Based on 1st hand experience with cultus cng:
A friend of mine is using Pioneer PRS sub in a 1 cuft sealed enclosure, bass is superb, tight, very detailed, does go adequately deep; but it aint that loud. since sealed enclosures are not that efficient.
In order to achieve loudness he is searching for 2 x 10s in a ported enclosure, around 35hz. In his car the enclousre for 2 x 10s can fit between cylinder n the rear seat.
We av also experimented with a sony 10inch sub sealed aswell.
But the SQ of the PRS was superb.