RES 06035 - Laserfiche WebLink

Draft Environmental Impact Report Bernal Property Phase II Specific Plan EI R Term Decibel, dB Frequency, Hz A-Weighted Sound Level, dBA LOl, Ll0, Lso, L90 Equivalent Noise Level, Leq Community Noise Equivalent Level, CNEL DayjNight Noise Level, Ldn Lmax, Lmin Ambient Noise Level Intrusive Table El Definitions of Acoustical Terms Definition A unit describing the amplitude of sound, equal to 20 times the logarithm to the base 10 of the ratio of the pressure of the sound measured to the reference pressure of 20 micropascals (20 micronewtons per square number of complete pressure fluctuations per second above and below pressure. The sound pressure level in decibels as measured on a sound level meter using the A-weighting filter network. The A-weighting filter de-emphasizes the very low and very high frequency components ofthe sound in a manner similar to the frequency response of the human ear and correlates well with subjective reactions to noise. All sound levels in this report are unless otherwise. The A-weighted noise levels that are exceeded 1 percent, 10 percent, 50 and 90 of the time the measurement The average A-weighted noise level during the measurement period. The average A-weighted noise level during a 24-hour day, obtained by adding 5 decibels to sound levels measured between 7:00 PM and 10:00 and 10 decibels to those measured between 10:00 PM and 7:00 AM. average A-weighted noise level during a 24-hour day, obtained after addition ofl0 decibels to levels measured in the night between 10:00 PM and 7:00 AM. Typically, the highest steady traffic noise level during the daytime is about equal to the Ldn and nighttime levels are 10 dBA lower. The maximum and minimum A-weighted noise level during the meas- urement The composite of noise from all sources near and far. The normal or level of environmental noise at a location. That noise which intrudes over and above the existing ambient noise at a given location. The relative intrusiveness of a sound depends upon its amplitude, duration, frequency, and time of occurrence and tonal or informational content as well as the prevailing ambient noise level. Source: Illingworth & Rodkin, Inc. Since the sensitivity to noise increases during the evening and at night - because excessive noise interferes with the ability to sleep - 24-hour descriptors have been developed that incorporate artificial noise penalties added to quiet-time noise events. The Community Noise Equivalent Level, CNEL, is a measure of the cumulative noise exposure in a community, with a 5 dB penalty added to evening (7:00 pm-10:00 pm) and a 10 dB addition to nocturnal (10:00 pm-7:oo am) noise levels. The Day/Night Average Sound Level, Ldn, is essentially the same as CNEL, with the exception that the evening time period is dropped and all occur- rences during this three-hour period are grouped into the daytime period. E2