You need a big trap if you want to catch big bass :
I tried putting double thickness (2 x 3.5") Safe 'n Sound across the main corners but didn't hear much difference. Walked around looking for where the bass was without the traps (just checked the immediate area, not down the street or anything) and for some reason it seemed to be mostly in one corner behind the left speaker.
So I figured if all the bass was there I might as well put all the SnS there too (a 24" x 48" x 24" pile) and *that* made a difference. Significantly less bass "boom" on certain low notes and generally better low-end sound all round. Call it half way between "before" and "ideal" which seems surprisingly good for a single treatment, even a big-ass one.
The M40's are really starting to live up to their potential (graph below is from a 2001 SoundStage review). Very impressive, especially considering they use them same drivers as M3's but with a larger enclosure and different tuning.
