First ideas for a revision of ISO 9614

Abstract

ISO 9614 describes the determination of sound power levels by the two microphone intensity technique. Despite some physical advantages the method is relatively seldom used. To improve this situation, theoretical and experimental investigations were performed, which focused mainly on the adequacy of the currently standardized indicators and criteria. This paper summarizes these results and develops first ideas for a revision of ISO 9614. One main proposal is to perform measurements generally in the one-third octave bands between 50 Hz and 10 kHz with a 12 mm spacer and to apply appropriate corrections in the highest three one-third octave bands. Furthermore, it is proposed to require additional measurements with a larger spacer at lower frequencies, if the dynamic capability of the instrument is insufficient. The A-weighted sound power level is calculated from the one-third octave band levels, which may have different grades of accuracy. Calculating different A-weighted sound power levels from different sets of frequency bands fulfilling criteria for different grades of accuracy then allows for designating a grade of accuracy to the A-weighted sound power level. This is considered to be a major improvement since the A-weighted sound power level is the main descriptor for the sound emission of sources.