Sound - Ldn - Day and Night Level

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

• A-weighted sound level
• Sound Exposure Level - L_s
• Equivalent Sound Level - L_eq
• Day-Night Sound Level - L_dn

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

Day-Night Sound Level - L_dn

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

L_dn = 10 log(1 / 24 (15 (10^L_d/10) + 9 (10^{((L_n + 10)/10)}))                            (1)

where

L_dn = day-night sound level (dB_A)

L_d = daytime equivalent sound level (dB_A)

L_n = nighttime equivalent sound level (dB_A)

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

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

L_dn = 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.

L_d - daytime equivalent sound level (dB)

daytime hours (h)

L_n - nighttime equivalent sound level (dB)

nighttime hours (h)