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You don’t need to replace your car’s factory stereo to add a subwoofer. Most factory head units have no subwoofer (RCA) output, but there are reliable ways around that. Here’s how it works and what you’ll need.
Choose a powered subwoofer with speaker-level (high-level) inputs, like the Kicker Hideaway HS10 or Rockford Fosgate P300-12. Tap its inputs into your rear speaker wires, connect power and ground, and you’re done.
Your three options
1. Powered sub with speaker-level inputs (easiest)
All-in-one powered subs often accept the speaker-wire signal directly, and many sense that signal to turn themselves on, so you may not even need a remote turn-on wire. See under-seat powered subs.
2. Amplifier with high-level inputs
Many mono amplifiers accept speaker-level inputs, so you can pair a component sub and box with an amp without extra converters. See best car subwoofers.
3. Line output converter (LOC)
A small box that converts speaker-level signals to RCA for amplifiers without high-level inputs. Better LOCs include a remote turn-on output and signal summing (useful for factory systems that filter bass out of some speakers).
What you’ll need
- The sub (and amp/box if not all-in-one).
- An amp wiring kit: power cable sized to the amp’s current draw, fuse holder, ground cable and remote wire.
- Posi-taps or solder connections for speaker-level inputs.
- Basic tools and, ideally, a multimeter.
Step by step (overview)
- Disconnect the battery.
- Run the power cable from the battery through a grommet in the firewall, with a fuse within about 18 inches of the battery.
- Ground the amp or powered sub to bare chassis metal close to where it’s mounted, with a short cable.
- Tap the rear speaker wires (or the outputs behind the head unit) for the speaker-level signal. Check polarity with a wiring diagram for your vehicle.
- Connect the remote turn-on, or use the unit’s signal-sensing auto-on.
- Reconnect the battery, set gains carefully with the head unit at about three-quarters volume, and listen for distortion. See clipping.
Watch out for
- Premium factory systems (Bose, Harman Kardon, etc.) may use their own amps and filtered outputs; tap after the factory amp or use a DSP-equipped LOC.
- Bass that drops at high volume: some factory head units reduce bass as volume rises; a LOC with bass restoration can help.
- Warranty and safety: if you’re not comfortable with car electrics, use a professional installer.