Audio diffuser

With the trays it would be about 54 inches tall and 36 inches wide behind each speaker.

What is the size and layout of your room? Is it dedicated for listening and where is your listening position? 

I think you have a great plan. How did you determine the size of the diffusion panels? I started with 2 panels behind speakers and i used absorbion in both corners. My room isn't very wide and I found that one panel between the speakers worked better.

@knighttodd , sounds like a well damped room so far. I also went 2" behind and to the side of speakers, I need all the bass I can get.

I don't know how much the high-end will be improved by your new diffusers. There's mostly backwave from speakers, your bass will probably tighten up and image may become more focused. For highs you may need to treat the ceiling.