Echo :
A repetition of sound produced by the reflection of sound waves from a wall, mountain, or other obstructing surface
Sound-absorbing materials :
Materials such as fibreglass, fluffy fabrics, and other porous materials, applied to walls and ceilings to eliminate sound reflections
Sound proofing:
The process of making a room or building resistant to the passage of sound
Sound reflection :
The bouncing back of sound waves from the surface of solids or liquids