About the declaration of noise emitted by technical devises

The article deals with estimation the uncertainty in determination of A-weighted sound power level. In the European countries producers and suppliers of potentially noisy equipment mandatory have obligations to declare noise emission value in the technical specification. According to the international (ISO) and counterpart European (EN) standards A-weighted sound power level LWA is mainly used as a declared value. There are seven standards (all are described in ISO 3740) available for sound power measurements with different characteristics. The A-weighted power levels may be calculated from measured levels in octave or in one-third-octave bands. In the article theoretically estimated, that the A- weighted sound power level calculations from octave levels LWA,1 and calculations from one-third-octave levels LWA,1/3 may be different up to (+-)1.0 dB. It is shown for which noise spectra the difference LWA,1/3 - LWA,1 is significant. As example household freezer emitted noise measurements carried out in the reverberation room. Declared value calculations in one-third octave bands in compare with calculations in octave bands gives a difference of 1 dB.