LpAeqT

LpAeqT denotes the A-weighted equivalent continuous sound pressure level over a specified period T. It is measured in decibels (dB) and reflects the time-averaged energy of the sound as filtered by the A-weighting, which approximates human hearing sensitivity. The quantity is defined as LpAeq,T = 10 log10 [ (1/T) ∫0^T (p_A(t)/p_ref)^2 dt ], where p_A(t) is the instantaneous sound pressure after A-weighting and p_ref is the reference pressure of 20 µPa. In practice, LpAeq,T is commonly referred to as LAeq,T, since the same A-weighted level is being computed; the "p" emphasizes the use of sound pressure in the definition.

Use and applications: LpAeqT is widely used in environmental and occupational noise assessments, building codes, and urban planning to summarize fluctuating noise into a single metric over a chosen period. The period T is selected according to regulatory or study needs, with common choices including 1 hour, 8 hours, or 24 hours for environmental noise, and shorter intervals for indoor or worksite measurements. Measurement is typically performed with integrating or integrating-averaging sound level meters equipped with an A-weighting filter, calibrated microphones, and proper location and mounting to approximate free-field or room conditions. Standards such as ISO 1996 and related national regulations specify procedures for instrument class, microphone height, wind screens, and field uncertainties.

Notes: A-weighting approximates human sensitivity at moderate sound levels; the metric does not capture all aspects of loudness or impulsive noise, nor does it reflect spectral content beyond A-weighting. LpAeq,T is sensitive to the chosen duration T: longer periods smooth variability, shorter periods emphasize bursts. See also LAeq, environmental noise, sound pressure level, A-weighting.