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The day-night average sound level (Ldn or DNL) is the average noise level over a 24-hour period. The noise level measurements between the hours of 10pm and 7am are artificially increased by 10 dB before averaging. This noise is weighted to take into account the decrease in community background noise of 10 dB during this period. There is a similar metric called day-evening-night average sound level (Lden or DENL) commonly used in other countries, or community noise exposure level (CNEL) used in California legislation; that is, the DNL with the addition of an evening period from 7 PM to 10 PM when noise level measurements are boosted 5 dB (or 4.77 dB in the case of CNEL) to account for the approximate decrease in background community noise during this period. In the US, the
Federal Aviation Administration The Federal Aviation Administration (FAA) is the largest transportation agency of the U.S. government and regulates all aspects of civil aviation in the country as well as over surrounding international waters. Its powers include air traffic m ...
has established this measure as a community noise exposure metric to aid airport noise analyses under
Federal Aviation Regulation The Federal Aviation Regulations (FARs) are rules prescribed by the Federal Aviation Administration (FAA) governing all aviation activities in the United States. The FARs comprise Title 14 of the Code of Federal Regulations (CFR). A wide variety o ...
Part 150. The FAA says that a maximum day-night average sound level of higher than 65 dB is incompatible with residential communities. Communities in affected areas may be eligible for mitigation such as
soundproofing Soundproofing is any means of impeding sound propagation. There are several basic approaches to reducing sound: increasing the distance between source and receiver, decoupling, using noise barriers to reflect or absorb the energy of the sound w ...
.


See also

*
Aircraft noise Aircraft noise pollution refers to noise produced by aircraft in flight that has been associated with several negative stress-mediated health effects, from sleep disorders to cardiovascular ones. Governments have enacted extensive controls that a ...
* Effective perceived noise in decibels rating of aircraft *
Noise pollution Noise pollution, also known as environmental noise or sound pollution, is the propagation of noise with ranging impacts on the activity of human or animal life, most of them are harmful to a degree. The source of outdoor noise worldwide is mai ...
*
Noise measurement In acoustics, noise measurement can be for the purpose of measuring environmental noise or measuring noise in the workplace. Applications include monitoring of construction sites, aircraft noise, road traffic noise, entertainment venues and neigh ...
* Day–evening–night noise level, the EU equivalent


References

{{reflist United States administrative law Federal Aviation Administration Aviation law Noise pollution Sound measurements