Question

Why are there soft materials on the walls of cinemas?

Answer 1

The sound waves coming from the instruments would get reflected by the walls and because a concert hall is mostly really big it would take some time for the sound waves to travel to the wall and back to your ear. If that happens you would hear echoes of the instrument because you hear two sounds, one being the sound waves directly traveling to your ear and the other being the ones reflected by the walls. If you put soft material or really odd shaped, pointed materials on the walls these reflections will get broken and wont return to your ear. Thus you will just hear the pure sound of the instrument. Reverberation.

Answer 2

The sound waves coming from the instruments would get reflected by the walls and because a concert hall is mostly really big it would take some time for the sound waves to travel to the wall and back to your ear. 

If that happens you would hear echoes of the instrument because you hear two sounds, one being the sound waves directly traveling to your ear and the other being the ones reflected by the walls. 

If you put soft material or really odd shaped, pointed materials on the walls these reflections will get broken and wont return to your ear. Thus you will just hear the pure sound of the instrument.