Leq and its cousins

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Leq and its cousins
Introduction to Acoustics

• University of Salford

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Learning Outcomes

• Manipulate Leq with confidence
• Define single event level and use SELs together
  with Leqs to evaluate noise exposure
• Understand the essential features of the Noise at
  Work Regulations

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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.

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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)

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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

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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.

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Sound Exposure Level
Definition This is the notional sound pressure
level which, if maintained constant over one
second, delivers the same amount of acoustic
energy at some point as the time-varying sound
pressure level would deliver at the same point
over its entire duration.
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SEL applications

• single aircraft flyovers
• single vehicle passages
• explosions
• single industrial impact noises

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SEL equation
Compare with
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SEL and Leq
For one event, over T seconds
For n events, all with the same SEL, over T
seconds
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SEL example
An airport uses a microphone to monitor the noise
of aircraft movements. During the first ten
minutes of monitoring, one aircraft arrives,
producing an A-weighted SEL of 112 dB. What is
the LAeq over this ten minute period?
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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