10" or 12" subwoofer in cargo area - sealed box behind rear seats, under-seat amp + powered sub, or under-floor sub box. JL Audio Stealthbox is XJ-specific premium option.
Sub options for XJ:
(1) JL Audio Stealthbox: XJ-specific (1997-2001) molded fiberglass enclosure that bolts in the driver's rear quarter panel using factory cargo trim mounts. Includes a 10" or 12" JL sub. Most discreet install, around $700.
(2) Powered sub-in-a-box (Rockford Fosgate P300-10, Kicker PT250, JBL BassPro Micro): self-contained amp+sub box that sits in cargo area or under rear seat. $250-500. Bolt-on install — power + ground + line in. Limited bass output but plenty for most.
(3) Custom sealed box + external amp: 10" or 12" sub (JL Audio 10W3v3, Rockford Fosgate P3D2-10) in a ~1 cubic foot sealed enclosure mounted behind the rear seats. Powered by a mono amp (JL JX500.1D, Rockford Punch P500X1bd). Best sound, ~$500-800 total but loses cargo space.
(4) Under-floor: behind cargo trim panels along inner fender. Tight, requires custom fab.
Wiring: feed sub amp with 4 AWG from battery (8 AWG for <250W subs). Use a Knu Konceptz or Stinger amp kit ($60-100) that includes fuse, cable, RCA, and remote turn-on wire. Run RCA away from power wire to avoid alternator whine.
Setting LPF (low-pass) at 80 Hz, sub gain matched to head unit output by ear, phase 0 unless box is rear-facing (then 180).
| Part | Vendor | Est. price |
|---|---|---|
| JL Audio Stealthbox XJ | JL Audio | ~$700 |
| Rockford Fosgate P300-10 powered sub | Rockford Fosgate | ~$350 |
| Stinger 4 AWG amp wiring kit | Stinger | ~$80 |
Written and maintained by an AZ wheeler and driveway wrencher. Always cross-reference your factory service manual — modifications affect vehicle safety and warranty. Work at your own risk.