LpAeq

LpAeq stands for the A-weighted equivalent continuous sound level. It is the constant sound pressure level, measured in decibels, that would contain the same amount of acoustic energy as a fluctuating A-weighted sound over a specified period. The A-weighting network is applied to approximate human hearing sensitivity, emphasizing mid-to-high frequencies and reducing the influence of very low and very high frequencies.

Calculation and notation: For a measurement period T, LpAeq,T is defined as 10 times the log base 10 of the ratio of the time-averaged squared A-weighted sound pressure to the squared reference pressure. In formula form, LpAeq,T = 10 log10 [ (1/T) ∫0^T pA^2(t) dt / p0^2 ], where p0 is 20 microPascals and pA(t) is the instantaneous A-weighted sound pressure. In practice, a sound level meter with A-weighting provides the LpAeq value over the chosen sampling interval.

Applications: LpAeq is widely used in environmental noise assessments and occupational noise control. In workplace contexts, LpAeq,8h is a common time-weighted average for an eight-hour shift. In environmental assessments, LpAeq can be reported over 24 hours or other periods. Related metrics include Lden and Ldn, which incorporate penalties for evening and night periods, and other weighted measures such as LpCeq for C-weighting.

Limitations: LpAeq summarizes fluctuating noise into a single energy-based value and may mask short-term peaks or impulsive noise. A-weighting also de-emphasizes certain low-frequency content, which can be relevant for specific health or nuisance considerations.