Absorb or Diffuse in between speakers?

Hi Kiwi - Very interesting thread you linked. I agree with many of the things you said. Among them, that the choice between absorption and diffusion is often the choice between imaging and soundstaging. Absorption often improves imaging at the expense of soundstaging. And diffusion often improves soundstaging at the expense of imaging.

IME, the rate at which absorption detracts from soundstaging is *much faster* than the rate at which diffusion detracts from imaging. And of course well placed diffusion results in *much better* imaging than an untreated room, so together that gives diffusion a significant advantage over absorption for many applications.

Again, IMO, IME, etc.

Bryon

>>Did you mean absorption behind Apogees that were hot off the rear wall?

Nope. In this case, diffusion worked best. This was a large-ish room, and absorption overly damped (deadened) that end of the room response.

Barfbag (interesting name),
As with most things there are so many variables at play and we don't know your desired end goals. You've heard that the following things matter:
* type of speaker
* current room's "aliveness" or "deadness" (ie. reverb time)
* imaging vs soundstage trade offs (although not mutually exclusive)
* effective bandwidth working range for a given absorber or diffuser
* what mix of absorption and diffusion provides the "right" sound
* what is the room's purpose - HT or stereo listening?
* and not least of which aesthetics may factor into things.

Personally, I am a fan of mixing it up. On my front wall I have the following sequence of treatments:
Diffusion. Absorption. Diffusion. Absorption. Diffusion.
All diffusion is of mid and high frequencies while doubling as bass traps. So bass trapping is used extensively while mixing the treatment effect for mid and high frequencies which aligns with my room strategy of absorbing below the transition zone and reflecting and diffusing above it. This is to preserve the aliveness to as close as possible match the natural tendencies of longer bass reverb times.

In the end treating the front wall is a necessary but insuffient condition for optimizing your listening pleasure. Be sure to treat the back wall as these reflections are equally 'damaging' meaning they are less advantageous than side wall and ceiling reflections. I would hazard to guess that if your listening chair is close to an untreated back wall that it likely doesn't matter much which kind of treatment you put on the front wall as what you're hearing is mostly indirect reflections from the back wall as front wall reflections will be attenuated by the time they reach you. So net net, be prepared to treat both front and back walls and not just one of them.