Sound waves react differently when they come in contact with an obstacle. Have you ever called out at the top of a mountain only to hear your call a few seconds later? This occurs because the sound waves that your voice box produced were reflected back to your ear. Reflection of a wave occurs when a sound wave bounces off an obstacle. When this occurs the wavelength and the frequency are unchanged.
Refraction occurs when sound waves cross a boundary and pass into or through objects. When this occurs the wave is bent as it crosses the boundary.
Absorption occurs when the sound wave pass through objects. As a sound wave is absorbed the amplitude of the wave gets smaller and smaller as it passes through the material. Heavy curtains are used in theaters so that audiences are unable to hear what is going on back stage. Earplugs are used to diffuse the amplitude of a loud noise that may be harmful to the delicate hair cells of the inner ear (Hsu Tom, 2003).