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- Average sound exposure over a 24-hour period is often presented as a
day-night average sound level (Ldn). Ldn values are calculated from
hourly Leq values, with the Leq values for the nighttime period (10:00
p.m.–7:00 a.m.) increased by 10 dB to reflect the greater disturbance
potential from nighttime noises.
- (DNL, denoted by the symbol Ldn): A 24-hour
time-averaged sound exposure level, adjusted for average-day sound source
operations. In the case of aircraft noise, a single operation is equivalent to a
single aircraft departure, approach, etc. The adjustment includes a 10 dB
penalty for operations occurring between 2200 and 0700 hours, local time.
Source:
http://www.volpe.dot.gov/acoustics/docs/1990-1999/1999-1.pdf
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