Reverberation

If the reflecting surface is CLOSER than roughly 15 m to the sound source, the geometry above flips: the returning reflected sound arrives back well within the ear's 0.1 s retention window, so instead of being heard as a separate echo, it simply MERGES with (joins onto) the tail of the original sound, making that sound seem prolonged. In an enclosed room, sound reflects not just once but repeatedly off multiple nearby walls, the floor and the ceiling -- so a single spoken sound is not heard just once, but as a continuous, lingering blur. This persistence of sound after its source has actually stopped, caused by repeated reflections off walls, ceilings and other nearby surfaces, is called reverberation. …