day-night sound level

acoustics

Also known as: DNL

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Last updated

July 23, 2026

Quick Summary

Noise pollution is unwanted or excessive sound that can harm human health, wildlife, and the environment. It is generated by various sources, including industrial activities, traffic, and construction. Sound is measured in decibels (dB), with the human ear able to detect sounds from 0 dB to about 140 dB.

To account for varying sensitivity to noise at different times, the day-night sound level (DNL or Ldn) is used. This metric adds a 10-dB penalty to sounds measured between 10 pm and 7 am, recognizing that people are more sensitive to noise during nighttime hours. This is particularly useful for assessing community exposure to noise, such as from aircraft.1

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noise pollution
Measuring and perceiving loudness
) A unit called day-night sound level (DNL or L_dn) accounts for the fact that people are more sensitive to noise during the night, so a 10-dBA penalty is added to SPL values that are measured between 10 pm and 7 am. DNL measurements are very useful for describing…
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) A unit called day-night sound level (DNL or L_dn) accounts for the fact that people are more sensitive to noise during the night, so a 10-dBA penalty is added to SPL values that are measured between 10 pm and 7 am. DNL measurements are very useful for describing…
Read More