A Quadratic diffuser comprises wells of different depths, causing a mixture of phase shifts that diffuse reflected sound. They are used to control reflections in the listening environment, particularly from rear walls and first-reflection points. They are based upon prime numbers and each prime number has a different frequency response. Quadratic diffusers can be used alone but the best way to achieve good results is to use multiple panels, side by side. A quadratic diffuser that is placed vertically, will diffuse sound energy back into our rooms in a horizontal, fan-like array and a diffuser place horizontally in our room, will spread sound energy out that enters it in a vertical, fan-like array. With both vertical and horizontal diffusers, one can have a two dimensional diffused sound field.
