Here's a very cool, very slick, very cheap solution for achieving both absorbtion and diffusion (and I can hear the screams, but I'm an architect, I've done this many times, so let me 'splain Lucy :~)
Have a company come in and spray a "cottage cheese" (acoustical plaster) ceiling. OK you can scream now, then shut up! This treatment actually works great acoustically, but nobody likes the way it looks, right? HOWEVER>> they look lush and velvety when painted a medium dark color like medium gray, dark tan or dusty rose, or leafy green. You get the picture. BUT, when you paint, you MUST use what's called and "airless" spray gun. (No rollers, brushes or regular paint sprayer!) Only an airless spray job will allow the pores of the "cottage cheese" to remain open which is essential to preserving its absorbtive properties.
The result is very rich looking and you'd never guess it's a "cottage cheese" ceiling.