This part of ISO 3743 specifies a relatively simple engineering method for determining the sound power levels of small, movable noise sources. The measurements are carried out when the source is installed in a hard-walled test room. A comparison method is used to determine to the octave-band sound power levels of the source. The spartial average (octave-band) sound pressure levels produced by the source under test are compared to the spatial average (octave-bamd) sound pressure levels produced by a reference sound source of known sound power output. The difference in sound pressure levels is equal to the difference in sound power levels if conditions are the same for both sets of measurements. The A-weighted sound power level is then calculated from the octave.band sound power levels.NOTE 1 Precision methods for the determination of sound power levels of small noise sources are specified in ISO 3741 and ISO 3745.