LeqA

LeqA, commonly written as L_Aeq or LeqA, stands for the A-weighted equivalent continuous sound level. It quantifies fluctuating noise by expressing it as a single steady level that would contain the same total acoustic energy over a defined period. The A-weighting filter emulates the human ear’s sensitivity, reducing emphasis on very low and very high frequencies.

Calculation: For a measurement period T, L_Aeq,T = 10 log10( (1/T) ∫_0^T 10^{L_A(t)/10} dt ), where L_A(t) is the instantaneous A-weighted SPL and p_ref = 20 μPa. Equivalently, L_Aeq,T can be derived from the time history of unweighted pressure p(t) after applying the standard A-weighting filter and then averaging the squared pressure over time.

Measurement and standards: Measurements require a sound level meter with A-weighting and integrating capability, and are reported for specific periods (e.g., 1 h, 8 h, 24 h) depending on regulatory requirements. International standards governing equipment and procedures include IEC 61672 for sound level meters and ISO 1996 for environmental noise assessment, with occupational guidelines often referencing ISO 11202 or national regulations.

Applications: L_Aeq is used in environmental impact assessments, urban planning, building codes, noise control design, and regulatory compliance. In workplaces, L_Aeq,8h is commonly used to compare exposure with occupational exposure limits.

Limitations: Although useful, L_Aeq summarizes energy over the period and cannot capture spectral details beyond A-weighting. It is influenced by measurement duration, source distribution, and microphone placement, and A-weighting may underrepresent some low-frequency or impulsive noises.