Take any restaurant, classroom, band room, conference room or recording studio. Stand in the centre of the room and clap your hands. If the room is properly treated for acoustics, the background sound wave reflections will bounce off perimeter surfaces and die off within two seconds. Two seconds is the threshold level for human ear. Sound wave reflections that die off within two seconds produce greater clarity to original sound. The room is user friendly with premium sound quality.
However, sound wave reflections that take longer than two seconds to die off produce what we know as echo. The longer the sound waves take to die off, the worse the blurred sound signals become. Original sound is now buried amidst a room filled with echoes bouncing in every direction. For some rooms, it can take up to 10 seconds for these echoes to die off on their own. These rooms are user unfriendly, with poor sound quality.
To turn an unfriendly room into an acoustically sound room, sound panel systems are introduced into the space, wall or ceiling mounted, to capture the echoes and force them to die off within two seconds. This method is called as the two-second rule in acoustics.