Most noise impacts to which we are exposed vary over time. Just think about the experience of traffic noise when you are standing beside a road and listening to it. Or the sounds at your workplace, which also vary throughout the day, switching between high and low intensity, breaks etc. The equivalent, continuous sound pressure level, Leq. was introduced to take account of these changing situations. It is a calculation of the average noise level measured over a certain time interval, for example eight hours. The concept was introduced in order to express sound levels that vary over time (for example traffic noise), resulting in a single decibel value which takes into account the total sound energy over the period of time of interest. Fluctuating noise which is measured over a certain time period represents the combined energy.
The fact that it is energy which is being compared ties in with the fact that the theories about noise damage and noise nuisance are linked to the noise energy to which you have been exposed. In other words, a strong, brief noise has the same harmful effect as weaker, longer lasting noise. It is not perfect, but at the moment it is the best model available. The Leq concept is inevitably linked to a period of time, as it expresses an energy. Therefore, whenever a Leq value is mentioned, it must be accompanied by a duration, otherwise it is meaningless. The official maximum limit for damaging noise in the workplace is thus:
“Leq = 85 dB(A) over an eight-hour working day”
The noise dose to which you are exposed therefore corresponds to 88 dB(A) for four hours, 91 dB(A) for two hours, and so on. In all three cases the noise dose is the same.
The reason for including the Leq concept in this review is that it features in all the requirements made the authorities in relation to noise in the workplace (as mentioned above), noise emitted by businesses to the outdoor environment, traffic noise etc. Also, the term is frequently misunderstood, as the fact that it is an average value is often overlooked. Thus, it is certainly possible for short periods of time to have higher noise levels than the Leq value yet to stay within the limit.