When you get into thicker traps (6-8" +) fluffier is better; for thinner panels the denser material.
But sometimes you have to go with what you can get (availability and cost).
An air-gap behind the trap equal to the thickness of it helps a lot, if you have the room. Ie. 2"+2", 4"+4" etc. Drops the effective range about an octave.
Remember that a ("normal") room has 12 corners, placing traps in as many as you can helps tremendously.
So called
superchunks in the corners made with the fluffier stuff is a very efficient and relatively easy to do.
Cut the material in triangles, stack 'em high, cover with a cloth (preferably nothing shiny/reflective) and you're good to go.
If the material is fluffy enough, it will compress so making shelves every meter or so helps to keep everything in place.
The ceiling above your mix position is a crucial point as well, a 4" panel with a 4" gap works a treat.
Make it large enough or with several panels to cover enough are so that the speakers are "inside".
The ol' mirror-trick is useful when deciding where to place panels, especially on the sides and the ceiling.
While sitting in the mix position, have a friend move a mirror on the walls and everywhere you see the tweeter from either monitor is where a panel should go.
Front wall symmetry is important, so make sure that your monitors are equidistant from the side and front wall(s).
Getting your monitors as close to the front wall as possible is "best" (debatable, let's not go there..).
Placing a panel behind them works to treat the front wall bounce that's causing cancellation(s) to the monitor response.
The closer you get to a boundary, the higher up the dip goes in frequency and therefore easier to treat with thinner panels.
(Note: there's been a huge debate over this @ GS..
)
However, it seems that the back wall is the most crucial in getting a decent low-freq response in a room so lots of trapping behind the mix position, as thick as you can.
If your room is large enough (most "normal" rooms aren't) you could place diffusors in front of these traps.
Same goes for the possible traps in the corners on the front wall and everywhere else that will not reflect back to the mix position.
Something reflective there will not harm the listening position response but will keep the room from getting too dead.
I've read about using FRK, thin plastic, even cardboard in front of the traps.
If you want to measure your room, Room EQ Wizard (REW) over at
www.hometheatershack.com (you need to register first..) comes highly recommended. It's free!
The important stuff to look at are the waterfall and ETC (envelope/energy time curve).
These may or may not help in what you're trying to achieve, since if we're not trying to make a "professional" studio, the answer will still be.. more traps!
Phew! I know this seems like a lot, but take as much from it as you want / can and apply to your situation.
Doing at least
some acoustic treatment is better than nothing.
Lots of great info @ GS, so don't dismiss it out of hand.
http://www.gearslutz.com/board/stud...tics-treatment-reference-guide-look-here.html
http://www.gearslutz.com/board/stud...basic-acoustic-measurement-primer-v2-1-a.html
