What is Reverberation? (Class 9 Physics)

When a sound is produced in a large enclosed space (like a hall or an empty room), the sound waves hit the walls, floor, and ceiling, and bounce back (reflect).

Definition: The repeated, multiple reflections of sound waves from the walls of an enclosed space, which causes the sound to persist (linger) even after the original source has stopped producing it, is called Reverberation.

Students often confuse the two, but they are physically different:

• Echo: This happens when the reflecting wall is very far away (at least 17 meters). You hear the original sound, a clear silence, and then a distinct, separate repetition of the sound (Hello... Hello).
• Reverberation: This happens when the reflecting walls are close (like inside a room). The reflections bounce back so incredibly fast (in less than 0.1 seconds) that your brain cannot separate them. The sounds mix together into one long, continuous, blurry boom.

While a little bit of reverberation is great for music (it makes a guitar sound rich), too much reverberation in a cinema hall or classroom makes it impossible to understand human speech. To reduce it, architects use Sound Absorbing Materials:

1. Covering the walls and ceilings with soft acoustic panels, compressed fiberboard, or heavy curtains.
2. Putting thick carpets on the floor.
3. In a cinema hall, the soft, cushioned seats are specifically designed to absorb bouncing sound waves.