How do you know what room treatments to use?

Someone not knowing that about acoustic dont know really his own audio system ....

i know mine.....

My point exactly. Unfortunately involves a lot of hard work. Much easier to buy something, push a button, pay for a readout, trust authority (who really these days can still trust authority???!?!? and yet they do!). Not realizing that as hard as it is to understand room acoustics its even more work to understand microphones and measurements.

There was a whole long thread recently where the difficulty and complexity of measuring something as seemingly simple as output level is way harder than anyone thinks. Yet they turn around and think they can push a button and a readout will tell them how to treat their whole room.

Oh well. At least a few of us get it.

This is one of those things where once you’ve done it, seen and heard, its easy - but until then it takes forever to explain. Owens Corning 703 acoustic panel is sold in a lot of hardware stores. A couple of the 1" thick sheets 2x3ft will be dirt cheap. This is almost exactly whats inside expensive GIK, they wrap in nice fabric with a frame and add a couple zeroes to the price.

Try the raw sheets in different locations in your room. Side walls at first reflection and ceiling corners are great places to try. With full sheets the effect will be obvious, and probably too much, which is why you experiment. Its very light weight, can be held temporarily with pins, just great stuff.

Your experiments with the raw sheets might look something like this. https://www.theanalogdept.com/c_miller.htm

Then when you figure it out you can cut them the size you want and cover with fabric and be done. It might look something like this. https://systems.audiogon.com/systems/8367

Or you might find your problem is something else. Or you might decide to go with GIK. Either way you will learn a lot and have a whole lot better idea what is going on than to just buy GIK on pure faith.

You should also strongly consider Synergistic Research HFT. These go way beyond any conventional panel type treatments and will get you 3D clarity no amount of acoustic panels can touch.