If the distance from the wave source to the hard surface is just right then the reflected wave will cancel out the original wave at certain points and increase the wave at other points. This is a standing wave and when evident you will notice areas of a room where a certain frequency is minimal and then in other areas that same frequency is exaggerated. For example, a sub woofer creating a standing wave will cause points within the room where there appears to be no bass and other points in the room where there is too much bass.
Our job at Seven Integration is to design a room for you that minimises the chaos and the cause of standing waves, within the constraints of your aesthetic requirements. We do this by using recognised ratios of room length, width and height when designing a home cinema room as well as (when possible) avoiding parallel walls and incorporating a sloping ceiling.