THE SCIENCE AND APPLICATIONS OF ACOUSTICS - H. H. Arnold ...

13.11 Evaluation of Community Noise 345Survey techniques, however, can range widely in the degree of their respectivesophistication.Empirical Dosage Response Relationship. Schultz (1978) documented quantitativedosage-response relationships through meta-analysis, which constituted amajor step toward the setting up of a standard method for predication of transportationnoise effects. Schultz executed a “best-fit” third order polynomial to a dataset relating the day–night average sound level (DNL) to the degree of annoyancein communities. A simple quadratic-fit equation provides a purely empirical basisfor predicting the prevalence of annoyance in communities:% highly annoyed = 0.036L 2 dn − 3.27L dn + 79.14 (13.19)However, Equation (13.19) produces meaningless predictions when evaluated outsidethe range 45 dB < L dn < 85 dB. The U.S. Federal Interagency Committeeon Noise prefers a different logistic fit to a subset of data reported by Fidell et al.(1991), which resulted from disregarding the results of certain studies in whichrelatively low levels of noise were associated with a high degree of reported annoyance:100% highly annoyed =(13.20)1 + e 11.13−0.141L dnEquation (13.20) predicts somewhat lower levels of annoyance at lower noiseexposure levels than the quadratic fit of Equation (13.19). For example, at L dn =65 dB. Equation (13.20) yields a prevalence rate of 12.3% in contrast to 18.8%obtained through the use of (13.19).Equal Energy Hypothesis. DNL has been adopted by many federal agencies asa convenient descriptor of long-term environmental noise descriptor, which soonenough became a predictor of annoyance. The DNL index is a time-weightedaverage (in effect, the average acoustic energy per second with arbitrary nighttimeweighting), which is sensitive to the duration and magnitude of individual noiseevents and directly proportional on an energy (10 log N) basis to number of events.Reliance on such an integrated energy metric is based on the “equal energy”hypothesis, which states the notion that the number, level, and duration of noiseevents are fully interchangeable determinants of annoyance as long as their product(energy summation) remains equal. This quantification of noise exposure in termsof DNL for the purpose of predicting annoyance carries the implication that aperson would be annoyed to the same degree by small numbers of very highlevel noise events as by large numbers of lower level noise and/or longer durationnoise events. The equal energy hypothesis has provided an adequate account fordata on the prevalence of annoyance to sporadic (e.g., urban) noise in the range55 < L dn < 75 dB, but the validity of the hypothesis falls off in extreme cases. Forexample, no community is likely to tolerate even infrequent operation of a noisesource powerful enough to damage hearing or a very occasional shock wave frompassing supersonic jet plane from a nearby military base.