What is DNL?
The Day-Night Average Sound Level (DNL) metric describes the total noise exposure during a 24-hour period. In computing DNL, an extra weighting of 10 dB is assigned to any sound levels occurring between the hours of 10:00 p.m. and 7:00 a.m. This penalty is intended to account for the greater annoyance that nighttime noise is presumed to cause for most people. Due to the logarithmic nature of the dB scale, this extra weight treats one nighttime noise event as equivalent to ten daytime events of the same magnitude. DNL is the standard metric used for Part 150 and other environmental noise analyses in the U.S. The exhibit below summarizes the calculation of DNL.
