The sound created in a big hall persists because of the repeated reflections. The phenomenon is called

The persistence of sound in a large hall due to repeated reflections is known as reverberation. When a sound source ceases, the waves continue to reflect off hard surfaces like walls, floors, and ceilings until they lose enough energy to die out. This phenomenon occurs when the reflected sound reaches the ear in less than 0.1 seconds after the original sound, causing the waves to overlap and be perceived as a single, prolonged sound. In contrast, dispersion refers to the direction sound is projected, refraction involves a change in direction when moving between different media or temperatures, and diffraction (though not explicitly detailed in the snippets) involves sound bending around obstacles. To manage excessive reverberation in halls, sound-absorptive materials are often used to control these reflections.