Reverberation is the presence of sound after its source has stopped – much like an echo. In a movie theater, reverberation often builds as sound reflects off surfaces such as walls, floors and ceilings.
For example, in an action film, such Iron Man, there are several instances where the movie’s hero (Tony Stark) is being chased through the sky by two fighter jets, followed immediately by quiet, more dialogue-driven moments. In a THX Certified Cinema with tightly controlled reverberation, the sound of jet engines and explosions ends immediately, never bleeding over into the next scene.
Among the methods THX uses to control reverberation is covering the rear wall of the auditorium with thick, absorptive material. This 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. This reduces the amount of sidewall reflections.
Acoustic paneling controls reverberation, or echo effect, in a THX Certified Cinema.
Sound bounces off the walls without acoustic paneling, interfering with the movie’s soundtrack.