Well I originally contacted cj about lvl 4's and he told me to wait because the m2's were being released a couple wks later (this was like 4 months ago) after talking to him he recommended the lvl 3's with all the upgrades...dont know why, just took the guys word for it...so far they've been great, best sounding setup that trucks ever had...everything set with dd-1 and infrasonic and crossover set with cc-1. I ended up using one 3" pvc port per chamber, tuned to 34hz and it sounds damn good with no noticable port noise, Im very happy with it!! DC ftw!!!