1 Scope
1.1 This standard specifies methods for measuring the sound pressure levels on a measurement surface enveloping a source, and for calculating the sound power level produced by the source. It gives requirements for the test environment and instrumentation, as well as techniques for obtaining the surface sound pressure level from which the A-weighted sound power level of the source and octave or one-third octave band sound power levels are calculated. This method may be used to perform acceptance tests.
1.2 The aim of this standard is a Class 2 (engineering) result (see Table 1). When the correction for background noise exceeds the limit of 1.3dB but is less than 3dB, and/or the correction for environment exceeds the limits of 2dB but is less than 7dB, then a Class 3 (survey) result is obtained (see Table 2).
The same rectangular parallelepiped measurement surface and microphone positions are used for both engineering method (designated "GB/T 1859 (idt ISO 6798) - Engineering") and the survey method (designated "GB/T 1859 (idt ISO 6798) - Survey").
1.3 This standard applies to all reciprocating internal combustion engines falling within the scope of application of GB/T 6072.1 and for other applications, if no suitable national standard exists.
1.4 The methods defined in this standard apply to the measurement of the noise emission of a reciprocating internal combustion engine under steady-state operating conditions.
Annex A specifies the methods for measuring noise levels emitted from exhaust outlets or combustion air inlets of reciprocating internal combustion engines.
1.5 Measurements made in accordance with this standard shall result in standard deviations which are equal to or less than those given in Table 3. The uncertainties in Table 3 depend not only on the accuracies with which sound pressure levels and measurement surface areas are determined, but also on the “near-field error” which increases for smaller measurement distances and lower frequencies (i.e. those below 250Hz). The near-field error always leads to sound power levels which are higher than the real sound power levels.
Note 1 If the methods specified in this standard are used to compare the sound power levels of similar machines that are omnidirectional and radiate broad-band noise, the uncertainty in this comparison tends to result in standard deviations which are less than those given in Table 3, provided that the measurements be performed in the same environment with the same shape of measurement surface.
Note 2 The standard deviations given in Table 3 reflect the cumulative effects of all causes of measurement uncertainty, excluding variations in the sound power levels from test to test which may be caused, for example, by changes in the mounting or operating conditions of the source. The reproducibility and repeatability of the test result may be considerably better (i.e. smaller standard deviations) than the uncertainties given in Table 3 would indicate.
Table 1 International standards used as a basis for determining the sound power level of a reciprocating internal combustion engine
International standard Classification of method1) Test environment Volume of source Character
of noise Sound power levels obtainable Optional information available
ISO 3744 Engineering
(Class 2) Outdoors or in large room Greatest dimension less than 15m Any A-weighted and in one-third octave or octave bands Directivity information; sound pressure levels as a function of time; other weighted sound power levels
ISO 3746 Survey
(Class 3) No special test environment No restrictions: limited only by available test environment Any A-weighted Sound pressure levels as a function of time; other weighted sound power levels
1) See ISO 2204 (Annex B).
Table 2 Limits for correction
In: dB
Accuracy class Background noise correction Environment correction
Class 2 ≤1.3 ≤2
Class 3 >1.3 but ≤3 >2 but ≤7
Special case1) >3 >7
1) For higher values of background noise and/or environmental corrections, the real sound power level cannot be determined with acceptable uncertainty, but the results can be useful to estimate an upper limit of the noise emission of the reciprocating internal combustion engine to be tested.
Table 3 Uncertainty in determining sound power levels, expressed as the largest value of the standard deviation
In: dB
Accuracy class Octave band center frequency A-weighted
31.5Hz to 63Hz1) 125Hz 250Hz to 500Hz 1,000Hz to 4,000Hz 8,000Hz
Class 2 5 3 2 1.5 2.5 2
Class 3 For a source which produces sounds that contain prominent discrete tones 5
For a source which produces sounds that are uniformly distributed in frequency over the frequency range of interest 4
1) If measurement is outdoors.
2 Normative references
The following standards contain provisions which, through reference in this text, constitute provisions of this standard. At the time of publication, the editions indicated were valid. All standards are subject to revision, and parties to agreements based on this standard are encouraged to investigate the possibility of applying the most recent editions of the standards indicated below.
GB/T 6072.1-2000 Reciprocating internal combustion engines - Performance - Part 1: Standard reference conditions, declarations of power, fuel and lubricating oil consumptions, and test methods (idt ISO 3046-1: 1995)
ISO 3046-3: 1989 Reciprocating internal combustion engines - Performance - Part 3: Test measurements
ISO 3744: 1994 Acoustics - Determination of sound power levels of noise sources using sound pressure - Engineering method in an essentially free field over a reflecting plane
ISO 3745: 1977 Acoustics - Determination of sound power levels of noise sources - Precision methods for anechoic and semi-anechoic rooms
ISO 3746: 1995 Acoustics - Determination of sound power levels of noise sources using sound pressure - Survey method using an enveloping measurement surface over a reflecting plane
IEC 225: 1966 Octave, half octave and third octave band filters intended for the analysis of sounds and vibrations
IEC 651: 1979 Sound level meters
IEC 804: 1985 Integrating-averaging sound level meters
3 Definitions
For the purposes of this standard, the definitions of ISO 3744 and ISO 3746 apply with the following additions.
Foreword i
ISO Foreword ii
1 Scope
2 Normative references
3 Definitions
4 Acoustic environment
5 Instrumentation
6 Installation and operating conditions
7 Measurement of weighted and octave band or one-third octave band sound pressure levels
8 Calculation of surface sound pressure level and sound power level
9 Information to be recorded
10 Information to be reported
Annex A (Normative) Measurement of noise emitted from exhaust outlets or combustion air inlets of reciprocating internal combustion engines (cylindrical pipes)
Annex B (Informative) Bibliography
