Is 70W enough for a car subwoofer?

70W max is a peak rating, so expect modest continuous power. It suits a small box or a factory replacement driven by a head unit or a small amp, not a high-output system.

Fitment is universal only if the cutout diameter and mounting depth match your location. Measure the opening and the space behind it before buying, and use a custom box if the door or shelf is too shallow.

Do I need an amplifier?

Yes for real bass output. A head unit alone will move it but won't deliver much low end. A small dedicated amp rated near its continuous handling is the sensible match.

What box works best with an 8-inch sub?

A small sealed box gives tighter, more controlled bass; a ported box tuned low gives more output but needs more space. Either way, match the box volume to the driver rather than guessing.

One subwoofer speaker in the size you select. No enclosure, grille, screws or wiring are included, so plan for those separately.

Paper cone or poly cone?

This uses a treated paper cone with a butyl rubber surround. Paper is light and efficient for the money; polypropylene cones resist moisture better but often cost more.