I have a 98 cherokee with pretty nice infinity door and rear roof speakers. With an after market Alpine deck. The highs are quite impressive but the mids and zero lows are disappointing. I put in the Alpine Power Pack today 45x4. Figured I would notice a difference in the bass output. I notice a little bit but not what I was expecting, but the highs are even better. I would really like to get more bass without bigger speakers, would I get much more bass if I built a box for my rear speakers?