Equivalent sound pressure level

Professional Definition

The equivalent sound pressure level (denoted as Leq or LAeq) is a constant sound pressure level that over a specified period of time would carry the same total acoustic energy as the actual, time-varying sound.

In physical terms, it is the average energy value rather than a simple arithmetic mean of the decibel readings. Since the decibel scale is logarithmic, short-term peaks of high intensity have an disproportionately large effect on the final result of Leq. This parameter forms the basis of legal standards (e.g., ISO 1996 standards) regarding environmental protection and health and safety regulations in assessing occupational risk.

Acoustics in Simple Words

Imagine a noise graph as an uneven terrain filled with small hills (background noise) and high, sharp mountains (the passage of a truck, a door slamming). The equivalent sound pressure level acts like a giant bulldozer that flattens the peaks of the mountains and fills in the valleys, creating a perfectly flat plain.

The height of this new flat surface is Leq. Crucially, due to the nature of sound, a single "high mountain" (very loud noise) raises the level of the entire plain much more than many hours of "valleys" (silence) can lower it. That is why this index so well reflects the actual fatigue of our hearing after a whole day of working in varying conditions.

Summary

The equivalent sound pressure level is the most important indicator of the "dose" of noise we are exposed to in a given period of time. It allows us to condense chaotic, variable street or industrial noise into a single, quantitative number that enables direct comparison with acceptable safety standards.