A QRD 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.
When a QRD panel is used stand-alone, the phase shifts introduced by the wells produce concentrations of energy in given directions. The interaction of these produces is a complex diffusion field as the number of wells is increased.
This picture and link buttons on the right side will help you to visualize this.
When multiple panels are used side by side, constructive and destructive reinforcement between the reflections from each panel produces lobes of concentrated energy at known angles.
Using Diffusers you can transform your listening room into the sound stage that is 2 time bigger, especially in small listening room.
Placing the 1D Diffusors horizontally or vertically to your front & back wall you can achieve huge sound stage, and your speakers are going to be "disappeared" from your room and live sound stage will show upon you.
Ceiling, Left & right wall you should treat symmetrically with panel bass trap units.
Sound reflection on Vertically positioned well
You can set up them horizontally or vertically to achieve 1D sound image, or combine them horizontally and vertically to achieve 2D sound image in your listening area