Noise Dose and Leq

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Noise Dose and Leq
Introduction to Acoustics

• University of Salford
• Acoustics, Audio Video Group

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Noise dose

• Response to noise dose depends on the sound
  energy received
• Energy intensity x time
• How can we compare different noise doses?
• How can we evaluate the effect of a noise which
  varies over time?

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Equivalent continuous sound level (graph)
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Equivalent continuous sound level (words)
Definition This is the notional sound pressure
level which, if maintained constant over a given
time, delivers the same amount of acoustic energy
at some point as the time-varying sound pressure
level would deliver at the same point and over
the same period of time.
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Equivalent continuous sound level (equation)
Compare with
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Calculation of Leq
Where constant SPL L1 operates for time t1 etc.
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Leq example

• An industrial process produces the following
  constant SPLs over an 8-hour shift
• SPL (dB(A)) time (hours)
• 80 4
• 75 2
• 85 2
• What is the 8-hour Leq?

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Measurement

• Need an integrating sound level meter
• Can be A-weighted - LAeq
• Common in environmental and industrial noise
• Time period depends on application
• 12 hr night-time noise survey
• 24 x Leq,1 hr for traffic noise survey

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Predicting human response

• Human response varies several factors
• Can use Leq to define critical dose (at which x
  will get y damage after z years
• Even harder - use Leq to predict sub-damage
  response - e.g. annoyance
• Most noise codes are moving to LAeq

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Conclusions

• NIHL related to sound energy
• Describe time-varying levels with the equivalent
  continuous level
• Leq can be measured or (sometimes) calculated
• LAeq is single most common metric used to predict
  human response to noise