Why the stage of an auditorium has curved background, curtains, carpets and false ceiling?

The stage of an auditorium has curved background so that the sound get reflected from the curved background and reaches to the every part of the auditorium.

There is a term called reverberation it is phenomenon of  persistence of audible sound after the source has stopped emitting sound . Since reverberation is due to repeated reflected sound from ceiling floors , wall so to reduce reverberation we should use absorbing material like curtain floor should be carpeted asbestos sheet should be use etc