As with light, wave propagation is strongly effected by propagation through media. Imagine a sound wave hitting an interior wall as someone yells from inside of a room. It may be helpful to think about a ray of sound approaching the wall. Due to reflection, much of the sound will bounce as if the wall were an acoustic mirror. However, some of the sound energy will penetrate the wall. Sounds propagates more quickly through more solid materials, resulting in a bending of the ray as it penetrates. This is refraction. Some of the sound escapes the far side of the wall and propagates through the air in an adjacent room, resulting in transmission. Thus, someone in the adjacent room can hear yelling. The total amount of energy contained in the sound waves before it hits the wall is split by reflection and transmission, with additional loss due to attenuation.