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"
- A-weighted sound level
- Sound Exposure Level - Ls
- Equivalent Sound Level - Leq
- Day-Night Sound Level - Ldn
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:
| Location | Ldn (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)
