# Acoustic Glossary

Sound Exposure (E) is the (sound-pressure)2 measured over a stated period of time or noise event. Measurements are normally A-weighted to relate to the human response.

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(8h) = 85 dBA for 8 hours.

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

Sound Exposure Action Values (EAV) is the 8-hour daily exposure to noise above which employers are required to take action to control exposure. For noise there are two action levels,

The Lower EAV is 80 dBA and a peak sound pressure of 135 dBC ≈ LCpeak
The Upper EAV is 85 dBA and a peak sound pressure of 137 dBC ≈ LCpeak

Sound Exposure Limit Value (ELV) is the maximum noise an employee may be exposed to on any single 8-hour day is 87 dBA and a peak sound pressure of 140 dBC.

Sound Exposure (IEC 801-21-23) time integral of the squared A-weighted, instantaneous sound pressure, over a stated period of time or event. The frequency-weighting may be other than A, if so specified.
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.

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

Sound Exposure Level (LE) 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 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.

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

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

Sound Exposure Level (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.

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.

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.