The correct option is (a).
Explanation
Reverberation is an acoustic phenomenon characterized by the persistence of sound in an enclosed space as a result of multiple reflections from surfaces such as walls, ceilings, and floors.
Statement-wise Analysis:
- Statement 1 is Correct: In a large hall, sound waves undergo repeated reflection from the walls and ceiling. This results in the sound persisting for a duration even after the source has ceased. This persistence of sound due to multiple reflections is technically termed reverberation.
- Statement 2 is Incorrect: While a specific, limited amount of reverberation is necessary to prevent a hall from sounding "dead," excessive reverberation is highly undesirable. It causes the overlapping of sounds, making speech unintelligible and music distorted or blurred.
- Statement 3 is Incorrect: To reduce reverberation, the surfaces of the enclosure must absorb sound energy rather than reflect it. Therefore, sound-absorbing materials like compressed fibreboard, rough plaster, heavy curtains, and carpets are utilized. Materials like glass are hard and smooth, acting as efficient reflectors, which would sustain or increase reverberation.
Key Takeaway:
Reverberation is the persistence of sound caused by repeated reflections. Acoustic design aims to control this by using sound-absorbing materials to prevent sound blurring, ensuring clarity in auditoriums and concert halls.