ABSTRACT

The problems of global indices or single number ratings (snrs) is re-examined, under the assumption that noise and noise protecting devices can be rated in a similar way. Then a general procedure to define snrs is developed than can account for level and spectrum characteristics of noise according to its psychophysic features. Frequency weighting procedures appear as its natural simplification. Loudness becomes a particularly convenient quantity and a loudness-based rating has been thoroughly used. Classical ratings are then analyzed from this point of view. Comparative studies of the influence of incident noise, shape of the insulation curve and “subjective effects” are done and the main features of different ratings are described. The convenience of rating IA becomes a major conclusion, as it represents a balance among simplicity and correlation with subjective effects, maintaining simultaneously a proper and nearly “unique” characterization of products as needed in product market. The work concludes with some considerations about further simplifications resulting for short methods in survey operations.