@ronboco, I've bought products from GIK and RealTraps. They both make excellent products. They both offer free advice on room treatment. Just be aware that they are in business to sell products, not to educate potential customers on room acoustics and relevant psychoacoustic principles. My advice to you is to spend a few months learning about room acoustics before you buy anything. I didn't do so, and wasted a bit of time and money. I wasn't going to get my room right based on advice from either one of these companies. Better, yes. Right, no.
Understand that 90% of getting a room right is getting the 20Hz-300Hz range right. Once you do that, finishing the room is rather trivial.
I'm convinced that the best, and arguably the most cost effective way to get the 20-100 Hz range right is not by using room treatments but by using multiple subs. Look on the forum for discussions regarding the Audiokinesis Swarm system.
The best, and certainly the most effective way to get the 100- 300 Hz region right is through optimal placement of speakers and main listening position. This is not trivial, but it is free, and you will never treat a room at any cost enough to overcome suboptimal placement of speakers and listening position. You can find guidance on how to do this online. However I found that a not so well known technique, which is to locate the main speakers 20% of the room width from the side walls, 20% of the room length away from the front wall, and finally positioning the listening position 20% of the room depth distance away from the rear wall works best. I found this to be optimal in my room via a laborious process using REW measurement. My experimentally optimized positioning ended up within inches of the predicted optimal positions calculated based on the 20% rule.
After doing these things, you will find adding commercial absorption and diffusion will readily address the remaining issues, e.g., slap echo, comb filtering, first reflection points, balanced direct vs reflected sound, and what ever low frequency ringing may remain.
Read and understand the information on the RealTraps and GIK websites. If you are technically inclined, install and use REW measurement to provide guidance. There is a learning curve, but most people are quite capable of catching on to how to use it profitably. Optimizing a room without measuring is like trying to find a diamond ring that is lost in a dark room. Adding REW measurement is like turning on the lights. It will still take some work to get the room right, but it becomes possible for most of us to pull it off. Good luck!
