Acoustics - Determination of Sound Power Levels of Noise Sources Using Sound Intensity - Part 2: Measurement by Scanning
|Publication Date:||1 January 1996|
|ICS Code (Acoustic measurements and noise abatement in general):||17.140.01|
This part of ISO 9614 specifies a method for measuring the component of sound intensity normal to a measurement surface which is chosen so as to enclose the noise source(s) of which the sound power level is to be determined.
Surface integration of the intensity component normal to the measurement surface is approximated by subdividing the measurement surface into contiguous segments, and scanning the intensity probe over each segment along a continuous path which covers the extent of the segment. The measurement instrument determines the average normal intensity component and averaged squared sound pressure over the duration of each scan. The scanning operation may be performed either manually or by means of a mechanical system.
Band-limited weighted sound power level is calculated from the measured octave or one-third-octave band values. The method is applicable to any source for which a physically stationary measurement surface can be defined, and on which the noises generated by the source under test and by other significant extraneous sources are stationary in time, as defined in 3.13. The source is defined by the choice of measurement surface. The method is applicable in situ, or in special-purpose test environments.
This part of ISO 9614 specifies certain ancillary procedures, described in annex B, to be followed in conjunction with the sound power determination. The results are used to indicate the quality of the determination, and hence the grade of accuracy. If the indicated indicated quality of the determination does not meet the requirements of this part of ISO 9614, the test procedure is to be modified in the manner indicated.
This part of ISO 9614 does not apply in any frequency band in which the sound power of the source is found to be negative on measurement.
This part of IS0 9614 is applicable to sources situated in any environment which is neither so variable in time as to reduce the accuracy of the measurement of sound intensity to an unacceptable degree, nor subjects the intensity measurement probe to gas flows of unacceptable speed or unsteadiness.
In some cases it will be found that the test conditions are too adverse to allow the requirements of this part of ISO 9614 to be met. Extraneous noise levels may exceed the dynamic capability of the measuring instrument or may vary to an excessive degree during the test. In such cases the method given in this part of ISO 9614 is not suitable for the determination of the sound power level of the source.
NOTE 1 Other methods (e.g. determination of sound power levels from surface vibration levels as described in ISO/TR 7849) may be more suitable.