EDT (Early Decay Time)

Early Decay Time (EDT) is the reverberation time derived from the initial 10 dB of the sound decay curve, extrapolated to a 60 dB range. Defined in ISO 3382-1:2009 §4.1, EDT correlates more closely with the subjective perception of reverberance than RT60 because human hearing is most sensitive to the early part of the sound field. In well-diffused rooms, EDT approximately equals T30. In rooms with early reflections or uneven absorption, EDT can differ significantly from T30, revealing acoustic issues such as flutter echoes or focusing. EDT is particularly important in concert halls, where values between 1.8 s and 2.2 s are considered optimal for orchestral music.