i'm eternally surprised anew at just HOW MUCH bass trapping is necessary to "catch all the bad waves" in a typical room that wasn't purpose-built as a recording space.
For DIY acoustics in a small room, by the time you install enough 703 it's usualy overdamped in the high end. I much prefer Themafiber SAFB for general use. It's less dense and about half the price.
Three possible DIY-friendly strategies that can help (bearing in mind that I am NOT an acoustician):
If you're covering the walls in 703, then wood 1-by slats in front of 703 (a la Power Station/Avatar and many other places, including ours) can bring a lot of life back to the high end, and the acoustic live/dead character is controlled by the spacing of the slats.
If you're making localized bass traps instead, and if you have the space, make the traps deep instead of broad... in other words, rather than just hanging 2" thick panels all over the walls (making the walls "soft"), if you can build corner traps that are reasonably deep, or create soffits or dedicate some space to frame very thick traps (single layer of 703 with fluffy behind, a couple of feet deep) you can get some bass trapping without just making everything soft.
If there's not the space, tools, or inclination to do anything but just hang 2' x 4' 703 panels on the walls, then facing the 703 in kraft paper or another semi-hard (but thin) surface can reflect a little it of high end back but be "invisible" to the low end.
Obviously, no DIY strategy is going to be as effective as a well-designed room by a trained acoustician. And I'm not one of those-- just a guy who has built a couple of rooms of various sizes-- so take the above with a grain of salt.