Leq - Equivalent Sound Level
Equivalent Sound Level - Leq - quantifies the noise environment to a single value of sound level for any desired duration
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.
Equivalent Sound Level - Leq
Equivalent Sound Level - Leq - quantifies the noise environment to a single value of sound level for any desired duration. It is designed to represent a varying sound source over a given time as a single number. Leq is also sometimes known as Average Sound Level - LAT even if this is not.
This descriptor correlates well with the effects of noise on people.
Equivalent Sound Level - Leq - can be calculated by integrating the sound pressure level over a time period as:
Leq = 10 log [(1/T) ∫ (pA / pref)2 dt ] (1)
where
Leq = equivalent sound level (dB)
T = time period (s)
pA = sound pressure (Pa, N/m2)
pref = reference sound pressure ( 2 10-5 Pa, N/m2)
Equivalent sound levels can be added together as
Leg_total = 10 log (1 / (t1 + t2 ... tn) (t1 10Leq_1/10 + t2 10Leq_2/10 + ... + tn 10Leq_n/10)) (2)
where
Leg_total = total equivalent sound level (dB)
Example - Equivalent Sound Level
A machine generates a sound pressure of 0.02 Pa half the time when idling and 0.1 Pa the other half of the time when working.
The equivalent sound level for half an hour idling can be calculated as
Leq_idling = 10 log [(1/(0.5 hour)) ((0.02 Pa)/(2 10-5 Pa))2 (0.5 hour)]
= 60 dB
The equivalent sound level for half an hour working can be calculated as
Leq_working = 10 log [(1/(0.5 hour)) ((0.1 Pa)/(2 10-5 Pa))2 (0.5 hour)]
= 74 dB
The equivalent sound level for one hour running can be calculated as
Leq_running = 10 log [ (1 / ((0.5 hour) + (0.5 hour))) ( ((0.02 Pa) / (2 10-5 Pa))2 (0.5 hour) + ((0.1 Pa) / (2 10-5 Pa))2 (0.5 hour) ) ]
= 71.2 dB
The equivalent sound level for one hour running can alternatively be calculated with (2) as
Leg_total = 10 log ((1 / ((0.5 hour) + (0.5 hour)) ((0.5 hour) 10(60 dB)/10 + (0.5 hour) 10(74 dB)/10))
= 71.2 dB
Equivalent Sound Level Calculator
Use the calculator below to calculate equivalent sound level:
Leq_1 - equivalent sound level 1 (dB)
time 1 (h, min, s)
Leq_2 - equivalent sound level 2 (dB)
time 2 (h, min, s)
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