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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.

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)

where

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)

## Related Topics

• Acoustics - Room acoustics and acoustic properties, decibel A, B and C, Noise Rating (NR) curves, sound transmission, sound pressure, sound intensity and sound attenuation.

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