Equivalent sound Level. The Leq of a sonic event is that constant SPL which has the same amount of energy as the actual event. Thus, the Leq is a long-term average, or integration, of an SPL. It is approximately the average of the powers of instantaneous levels taken at equal intervals over time during the measurement period. Leq is a convenient way of accurately measuring the level of a fluctuating sound over a range of a few seconds to several hours.