Leq

Leq, or equivalent continuous sound level, is a measure of the energy of a fluctuating sound signal over a specified period T, expressed in decibels. It represents the constant level that conveys the same acoustic energy as the time-varying signal.

For a sound pressure level L(t) in decibels, Leq is defined as Leq = 10 log10( (1/T) ∫0^T 10^{L(t)/10} dt ). In discrete form with N samples, Leq ≈ 10 log10( (1/N) Σ_{i=1}^N 10^{L_i/10} ). When human hearing response is considered, Leq is often quoted with A-weighting: Leq,A = 10 log10( (1/T) ∫0^T 10^{L_A(t)/10} dt ), where L_A is the A-weighted level.

Applications of Leq include environmental noise assessments, workplace noise exposure, and building acoustics. It provides a single value to summarize fluctuating sound over a period, enabling comparisons across time and space. Leq is a measure of energy over time and is not a peak value; peak levels are described by Lmax or subject to other descriptors.

Measurement and interpretation require a sound level meter with appropriate frequency weighting and time constants. The integration period T is chosen to reflect regulatory requirements or the duration of interest. In occupational settings, exposure is often expressed as L_Aeq,8h, the A-weighted Leq over an 8-hour workday.

Standards defining Leq and its implementations exist in international guidelines, including ISO 1996 for environmental noise and IEC 61672 for sound level meters, with various weighting and averaging conventions.