This standard sets out a survey method for determining the weighted sound power level of a device or machine. The sound power level of the source is calculated from the measured values of the weighted sound pressure levels at prescribed microphone positions. The method is particularly useful for rating the sound output of a source that produces steady noise (as defined in AS 1633) and cannot be moved from its position to a special test environment.The method requires measurement of the A-weighted sound pressure level at four or more microphone positions on a hypothetical measurement surface which envelops the source. One of two alternative measurement surfaces may be selected, either a hemisphere or a rectangular parallelepiped. The hemispherical surface is best suited for measurement of the noise emitted by small sources as well as that emitted by larger sources which are approximately cubical in shape. The rectangular parallelepiped is best suited for long or tall sound sources as well as for those situations in which measurement must be carried out close to the source. This may occur when use of the hemispherical surface leads to microphone positions that are not sufficiently far away from reflecting surfaces, when measured levels with the source in operation are close to the background noise levels, or when other unfavourable environmental conditions are present. In general, the hemispherical surface is preferred when the measuring distance is large compared with the dimensions of the source and the rectangular parallelepiped is preferred for close-in measurements.The method yields physical data that may be useful for-(a) comparing machines which are similar in size and kind; or (b) rating apparatus in terms of its overall weighted sound power output.This method should not be used when it is feasible to use a more precise method, e.g. when a laboratory hemi-anechoic room is available for the measurements. The method requires that the background noise be at least 3 dB lower than the noise produced by the source. Appendix A gives a procedure for qualifying the acoustic environment for the purposes of measurements made according to the requirements of this standard. If the test environment does not comply with the requirements of Appendix A, the method is not to be used for determining the sound power level of a source.The method permits the determination of the A-weighted sound power level of a noise source. If additional information is required, e.g. the sound power levels in frequency bands (see AS 1217.4) should be used.