What is Day-Night Average Sound Level?
DNL is the average noise level over a 24-hour period, including an artificial increase of 10-dB between the hours of 10 p.m. and 7 a.m. to account for lower background sound levels at night. The 24-hour average sound level, including this 10-dB penalty, is known as the day-night average sound level (abbreviated DNL). The 10-dB penalty means that one nighttime sound event is equivalent to 10 daytime events of the same level.
