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APPENDIX A <br /> ACOUSTICAL TERMINOLOGY <br /> AMBIENT NOISE The composite of noise from all sources near and far. In this <br /> LEVEL: context, the ambient noise level constitutes the normal or existing <br /> level of environmental noise a given location. <br /> CNEL: Community Noise Equivalent Level. The average equivalent sound <br /> level during a 24-hour day, obtained after addition of approximately <br /> five decibels to sound levels in the evening from 7:00 p.m. to 10:00 <br /> p.m. and ten decibels to sound levels in the night before 7:00 a.m. <br /> and after 10:00 p.m. <br /> DECIBEL, dB: A unit for describing the amplitude of sound, equal to 20 times the <br /> logarithm to the base 10 of the ratio of the reference pressure, <br /> which is 20 micropascals (20 micronewtons per square meter). <br /> Ldo: Day-Night Average Sound Level. The average equivalent sound <br /> level during a 24-hour day, obtained after addition of ten decibels <br /> to sound levels in the night after 10:00 p.m. and before 7:00 a.m. <br /> L�q: Equivalent Sound Level. The sound level containing the same total <br /> energy as a time varying signal over a given sample period. L�q is <br /> typically computed over 1, 8 and 24-hour sample periods. <br /> Note: CNEL and Ld" represent daily levels of noise exposure averaged on an annual <br /> basis, while L�q represents the average noise exposure for a shorter time <br /> period, typically one hour. <br /> Lam: The maximum sound level recorded during a noise event. <br /> Lo: The sound level exceeded "n" percent of the time during a sample <br /> interval. L10 equals the level exceeded 10 percent of the time (L9,, <br /> L51), etc.) <br /> BBA <br />