The decibel (dB) is a logarithmic unit: every 10 dB represents a tenfold change in sound intensity, which most people perceive as roughly a doubling or halving of loudness. Because the ear is more sensitive to some frequencies than others, the dBA weighting filters raw sound to approximate human hearing and is the default for environmental measurement.
Aircraft certification uses EPNdB (effective perceived noise level), which adds penalties for discrete tones and for how long a sound lasts, measured at three fixed points during take-off and approach. Community exposure is tracked with Lden, a 24-hour average that adds 5 dB to evening hours and 10 dB to night hours, and Lnight, the night-only average the WHO uses for its health-based recommendations.