Which subwoofer for alpine m450

I recently replaced my rear deck subs and placed in 2 free air subs. I installed a Alpine MRP-M450 Mono subwoofer amplifier, 220 watts RMS x 1 at 4 ohms (400 watts RMS x 1 at 2 ohms) in parallel. However the amp way outperforms the free air subs. I was looking to replace these subs with a single sub in a box so i dont give up to much space in my trunk, but still performs great. I was just looking for any suggestions on which sub and/or box will match my mp and give top performance.



Thanks
Rks319

you have to use subs that are designed for free-air if you are running them that way. I would look for a sub that needs 300-400 watts RMS and provides a 2 ohm load to maximize your amps potential.