day-night average sound level: Twenty-four hour average sound level for a given day, after addition of 10 decibels to levels from 0000 to 0700 hours and from 2200 (10 p.m.) to 2400 hours. Unit, decibel (dB); abbreviation, DNL; symbol, Ldn.

Notes:

Day-night average sound level in decibels is related to the corresponding day-night sound exposure level, LEdn, according to:

Ldn = LEdn − 10 log (86,400/1)

where 86,400 is the number of seconds in a 24-hour day.

A-frequency weighting is understood, unless another frequency weighting is specified explicitly.

instantaneous sound pressure: Total instantaneous pressure at a point in a medium minus the static pressure at that point. Unit, pascal (Pa); symbol, p.

loudness level: Of a sound, the median sound pressure level, in a specified number of trials, of a free progressive wave having a frequency of 1,000 Hz that is judged as loud as the unknown sound when presented to listeners with normal hearing who are facing the source. Unit, phon.

Note:

The manner of listening to the unknown sound must be specified.

maximum sound level; maximum frequency-weighted sound pressure level: Greatest fast (125 ms) A-weighted sound level within a stated time interval. Alternatively, slow (1,000 ms) time-weighting and C-frequency-weighting may be specified. Unit, decibel (dB); abbreviation, MXFA; symbol, LAFmx (or C and S).

night average sound level: Time-average sound level between 0000 and 0700 hours and 2200 and 2400 hours. Unit, decibel (dB); abbreviation, NL; symbol, Ln.

Note:

Night average sound level in decibels is related to the corresponding night sound exposure level, LEn, according to:



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