The SI unit of sound exposure is the
Pa2·s (pascal-squared second), however Occupational Noise Exposure Meters, also known as noise dose meters, record the Pa2·h (pascal-squared hour) levels throughout over the working day.
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.
0.2 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
● 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; the pascal-squared kilosecond (Pa2·ks), if time is in kiloseconds; 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.
Sound Exposure Level is similar to the 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.
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 Levels normalized to 1 second are a very useful way of comparing different sound events and sources.Sound Exposure Level Definition IEC 801-22-17, 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.
● Note : the reference sound pressure and the frequency weighting may be different, if specifically stated with the sound exposure level.
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.
Sound Exposure Meters measuring Pa2·h directly are also known as noise dosimeters.
Noise Dosimeter or Noise Dosemeter is a more general term for instruments having a similar purpose but may be calibrated to suit differing standards around the world.See also • personal hearing protectors
See also • noise dose • Leq (equivalent continuous sound level)