DNL (Day-Night Average Sound Level)

What is DNL and how is DNL used?

DNL is the acronym for Day-Night Average Sound Level.

Day-Night Average Sound Level (DNL) represents an average of the sound levels from aircraft, together with other noise sources at a location, over a complete 24-hour period.  The number of aircraft operations does not affect average sound levels and an increase in operations will not change the noise imprint.

Single event noise levels do not affect DNL and are not used to determine whether a project is compatible with development of property near airports.

DNL is used for the evaluation of community noise effects, particularly, aircraft noise effects. 

The Federal Aviation Administration has established this measure as a community noise exposure metric to aid airport noise analyses under Federal Aviation Regulation Part 150.

DNL is the only measurement that should be used to determine noise levels for land development projects.  All other measurements and statistics, such as time over a location etc., are inappropriate for land compatibility determinations or noise attenuation requirements.