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Table H-1 <br /> DEFINITIONS OF ACOUSTICAL TERMS <br /> TERM DEFINITIONS <br /> Decibel, dB 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 The number of complete pressure fluctuations per second <br /> above and below atmospheric pressure. <br /> A-Weighted Sound Level, The sound pressure level in decibels as measured on a sound <br /> dBA 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 <br /> are A-weighted. <br /> 41, Lg®, L5D, Lm The A-weighted noise levels that are exceeded 1%, 10%, <br /> 50%, and 90% of the time during the measurement period. <br /> Equivalent Noise Level, Lq The average A-weighted noise level during the measurement <br /> period. <br /> Community Noise The average A-weighted noise level during a 24-hour day, <br /> Equivalent Level, CNEL 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, Ld. 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 /> Lam, L. The maximum and minimum A-weighted noise level during the <br /> measurement period. <br /> Ambient Noise Level 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 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 /> H-3 <br />