Reciprocating internal combustion engines. Measurement method for exhaust silencers. Sound power level of exhaust noise and insertion loss using sound pressure and power loss ratio

Reciprocating internal combustion engines. Measurement method for exhaust silencers. Sound power level of exhaust noise and insertion loss using sound pressure and power loss ratio

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1   Scope

This International Standard specifies the measurement method and requirements for exhaust silencers which is installed on reciprocating internal combustion engines, including laboratory measurement and site measurement.
The following parameters are measured for laboratory measurement (engineering method):
  • — the sound power level (A-weighted or in frequency bands) of exhaust noise using sound pressure, accuracy grade 2;
  • — the insertion loss (A-weighted or in frequency bands) of exhaust silencers;
  • — the power loss ratio of reciprocating internal combustion engines.
The following parameters are measured for site measurement and laboratory measurement (survey method):
  • — the sound power level (A-weighted) of exhaust noise using sound pressure, accuracy grade 3;
  • — the insertion loss (A-weighted) of exhaust silencers.

NOTE 1 The aim of laboratory measurement in measuring the sound power level of exhaust noise is accuracy grade 2 (engineering method) result. When the correction for background noise and/or the environment conditions and/or the location of exhaust outlets cannot meet the requirements of the engineering method of this International Standard, then accuracy grade 3 (survey method) result is obtained. The aim of site measurement in measuring the sound power level of exhaust noise in this International Standard is accuracy grade 3 (survey method) result.

The laboratory measurement (engineering method) of this International Standard can be used to make acceptance tests and engineering measures. The site measurement and laboratory measurement (survey method) of this International Standard can be used to make comparative tests.
This International Standard applies to all exhaust silencers installed on reciprocating internal combustion engines falling within the field of application of ISO 3046-1 and other exhaust silencers, if no suitable International Standard exists.

NOTE 2 Throughout the text, exhaust silencer is referred to as silencer and reciprocating internal combustion engine as engine.

1.1   Measurement uncertainty

1.1.1   Engineering method

The standard deviation of reproducibility is equal to or less than 1,5 dB for A-weighted sound power levels. In one-third octave bands, it is equal to or less than 5 dB from 50 Hz to 80 Hz, 3 dB from 100 Hz to 160 Hz, 2 dB from 200 Hz to 315 Hz, 1,5 dB from 400 Hz to 5 000 Hz, and 2,5 dB from 6 300 Hz to 10 000 Hz. In octave bands, it is equal to or less than 5 dB for 63 Hz, 3 dB for 125 Hz, 2 dB for 250 Hz, 1,5 dB from 500 Hz to 4 000 Hz, and 2,5 dB for 8 000 Hz.

1.1.2   Survey method

The standard deviation of reproducibility is equal to or less than 4,0 dB for A-weighted sound power levels.

NOTE 1 The standard deviations listed in 1.1 are associated with the test conditions and procedures defined in this International Standard and not with the noise source itself, including variations of installation and/or operation conditions. They arise in part from variations between measurement laboratories, changes in atmospheric conditions if outdoors, the geometry of the test room or outdoor environment, the acoustical properties of the reflecting plane, absorption at the test room boundaries if indoors, background noise, and the type and calibration of instrumentation. They are also due to variations in experimental techniques, including the size and shape of the measurement surface, measurement distances, number and location of microphone positions, sound source location, determination of environmental corrections, if any, and integration time. The standard deviations are also affected by errors associated with measurements taken in the near field of the source. Such errors depend upon the nature of the sound source, but generally increase for smaller measurement distances and lower frequencies (below 250 Hz).

NOTE 2 If several laboratories use similar facilities and instrumentation, the results of sound power determinations on a given source in those laboratories may be in better agreement than would be implied by the standard deviations of 1.1.

NOTE 3 For a family of silencers, of similar size with similar sound power spectra and similar operating conditions, the standard deviations of reproducibility may be smaller than the values given in 1.1.

NOTE 4 The standard deviations of reproducibility, as listed in 1.1, include the uncertainty associated with repeated measurements on the same noise source under the same conditions (for standard deviations of reproducibility). This uncertainty is usually much smaller than the uncertainty associated with interlaboratory variability.

NOTE 5 The procedures of this International Standard and the standard deviations given in 1.1 are applicable to measurements on an individual silencer.

The measurement uncertainty depends on the standard deviation of reproducibility and on the degree of confidence that is desired. As examples, for a normal distribution of sound power levels, there is 90 % confidence that the true value of the sound power level of a source lies within the range ±1,645σR of the measured value and a 95 % confidence that it lies within the range ±1,960σR of the measured value.

NOTE 6 For a normal distribution of sound power levels, there is 90 % confidence that the probability of acceptance is 95 % and a 95 % confidence that the probability of acceptance is 97,5 %.