To diffuse something means to pour out and spread, as a fluid, or scatter widely and thinly. And that is the best way we have of taming a room's problems. We can absorb unwanted sound, but it's always better to keep what's broadcast by the loudspeakers, and spread the energy around to keep the room live, though most people seem to over damp their rooms.
Yet, both damping and diffusing have their places in listening rooms. Damping's great, if used sparingly, to eliminate slap echoes. Clap your hands in a live room and you'll hear the quick retort bouncing off walls, and this is called slap echo. It's not something we want as it can smear the stereo image by wreaking havoc on phase relationships. We tame slap echo with either absorbers or diffusers, on walls or in corners, where sound builds up.
If you want to test for slap echo, do a 'walk about' in your room, staying close to its boundaries and loudly and quickly clap your hands together. If you hear an echo reply, that needs to be eliminated for best sound. The first place I start with is corners, as sound more easily builds up there. If you find echo, have an assistant place a pillow or a heavy blanket where you suspect it is reflecting from, to identify the problem area. Once you've located it, and there may be several, you can use any number of tricks to reduce it. For example, you can damp it or change the angle sound is reflected back at parallel walls. I did this in Music Room One when I discovered the junction between the wall and ceiling were culprits. I placed some wide trim at a 45˚ angle along the junction and eliminated echo by refocusing the return energy, dissipating it into the room. I could also have absorbed it, but I prefer absorbing as little as possible.
Whatever you do to eliminate slap echo, just make sure you start one step at a time, add/change as little as possibly until the echo's tamed.
Never over-damp the room. It just robs the life out of the music.
Once slap echo's been tamed, it's time for bigger fish to fry.
