leq and its cousins

1. Leq and its cousins University of Salford

2. Intro to Acoustics: Leq 2

3. Intro to Acoustics: Leq 3 Daily personal exposure level, LEP,d This is an Leq where: the measuring position is at or near the ear of a particular worker; all levels are measured A-weighted; the period of measurement is a working day for that worker; the period of calculation T is 8 hours.

4. Intro to Acoustics: Leq 4 Noise at Work Regulations 2005: Levels Reduce noise to lowest practicable level Lower Action Level: LEP,d = 80 dB Upper Action Level: LEP,d = 85 dB Exposure Limit: LEP,d = 87 dB Also corresponding peak limits of 135, 137, 140 dB (C-weighted)

5. Intro to Acoustics: Leq 5 Noise at Work Regulations: Actions General: reduce noise to lowest practicable level LAL: offer protection, training, notices UAL: as LAL plus reduce exposure, zoning, protection mandatory in UAL zones

6. Intro to Acoustics: Leq 6 LEP,d example A factory supervisor is exposed during his working day to: 80 dB(A) for 2 hours 88 dB(A) for 3 hours 55 dB(A) for 3.5 hours Calculate his LEP,d and advise him. 10 lg ((10^8.0 x 2 + 10^8.8 x 3 + 10^5.5 x 3.5) / 8) = 84.2 dB Note: He is over the LAL, but not the UAL Even though part of the exposure is at 86 dB - what matters is the energy average over the day (unless any one event hits the peak, but that is much higher than 91 dB) The total of the times above is less than 8 hours. This is fine, as long as the record is an accurate picture of his typical working day, it doesn�t have to total 8 hours. The denominator in the calculation, however, is always 8 hours.10 lg ((10^8.0 x 2 + 10^8.8 x 3 + 10^5.5 x 3.5) / 8) = 84.2 dB Note: He is over the LAL, but not the UAL Even though part of the exposure is at 86 dB - what matters is the energy average over the day (unless any one event hits the peak, but that is much higher than 91 dB) The total of the times above is less than 8 hours. This is fine, as long as the record is an accurate picture of his typical working day, it doesn�t have to total 8 hours. The denominator in the calculation, however, is always 8 hours.

7. Intro to Acoustics: Leq 7 Sound Exposure Level

8. Intro to Acoustics: Leq 8 SEL applications single aircraft flyovers single vehicle passages explosions single industrial impact noises SEL actually is the American abbreviation. The UK one is supposed to be LAE. You sometimes see LAx (old-fashioned).SEL actually is the American abbreviation. The UK one is supposed to be LAE. You sometimes see LAx (old-fashioned).

9. Intro to Acoustics: Leq 9 SEL equation Notice the infinite limits on the integral. This is just an expression of the fact that we are not specifying how long the noise event lasts. Many events rated by SEL have a gradual increase and decrease. Think of a train going past. ** sketch typical level vs time curve ** As long as we start the measurement when the level is near the background, and keep measuring until its gone back down to near the background, we will get an accurate figure for SEL. Again, most integrating SLM�s can directly measure SEL. E.g. B&K 2231 (old) or B&K Investigator (modern)Notice the infinite limits on the integral. This is just an expression of the fact that we are not specifying how long the noise event lasts. Many events rated by SEL have a gradual increase and decrease. Think of a train going past. ** sketch typical level vs time curve ** As long as we start the measurement when the level is near the background, and keep measuring until its gone back down to near the background, we will get an accurate figure for SEL. Again, most integrating SLM�s can directly measure SEL. E.g. B&K 2231 (old) or B&K Investigator (modern)

10. Intro to Acoustics: Leq 10 SEL and Leq Where do these eqns come from? If a sound has a certain SEL, then we are saying that the energy from this sound is the same as that given by a sound pressure level of (SEL) for 1 second. If this energy is averaged over T seconds to give an Leq then we use the same formula as before to calculate the Leq: Leq = 10 lg(( 10^SEL x 1) / T ) i.e. Leq = 10 lg( 10^SEL ) - 10 lg (T) Leq = SEL - 10 lg (T) Similarly, if there are n events with the same SEL within the period T, then the Leq will be given by Leq = 10 lg(( 10^SEL x 1 x n) / T ) Leq = 10 lg( 10^SEL ) + 10 lg (n) - 10 lg (T) Leq = SEL + 10 lg (n) - 10 lg (T)Where do these eqns come from? If a sound has a certain SEL, then we are saying that the energy from this sound is the same as that given by a sound pressure level of (SEL) for 1 second. If this energy is averaged over T seconds to give an Leq then we use the same formula as before to calculate the Leq: Leq = 10 lg(( 10^SEL x 1) / T ) i.e. Leq = 10 lg( 10^SEL ) - 10 lg (T) Leq = SEL - 10 lg (T) Similarly, if there are n events with the same SEL within the period T, then the Leq will be given by Leq = 10 lg(( 10^SEL x 1 x n) / T ) Leq = 10 lg( 10^SEL ) + 10 lg (n) - 10 lg (T) Leq = SEL + 10 lg (n) - 10 lg (T)

11. Intro to Acoustics: Leq 11 SEL example Laeq, 10 min = 112 - 10lg(10 x 60) = 84.2 dB Then try: what happens if there are two identical aircraft landings within that 10 mins? Ans: + 10 lg(2) = + 3 dB Then try: T6 Q7 Ans: n = 8 x 12 + 4 x 5 + 2 x 7 = 130 T = 24 x 60 x 60 = 86400 So LAeq = 94 + 10lg(130) - 10lg(86400) = 65.8 dBLaeq, 10 min = 112 - 10lg(10 x 60) = 84.2 dB Then try: what happens if there are two identical aircraft landings within that 10 mins? Ans: + 10 lg(2) = + 3 dB Then try: T6 Q7 Ans: n = 8 x 12 + 4 x 5 + 2 x 7 = 130 T = 24 x 60 x 60 = 86400 So LAeq = 94 + 10lg(130) - 10lg(86400) = 65.8 dB

12. Intro to Acoustics: Leq 12 Conclusions SEL is level as if all energy delivered in one second SEL is useful for single events, impulsive sounds LEP,d is Leq applied to measure noise exposure at work Lower and Upper Action Levels