Early Decay Time EDT(s)
The Early Decay Time is measured in the same way as the reverberation time, except that it relates to the early part of the reverberation curve (0 to -10 dB). EDT is also called “Early reverberation time”. The EDT can vary locally in a room much more than the reverberation time T20 or T30 and is therefore more used as a local parameter for a part of the room (e.g. the stage in a concert hall) and not as a global parameter for the whole room.

Echo
An echo is the delayed reflection of a sound, which is detected from the human ear independent of the direct sound. An echo can be very disturbing for the human ear and can make speech unintelligible.
Equivalent absorption area The area of a surface multiplied with its absorption coefficient. The equivalent

absorption area of an element differs with the frequency and is normally stated per octave band or 1/3 octave band. The total absorption area of a room is used to calculate the reverberation time acc. to Sabine’s formula.