Question

explain giving reason the purpose of using curved ceilings in cinema halls.

Answer 1

It is because of the fact that sound should reach each and every corner of the cinema hall. Sound is being produced from one end and its waves are spreading everywhere, to people sitting there and walls and roof of the cinema hall. By bouncing with walls and ceiling some sound waves bounce back and some are absorbed there so sound is lost.
Sound waves bounce back in a specific angle that's why curved panels are used in cinema hall ceilings by which sound travels to backside audience.

Answer 2

In big cinema hall, sound can be absorbed by the walls, ceiling,floor and seats and even by the clothes of people sitting inside. This lead to too much absorption of sound due to which the speech cannot be heard clearly. This problem is overcome by using a soundboard. The sound board reflects sound and helps to spread sound evenly in the big ball.
The soundboard is a concave board [curved ceiling ] which  prevents the spreading of sound in various direction.
Due to this sound is distributed uniformly throughout the hall and even the persons sitting at the back of the hall can hear clearly.
Soundboard works on the multiple reflection of sound