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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.

  • Ted from Syracuse

    Posted on 12/24/2023

    I have a four channel amp with eight terminals which can be bridged can I bridge to bridge together to go into one terminal into a set of a sub (3) basically trying to get full power of amplifier

    Commenter image

    Buck Pomerantz from Crutchfield

    on 12/26/2023

    Ted, Bridging combines the power of two adjacent amplifier channels. That's it - no more than two together, and they must be next to one another - for instance the two rear channels can get bridged together but not a front and a rear channel.
  • Mazhar Ali from Sargodha Pakistan

    Posted on 12/7/2023

    Hi sar I have pioneer a 12 inch double voice coil subwoofer Which is the model ts-w311d4 Its power is 400 watts I have an audiobank amplifier with 4 channels 2000watt I have a woofer of the first pioneer model on it ts-w307f 12 inch 300 watt was running Now playing this double coil woofer My problem is that I was using a woofer before He was playing very well and his bass was touching Heart and his sound quality was very good This woofer is damaged After that I bought this double voice coil woofer Its sound quality is not good And this woofer doesn't even touch the heart Please give me some good advice as to what I should do now Thanks

    Commenter image

    Buck Pomerantz from Crutchfield

    on 12/7/2023

    Mazhar, If your amplifier can handle a 2-ohm load, you could wire that sub like this to get the most power out of it.
  • Johnny

    Posted on 9/17/2023

    How do I add a 3rd sub to a bridged 4 channel

    Commenter image

    Buck Pomerantz from Crutchfield

    on 9/18/2023

    Johnny, Without knowing precisely what amp and subs 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.
  • Jacob from Omaha

    Posted on 9/8/2023

    I have a amp that supports bridging to a 4ohm sub and it says on the back of the amp to not use a 2ohm load. My subwoofer only has 2ohms. Can i still bridge it like normal?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 9/11/2023

    Jacob, Don't know why you would want to hook up your amplifier and sub in a manner that won't work. If you did, the amplifier will either get damaged, go into "protection mode" to prevent that damage, or work okay for awhile.
  • Alex from Lillington

    Posted on 7/4/2023

    Hi I'm looking at getting a 4 ohm 400watt rms subwoofer and i can't find any amps that are 4 ohm 400 watt rms. could i get a 100w 4x amp and bridge all 4 100w channels into 1 400w channel and keep my ohms at 4?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 7/5/2023

    Alex, You didn't indicate whether your sub has a single or double voice coil, so Without knowing precisely what sub you have, we can't help you with accurate 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. BTW, a Kenwood Excelon XR601-1 puts out 400 watts RMS at 4-ohms, if that'll actually work for your sub.
  • Wayne

    Posted on 3/8/2023

    In your diagram of "Using a bridged 4-channel amplifier to power a pair of component speakers", I notice there is an unused Pos & Neg for the left and right side.....Can these be used for rear door speakers? What affect would adding two rear door speakers have on the front component speakers, in terms of power? Thanks

    Commenter image

    Buck Pomerantz from Crutchfield

    on 3/9/2023

    Wayne, I'm not absolutely sure of this - but I think if you wired a speaker to the "unused" terminal pair of a bridged amplifier it would result in that speaker being wired in parallel and out of polarity/phase with the original speaker driven by the bridged channels. This may result in the amplifier shutting down due to low impedance, or the speakers will split the available power and play softer than they would when just wired one speaker to each channel of the unbridged amp.
  • Billy Sherman from Las vegas

    Posted on 3/6/2023

    I want to get into the local spl contest my gear is kicker 15in dvc x3,infinity 12in kappa x2,spl 12 in svc x 2,alpine R 12 in svc x1,kicker 10in dvc x2, kicker 8in svc x2, Pyle 6in midrange x4,kicker 6x9 3way 260 w x4,pioneer premier 2ch crossover x4 ,I have a 6800 w 4ch amp,. 3200 w 4ch amp,kicker 1100 2ch amp , and 1500 w 4ch amps x 2, stinger 2mf capacitor x 2, I have a pioneer avh 2600 stereo and a 7 band eq and have extra 1000 cca battery with a 280 a alternator already installed. I have all the cables,wire,splitters etc. Needed to do the job. I'm 60 yrs old and love it loud! is there any way you can give me the best combination and hookup of these components to compete in the spl contest ?I know it a hodge podge of equipment but it's what I have to work with. I can build my own box for the bed of my dodge ram 4door if I knew the cubic feet needed. I plan on a pass thru with 3-15 in custom box and 3 17 in holes for pass thru ,2 -12 under rear seats (can hold 4-12 in) ,10 +6 to crossover in rear drs.,8+6 to crossover in front drs ,and 6x9 in each door also. I'll cut the doors as needed . I have already built the custom diamond plate door panels to mount any combo of speakers you suggest . could you give me some kind of ideal how to use these pieces to produce the loudest sound to compete ?thank you for any guidance you can give. I don't have to win, just show em this old man has got it loud too??! Bill

    Commenter image

    Buck Pomerantz from Crutchfield

    on 3/7/2023

    Billy, You certainly have a large amount of items planned for your system, but without knowing precisely what amps, subs, and other devices 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. FWIW, your stated total amplifier wattage value, 14,100 watts, is outlandish and probably reflects the manufacturers' maximum output claims which are worthless for planning a system. Always use RMS power ratings when building a system.
  • Dan Shotz from Las Vegas

    Posted on 2/7/2023

    I have an LOC to 4 channel amp connected to 4 door speakers, than i go out to my mono amp that goes to sub. Will this work? Do i need rca Y splitter? Thank you

    Commenter image

    Buck Pomerantz from Crutchfield

    on 2/8/2023

    Dan, It's impossible to tell what will work without knowing what gear and what vehicle you're referring to.
  • Nicholas Van Elzen from MOUNT PLEASANT

    Posted on 12/20/2022

    I have a kenwood d8105 5 channel amp the does 50×4 or 150×2 watts rms bridged at 4 ohms. I'm running the sub channel at 2 ohms 500w rms. Would I be able bridge them and run something like the morel maximos or maximo mkII in the fronts and run the rears off head unit power?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 12/21/2022

    Nicholas, You can bridge the front and tear channels of that amplifier to achieve two channels of 150 watts RMS each - but that'll be too much for the speakers you mention and will probably damage them.
  • Kevin Lee

    Posted on 11/28/2022

    If i bridge 2 speakers on a 4 channel amp does the impedance cut in half, double, or remain?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 11/28/2022

    Kevin, You don't bridge speakers, you bridge two amplifier channels together to form one amp channel. This does not change the impedance of the speakers. I think you may be referring to the fact that bridged amp channels can only handle the sum of each channel's minimum impedance capabilities. In other words, if each amp channel can handle loads as low as 2-ohms, bridged together they will only be able to handle loads as low as 4-ohms.

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