1.1 This International Standard specifies a method for determining the sound power levels of sound sources in
situ, especially if non-movable. A comparison method is used and all measurements are carried out in octave
bands. The measurement uncertainty depends on the test environment. The measurement uncertainty is evaluated
by comparing with an indicator describing the spatial sound distribution. The accuracy will either be that of an
engineering method or a survey method.
The sound power level of the source under test is calculated from the measured values of the sound pressure
levels produced at specified measurement points by the source and by a reference sound source, respectively. The
sound power level is calculated using the calibrated values of the reference sound source and the differences
between the values obtained with the source under test and those of the reference sound source. All calculations
are carried out in octave bands, from which the A-weighted sound power level is determined.
1.2 This International Standard is applicable to all kinds of test environments which are to be found outside a
laboratory environment, provided that the background noise level is sufficiently low and the sound pressure level at
the microphone positions depends mainly on reflections from the room surfaces.
1.3 This International Standard is primarily applicable to sources which radiate broad-band noise. It may,
however, also be used for sources which radiate narrow-band noise or discrete tones, although the measurement
uncertainty might then become larger than stated herein.
BS EN ISO 3747:2009 history
2011BS EN ISO 3747:2010 Acoustics. Determination of sound power levels and sound energy levels of noise sources using sound pressure. Engineering/survey methods for use in situ in a reverberant environment
2010BS EN ISO 3747:2009 Acoustics - Determination of sound power levels of noise sources using sound pressure - Comparison method in situ