Studio Acoustic Tiles/Panels for listening room?

Atzen811,
I use sonex tiles throughout my listening room (a 4ft tall strip that runs the circumference of the room, centered at tweeter level). I have a dedicated room however, and I can see why this would not be practical in a family room. I use it to iliminate slap echo in the high frequencies that can translate into image blur.

One problem with using too much of this material (i.e. 2", 3", 4" thick) is that it is not linear through the audio range. It attenuates less and less as you go down in frequency. Therefore, if you cover the whole room, you will have an unbalanced sound. Now, if you could have an ideal room with professional quality absorbers (very thick) that responded linearly down to a very low frequency, you wouldn't have to worry about this as much. Keep in mind that this is all theory, I've never experimented with this. But, as a general rule, the thicker the absorber material, the lower the frequency it can absorb.

Found even a little sonex or acoustic tile does something bad to the sound, maybe changes the phase, who knows...