Acoustic Glossary


 

Sound Exposure : Definitions, Terms, Units. Measurements, see also Noise Dose

Sound Exposure is the time integral of the sound pressure squared. The SI unit of sound exposure is the pascal-squared-hour (Pa2┬Ěh)

Sound Exposure Meters (Noise Dosimeters) measure Pa²·h.
 

For a given period of time, an increase of 10 dB(A) in sound pressure level corresponds to a tenfold increase in the sound exposure.

1 Pa²·h = 100% Dose = 85 LAeq(8 h) = 85 dBA for 8 hours.

  0.1 Pa²  =  74.9 LAeq,8 h
  0.2 Pa²  =  78.0 LAeq,8 h
  0.5 Pa²  =  81.9 LAeq,8 h
     1 Pa²  =  84.9 LAeq,8 h  =  100% Dose
     2 Pa²  =  88.0 LAeq,8 h
     5 Pa²  =  91.9 LAeq,8 h
   10 Pa²  =  94.8 LAeq,8 h
 

Sound Exposure Action Value : EAV is the 8-hour daily noise exposure above which employers are required to take action to control exposure. There are two action levels :

The Lower EAV is 80 dBA and a Peak Sound Pressure Level of 135 dBC
The Upper EAV is 85 dBA and a Peak Sound Pressure Level of 137 dBC.
 

Sound Exposure Limit Value : ELV is the maximum noise exposure employees may be exposed to on any single 8-hour day. The daily or weekly exposure is 87 dBA and a Peak - Sound Pressure of 140 dBC.

 

Sound Exposure Definition : time integral of squared instantaneous A-weighted, sound pressure, over a stated period of time or event. The frequency weighting may be other than A, if so specified. (IEC 801-21-23)
Note 1 : duration of integration is implicitly included in the integral, and need not be reported explicitly.
Note 2 : the unit of sound exposure is the pascal-squared-second (Pa2·s), if time is in seconds and the pascal-squared-hour (Pa2·h), if time is in hours.

 

Most modern sound level meters measure sound exposure and then calculate the required parameters.

To see a range of Noise at Work Meters click here.


Sound Exposure Level : SEL is the constant sound level that has the same amount of energy in one second as the original noise event. A-weighted sound exposure levels are denoted by the symbol LAE.

Sound Exposure Level is similar to Leq - equivalent continuous sound level as the total sound energy is integrated over the measurement period. However instead of averaging over the measurement period, a reference duration of 1 second is used.

It follows that the sound exposure level = Leq + 10·Log10T where T is in seconds for the whole measurement period.

Note : Log10 is also written as lg = logarithm to the base 10; recommended by ISO the International Standards Organisation.

Sound Exposure Level is numerically equivalent to the total Sound Energy.

For example a noise level of 90 dBA lasting 1 second would have a SEL of 90 dBA but if the event lasted 2 seconds the SEL would be 93 dBA.

Put another way if a second event of 80 dBA occurred it would have to last 10 seconds to register a 90 dBA SEL.

Sound Exposure Level Leq and Dose are mathematically related if the Time is known.

Sound Exposure Levels normalized to 1 second are a very useful way of comparing different sound events and sources.

Sound Exposure Level Definition : logarithm of the ratio of a given time integral of squared A-frequency weighted sound pressure, over a stated time interval or event such as an aircraft flyover, to the product of the squared reference sound pressure of 20 μPa and the reference duration of one second. Sound exposure level in decibels is ten times the logarithm to the base ten of that ratio. The reference sound pressure and the frequency weighting may be different, if specifically stated with the sound exposure level (IEC 801-22-17)

See also : Single Event Noise Exposure Level and the IEC Definition of Level


Sound Exposure Meter a small instrument designed to be worn by an individual to provide a measure of the accumulated sound exposure received by the wearer while moving about during the workday.

The instrument is calibrated in Pa²·h. If the meter is worn for only a representative part of the working day, the reading must be corrected appropriately.

Also known as PSEM - Personal Sound Exposure Meter.

Noise Dosimeter (or dosemeter) is a more general term for instruments having a similar purpose but may be calibrated to suit differing standards around the world.


Sound Exposure Time the time a person is exposed to noise during a workday - used for calculation of LEP,d the Daily Personal Noise Exposure.


See also : Noise DoseLeq - Equivalent Continuous Sound Level

 

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