Acoustics-Determination of sound power levels of noise sources using sound pressure-Survey method using a reference sound source
other information
Release date:1996-09-09
Review date:2004-10-14
drafter:Feng Yuzheng, Liu Kaisheng
Drafting unit:Institute of Acoustics, Chinese Academy of Sciences
Focal point unit:National Technical Committee on Acoustic Standardization
Proposing unit:National Technical Committee on Acoustic Standardization
Publishing department:State Bureau of Technical Supervision
competent authority:Chinese Academy of Sciences
Some standard content:
GB/T16538—1996
This standard is formulated with reference to the international standard ISO3747:1987 "Determination of sound power level of acoustic noise source - Simple method using standard sound source".
There are many methods for determining the sound power level of noise sources such as machinery and equipment, each suitable for different test environments and accuracy requirements. The simple method using standard sound source is one of the available methods. This method is suitable for testing the sound power level of noise source A in various indoor and outdoor acoustic environments.
The formulation of this standard makes the series of standards for the determination of sound power level of noise sources more complete, and plays a role in promoting the work of detection methods and limit standards for noise of machinery and equipment. This standard is proposed and managed by the National Technical Committee for Acoustics Standardization. The drafting unit of this standard: Institute of Acoustics, Chinese Academy of Sciences. The main drafters of this standard: Feng Lizheng and Liu Kaisheng. 262
1 Scope
National Standard of the People's Republic of China
Acoustics--Determination of sound power levels ofnoise sources using sound pressure-Survey methodusing a reference sound sourceGB/T16538—1996
1.1 This standard specifies a simple method for determining the sound power level of a sound source (including equipment, machinery, components or parts) using a reference sound source. The sound pressure levels generated by the measured sound source and the reference sound source at the specified measuring point are measured, and the sound power level of the measured sound source is obtained by correcting the measured sound pressure level for the environment. The environmental correction is obtained by calculating the calibration value of the sound power level of the reference sound source and the measured sound pressure level. The position of the microphone and the position and number of the reference sound sources are determined by the acoustic conditions such as the size of the measured sound source, the size, number and orientation of the reflecting surfaces near the sound source.
This standard is a supplementary method to the national standard GB/T3768. 1.2 The data measured by the method specified in this standard can be used for the following purposes: a) Evaluate the noise of equipment using A sound power level; b) Compare the noise of equipment of the same type;
Compare the noise of equipment of different types.
1.3 The names and symbols of acoustic terms, quantities and units used in this standard shall comply with the provisions of GB/T3947 and GB3102.7.
1.4 Test environment
It can be installed indoors or outdoors without restrictions, and there can be one or more reflective surfaces or reflective objects near the sound source. 1.5 Type of sound source
It is applicable to steady-state noise radiating broadband, narrowband, discrete frequency and their composite sounds, and also to non-steady-state noise except burst sound with a repetition rate of less than five times per second.
1.6 Test frequency range
Unless otherwise specified, the test frequency range shall include all octave bands with center frequencies between 125 and 8000 Hz. 1.7 Measurement uncertainty
The standard deviation of the sound power level of a sound source measured in accordance with this standard method is: a) for a sound source with uniform radiation frequency density, the standard deviation is not greater than 4 dB; b) for a sound source with obvious discrete frequencies, the standard deviation is not greater than 5 dB; for similar sound sources that are non-directional and radiate broadband noise, when compared in a similar test environment, the standard deviation is not greater than c)
3 dB.
Note: This refers to the cumulative standard deviation caused by various factors. Approved by the State Administration of Technical Supervision on September 13, 1996, and implemented on March 1, 1997
2 Referenced standards
GB/T16538—1996
The following standards contain provisions that constitute the provisions of this standard through reference in this standard. When the standard is published, 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. GB3102.7--1993 Acoustic quantities and units GB/T3768-1996 Acoustics Sound pressure method for determining the sound power level of noise sources. A simple method using an envelope measurement surface above the reflecting surface. (eqvISO3746—1995)
GB3785—83 Electroacoustic properties and test methods of sound level meters (neqIEC651:1979)GB/T3947—1996 Vocabulary of acoustic terms
GB/T4129—1995 Determination of sound power level of acoustic noise sourcesPerformance requirements and calibration of standard sound sources (egvISO6929:1990)
Trial verification procedure for sound pressure level calibrators
JJG176-84
JJG188-90 Trial verification procedure for sound level meters 3 Definitions
This standard adopts the following definitions:
3.1 Reference sound sourceA sound source with stable sound power output and a broadband spectrum. The difference between the maximum and minimum sound power levels of all 1/3 octave bands within the range of 100 to 10000Hz is within 12dB, and the deviation of the sound power levels of two adjacent 1/3 octave bands does not exceed ±3dB. The directivity index of any 1/3 octave band does not exceed 9dB, and the output sound pressure level should be at least 10dB higher than the background noise. There are pneumatic sources, electric sources and mechanical sources.
Note: It can be used to measure the sound power of noise radiated by machinery and equipment by comparison method. 3.2 Substitution procedure The method of removing the measured sound source from the installation position and placing the standard sound source in the position of the measured sound source. 3.3 Superposition procedure When the measured sound source cannot be moved from the installation position, the standard sound source is placed on the top of the measured sound source. 3.4 Juxtaposition procedure When the substitution method and the superposition method cannot be applied, the standard sound source is placed near the measured sound source. 3.5 Sound pressure level L The logarithm to the base 10 of the ratio of the sound pressure to the reference sound pressure multiplied by 2, in bels, B, but usually in dB. The reference sound pressure must be specified.
Note: The reference sound pressure is: 20 μPa (in air). 3.6 Sound power level Lw The logarithm to the base 10 of the ratio of the sound power to the reference sound power, in bels, B, but usually in dB. The reference sound power must be specified.
Note: The reference sound power is 1 pW.
3.7 Measurement surface measurement surface An imaginary surface enveloping the sound source; the microphone positions are distributed on its surface. 3.8 Reference rectangular parallelepiped The smallest rectangular hexahedron that just envelops the sound source being measured and ends on the reflecting surface. 3.9 Measurement distance measurement distance The distance between the reference surface and the measurement surface. 3.10 Background noise background noise261
GB/T 16538--1996
All interferences in the system that is generated, checked, measured or recorded that are not related to the presence or absence of the signal. 4 Acoustic environment
4.1 Measurement site
It can be applied to any type of indoor or outdoor space. There is no restriction on its acoustic and geometric properties. There can be one or more reflective surfaces or reflective objects near the sound source.
4.2 Background noise
The average value of the background noise A sound level at each measuring point on the measurement surface should be at least 3dB lower than the average value of the A sound level at each measuring point on the measurement surface when the measured sound source or the standard sound source is working. If the octave band sound pressure level is measured, the sound pressure level of each octave band should meet this requirement. 4.3
When measuring outdoors, the wind speed should be lower than 5m/s. When the wind speed is greater than 1m/s, a wind shield should be added to the microphone. 5 Test instruments
5.1 Overview
The test instruments shall be Type 2 or above sound level meters specified in GB3785, as well as other test instruments with equivalent accuracy, and measured at slow speed. It is best to use an extension cable or extension rod between the sound level meter or other test instruments and the microphone to reduce the influence of the observer on the measurement. The observer should not stand between the microphone and the sound source. 5.2 Calibration
Before and after each series of measurements, the entire test system (including cables) shall be calibrated at one or more frequencies using a sound calibrator with an accuracy better than ±0.5dB. The calibration frequency shall be within the frequency range of 125 to 1000Hz. The sound calibrator shall be calibrated regularly in accordance with JJG176, and the sound level meter and other test instruments shall be calibrated regularly in accordance with JJG188 to ensure the accuracy of the test instruments. 5.3 Standard sound source
The standard sound source used shall comply with the provisions of the national standard GB/T4129. 6 Installation and operation of sound source
6.1 Sound source to be measured
The sound source to be measured shall be clearly identified, and the noise generated by other components shall be regarded as background noise. 6.2 Operation of sound source during measurement
During measurement, the sound source shall operate in the normal manner as specified. If there are experimental regulations for the machine or equipment to be measured, it shall be operated in accordance with the regulations. The following working conditions may also be appropriately selected: under the specified load,
under full load (if different from a),
under no load;
d) under the working condition of maximum sound radiation, e) under the working condition of simulated load.
6.3 Placement of standard sound source
The standard sound source can be placed by substitution method, top method or parallel method (see 3.2, 3.3 and 3.4). The method and number of positions for placing the standard sound source depend on the size of the sound source to be measured and the possibility of placing the standard sound source (see 7.3 for details). Note: When the reflective surface near the standard sound source during measurement is different from that during calibration of the standard sound source, it may affect the sound power radiated by the standard sound source. For the simplified method, no correction is required for this effect.
7 Sound pressure level measurement
7.1 Reference body surface and measurement surface
GB/T16538—1996
According to 3.8, the reference body surface is a minimum rectangular hexahedron that just envelops the sound source to be measured and the standard sound source and ends on the reflective surface. When determining the reference body, the protruding part that is not the main radiated sound energy can be ignored. The microphone is placed on a measurement surface, which is an imaginary surface that envelops the sound source to be measured and the standard sound source and ends on one or more reflective surfaces. The reflective surface refers to a surface with a sound absorption coefficient a less than 0.2. When this requirement is not met, it can be extended along a surface ≥0.2. Select a parallelepiped imaginary surface surrounding the reference body surface as the measurement surface. The distance between it and the reference body surface (measurement distance d) d≥1m, generally d=1m (see Figures 1-5). 7.2 Microphone position
7.2.1 Overview
The microphone position should be placed on the measurement surface. Each surface in the measurement surface is called a free surface, and the intersection angle of three free surfaces is called a free vertex angle.
7.2.2 Number of microphone positions
7.2.2.1 Five free surfaces (one reflecting surface) There are at least five microphone positions, namely the midpoint of each free surface. For sound sources with a horizontal size exceeding 1m, one point is added for each of the four free vertex angles, for a total of nine points (see Figure 6). For sound sources with a horizontal size exceeding 5㎡, in addition to the above provisions, the distance between two adjacent microphone positions should be less than 2d, where d is the measurement distance.
7.2.2.2 Four free surfaces (two reflecting surfaces) The microphone position is at the midpoint of each free surface and one point each at the two free angles (see Figure 7). 7.2.2.3 Three free surfaces (three reflecting surfaces) The microphone position is at the midpoint of each free surface and one point at the free angle (see Figure 8). 7.2.2.4 Two free surfaces (four reflecting surfaces) The microphone position is at the midpoint of each free surface and the midpoint of the intersection of the two free surfaces (see Figure 9). 7.2.2.5 One free surface (five reflecting surfaces) The microphone position is regularly distributed at three points on the free surface (see Figure 10). 7.2.2.6 No free surfaces (six reflecting surfaces) The microphone position is regularly distributed at three points at the opening of the experimental room used as the measurement surface (see Figure 10). 7.3 Position of standard sound source
7.3.1 Overview
The position of standard sound source is as follows:
a) If the height L of the reference body is not greater than 1.5d, it is placed on the top surface of the sound source to be measured. b) If the height of the reference body is greater than 1.5d or cannot be placed on the top of the sound source to be measured (for example, for safety and operation considerations), it is placed near the sound source to be measured.bZxz.net
c) If the sound source to be measured can be moved, move the sound source to be measured and place the standard sound source at the original position of the sound source to be measured. 7.3.2 Top-mounted method
If the height L of the reference body is not greater than 1.5d, the top-mounted method is preferred. If the top-mounted method does not meet the requirements, an additional side-mounted position can be added.
7.3.2.1 If the length L or width L of the reference body is not greater than 2d, the standard sound source is placed at a position on the top surface of the sound source to be measured (see Figure 11).
7.3.2.2 If the width L, of the reference body does not exceed 2d but the length L, is greater than 2d, then the number of standard sound source positions (j1,,M) is at least two, and the standard sound source positions are placed on the top surface of the sound source to be measured along the symmetry axis of the length L, with a spacing of no more than 3d (see Figure 13 for example 3 d2 If the width L, of the reference body does not exceed 2d but the length L, is greater than 2d, then the number of standard sound source positions (j1,,M) is at least two, and the standard sound source positions are placed on the top surface of the sound source to be measured along the symmetry axis of the length L, with a spacing of no more than 3d (see Figure 13 for example 3 d2 If the width L, of the reference body does not exceed 2d but the length L, is greater than 2d, then the number of standard sound source positions (j1,,M) is at least two, and the standard sound source positions are placed on the top surface of the sound source to be measured along the symmetry axis of the length L, with a spacing of no more than 3d (see Figure 13 for example 3 d
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