I had an old school kicker cvr 15" in a 4.0 cuft enclosure in my car, it was tuned in the high 30's. it hit hard & near low. if you want to go low enough to listen those jeezy's etc I suggest you try the lower 30's. be aware that there are some rap songs that stretch as far as in the 20's (jeezy's "white girl" & "put on") so to avoid damage to your subs set your subsonic filters to about a 3-5 hz below your enclosure tuning frequency.