Is my room doomed? Pic

". . .I'll have sidewalls but no front and back walls. Would that be a problem?"

The side wall lateral reflections are beneficial - particularly in stereo - since they can produce greater apparent source width and spaciouness, while the front/rear reflections can decrease these attributes since they come from the same direction as the direct sound and thereby increase the Interaural Cross Correlation Coefficient (IACC) which is a bad thing. So in short the situation of having side walls with no front/back wall is preferred over the opposite situation. Have you considered mounting some diffuser panels (DIY or store bought) on a moveable stand with wheels that can be moved to the side out of the way when not in use or put behind your listening chair for critical listening sessions? Just a thought.

"Why do thin windows act as an absorber of bass?"

Windows don't technically absorb bass unless they're loosely installed and their vibration back and forth acts like a diaphragmatic bass trap . . . As low frequencies have long wavelengths they don't "see" the window and easily pass through it; if they pass through it then they can't be reflected back into the room so therefore the windows function more like a bass trap/absorber. Higher frequencies with much shorter wavelengths will in fact "see" the window and reflect off of it. The biggest problem with the windows is that it's too good of a bass trap and allow too much bass energy to be drained out of the room while maintaining the higher freq energy and therefore acts like a high-pass filter throwing off the timbral balance which you hear. So diffuse or absorb in front of the windows to attenuate the higher frequencies.

I don't know your ceiling height but you could experiment with reflection, diffusion, or absorption at 1st reflection points there to see which you like best.

Thanks for all the help guys.

I've added some diffusion to the corners of the front wall, switched around the speakers so the woofers now fire inwards, pulled out the speakers even further (now about 2.2m into the room from front wall to tweeter), and moved the speakers closer so they aren't so wide apart.

The sound has vastly improved, maybe from a 5 to a 7 (if the dealer was a 10 in his properly treated dedicated room), and I expect I can get it maybe up to an 8-8.5 max with more diffusion on the front wall, maybe get rid of the TV in the middle, a bit more speaker placement adjustments, and a better preamp.

The soundstage depth is finally there, the sense of reverb/echo sounds more proper, the bass tighted up with more SPLs, and now the weight of the notes finally sound like Rockports.

My complaint has drastically decreased, but right now the biggest issues are probably 1) soundstage height is a bit too low and 2) I still want more overall bloom in the soundstage (envelopment from up down left right).

Does anyone know how to get more soundstage height? Seems like width and depth are the easier ones to get but height is really hard. Should I tilt the speaker more forward or backwards (by adjusting the footers)?

Anyway, thanks again for all your guys's help. I'm finally getting happy with this system after spending all the money and it just goes to show you proper setup is SO damn important. I was adjusting centimeters with speaker position when I should have been adjusting them in much bigger gaps. I had to basically pull the speakers 1/2 way into the room (guess I bought too big of a speaker!!) and space them much less far apart. I'm happy that the Rockport's tweeter/mid/bass integrate fast between the drivers or else it would be a bigger problem to deal with running out of room space.

Enzo618, thanks for updating your situation. So many people asked questions, get tons of advice and then they never report back what worked, or didn't work. IMO your feedback is a critical part of the forum process.

Good luck with future adjustments!

Enzo, sounds like you're making progress. Congratulations. I did read above a suggestion to add a carpet to the floor. Have you tried this? I have one and added a second pad underneath it. This reduced floor reflections resulting in a cleaner, more accurate sound. I suppose treating the ceiling would help, though it is not as easy and aesthetics come in, but these two additions may effect soundstage hight.

Good on 'ya for trying various things and noting the differences. Measuring the frequency response / SPL (dB) is also important for trying different things so you have a record of the sound for each setup variation.

You wrote: "the biggest issues are probably 1) soundstage height is a bit too low and 2) I still want more overall bloom in the soundstage (envelopment from up down left right)."

1) Sound stage height too low: Try sitting on the floor ;) Seriously, put a rug on the floor to kill flutter echo between floor and ceiling and see if that does anything for soundstage height. Otherwise, keep the wood floor bare and raise the front of the speakers (or lower the back of the speakers) with the thinking that just as side wall 1st reflections that aren't absorbed or diffused help with widening the apparent sound source and increase listener envelopement, so too should it work in the vertical domain. Raising the front of the speaker's will put more HF energy up to the speaker and subtly call your attention to the height. However, it's not likely to be as drastic a change as lateral reflections because we hear more effectively latteraly rather than vertically due to our ear positioning on our heads. Lastly, you could add white RPG Skylines (see my system or others that use it) to gauge if this impacts the height. Personally I didn't find it added much but that could be due to my speaker's vertical dispersion pattern, or lack thereof or the sheer angle that the 1st reflection is at given I sit near field.

2) Soundstage bloom and envelopment is a funtion of indirect sound resulting from reflections from bare or diffused surfaces, and mostly from side walls which you lack. Have you considered rotating your system 90 degrees like I mentioned previously? I know it's a lot of work - ugh.