GB/T 3768-1996
Acoustics--Determination of sound power levels of noise sources using sound pressure--Survey method using an enveloping measurement surface over a reflecting plane (English Version)

Standard No.

GB/T 3768-1996

Language

Chinese, Available in English version

Release Date

1996

Published By

General Administration of Quality Supervision, Inspection and Quarantine of the People‘s Republic of China

Status

Be replaced 2018-04

Replace By

GB/T 3768-2017

Latest

GB/T 3768-2017

Replace

GB 3768-1983

Scope

This standard specifies the method for calculating the sound power level of a noise source by measuring the sound pressure level on a measurement surface enveloping a sound source. At the same time, the test environment, the requirements of measuring instruments and the calculation methods of surface sound pressure level and sound power level are given. The accuracy level of the measurement results of the sound power level is grade 3. For various types of equipment, it is very important to formulate and use its specific noise test specifications according to this standard. The noise test specification should give a detailed description of the installation, load, working conditions, measurement surface and microphone array selection of the sound source to be tested. Note 1 to entry: For a particular type of equipment, the noise test specification should give details of the particular measurement surface selected, since the use of different shapes of measurement surfaces will result in different evaluations of the sound power level of the sound source. The method specified in this standard is 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/T 14259. This standard applies to sound sources of all types and sizes (equipment, machines, component assemblies, etc.). This standard does not apply to super high or long sound sources (chimneys, pipelines, conveying machinery, multi-source industrial equipment, etc.). This standard applies to indoor or outdoor test environments that require one or more reflective surfaces. For a sound source that radiates steady-state narrow-band noise, the standard deviation of the reproducibility of the A-weighted sound power level is equal to or less than 3dB (K_2A<5dB) or 4dB (5dB≤K_2A≤7dB). For sound sources radiating discrete pure tones, the standard deviation of reproducibility generally increases by 1 dB. There is likely to be a difference within the uncertainty range between the single value of the sound power of a noise source measured in accordance with this standard and its true value. The uncertainty of the sound power level measurement comes from the comprehensive influence of the environmental conditions of the measurement laboratory and the experimental technology. If the sound power level of a specific noise source is measured according to this standard in different test places, the measurement results will show dispersion. See GB/T 14573.4 for calculation of standard deviation of measurement results. Except for individual cases, the above standard deviations do not exceed the values in Table 1. The reproducibility standard deviation σR 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 operating conditions (speed, power supply, voltage) or installation conditions. Measurement uncertainty is not only related to the reproducibility standard deviation, but also to the required confidence level. For example, for a sound power level with a normal distribution, when the confidence level is 90%, the true value of the sound power level of the sound source is within the range of ±1.645_σR of the measured value. When the confidence level is 95%, the true value lies within the range of ±1.960_σR of the measured value. See GB/T14573 series and ISO9296 for details. Note 3 If K_2A is greater than or equal to 5dB, σR may be 1dB larger than the value in Table 1. 4 Lower reproducibility standard deviations may be given in noise test specifications for certain types of noise sources. 5 The standard deviation listed in Table 1 is the comprehensive effect of the measurement conditions and methods defined in this standard, not including the influence of the sound source itself. They are caused by: variations between measurement sites, including outdoor environmental and climatic conditions; indoor test room geometry, absorption by test room boundaries, acoustic properties of reflective surfaces; background noise; calibration form of instruments; and experimental technique Changes in the measurement surface, including the shape and size of the measurement surface, the number of measuring points and the positioning of the microphones, the position of the sound source, the integration time, the determination of the environmental correction (if any). The standard deviation is also affected by the error caused by the near-field measurement, which is related to the characteristics of the sound source. When the measurement distance is small and the frequency is low (below 250Hz), the error will generally increase. 6 If a given sound source is measured at several test locations using similar instrumentation, the consistency of the measured sound power level results may be better than that reflected in the standard deviations in Table 1. 7 For a particular type of sound source of similar size, similar sound power spectrum, and similar operating conditions, the standard deviation of reproducibility may be less than the values in Table 1. When formulating noise test specifications with reference to this standard, standard deviations smaller than the values in Table 1 may be indicated in the noise test specifications if proven feasible by appropriate laboratory verification. 8 The reproducibility standard deviations of Table 1 include the same conditions

GB/T 3768-1996 history

• 2017 GB/T 3768-2017 Acoustics—Determination of sound power levels and sound energy levels of noise sources using sound pressure—Survey method using an enveloping measurement surface over a reflecting plane
• 1996 GB/T 3768-1996 Acoustics--Determination of sound power levels of noise sources using sound pressure--Survey method using an enveloping measurement surface over a reflecting plane
• 0000 GB 3768-1983