On the addition of two incoherent unsteady noise records of similar statistical structures. Part 2: Effects of long time span and diurnal variations

The present study is a follow-up of a previous investigation of the author in an attempt to understand how the statistical structures of noise records will affect that of the resultant noise record formed from their addition. This issue becomes particularly important when statistical indices such as L10and L90of the resultant noise record are required for planning or assessment purposes. Long time span sound pressure level records were obtained from 18 well-separated independent sites in the high-rise residential areas of Hong Kong. The results obtained from their addition are compared with those of the 25-min record addition done by the author previously. The diurnal variations of the addition results are also discussed. In general, the present results suggest that there is weak correlation between the long time span records. The currently adopted logarithmic addition procedure still over-estimates the noise climate and only limited improvement is found when compared to the results of the 25-min cases. The present results further confirm the importance of the noise statistical structures in the environmental noise impact assessment.