Reverberation is the presence of sound after the source has stopped – similar to an echo. In movie theaters reverberation often builds when sound is reflected off walls, floors and ceiling surfaces. For example, with action films there are typically loud action sequences, immediately followed by quieter, more dialogue-driven moments. In a THX Certified Cinema with tightly controlled reverberation, the sound of explosions ends immediately and never bleeds over into the next scene. To control reverberation, THX cover the rear wall of the auditorium with thick, absorptive material which prevents the direct sound of the screen speakers from reflecting into the seating area. THX also requires the placement of absorptive materials on the sidewalls, down to the audience’s ear level which reduces sidewall reflections. WITH ACOUSTIC PANELING Acoustic paneling controls reverberation, or echo effect, in a THX Certified Cinema. WITHOUT ACOUSTIC PANELING Sound bounces off the walls without acoustic paneling, interfering with the movie’s soundtrack.