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

13.7 Equivalent Sound Level, Day–Night Equivalent Sound Level 331by Equation (3.30), which we repeat here in modified form:L dn = 10 log 15 ( 10 L d /10 ) + 9 ( 10 (L n+10)/10 )24(13.7)where L d represents the 15-h daytime A-weighted equivalent sound level (from7:00 a.m. to 10:00 p.m.) and L n is the 9-h nighttime equivalent A-weighted soundlevel (from 10 p.m. to 7:00 a.m.). The nighttime value carries a penalty of 10 dBbecause noise at night is deemed to be much more disturbing than noise generatedduring the day. The use of the day–night equivalent level as a parameter is increasingin the United States and some nations for evaluating community noise andsome cases of airport noise. The U. S. Federal Interagency Committee on UrbanNoise (FICON) adopted DNL as the descriptor of environmental noise that affectsresidences.In 2002, the European Union Parliament and Council issued Directive2002/49/EC in an effort to establish common assessment methods for rating environmentalnoise in terms of harmonized indicators for the determination ofnoise levels. The concrete figures of any limit values are to be determined bythe Member States of the European Union. The common noise indicators adoptedare day–evening–night equivalent level L den to assess annoyance and the nightequivalent level L night to assess sleep disturbance. L den and L night are defined asfollows:L den = 10 log 1)(12 × 10 L day10 + 4 × 10 L evening +510 + 8 × 10 L night +101024whereL day = A-weighted average sound level determined over 12-h day periodsof the yearL evening = A-weighted average sound level determined over 4-h evening periodsof the yearL night = A-weighted average sound level determined over 8-h night periodsof the year.We note that +5 dB(A) and +10 dB(A) penalties have been imposed to reflect theneed for quieter periods of evenings and nights, respectively. While the day spans12 h, the evening 4 h, and night, 8 h, the Member States may shorten the eveningperiod by 1 or 2 h and lengthen the day and/or the night period, correspondingly,provided the measurements are consistent for all sources and the reporting Statesprovide the European Commision with information on any systematic differencefrom the default option. The default values of (local) time are 0700–1900 h forday, 1900–2300 h for evening, and 2300–0700 h for night. Use of L den will likelyincrease in the future for airport noise and other environmental assessments inEuropean Union.