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Noise - Terms - Energy Averaging [LAeq]

When dealing with a new or proposed noise LAeq is often used [also written dBA Leq]; this term is the Equivalent Continuous Level.  The formal definition is "when a noise varies over time, the Leq is the equivalent continuous sound which would contain the same sound energy as the time varying sound". However, you can think of it as a type of average, where noisy events have a significant influence.  The results of calculations or measurements Such measurements are designated say 46.3 dBA Leq or 46.3 LAeq. LAeq is the main unit used for assessing Occupational Noise.

Graph of Noise Trace with LAeq

If we again look at our noise trace, two successive 10 second LAeq's  and the cumulative LAeq can be plotted in yellow, green and blue respectively. Note the large variation in values.

As with all forms of average it is important to consider the period over which the average is taken; in the above example, if a limit had been set at say 55 LAeq, there is no breach; however if the limit of 55 LAeq had been set 10 seconds, it can be seen that the "yellow" period breached the limit.

The other important feature of LAeq's, is that a large number of quiet events can produce the same period LAeq as a few (possible one single) very loud event(s); therefore any limit set in terms of LAeq considers the two conditions as being equivalent.

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