LAeq

LAeq, the A-weighted equivalent continuous sound level, is a metric used to summarize fluctuating sound energy over a specified period in a single value. It applies the A-weighting curve to reflect the human ear’s sensitivity and is widely used in environmental, occupational, and building acoustics to assess noise exposure and regulatory compliance.

Mathematically, LAeq,T is defined as 10 log10((1/T) ∫_0^T 10^{L_A(t)/10} dt), where L_A(t) is the instantaneous A-weighted sound pressure level in decibels and T is the measurement period. If measurements are discrete, the integral is approximated by a time-weighted average of the sampled levels. LAeq,T is not a peak measurement; it represents the energy-equivalent level over the entire period.

LAeq,T is distinct from peak or percentile metrics such as L_A,max or LA,90. It provides a single value that corresponds to the total acoustic energy over the specified time window. Standards often specify the time window (for example LAeq,24h for a full day or LAeq,8h for occupational exposure) and use LAeq as the basis for noise limits and exposure assessment (ISO 1996, IEC 61672).

Applications include environmental impact assessments around roads, airports, and industrial sites, as well as indoor and occupational noise control planning. A higher LAeq generally indicates greater total sound energy over the period, but two periods with the same LAeq can differ in how the sound levels rise and fall.

Limitations include insensitivity to brief spikes and the reliance on A-weighting, which may not suit all frequency content or impulsive sounds. Typical environments vary widely, with quiet areas around the low tens of dBA and busier urban or industrial settings reaching higher ranges, depending on time and context.