Which of the following points should be considered while designing an auditorium?

A: reverberation time should be reduced

B: backstage should be concave

C: echo should be increased

D: use sound absorbing materials

A, B & D only.
Reverberation time is the time taken to dampen the loudness of the sound to zero. It should be a minimum. The backstage is made curved to reflect the sound wave in every corner of the auditorium. And absorbing materials are used to absorb noise in the hall. An echo is the reflection of the sound multiple times. It should be zero.