.). The test conditions shall be selected in advance and kept constant during the test. Before any measurement begins, the sound source shall be under the required working conditions. If the noise radiation is related to secondary working parameters, such as the type of material being processed or the model of the tool used, appropriate parameters should be selected as much as possible to minimize the change in sound radiation and be in a typical working state. The tools and materials used in the test should be described in detail in the special test specifications for mechanical equipment. For tests of special purposes, one or more operating conditions may be appropriately set. It may allow a high reproducibility of the noise radiation of the same machine and it may be the most common and typical for the type of machinery involved. Such operating conditions shall be specified in the specific noise test specification.
If simulated operating conditions are used, they shall be chosen so that the source under test is in normal use and the radiated sound power is maximum. In the case of several operating conditions, each condition lasts for a set time interval, if appropriate, and the results of the entire operating procedure are combined by energy averaging.
The operating conditions of the source during the acoustic measurement shall be described in detail in the test report. 7 Measurement of sound pressure level
7.1 Selection of measurement surface
In order to facilitate the positioning of the microphone position on the measurement surface, a reference body shall be set. When setting the reference body, units protruding from the source but not radiating significant sound energy may be disregarded. For different types of equipment, the protruding units shall be noted in the specific noise test specification. The position of the source under test, the measurement surface and the microphone position are defined by a coordinate system. The X-axis and Y-axis of the coordinate system are located on the ground and are parallel to the length and width of the reference body, and the specific sound source size d. As shown in Figure 1. The measurement surface can use the following two shapes: a) hemispherical or partially hemispherical surface;
b) rectangular parallelepiped surface with each side parallel to the corresponding reference body. 16
GB/T 3767-1996
reference body on one reflection plane
dg—V/2)2+(t2/2)2+
b) reference body on two reflection planes
d= V1/2)2+12+13
reference body on three reflection planes
do= ++3
Figure 1 Reference body and characteristic sound source size d. Example of relationship with the origin Q of the coordinate system For sound sources located in rooms or spaces with unfavorable acoustic conditions (such as many reflectors and high background noise), a smaller measurement distance can be selected. It is usually specified to select a parallelepiped measuring surface. For sound sources that are often installed or tested in large outdoor spaces where acoustic conditions are met, a larger measuring distance is generally selected. Hemispherical measuring surfaces are preferred. Directivity measurements require a hemispherical or partially hemispherical measuring surface. Note 16: For detailed information, refer to the special noise test specification for the sound source being studied. The composition of the reference body, the shape and size of the measuring surface, and the measuring distance d or hemispherical radius are described in the test report.
7.2 Hemispherical measuring surface
The center of the hemisphere is located at the center of the box formed by the reference body and its virtual image in the adjacent reflecting surface (origin Q in Figure 1). The radius r of the hemispherical measuring surface should be greater than or equal to twice the size d of the characteristic sound source and not less than 1 m. Note 17: The hemispherical radius should be one of the following values (m): 1, 2, 4, 6.8, 10, 12, 14, 16. Some radii are too large and the environmental conditions in Appendix A (Standard Appendix) are difficult to meet. These radii should not be used. 7.2.1 Area of hemispherical measurement surface and basic microphone positions When there is only one reflecting surface, the area of the imaginary hemispherical surface where the microphone position is located is S=2 yuan2. When the sound source to be measured is located in front of a wall, S=yuanr2. If it is located at a corner of a wall, S=0.5 yuanr2. The microphone positions on the hemispherical surface are shown in Figures B1 and B2 of Appendix B (Standard Appendix). Figure B1 shows 10 basic microphone positions, which are connected with equal areas on the hemispherical surface with a radius of r. The hemispherical array selected in Figures B1 and B2 minimizes the error caused by interference between the direct sound wave and the reflected wave of the reflecting surface. If the sound source is placed close to more than one reflecting surface, refer to Figure B3 of Appendix B (Standard Appendix) to set the appropriate measurement surface and microphone position.
In special cases (i.e. for special types of machines, such as construction equipment or earth-moving machinery, which are measured in motion or in a driven mode) different numbers of microphones and arrays may be used, provided that preliminary investigations have demonstrated that the sound power level values deviate by less than 1 dB from those determined using the array given in this standard.
7.2.2 Additional microphone positions on the hemispherical measurement surface Additional microphone positions are required on the measurement surface in the following cases: a) the range of sound pressure level values measured at the basic microphone positions (i.e. the dB difference between the highest and lowest sound pressure levels) exceeds the number of basic measurement points,
b) the noise radiated by the sound source is highly directional; c) a loud source whose noise is radiated outwards only through a small local part of the sound source, such as an opening in a machine that is enclosed around it.
For a) the additional 10 measurement points are obtained by rotating the original array of Figure B1 by 180° about the Z axis (see Table B1 and Figure B2). Note that the vertex of the new array on the Z axis coincides with the vertex of the original array, so the total number of microphone positions increases from 10 to 19. For b) or c), additional microphone positions should be used in the high noise radiation area of the measurement surface (see 7.4.1). 7.3 Parallelepiped measurement surface
The measurement distance d is preferably 1m, at least 0.25m. Note 18: d should be one of the following values (m): 0.25, 0.5, 1, 2, 4, 8 The measurement distance of the sound source should be greater than 1m. When selecting d, the environmental requirements given in Appendix A (Standard Appendix) should be met first. 7.3.1 Area and microphone positions of parallelepiped measurement surface The measurement surface where the microphone positions are located is an imaginary surface with an area S, enveloping the sound source, with each side parallel to the side of the reference body, and a distance d (measurement distance) from the reference body. The microphone positions on the parallelepiped measurement surface
are shown in Figures C1 to C8 of Appendix C (Standard Appendix). According to Figures C1 to C6, the area S of the measurement surface is given by formula (3):
S = 4(ab + ac + bc)
a=0.5l+d;
b=0. 512+d;
c=ls+d;
where: 11, 12, l3 are the length, width and height of the reference body respectively. (3)
If the sound source is placed close to more than one reflecting surface, an appropriate measurement surface should be set with reference to Figures C7 and C8 of Appendix C (Standard Appendix). In this case, the calculation of the measurement surface area S is given in the respective figures. The microphone positions are arranged according to Figures C1 to C6. 7.3.2 Additional microphone positions on the parallelepiped measurement surface Additional microphone positions are required on the parallelepiped measurement surface in the following cases: a) The range of sound pressure level values (dB difference between the highest and lowest sound pressure levels) measured at the basic microphone positions exceeds the number of measurement points;5 Working conditions of the sound source during measurement
During the measurement, if the mechanical equipment has a noise test specification, the working conditions specified in the test specification shall be used, otherwise the sound source shall work in a typical manner in normal use. In this case, the following working conditions should be selected: under the specified load and working conditions;
- full load;
- no load (idle);
- working conditions corresponding to the maximum noise output in normal use; - working under the set conditions with a simulated load; under the conditions where the characteristic working cycle is available.
The sound power level of the sound source can also be determined under any desired working conditions (i.e. load, speed, temperature, etc.). The test conditions shall be selected in advance and kept constant during the test. Before any measurement begins, the sound source shall be under the required working conditions. If the noise radiation is related to secondary working parameters, such as the type of material being processed or the model of the tool used, appropriate parameters should be selected as much as possible to minimize the change in sound radiation and be in a typical working state. The tools and materials used in the test should be described in detail in the special test specifications for mechanical equipment. For tests of special purposes, one or more operating conditions may be appropriately set. It may allow a high reproducibility of the noise radiation of the same machine and it may be the most common and typical for the type of machinery involved. Such operating conditions shall be specified in the specific noise test specification.
If simulated operating conditions are used, they shall be chosen so that the source under test is in normal use and the radiated sound power is maximum. In the case of several operating conditions, each condition lasts for a set time interval, if appropriate, and the results of the entire operating procedure are combined by energy averaging.
The operating conditions of the source during the acoustic measurement shall be described in detail in the test report. 7 Measurement of sound pressure level
7.1 Selection of measurement surface
In order to facilitate the positioning of the microphone position on the measurement surface, a reference body shall be set. When setting the reference body, units protruding from the source but not radiating significant sound energy may be disregarded. For different types of equipment, the protruding units shall be noted in the specific noise test specification. The position of the source under test, the measurement surface and the microphone position are defined by a coordinate system. The X-axis and Y-axis of the coordinate system are located on the ground and are parallel to the length and width of the reference body, and the specific sound source size d. As shown in Figure 1. The measurement surface can use the following two shapes: a) hemispherical or partially hemispherical surface;
b) rectangular parallelepiped surface with each side parallel to the corresponding reference body. 16
GB/T 3767-1996
reference body on one reflection plane
dg—V/2)2+(t2/2)2+
b) reference body on two reflection planes
d= V1/2)2+12+13
reference body on three reflection planes
do= ++3
Figure 1 Reference body and characteristic sound source size d. Example of relationship with the origin Q of the coordinate system For sound sources located in rooms or spaces with unfavorable acoustic conditions (such as many reflectors and high background noise), a smaller measurement distance can be selected. It is usually specified to select a parallelepiped measuring surface. For sound sources that are often installed or tested in large outdoor spaces where acoustic conditions are met, a larger measuring distance is generally selected. Hemispherical measuring surfaces are preferred. Directivity measurements require a hemispherical or partially hemispherical measuring surface. Note 16: For detailed information, refer to the special noise test specification for the sound source being studied. The composition of the reference body, the shape and size of the measuring surface, and the measuring distance d or hemispherical radius are described in the test report.
7.2 Hemispherical measuring surface
The center of the hemisphere is located at the center of the box formed by the reference body and its virtual image in the adjacent reflecting surface (origin Q in Figure 1). The radius r of the hemispherical measuring surface should be greater than or equal to twice the size d of the characteristic sound source and not less than 1 m. Note 17: The hemispherical radius should be one of the following values (m): 1, 2, 4, 6.8, 10, 12, 14, 16. Some radii are too large and the environmental conditions in Appendix A (Standard Appendix) are difficult to meet. These radii should not be used. 7.2.1 Area of hemispherical measurement surface and basic microphone positions When there is only one reflecting surface, the area of the imaginary hemispherical surface where the microphone position is located is S=2 yuan2. When the sound source to be measured is located in front of a wall, S=yuanr2. If it is located at a corner of a wall, S=0.5 yuanr2. The microphone positions on the hemispherical surface are shown in Figures B1 and B2 of Appendix B (Standard Appendix). Figure B1 shows 10 basic microphone positions, which are connected with equal areas on the hemispherical surface with a radius of r. The hemispherical array selected in Figures B1 and B2 minimizes the error caused by interference between the direct sound wave and the reflected wave of the reflecting surface. If the sound source is placed close to more than one reflecting surface, refer to Figure B3 of Appendix B (Standard Appendix) to set the appropriate measurement surface and microphone position.
In special cases (i.e. for special types of machines, such as construction equipment or earth-moving machinery, which are measured in motion or in a driven mode) different numbers of microphones and arrays may be used, provided that preliminary investigations have demonstrated that the sound power level values deviate by less than 1 dB from those determined using the array given in this standard.
7.2.2 Additional microphone positions on the hemispherical measurement surface Additional microphone positions are required on the measurement surface in the following cases: a) the range of sound pressure level values measured at the basic microphone positions (i.e. the dB difference between the highest and lowest sound pressure levels) exceeds the number of basic measurement points,
b) the noise radiated by the sound source is highly directional; c) a loud source whose noise is radiated outwards only through a small local part of the sound source, such as an opening in a machine that is enclosed around it.
For a) the additional 10 measurement points are obtained by rotating the original array of Figure B1 by 180° about the Z axis (see Table B1 and Figure B2). Note that the vertex of the new array on the Z axis coincides with the vertex of the original array, so the total number of microphone positions increases from 10 to 19. For b) or c), additional microphone positions should be used in the high noise radiation area of the measurement surface (see 7.4.1). 7.3 Parallelepiped measurement surface
The measurement distance d is preferably 1m, at least 0.25m. Note 18: d should be one of the following values (m): 0.25, 0.5, 1, 2, 4, 8 The measurement distance of the sound source should be greater than 1m. When selecting d, the environmental requirements given in Appendix A (Standard Appendix) should be met first. 7.3.1 Area and microphone positions of parallelepiped measurement surface The measurement surface where the microphone positions are located is an imaginary surface with an area S, enveloping the sound source, with each side parallel to the side of the reference body, and a distance d (measurement distance) from the reference body. The microphone positions on the parallelepiped measurement surface
are shown in Figures C1 to C8 of Appendix C (Standard Appendix). According to Figures C1 to C6, the area S of the measurement surface is given by formula (3):
S = 4(ab + ac + bc)
a=0.5l+d;
b=0. 512+d;
c=ls+d;
where: 11, 12, l3 are the length, width and height of the reference body respectively. (3)
If the sound source is placed close to more than one reflecting surface, an appropriate measurement surface should be set with reference to Figures C7 and C8 of Appendix C (Standard Appendix). In this case, the calculation of the measurement surface area S is given in the respective figures. The microphone positions are arranged according to Figures C1 to C6. 7.3.2 Additional microphone positions on the parallelepiped measurement surface Additional microphone positions are required on the parallelepiped measurement surface in the following cases: a) The range of sound pressure level values (dB difference between the highest and lowest sound pressure levels) measured at the basic microphone positions exceeds the number of measurement points;2 Additional microphone positions on the parallelepiped measurement surface Additional microphone positions are required on the parallelepiped measurement surface in the following cases: a) The range of sound pressure level values (dB difference between the highest and lowest sound pressure levels) measured at the basic microphone positions exceeds the number of measurement points;2 Additional microphone positions on the parallelepiped measurement surface Additional microphone positions on the parallelepiped measurement surface are required in the following cases: a) The range of sound pressure level values (dB difference between the highest and lowest sound pressure levels) measured at the basic microphone positions exceeds the number of measurement points;1 Selection of measurement surface
In order to facilitate the positioning of the microphone on the measurement surface, a reference body should be set. When setting the reference body, units that protrude from the sound source but do not radiate significant sound energy can be ignored. For different types of equipment, the protruding units should be noted in the specific noise test specifications. The position of the sound source to be measured, the measurement surface and the microphone position are all defined by a coordinate system. The X-axis and Y-axis of the coordinate system are located on the ground and are parallel to the length and width of the reference body, with a specific sound source size d. As shown in Figure 1. The measurement surface can use the following two shapes: a) hemispherical or partially hemispherical surface;
b) a rectangular parallelepiped surface with each side parallel to the corresponding reference body. 16
GB/T 3767-1996
Reference body on one reflecting plane
dg—V/2)2+(t2/2)2+
b) Reference body on two reflecting planes
d= V1/2)2+12+13bzxZ.net
Reference body on three reflecting planes
do= ++3
Figure 1 Reference body and characteristic sound source size d. Example of relationship with the origin Q of the coordinate system For sound sources located in rooms or spaces with unfavorable acoustic conditions (e.g. many reflectors, high background noise), a smaller measurement distance can be selected. Generally, a parallelepiped measurement surface is specified. For sound sources that are often installed or tested in large outdoor spaces with satisfactory acoustic conditions, a larger measurement distance is generally selected. A hemispherical measurement surface is preferred. Directivity measurements require a hemispherical or partially hemispherical measurement surface. Note 16: For detailed information, refer to the special noise test specification for the sound source being studied. The composition of the reference body, the shape and size of the measuring surface and the measuring distance d or the hemispherical radius shall be described in the test report.
7.2 Hemispherical measuring surface
The center of the hemisphere is located at the center of the box formed by the reference body and its virtual image in the adjacent reflecting surface (origin Q in Figure 1). The radius r of the hemispherical measuring surface shall be greater than or equal to twice the size d of the characteristic sound source and not less than 1 m. Note 17: The hemispherical radius shall be one of the following values (m): 1, 2, 4, 6.8, 10, 12, 14, 16. Some radii are too large and it is difficult to meet the environmental conditions of Appendix A (Appendix to the standard). These radii should not be used. 7.2.1 Area of hemispherical measurement surface and basic microphone positions When there is only one reflecting surface, the area of the imaginary hemispherical surface where the microphone position is located is S=2 yuan 2. When the sound source to be measured is located in front of a wall, S=r2. If it is located at a corner of a wall, S=0.5 yuan r2. The microphone positions on the hemispherical surface are shown in Figures B1 and B2 of Appendix B (Standard Appendix). Figure B1 shows 10 basic microphone positions, which are connected with equal areas on the hemispherical surface with a radius of r. The hemispherical array selected in Figures B1 and B2 minimizes the error caused by interference between the direct sound wave and the reflected wave of the reflecting surface. If the sound source is placed close to more than one reflecting surface, refer to Figure B3 of Appendix B (Standard Appendix) to set the appropriate measurement surface and microphone position.
In special cases (i.e. for special types of machines, such as construction equipment or earth-moving machinery, which are measured in motion or in a driven mode) different numbers of microphones and arrays may be used, provided that preliminary investigations have demonstrated that the sound power level values deviate by less than 1 dB from those determined using the array given in this standard.
7.2.2 Additional microphone positions on the hemispherical measurement surface Additional microphone positions are required on the measurement surface in the following cases: a) the range of sound pressure level values measured at the basic microphone positions (i.e. the dB difference between the highest and lowest sound pressure levels) exceeds the number of basic measurement points,
b) the noise radiated by the sound source is highly directional; c) a loud source whose noise is radiated outwards only through a small local part of the sound source, such as an opening in a machine that is enclosed around it.
For a) the additional 10 measurement points are obtained by rotating the original array of Figure B1 by 180° about the Z axis (see Table B1 and Figure B2). Note that the vertex of the new array on the Z axis coincides with the vertex of the original array, so the total number of microphone positions increases from 10 to 19. For b) or c), additional microphone positions should be used in the high noise radiation area of the measurement surface (see 7.4.1). 7.3 Parallelepiped measurement surface
The measurement distance d is preferably 1m, at least 0.25m. Note 18: d should be one of the following values (m): 0.25, 0.5, 1, 2, 4, 8 The measurement distance of the sound source should be greater than 1m. When selecting d, the environmental requirements given in Appendix A (Standard Appendix) should be met first. 7.3.1 Area and microphone positions of parallelepiped measurement surface The measurement surface where the microphone positions are located is an imaginary surface with an area S, enveloping the sound source, with each side parallel to the side of the reference body, and a distance d (measurement distance) from the reference body. The microphone positions on the parallelepiped measurement surface
are shown in Figures C1 to C8 of Appendix C (Standard Appendix). According to Figures C1 to C6, the area S of the measurement surface is given by formula (3):
S = 4(ab + ac + bc)
a=0.5l+d;
b=0. 512+d;
c=ls+d;
where: 11, 12, l3 are the length, width and height of the reference body respectively. (3)
If the sound source is placed close to more than one reflecting surface, an appropriate measurement surface should be set with reference to Figures C7 and C8 of Appendix C (Standard Appendix). In this case, the calculation of the measurement surface area S is given in the respective figures. The microphone positions are arranged according to Figures C1 to C6. 7.3.2 Additional microphone positions on the parallelepiped measurement surface Additional microphone positions are required on the parallelepiped measurement surface in the following cases: a) The range of sound pressure level values (dB difference between the highest and lowest sound pressure levels) measured at the basic microphone positions exceeds the number of measurement points;1 Selection of measurement surface
In order to facilitate the positioning of the microphone on the measurement surface, a reference body should be set. When setting the reference body, units that protrude from the sound source but do not radiate significant sound energy can be ignored. For different types of equipment, the protruding units should be noted in the specific noise test specifications. The position of the sound source to be measured, the measurement surface and the microphone position are all defined by a coordinate system. The X-axis and Y-axis o
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