I bought some Owens Corning 703. Now what?

There is so much great info on the net regarding acoustics and seeing that it is the acoustics of your room that is going to be the final say on what you will hear that I once again encourage you to delve deeper into this fascinating aspect of optimising the speakers into your chosen room.

It's of course possible to get a professional company to supply and fit the treatment but without an understanding of 'what and why' you will find yourself needing to hire them again at great expense to analyse and fit out the next room you decide to use for system. Also appreciate the fact that you, armed with the knowledge and REW, can design a huge bass trap to sort out a specific problem. Acoustics companies are reluctant to design and provide custom service. They have standard designs which in knock-down form can be couriered easily and a few of them tend to oversell.

This brings up another point which is if you have REW sussed out you can measure any treatment fitted by the pro's and tell them to stop when RT60 is where you want it. A friend of mine had to remove a bunch of panels that rendered his room too dead.

http://arqen.com/bass-traps-101/placement-guide/#quarter-wavelength-rule
https://www.youtube.com/watch?v=LJ59AQU1FUY
https://www.youtube.com/watch?v=R4agj6oZIaI
https://www.youtube.com/watch?v=41liBn-QNW4&list=RD41liBn-QNW4&start_radio=1&t=375

You may find these links useful. The last one shows a super-chunk bass trap. It's a little sloppy but provides an idea.

@mitch2 
A/V Room Service EVPs are made with/of:
"The EVP core is a matrix of precisely compressed high-density molded glass fibers, which allows controlled air movement through the fibers." (from his web site specs)
They work well for isolating equipment.

Brief update. I did some critical listening with one interesting variation: (a) the entire box of panels against the front wall with the front face of it OPEN or (b) with the cardboard flaps closed. Very, very noticeable difference in what it did to the bass. When open and absorbing (and not even ideally), it sucked in enough energy to render the bass much crisper, located, defined. No muddiness even when the string bass in the jazz I was listening to went to the lowest notes; I could hear fretting and very distinct notes. Closed up again, and the muddiness came right back to the low bass notes.

FWIW, a noticeable difference. I didn’t focus on much except the bass region, so I have no idea if it was over-absorbing or disrupting upper balance. But it helped the bass a lot.

Hilde45 “Posts on this site have convinced me that I'm done thinking about gear. (And I just put a system together.). So now I'm looking for a correctly treated room, or at least the path which leads there”

I am at the same juncture, Hilde45.  While I have been interested in utilizing REW for a few years, the perceived learning curve has kept me from even attempting it.  Hopefully that changes now, thanks to your thread and some of the very helpful posts from many including Lemonhaze, Tomic601,  Shalommorgan.

Like many in the hobby, I have been working on my tweaking my room set-up for years.  Implementing several tips in Jim Smith’s book, Get Better Sound, improved my SQ.  Then I paid Jim a very reasonable consultation fee for room-specific guidance aimed at finding the all-important (according to Jim and others) ideal place for one’s chair. Called the anchor spot or chair, IIRC.  I sent photos and dimensions of my room.  Using the RTA app on my phone I took readings of white or pink noise (forget which it was right now) playing as I moved my chair further from the front wall.  Did 6 readings.  He identified the two best spots and my chair has been at one of them for close to 2 years now.

Why my interest in REW, then?  Because we took no readings of corners, center of front wall (between speakers) or anything else.  And, I also wonder how much better REW and a microphone may be compared with an RTA phone app.

My room sounds more than “quite good”.  It really does.  However, I have felt that way many times and then found ways to make it better.  There is sheetrock bump-out that houses an HVAC chase that has discouraged me from moving my speakers further into the room because the left speaker will eventually be so close to it the SQ will suffer—I presume.  The other “deterrent” is that my speakers are on DIY adjustable platforms that make moving the speakers and resetting them with OCD symmetry a bit “involved”.  However, last nite I DID move my speakers further into the room by almost 3 inches and thus also reduced the distance to my ears by the same.  I fine-tuned toe-in and assessed the closer triangle.  While I do believe in assessing over at least multiple sessions over time, Wow.  I should have done this sooner.  One key improvement seems to be dynamics, but there are others.  Doing the “ears cupped by hands” test, the impact of my hands is vastly decreased.  Does anyone know if that is an indication of improved dynamics, per se?

I like my equipment, believe it is well engineered and have even improved it by employing the services of a very gifted mod-er here on AG.  Like the OP and others who’ve posted, I wish to address my room’s SQ-robbing deficiencies a bit more methodically now because I suspect I’ve still not heard my rig at its best.

Thanks, rc22. I continue to use REW and have benefited from help from numerous nice people and also from videos online. I think some of those videos can help push you further toward more measuring, and if I can tell you anything useful, please P.M. me. We could chat.