The major term for this is 'diffusion' and it involves the scattering of sound energy using multi-faceted surfaces. Which amongst wood, polystyrene or plastic makes good materials for diffusers?
Sound diffusers don't absorb much sound energy hence the liveliness of the room is preserved. There are DIY sound diffusers that anyone can use as well. I had no idea that items around the house can be natural diffusers.