Refraction:
Refraction is the how much the direction of energy changes when it encounters a different medium. If a person in the air is shouting to a person below the surface of water then the angle at which the sound travels will change. The sound traveling through the medium it was produced in is called the incident sound, while the sound traveling through the next medium it encounters is called the refracted sound. The angle of the refracted sound can be found by using Snell's Law involving the incident sound's angle and the velocities of both mediums, listed below.
SinTheta1=V1
SinTheta2=V2
SinTheta1=V1
SinTheta2=V2
Reflection:
When sound hits an obstacle it can reflect. A sound will reflect at the same angle it hit an object at. Reflection can either result in an echo or reverberation. A reverberation occurs when a sound reflects off an object and travels back within 0.1 second of when the original sound was heard. This caused the sound to seem prolonged. An echo occurs when the reflection of a sound is heard after 0.1 seconds of the original sound. This causes the sound to seemingly die out and then reappear. This is possible because the human brain can retain a sound in memory for 0.1 second. Anything longer than this, and the sound will be forgotten. Some animals use sound reflection to direct sound in wildlife.
Diffraction:
Diffraction is what helps us hear sounds around objects and through small openings. Sounds that are lower in frequency are more easily heard than sounds of higher frequencies because the waves are longer. When a sound is diffracted through a small opening the waves then spread out, and can be heard on the other side. When a sound encounters a small obstacle diffraction allows it to be heard behind that obstacle. The obstacle will not affect the sound wave forever.