Arturos
Lots of info sites and manufacturers for acoustic panels and placement.
If you have the cash any number of places will be happy to sell you their room treatment panels...................I'm a D-I-Y guy and like getting the best bang for the buck, so I built my own. I used 3/4 plywood cut to size for the frames. You can make quite a few frames from a single sheet, so cost per is pretty cheap. Stuffed them with 3" rock wool, although there are other choices at roughly $1 per square foot, again pretty cheap. I wrapped each panel with fabric from Joann's fabric store, but pretty much any fabric will work as long as it's reasonably light weight. I used 100% cotton print that I liked. The fabric was the most expensive part of the equation, but that was simply because I went with something I felt would be attractive in the room. What I used was about $13 a yard and I probably used 25 yards or so, but you can buy something suitable for half that price, less on sale...........Even still, to do a rather extensive room treatment cost me less than $500, a fraction of what we typically spend on gear or even cables and the difference was quite significant and positive. You won't need super hearing to appreciate it and you'll be quite amazed at how much better music you thought you knew well is going to sound. Built frames, cut and stuffed with mineral wool....easy to cut BTW, stretched the fabric neatly over it, like wrapping a Christmas present and stapled from the back.............Let your wife or significant other choose the fabric if she wishes. That way she's more likely to be receptive to the whole idea and these "boxes" can actually be made quite attractive as well as functional with a little creativity.............Enjoy!!.....What I built, BTW is virtually the same thing that most manufacturers will sell you for significantly more money.........There's no magic to it and it works.