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Sound Exposure Level
This is more commonly known as LAe or previously SEL and is expressed in
decibels.
It is the sum of the ‘A’ weighted sound exposure over the recording period but
normalised to one second.
It is very useful for many applications including noise events such as an airplane
fly over a train pass by and many other environmental applications.
With the total sound exposure normalised to 1 second regardless of the time
period of the event, each individual sound exposure level can be compared with
each other.
As the LAe is normalised to a period of 1 second, the value it produces is almost
always greater than the maximum rms sound pressure level for the same noise
event.
Again as this a cumulative measurement be aware that low noise events
recorded over a longer period may give the same or greater sound exposure
level as noise events with higher levels recorded over a shorter period of time.
An example screen display may be: -
Percentiles
These are more commonly known as Ln’s and are expressed in decibels.
The selected Ln displays the ‘A’ frequency weighted and time weighted sound
pressure level that has been exceeded for n% of the time.
For example, if the selected Ln is L90 then the value shown is the sound
pressure level that has been exceeded for 90% of the time period. In the UK
standard BS 4142 L90 is described as the Background Level.
Percentiles are used widely for measuring environmental noise.
An example screen display may be: -
LAe 79.8
Frequency Weighting
L90 67.5
Percentile Selected
