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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.

  • Glenn from Phoenix

    Posted on 5/2/2021

    How would you or can you wire two 4 ohm SVC's and one 4 ohm DVC to a two -channel amp?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 5/3/2021

    Glenn, That would depend on the amp and subs' RMS power ratings. One of the problems using a 2-channel amp is that there is only one gain control for both channels and unless the loads and sensitivities are the same, it won't be able power both subs very well.
  • Greg Christman from Edinburg

    Posted on 4/21/2021

    I did the bridge thing. Now I have a kenwood 1000 watt mono amp. This the best way to go.

  • Daniel from Sweden

    Posted on 4/19/2021

    Hi Planning to bridge a brand new Alpine X-A90 into 2ch. Is there any sonical drawbacks from bridgin. THD and noise for example, will it increase?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 4/19/2021

    Daniel, Each amp channel uses the same circuitry, so I doubt there would be any degradation in sound when bridging.
  • Jay from Jacksonville

    Posted on 4/18/2021

    Hi, I have a 2019 Honda Accord Hybrid touring, with a 450 Watts 10 speakers factory set up. I'm looking to add a 6 channel amp ( AudioControl LC-6.1200 6-channel car class D amplifier - 125 watts RMS x 6 ), and replace the 3 speakers on the rear deck, left side mid range, middle factory sub, and right side mid range. The speakers I intend to replace them with are two Eminence KAPPA PRO-10A mid range, left and right mid range, and a 8" JL Audio 8W1v3-4 middle sub. (Separately, I will be adding a ACP208LG-W3v3 Dual 8W3v3 MicroSub+T with DCDT Amplifier, Ported, 0.20 O , as an independent subwoofer in the trunk). Two questions; In regards to bridging, the 6 channel amp is at a 8 ohm which is fine for my two Eminence PRO-10A mids rated at 8 ohm, but the 8" JL Sub is rated at 4 ohm. Will this 6 channel amp still work efficiently bridged to 3 channels powering 2 voice speakers rated at 8 ohm and 1 sub speaker rated at 4 ohm?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 4/20/2021

    Jay, That amp should work just fine wired the way you describe.
  • Parker Young from Chicago

    Posted on 3/15/2021

    I have an Sony head unit with four RCA plugs, 2 sets, and want to add a 5 channel amp so I can also add a sub to my four speaker currently in use. Would I Just need to use a Y adapter for the set of RCA plugs labeled "rear/sub" so I could run two sets of RCAs to the to corresponding plugs on the amp?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 3/31/2021

    Parker, Some 5-channel amps have a switch that can route the signals from the front and rear channels to the sub channel. Otherwise, use Y-cords to create the left/right sub inputs from another pair of cables, front or rear.
  • Ryan Byington from Tulsa

    Posted on 2/25/2021

    Hello I'm looking to redo the speakers and wiring in my truck along with adding an amp. The speakers I found are 4 ohm (6.5 and 6x9) and the amp is a 4 channel 2 ohm. I am needing some help on the wire set up. Thank you for your assistance

    Commenter image

    Buck Pomerantz from Crutchfield

    on 3/25/2021

    Ryan, What that spec means is that the amp is capable of driving 2-ohm loads. It'll work fine with 4-ohm speakers. Give us a call, so an Advisor can help you pick the perfect gear for your system.
  • Christian from Reno NV from Reno

    Posted on 1/26/2021

    So I have an amp that puts out 500W at 4ohm in bridge mode. I hooked a 4ohm 12"kenwood to it. Would my final load impedance be 4ohms? Or 2? **The sub is a single voice coil**

    Commenter image

    Buck Pomerantz from Crutchfield

    on 1/27/2021

    Christian, A single voice coil (SVC) 4-ohm sub will present a 4-ohm final impedance load to an amp.
  • Gordon from Rowland

    Posted on 1/19/2021

    I got a better understanding of what bridge mode is and how much more power your amp can output.

  • Tang

    Posted on 1/18/2021

    Hi, I have an Alpine MRP-F300 4 channel, currenlty powering a pair of components in the front doors and bridged to the rear. I am planning to use all 4 channels on the Alpine to power the components and then add a monoblock amp for the sub. Does the bridging function operate due to the wiring as per the diagram, or does the amp need to be specified for channels to be bridged?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 1/19/2021

    Tang, Different amps are bridged different ways. Most are done via wiring, but some employ switches.
  • Mark jones from Chesapeake

    Posted on 1/8/2021

    consider revising The " Four channels in, two channels out" diagram to replace the + and - on the amp with Front and Right , for both left and right RCA inputs so it will be obvious to beginners what the Y adapters are for. This appears to be what Jamie 10-25-2020 was asking about.

  • Kevin from Pittsburgh

    Posted on 12/10/2020

    Hey guys, I bought a set of JBL (3 ohm, 50RMS) concert series front door and tweeter speakers and rear JBL (3 ohm, 40RMS) from you guys. I installed a Pioneer GM-A4704 520W 4 channel amplifier. The sound is definitely improved from stock but I was looking to maybe add a 8 or 10 inch sub for a bit more low end. Can I bridge the rear speakers on the amp to make room to wire the sub in? And if so which sub would you recommend? I am also running the stock stereo on my 04 Saturn Ion Redline. Also Bridging is not stacking correct, meaning you can't wire the pair of rear speakers to the same pos/neg terminal lugs right?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 12/14/2020

    Kevin, First of all, adjacent amplifier channels can get bridged together. What you're describing is wiring two speakers together in parallel, and yes, normally you could do that, but not in your case. Two 3-ohm speakers wired in parallel create a 1.5-ohm load, which your amp can't handle. It sounds like you just need to add an amp along with a sub. Give us a call so an Advisor can help you get the setup you want.
  • greg

    Posted on 11/15/2020

    From my previous question, I'm only running 2 speakers. Experimenting with some extra equipment, to get more power out of a 4 channel amp, but retain stereo sound. Doing this I have all left side inputs to channel A, which I bridged to the left speaker. All right inputs to channel B, which I bridged to the right speaker. I got a big bump in output, and still have full stereo sound.

  • greg

    Posted on 11/5/2020

    I want to bridge a 4 channel amp to keep Stereo sound. I run the front left and rear left from the HU to the front inputs on the amp, and run front right and rear right to the rear inputs on the amp. I then bridge the front outputs to the left front speaker, and the rear outputs to the right front, I should keep stereo separation?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 11/9/2020

    Greg, Whatever it is you're attempting sounds very very wrong. If you want to power four speakers, connect each to one channel of the 4-channel amp. No bridging necessary, or even possible.
  • Jonathan Torres from Metaire

    Posted on 11/1/2020

    Hi I'm trying to understand how to bridge my jl audio hd600/4 amp.I'm running a set of component speakers in my front doors and a sub in the back. It says the amp is capable of doing this but I don't understand how to us the rca cables with the y adapter. And I can't find a diagram or my info about this setup for this amp. Jl says To bridge a pair of channels, use the "Left +" and "Right -" speaker connectors only (the "Left -" and "Right +" remain unused). Then connect a mono signal to both left and right RCA inputs for that channel pair. This requires an RCA "Y-Adaptor" (sold separately), because a bridged pair of channels requires that both amplifier channels of the bridged pair receive input. Connection of only one RCA input will result in reduced power output, increased distortion and can cause the amplifier to overheat. can you explain this please? Thanks

    Commenter image

    Buck Pomerantz from Crutchfield

    on 11/2/2020

    Jonathan, The basic explanation is that amplifiers don't like getting connected improperly. In this instance, the amp wants both signals on the bridged channels' inputs to be identical. If you're using the subwoofer outputs of your receiver, you won't need a Y-cord.
  • Jaime from San Ramon,CA

    Posted on 10/26/2020

    Your diagrams are a little confusing. In your 4-channel amp bridging to 2-channel separates diagram shows a left and right rca cable coming from the stereo head unit. Wouldn't a single rca cable have a positive and negative? I'm assuming after the y-split, each rca plug would have both positive and negative. There would be two rca connections per side but in your diagram it shows the amp input as a single positive and a single negative connection. Unless I'm missing something, it's confusing to me.

    Commenter image

    Buck Pomerantz from Crutchfield

    on 10/26/2020

    Jaime, Every single line drawing of a wire actually represents both a positive and negative conductor.
  • pohaku from Hilo

    Posted on 9/30/2020

    Like Charles, I have a truck with only front door speakers. I want to bridge the 4 channels of a JVC KD-T91MBS to the 2 crossovers of a Polk Audio DB 6502 system. Is this feasible, and if so, are there any specific audio settings that I should use on the receiver? Thanks!

    Commenter image

    Buck Pomerantz from Crutchfield

    on 10/2/2020

    Pohaku, There are no bridgeable output channels on that receiver. Check out this link for tuning help.
  • Mark Ossman from Montclair

    Posted on 9/19/2020

    If I bridge a 4 channel amplifier to 2 channels in order to power two component speakers (front channel speakers), does this negatively affect the S/N ratio or sound quality?

  • Thomas cutler from Niagara Falls ny

    Posted on 8/17/2020

    Hello, I recently purchased jl audio marine m770..I have an alpine pdx 400..4 m marine 400 wat 4 channel amp..I want to bridge it to the 2 7.7 jl marine cockpit a crossover (as shown in above diagram) necessary?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 8/18/2020

    Thomas, That speaker's crossover is built-in and is absolutely necessary for safe operation.
  • Kai from Honolulu

    Posted on 8/5/2020

    If I have a 2 channel amp, according to the specs, bridge mode output is 550W rms at 2ohms. If I connect a 4ohm sub in bridge mode, what can I expect the output of the amp be. Since the specs are only showing bridge mode output at 2ohms. Thanks

    Commenter image

    Buck Pomerantz from Crutchfield

    on 8/6/2020

    Kai, Without knowing precisely what amp and sub you're referring to, we can't help you with advice. If you want a question answered about a system, you must identify the gear by brand names and model numbers so we can get the right information to you.
  • David Lemen from Tampa

    Posted on 7/24/2020

    I have a 6 channel amp with three zones. I want to bridge zine 2 and 3 to have more output. I bought two y connectors but am confused how to wire. Do I cut the wires and open the pos and neg up so it can be connected? This is a marine app

    Commenter image

    Buck Pomerantz from Crutchfield

    on 7/29/2020

    Jess, Bridging involves adjacent channels being combined, so I doubt separate zone channels can be bridged together. Without knowing precisely what amp you're referring to, we can't help you with advice. If you want a question answered about a system, you must identify the gear by brand names and model numbers so we can get the right information to you.
  • Charles from Santee, CA

    Posted on 7/20/2020

    I have a truck with only front door speakers. Can I bridge a 4 channel receiver to 2 channels and get more power to the door speakers?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 7/28/2020

    Charles, Yes you can.
  • Travis Russell from Leander

    Posted on 7/5/2020

    Hello, I'm planning my audio system in my old truck, I plan on running a pair of 3.5" Infinity References in the dash off of the head unit that puts out 22w RMS, and a pair of 6.5" Infinity References in the rear powered by an amp, I'd like to run my Kicker TC10 off of the same amp as the 6.5" could I get a 4-channel amp and only bridge half of it to make it a 3-channel amp running the 6.5"s off of 1 & 2 channels and the sub off of 3/4 channels bridged? Or do I need to run either two 2-channel amps (1 for the speakers, 1 bridged for the sub) or a 2-channel for the speakers and a mono for the sub?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 7/6/2020

    Travis, Putting a 4-channel into 3-channel mode is an excellent way to power a sub and two speakers. Make sure the sub is 4-ohms, so the bridged channels can handle it.
  • Randy from San Jose

    Posted on 6/12/2020

    "Four channels in, two channels out" So this would be the way you hook up a 4 channel amp, to a receiver that only has 2 pre amp outputs, to power 4 speakers? Very new to all this. Thank you!

    Commenter image

    Buck Pomerantz from Crutchfield

    on 6/15/2020

    Randy, If your receiver has only a left/right output, you'll need to use two Y-cord adapters to obtain all the inputs for a 4-channel amp. This has nothing to do with bridging.
  • John from Reno NV

    Posted on 4/14/2020

    I have an Alpine MRV-300, 4 channel amp. I have a pickup with only 2 front speakers. The Alpine speaker output is Channels 1, 2, 3, and 4. LEFT and RIGHT are not noted. Reading a previous answer: Brent, When bridging a 4-channel amp to 2-channel mode, you combine the front left and right channels to form one channel, let's call it the left speaker channel. The rear left and right channels are bridged together forming another channel, let's call this one the right speaker channel. Right and left channels playing together is stereo reproduction. It wasn't simply stated but are you saying there is NO LEFT RIGHT any longer when bridged? Therefore there is no stereo output? Left and Right speakers will be carrying identical sounds, stereo is merged into MONO?? Is there anyway this amplifier can be connected and produce stereo??

    Commenter image

    Buck Pomerantz from Crutchfield

    on 4/15/2020

    John, A 4-channel amp bridged into 2-channel mode will not merge the left and right stereo signals to mono.
  • Jeff from Barnhart

    Posted on 4/3/2020

    I have a apline 4 channel amp and a mono amp for 2 10" alpine subs svc @4 ohms each .what would be the best way to wire both amps up to get the most out of them .Ps. I also have a pair of comp.speakers infinity I got from u . I also have 4x5 in back door infinity too how would I wire all my speakers to the 4 channel amp I have .thank you very much

    Commenter image

    Buck Pomerantz from Crutchfield

    on 4/6/2020

    Jeff, If you bought your speakers from Crutchfield, you could call Tech Support for free help wiring your system. Their toll-free number is on your invoice.
  • Patrick Kane from Altha

    Posted on 12/13/2019

    Hello Buck. I need your expert advice because I've confused myself. I'm wanting to get a set of Rockford components that are rated for 100rms and I currently have a DVC sub rated for 125rms. In an effort to save space and keep things as simple as possible I'd like to stick to one amp running both so I'm looking into getting a 4 channel amp and I've found one that's rated as follows 75x4@4ohm and 150x4@2ohm So my question is can I wire the components into two channels @ 4 ohms and then wire the sub to the remaining two channels in parallel in order to achieve a 2ohm load and draw the 150rms? Thank you for you time and response

    Commenter image

    Buck Pomerantz from Crutchfield

    on 12/14/2019

    Patrick, You can drive two speakers with two of the amp channels, and drive a 2-ohm sub with a third channel, leaving channel 4 unused. Most car amplifiers will not work with a 2-ohm load when bridged.
  • Sajad

    Posted on 12/8/2019

    Hi how bridging effects the output quality? For example : i have a pair of component speakers which are connected to a 4 channel amp i bridge mode; is the output quality the same as normal mode? if not how much different?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 12/9/2019

    Sajag, Bridging means that two channels work together to create a single output. The quality of the sound is not affected in any way, except in volume.
  • Jack from Margaret river

    Posted on 10/5/2019

    Hey mate I'm looking at getting an orion xtr1000.4 4 channel 1000w max and 500w bridged at 4ohm on one channel. I'm just wondering will wattage over two bridged channels or will they both run at 500w. This is for speakers and not subwoofers. I cant fine a crossover that can handle 500w so i might need a different amp. I have crossovers with a max of 300w and I dont wanna shove 500w through it em. Cheers

    Commenter image

    Buck Pomerantz from Crutchfield

    on 10/7/2019

    Jack, That amp can put out 165 watts RMS x 4 at 4 ohms, 250 watts RMS x 4 at 2 ohms, and 500 watts RMS x 2 bridged at 4 ohms. You are right not to hook the amp up to a component system rated for under 500 watts RMS.
  • Brent from Royal Oak, MI

    Posted on 9/11/2019

    When bridging an four channel amp to a two channel configuration, it looks like you are using the LH+ output from each front and rear to power the LH and RH speakers. When you do this, how do you get stereo. Wouldn't the LH positive and RH Negative for both front and rear give you a mono signal? I am considering using a Kenwood KAC-M1824BT bridged to run two speakers on my motorcycle fairing. The amp can be bridged and shows a diagram just like reviewed here on how to do it. I just don't understand how this could be a stereo output.

    Commenter image

    Buck Pomerantz from Crutchfield

    on 9/12/2019

    Brent, When bridging a 4-channel amp to 2-channel mode, you combine the front left and right channels to form one channel, let's call it the left speaker channel. The rear left and right channels are bridged together forming another channel, let's call this one the right speaker channel. Right and left channels playing together is stereo reproduction.
  • Johnny Lee from KL

    Posted on 8/7/2019

    Alpine f1200 bbx 4ch amp 50w at 4 ohms But when bridging . They say it's 130rms x 2 at 4ohms I thought when you bridge it drops from 4omhs to 2ohms... It this correct

    Commenter image

    Buck Pomerantz from Crutchfield

    on 8/7/2019

    Lee, Amps don't have ohms, subs do. You're confounding an amplifier's capability with its load. That amp can put out four channels of 50 watts RMS through 4-ohm loads (speakers). That amp can put out 70 watts per channel through 2-ohm speakers. The amp can put out two channels of 130 watts RMS when bridged powering 4-ohm loads. The amp is not stable to drive a 2-ohm load when bridged.
  • Jason mitchell from Rancho Cucamonga, ca

    Posted on 6/8/2019

    I'm looking to install 3 12 in 4 ohm kicker solo thin profile in my truck what amp would you guys recommend

    Commenter image

    Buck Pomerantz from Crutchfield

    on 6/10/2019

    Jason, Assuming you're referring to Kicker's 12" Solo-Baric L7T subwoofer - three DVC 4-ohm subs rated for 600 watts RMS each will work best with an amplifier that can put out between 1350 and 2700 watts RMS at 2 ohms, like Kicker's CXA1800.1. Wire it all together like this.