Long term audiophile seeks room acoustic experience...,

I'm looking for real word exp with room acoustic treatments ideally from those that have had success and more importantly those that have not. I have done almost everything but acoustically treat my room/rooms. So questions are...

Is it possible to over treat a room? What should I start with? Corners? Behind the speakers, if so to the left or right or directly behind the main speakers? Behind my head? Ceiling? Whats most critical. In your mind? What is just about the correct in balancing liveliness vs damped? How do you know if your too lively or damped?

My current listening room is small!!! 20 x 16 x 8 feet ceiling with windows on one side and a large 7 X 7 foot opening on the other. Floors are Pergo over cement and brick wall behind my head. Unfortunately given the small room that is my seating position and cant be changed. I do however have an extra Large all fabric L section couch that is very damped but only to about 30 inches high. I also have some cheap 12 x 12 square treatments on my armoire doors just on the inside of my speakers that are angled and I feel help a bit.

Thank you for all you Obi"1" ness so I can start on the right track!

It is dependent on speaker technology and speaker location. My best results for cone floor standing speakers has been:

1) wall behind speaker first (I use heavy Afghan carpet as a wall hanging). There are products to do this as well. For ribbon speakers it was better without this. Behind each speaker and center.
2) side wall reflections. Currently I have a big room and racks and racks of albums and CDs on the side walls (25’+ Width though). Diffuser panels available.
3) my floors have always been carpeted... but this will be important. You want carpet at reflection from the speakers.
4) bass traps in front corners (the tall tubes)
5) Rear reflections... my current room is big and dampened so not a prblm
5) Front ceiling corners (these are cheap)

There is more possible, obviously. These have provided improvements in this order for me.

for dynamic speakers don’t put the whole system in the middle between the speakers against the wall... it screws up the imaging. I just have my amp on the floor.

First Thank for the reply and sorry i should have added that. I think my profile pic has the basic set up. They are sealed Dunlavys (very fast for cones) and sealed subs Kinergertics SW 800s in stereo. Speakers are pulled out about 38 inches from the rear wall and roughly 7.5 feet apart tow'd in to the inside of the cabinets from the listening position.
Here are a few tried and true steps you can take to figure this out. 

Sit in your listening spot. Clap your hands. Listen closely to the echo. Does it decay nice and smooth and uniform? Or do you hear a flutter? If the sound trails off nice and smooth, how long does it take? Do you hear the sound in the room die out, but the echo coming from the 7x7 opening lingers longer? All these little things you are hearing, they are telling you where to focus your efforts. 

Now clap and listen from different places in the room. If you have parallel walls go stand near one and clap. If the walls are parallel and untreated you will probably notice some flutter echo. Instead of trailing off smooth the echo flutters. This is the clap sound literally going back and forth across the room, a fraction of a second each time, so the echo comes back and forth so fast it flutters. 

Now in a small room, any room really but small ones are worse, if you try and treat this with all absorption the room can become dead. Also it will be real easy to kill the room you are in making the sound coming in from the opening all the more noticeable. This is a balance and another reason no one here can tell you what to do. 

I know all this because like you said I made all the mistakes and learned from them. Had my room all treated and sounding great until I realized it was too much. Took a lot of panels down and it was better. Still have a lot more I can do. Diffusers will help a lot. Even with a dedicated room it takes time and money, I have only so much, and you can see where and what I have prioritized. Stuff like Synergistic Research HFT and Schumann generators are way more cost effective than most room treatments, and are practically invisible. You could get a FEQ plop it down in a corner and have more improvement than hours and money spent on GIK or whatever. 

If you do want to try panels go to the hardware store, get some Owens Corning 703, just one 2x3' panel, cut it up and try clapping and listening to music with it in different places. This costs next to nothing. Not as cheap as advice here, which is free. Either way you get out of it what you put into it.  https://systems.audiogon.com/systems/8367

It’s the best money you can spend for sound improvement, IMO.
ASC or GIK (manufacturers of acoustic treatment) will send you a proposed treatment plan for a small fee, refundable on your first order. It’s not a bad way to get started if you have no experience reading about room acoustics (and I don't mean reading forum posts, including mine).

It is possible to overtreat a room with too much plain absorption. To avoid that, apply the treatment in stages and evaluate frequently. IMO it’s critical to avoid using much plain absorption, in favor of products that combine absorption and scattering (e.g., GIK Alpha panels, RPB BAD panels, any panel or trap made by ASC).

Avoid advice from anyone who says, "Product XX from manufacturer YY blows everything else away" or "Product ZZ can treat your room with just a few small dots / cones / pucks / gongs / mini panels." No manufacturer has reinvented physics.

Good luck!