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Lead image

How to bridge a car amplifier

Maximizing your amp's bang for the buck

Most car amplifiers have a feature called "bridging" or "bridge mode," where two channels are combined to produce one channel with maximum output power. In this article, I'll describe two different scenarios where installing a bridged amplifier is useful and appropriate.

Using a bridged 2-channel amplifier to power a subwoofer

A subwoofer added to a factory stereo system doesn't need a huge amount of power in order for the bass to keep its level up with the rest of the music. Let's say you're looking to power a 200 watts RMS rated 4-ohm sub, without gutting your bank account with an expensive mono subwoofer amplifier. You could get a small 2-channel amp that normally puts out two channels of 60 watts RMS, and bridge it, so it could produce an output of 190 watts RMS, which would be perfect for driving the sub.

Please note: Most amplifiers, when bridged, cannot drive a speaker or sub with an impedance less than 4 ohms. Some amps are unbridgeable. Each amp is different. In order to safely and successfully bridge your amplifier, you must follow the instructions given in its owner's manual.

Components matched, time to wire

We've picked an amplifier that can put out the right amount of power through the right impedance load (4 ohms or more), and has speaker-level inputs, so it'll work with the factory system. Successful bridging depends on there being signal in both the right and left channels of the amp.

You tap into the rear left and right factory speaker wiring, and run speaker wires to a speaker-level input plug that comes with the amp. For output, connect the amp's right negative output terminal to the sub's negative terminal, and the amp's left positive terminal to the sub's positive terminal.

2-channel diagram

Similarities and differences

When installing a car amplifier, you need to install power, ground, and remote turn-on wires. The onboard gain and tone controls function the same as in unbridged mode, and need to be adjusted properly. You should note that in this bridging scenario, the amp's left positive and right negative terminals are used for the output. A different amp may use the left negative and the right positive outputs instead.

Using a bridged 4-channel amplifier to power a pair of component speakers

Another common amp-bridging scenario is to power a pair of high-performance component speakers for the front only and we're using an aftermarket receiver. You can run rear speakers off of the stereo's power, and to keep our example simple, there's no subwoofer.

You can get a 4-channel amplifier that normally puts out a mere 30 watts RMS per channel, but can deliver two channels of 125 watts RMS when bridged.

4-channel diagram

Four channels in, two channels out

You run a dual RCA cable from the receiver's front left and right RCA outputs. Then at the amp end of the cable, you attach a Y-adapter to each RCA connector, so you end up with four RCA connectors to plug into the amp's four RCA inputs.

For the outputs, connect the amp's front right negative output terminal to the left speaker's negative terminal, and the amp's front left positive terminal to the left speaker's positive terminal (well, these connection are made to the crossover box, actually). The same connection scheme applies for the rear amp channels going to the right speaker.

For convenience, we refer to the pairs of channels in a 4-channel amp as the front pair and the rear pair. As we see, in this set-up the roles of the channel pairs have been changed from powering front and rear speakers to powering a left and a right speaker.

How does bridging work?

Where does all this extra power come from? Using the negative signal of one channel with the positive signal of the other channel effectively doubles what each channel alone could put out through a 2-ohm load. Usually, this is the maximum wattage the amp can put out. So, when you bridge your amplifier, you're also optimizing your system's power potential. And that's good.

Diagram showing that bridging the amp gives you more power.

Looking for gear?

I used real subwoofers, speakers, and amplifiers in the above examples of bridging. That is, I used the specifications of the different components to plan out how they'd connect together and perform. I perused Crutchfield's extensive selection of car amplifiers, subwoofers, and component speakers to find suitable examples that would clearly illustrate bridging.

You can do the same on our site to shop for your bridgeable amplifier, or you could click on the chat icon at the top of the page for more personalized online information about a selection. Better yet, give us a toll-free call at 1-888-955-6000 and talk to a knowledgeable Advisor about which system configuration will work best for you.

  • Marin from London

    Posted on 9/30/2021

    If i have a 6 channel amp (Helix A6 Competition), can i bridge only 2 channels (C+D) for a sub, and use the other 4 channels normally?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 10/1/2021

    Marin, According to the specs I can find, yes.
  • Lachlan Dawes from Brisbane, QLD, AU

    Posted on 9/4/2021

    Hi, my question is in regards to setting gain on a front speaker pair in a bridging scenario. How can I best ensure both speakers are outputting the same, now that the gain for each is separated across two channels instead of just the one?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 9/7/2021

    Lachlan, First of all, you set each channel's gain individually so that no distortion plays out the speakers at maximum volume. Then, there are a few way to "ensure both speakers are outputting the same." You could play noise and use an SPL meter to measure the sound at each speaker and adjust the amp gains to read the same volume. But you probably want things to sound equal where you sit in your car, which isn't in the center. So you'd be better off using an RTA and microphone set up at your listening position to get it sounding the way you want. For simplicity, I recommend just playing familiar music and using your ears.
  • David Long from Charlotte

    Posted on 9/3/2021

    I'm kinda lost on how my amps should be wired. I'm trying to run my Pioneer Z series speakers on x2 4 channel Kicker 360.4 amps in bridged mode mono. I have decided to run actually high quality shielded speaker wire to rear trunk from the head unit and these reach a terminal block then I have to convert the speaker wire to RCA cause kicker only has RCA for both high and low level signal. I guess my question is how do I arrange my RCA input signals, and which speakers should go to each amp. I would like to retain my fader controls if possible, balance I don't care but keeping stereo is key for me even if it's gotta be wired a certain way. Kicker makes no note of bridge mono mode use and what RCA inputs to use however I'm using the high level signal wires to power up the amps, and I noticed that only RCA 1 powers the amp up, I'm still playing around with the inputs but do I need all 4 RCA inputs to be used on both amps and use a Y Splitter? If If only need 1 input Can I combine my speaker wire at my screw type terminal block and basically create my own Y splitter and have my L/R going into 1 RCA I guess this only would work if the amp routes input to all channels tho. and I don't need multiple RCA inputs Anyways I'm stuck on RCA inputs trying to save myself time and see what the proper wiring is. Thanks.

    Commenter image

    Buck Pomerantz from Crutchfield

    on 9/3/2021

    David, Not knowing what vehicle you have makes it impossible to know how to connect an amp to its factory radio. If that's what you intend. Using shielded speaker wires connected to a terminal block connected to RCA adapters will be a lot noisier than using cables and adapters without the block. Kicker, actually, is very clear on how to bridge this amplifier - using the inputs of all four channels to create two high-powered outputs. However, that amp's bridged output power, 180 watts RMS per channel, is enough to damage those 110 watts RMS rated speakers, so I wouldn't recommend using one for your application.
  • Steven Quelch from ???? uk

    Posted on 8/4/2021

    Hi I have a Rockford fosgate p325.2 amp apparently 4ohm wen bridged but if I don't bridge does that mean 1 channel is 2ohm. I have prime R1 -12"x2 loaded subs from Rockford fosgate which is 2ohm. I have already blown a 15" punch sub so bought 2x12" prime I hope u can help me thank you regards Stev ps hope I make sense

    Commenter image

    Buck Pomerantz from Crutchfield

    on 8/4/2021

    Steven, I can see no way for that amp and sub to work together very well at all. The best that amp can do is drive the 2-ohm sub from one channel with up to 160 watts RMS. Most 2-channel amps can't drive loads lower than 4 ohms when bridged, and don't have enough power to drive 2 subwoofers. I recommend getting a new mono, 1-channel amp, designed to work with a wider range of impedances, and have tone controls and filters specifically made to help reproduce bass.
  • Lex Las from CoCo County, CA

    Posted on 7/19/2021

    I actually remember doing this when i was 16, i am now 46. I drove a classic 1969 Skylark, and the battery and alternator were definitely not strong enough. I grabbed one positive, and a negative from each speaker wire output from the rear. I did this because adding a AMP would have drained my battery so much that it was a risk. So i added it just so i can have some bass instead of none. Although i don't remember if that did any damage to the car stereo, due to so much power being output as the volume went high. It might have blown out the fuse. I might have added a higher number fuse and used it anyway. Would this damage today's car stereo's ? Just like anything these days, i find most things are weaker. Thanks for your time.

    Commenter image

    Buck Pomerantz from Crutchfield

    on 7/20/2021

    Lex, Changing out a blown fuse with one of a higher rating is an extremely dangerous practice. The fuse is there to protect the power wire (and your vehicle and your life) from burning up in the event of a short circuit. If you put in a fuse larger than required, when there's a short, the wire might burn through before the fuse blows. We recommend using an amplifier wiring kit, containing the proper-sized wires and fuse, when installing an amp.
  • Mike from WARREN

    Posted on 7/4/2021

    I have a skar 2000 rp I'd...can it be bridged?also have 2 12 inch skar evls.. it's slamming now..but was just curious..thx

    Commenter image

    Buck Pomerantz from Crutchfield

    on 7/6/2021

    Mike, Bridging combines the power of two adjacent amplifier channels together into one output. A mono, 1-channel amp like yours can't be bridged.
  • Ross Boardman from Melbourne Australia

    Posted on 7/1/2021

    Thanks, very clear explanation given with diagrams and plain language. Makes this easy to understand and apply. Information given with no expectation of a sale. Refreshing to find such helpful people.

  • Danny from Nederland

    Posted on 6/23/2021

    I Have a jl xv10005v2 with 2 front speakers and 2 rear speakers if I bridge this amp do I loss 2 speakers by doing this?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 6/24/2021

    Danny, Most people bridge front and rear channels in order to drive two high-performance speakers. You can run four speakers from two channels by wiring pairs of speakers together in parallel.
  • Phil from Salt Lake City, UT

    Posted on 6/12/2021

    Does bridging 2 channels sum the input of both channels? i.e. if you have 2 inputs, left and right, and you bridge the output, do you get both the left and right channels? My specific use case is in a 2017 Tundra with a center channel dash speaker. Stock center is a dual voice coil running parallel with the left and right dash speakers. The left connects to one voice coil, the right connects to the other, so the speaker is outputting both channels simultaneously. With an AudioControl D-6.1200, could I take a left and right input and use a bridged output to get both channels going to the single center dash speaker?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 6/15/2021

    Phil, Bridging an amp's channels combines the two inputs into one signal, so instead of two amp channels each running a voice coil of a dual voice coil center channel speaker, you can have a single amp running an aftermarket single voice coil center channel speaker.
  • Stephen Butler from Summerville

    Posted on 5/28/2021

    I have (2) 4ohm DS18 Pro 6.5 Mid Speakers rated at 250 watts rms each one in each door of a mustang. There is also a Tweeter in each door rated at 200 Watts RMS. They are being powered off a Skar RP 150.4 which is rated at 250RMS x4 at 2ohm 150RMS x 4 at 4ohm 500 RMS x 2 at 4ohm Bridged. Currently the amp is set up with each speaker to assigned channel, so 150 watts RMS each, but it appears that I could bridge 2 channels to get 500RMS and use that channel to power the 6.5 mids, increasing the power to 250RMS for those speakers, is that correct?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 6/1/2021

    Stephen, Two 4-ohm speakers can only get wired together to form a 2-ohm or an 8-ohm load. The bridged amp channels cannot safely drive a 2-ohm load and will send each speaker 150 watts RMS in an 8-ohm setup. You won't gain any power simply by bridging the amp.