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u <br />F <br />L <br />P" <br />u <br />0 <br />P <br />TABLE 4.6.1 <br />DEFINITIONS OF ACOUSTICAL TERMS <br />TERM <br />DEFINITIONS <br />Decibel, dB <br />A unit describing the amplitude of sound, equal to 20 times the <br />logarithm to the base 10 of the ratio of the pressure of the <br />sound measured to the reference pressure, which is 20 <br />micropascals (20 micronewtons per square meter). <br />Frequency, Hz <br />The number of complete pressure fluctuations per second <br />above and below atmospheric pressure. <br />A -Weighted Sound Level, <br />The sound pressure level in decibels as measured on a sound <br />dBA <br />level meter using the A -weighting filter network. The A - <br />weighting filter de-emphasizes the very low and very high <br />frequency components of the sound in a manner similar to the <br />frequency response of the human ear and correlates well with <br />subjective reactions to noise. All sound levels in this report are <br />A -weighted. <br />Lot, L10, L50, Lgo <br />The A -weighted noise levels that are exceeded 1%, 10%, 50%, <br />and 90% of the time during the measurement period. <br />Equivalent Noise Level, Leq <br />The average A -weighted noise level during the measurement <br />period. <br />Community Noise Equivalent <br />The average A -weighted noise level during a 24-hour day, <br />Level, CNEL <br />obtained after addition of 5 decibels in the evening from 7:00 <br />pm to 10:00 pm and after addition of 10 decibels to sound <br />levels in the night between 10:00 pm and 7:00 am. <br />Day/Night Noise Level, Lcln <br />The average A -weighted noise level during a 24-hour day, <br />obtained after addition of 10 decibels to levels measured in the <br />night between 10:00 pm and 7:00 am. <br />Lmax, Lmin <br />The maximum and minimum A -weighted noise level during the <br />measurement period. <br />Ambient Noise Level <br />The composite of noise from all sources near and far. The <br />normal or existing level of environmental noise at a given <br />location. <br />Intrusive <br />That noise which intrudes over and above the existing ambient <br />noise at a given location. The relative intrusiveness of a sound <br />depends upon its amplitude, duration, frequency, and time of <br />occurrence and tonal or informational content as well as the <br />prevailing ambient noise level. <br />ER -93-1 -76- (9-27-93) <br />