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Sound - Ldn - Day and Night Level

The EPA A-weighted sound level day and night equivalent definition - Ldn - for a 24 hour period.

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The Environmental Protection Agency - EPA - has adopted a system of four "sound descriptors"

to summarize how sound is heard and measured and to determine the impact of noise on health and welfare.

Day-Night Sound Level - Ldn

is the A-weighted equivalent sound level for a 24 hour period with an additional 10 dB imposed on the equivalent sound levels for night time hours of 10 pm (22) to 7 am (07).

Day-Night Sound Level can be expressed as

Ldn = 10 log (1 / 24 (15 (10Ld/10) + 9 (10((Ln + 10)/10)))                            (1)


Ldn = day-night sound level (dBA)

Ld = daytime equivalent sound level (dBA)

Ln = nighttime equivalent sound level (dBA)

Examples of typical outdoor Day-Night Average Sound at various locations:

LocationLdn (dBA)
Apartment next to freeway 87
3/4 mile from runway at major airport 86
Downtown with construction activity 79
Old urban residential area 59
Wooded residential 52
Agricultural crop land 44
Rural residential 39
Wilderness ambient 35

Example - Day-Night Sound Level

The equivalent daytime sound level is 70 dB and the equivalent nighttime sound level is 50 dB. The Day-Night sound level can be calculated as

Ldn = 10 log (1 / 24 (15 (10(70 dB)/10) + 9 (10((50 dB)+ 10)/10))

      = 68.2 dB

Day-Night Sound Level Calculator

Use the calculator below to calculate EPA 24 hour Day-Night sound level.

Ld - daytime equivalent sound level (dB)

daytime hours (h)

Ln - nighttime equivalent sound level (dB)

nighttime hours (h)

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