A 4-channel amp is the easiest way to wake up your door speakers. It can run four speakers, or two speakers and a sub off the same amp. Here is how we wire a 4-channel amp in the bay, from the power wire to the last crossover setting.
- Pick a layout
- What you need
- 1. Mount it
- 2. Power and ground
- 3. Inputs
- 4. Speaker wires
- 5. Bridge a sub
- 6. Crossovers
- 7. Gains
- Mistakes
Four Speakers or Two Plus a Sub
Most people wire a 4-channel one of two ways. The first is the classic: front left, front right, rear left and rear right, each on its own channel. The second drops the rear speakers and bridges channels 3 and 4 into one sub.
Both work. Pick the one that matches the speakers you actually have before you run a single wire.
What You Need
An amp install kit covers the power wire, ground, fuse, remote wire and RCAs. Most 4-channel amps are happy on an 8 AWG kit. Bigger amps over about 1000 watts RMS total want 4 AWG.
- Install kitPower, ground, fuse and remote.
- RCA cablesFour channels, or two with a Y.
- Speaker wire16 AWG for door speakers.
- Crimp toolsStrippers, crimper, ring terminals.
- MultimeterFor voltage and gain setting.
- Your amp manualBridge terminals and ohm rules.
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Step 1 Plan and Mount the Amp
Pick a spot with airflow, like under a seat or on the back of the rear seat. Amps make heat, so keep them off carpet padding and out of tight cubbies. Mount it to something solid so it can't slide around.
Before you screw it down, make sure you can still reach the gain knobs and crossover switches.
Step 2 Run Power and Ground
Power, ground and remote wiring is the same for every amp. Fuse the power wire within 18 inches of the battery, ground the amp to bare metal with a short wire and run the remote wire from the radio's blue/white lead. We walk through every step in our guide on how to install a car amplifier. Not sure your charging system can keep up? Run your numbers through Power Planner.
Step 3 Connect the Inputs
How you feed the amp depends on your radio. Aftermarket radios with front and rear outputs get four RCAs, which keeps your fader working. If your radio only has one pair of outputs, run two RCAs and flip the amp's input switch to 2CH.
Factory radio? Use the amp's speaker-level inputs if it has them, or add a line output converter. Here is how to install one.
Run your RCAs down the opposite side of the car from the power wire. Power wire next to RCAs is the number one cause of alternator whine we fix.
Step 4 Wire the Speakers
Each channel gets its own positive and negative to one speaker. Channel 1 to front left, channel 2 to front right, channel 3 to rear left, channel 4 to rear right. Keep positive to positive on every one. A speaker wired backwards fights the others and kills your midbass. Not sure which factory wire is which? Here is how to find speaker wire polarity.
Step 5 Bridge Channels 3 and 4 to a Sub
Bridging joins two channels into one stronger channel. On most amps you use channel 3 positive and channel 4 negative, but check the label next to the terminals. Some amps mark the bridge points right on the case.
Watch the load. Most 4-channels want 4 Ω or more when bridged. Go lower and the amp runs hot or goes into protect.
Want the full picture on bridging and strapping? Read our guide to bridging amplifiers.
Step 6 Set the Crossovers
Set the front and rear channels to HPF, or high pass, around 80 Hz. That stops deep bass from reaching small speakers so they play louder and cleaner. If channels 3 and 4 are bridged to a sub, set them to LPF, or low pass, around 80 Hz.
Every car is different, so treat these as starting points and fine tune by ear. Our crossover chart by speaker size has more.
Step 7 Set the Gains
Gain is not a volume knob. It matches the amp to your radio's output so you get clean power without clipping. Turn all gains down, set the radio to about three quarters volume and bring each pair up until it starts to distort, then back off. For the most accurate result, use a multimeter. We show every method in how to set amplifier gain correctly.
Common Mistakes We See
- Power wire and RCAs on the same side
- No fuse near the battery
- One speaker out of polarity
- Bridging below the amp's rated load
- Full range bass to small door speakers
- Using gain as a volume knob
Gear Up for Your 4-Channel Install
Everything in this guide is in stock and ready to ship.
Still picking an amp? Our guide to amplifier classes explains which type runs cooler and why. Adding a bigger sub later? Here is how to wire subwoofers. Upgrading speakers too? Read how to install car speakers.
