Ans: The repeated multiple reflections of sound in any big enclosed space, is called reverberation.
When a sound is produced in a big hall, its wave reflects from the walls and travel back and forth. Due to this, energy does not reduce and the sound persists. Small amount of reverberation for lesser time helps in adding volume to the programmers. Too much reverberation confuses the programmers and must be reduced.
To reduce reverberation, the roof and walls of the hall are covered with a sound absorbing material like rough plaster and thick curtains.