Amilcar, regarding the suitability of your room to omnis, let me describe some pertinent aspects of how the ear/brain system processes incoming sound. I think this is useful background for people considering omni, dipolar, or bipolar speakers. This will be a brief introduction rather than an in-depth study of the topic.
The ear derives directional cues primarily from the first .68 milliseconds of a sound impules (corresponding to the roughly 9 inch path length around your head from one ear to the other). After this initial .68 milliseconds the ear suppresses directional cues from repetitions of the original signal (reflections), but still accepts loudness and timbre cues from the reflected energy. That being said, a strong, distinct reflection arriving after that initial .68 millisecond window can still skew the imaging.
The subjective effect on sound quality of reflections is related to their arrival time. In general, reflections arriving earlier than 10 milliseconds behind the first-arrival sound (corresponding to a path length difference of 11 feet) tend to be perceived as coloration, and reflections arriving later than 10 milliseconds (assuming their spectral balance is good) tend to be perceived as richness, warmth, ambience, spaciousness, texture, and liveliness. That's why music in a good recital or concert hall sounds so good, and that's why omnis often sound so good.
You've probably noticed that owners of dipole speakers (Maggies, Quads, etc.) like to position them pretty far out into the room. This is because they sound better when the extra reverberant energy from the backwave arrives after as much time delay as is reasonably feasible. The same principle applies to omnis, only their equally strong radiation to the sides makes the first sidewall reflection a concern. Often diffusion in the first sidewall reflection zone is beneficial with omnis. Likewise, diffusion in the first reflection zone behind the speakers is usually beneficial, especially if they must be placed within 5 or 6 feet of that wall.
Since lots of early sidewall reflection energy is inevitable with an omni, you might well get some image imbalance with that big opening along the right-hand side of your room. In my experience even heavy absorption in the corresponding area on the opposite side of the room may not even things out with that type of speaker. In general I don't like to use any more than the bare minimum amount of absorption necessary to prevent slap-echo when using dipoles, bipoles, omnis or polydirectionals, because much of what they do well comes from having a strong, diffuse, spectrally correct, slowly decaying reverberant field.
I'm a big fan of getting the reverberant field right; in my opinion that and dynamic contrast are among the primary differences between live and reproduced sound from a perceptual standpoint.
Duke
dealer/manufacturer
