Best subwoofers under $100

Top pick: TROPO BIO-12 — a 12-inch dual-voice-coil sub that works sealed or ported, so it's the most flexible of the bunch and the one most likely to give you real low-end thump in a car. Rated 4.8 from 47 ratings.

Who the others suit:

• TROPO BIO-10 — same family, smaller footprint; pick it if trunk space is tight.
• TROPO-8 / BIO-8 — 8-inch options for tight installs or modest amps; the BIO-8 is the budget-minded one.
• HYDRO-8 shallow-mount — for doors or under-seat spots where depth is the problem.
• Audiopipe TXX-BDC1-12 — if you have a beefy amp and want the most power handling here.
• Rockville VS8K52 — comes already in a vented box, so no enclosure build.
• PYLE PLPW8D — cheapest way to add bass; expect modest sound.

All are passive car subs, so you'll need an amp and an enclosure (unless noted).