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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.

  • 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.
  • Ken from Greensborough

    Posted on 11/3/2022

    Hi I have a pair of focal k2 component speakers with crossovers paired with a focal class ab 4 channel amp I was wondering if it's best to just bridge the amp for those 4 front speakers or if I should run my back door 6.5 speakers through the amp as well ? I also run a 15inch sub through another monoblock amp. What do you recommend? Any wiring diagrams of how i should wire it up.would be much appreciated. Thanks

    Commenter image

    Buck Pomerantz from Crutchfield

    on 11/4/2022

    Ken, You don't say why you think bridging an amp might be "better" than powering all your speakers from the 4-channel amp, but without knowing precisely which amp and speakers you're referring to, we can't help you with meaningful advice. If you want a question answered about a system, you must identify the gear by model numbers as well as brand names so we can get the right information to you.
  • Mats

    Posted on 9/22/2022

    Thanks Buck... Some people says that in bridged mode is only 250W and some 400W. For example one web page showing bridged more 301-500W RMS. There must be something wrong... Is there any 100% proof for 400W are really seding into sub? I mean it is possible measure W with multimeter terminals for example to see exact value? And also can i with multimeter measure exact Hz? Because on amps there are not exact setup i mean for example minimum 50Hz and 400Hz and i want set for example 150Hz and there are not displayed value only 50 and 150Hz. So i need measure for exact value.

    Commenter image

    Buck Pomerantz from Crutchfield

    on 9/23/2022

    Mats, If you don't trust a piece of gear's published specifications, there are a few ways to measure and verify them. A standard multimeter can be used to measure AC voltage at 60 Hz, but wouldn't be of much use at any other frequency. You can use the amp-meter function to measure an amplifier's current draw from the battery, and make a good estimate of it's output from that. Or you could use a signal generator of some sort and an oscilloscope to picture and measure the amplifier's exact output power and level of distortion. There are also dedicated and expensive "amp-dyno" testing devices that measure wattage directly, using signal sweeps, load resistors, and a strong voltage source. Frankly, there are no reasons that I can see why you shouldn't just build your system and hear how it sounds, and not worry about whether the published specs are accurate or not.
  • Mats

    Posted on 9/22/2022

    Dont know why my comment not displayed... I posted links directly to my products... Maybe links not allowed. So my amp is Audio system germany R.110.4 and my subwoofer Audio system germany R12 FLAT EVO G.

    Commenter image

    Buck Pomerantz from Crutchfield

    on 9/22/2022

    Mats, We do not print or even go to web links provided by outside sources.
  • Mats

    Posted on 9/22/2022

    Ah again i forgot some info... Subwoofer is one voice coil (maybe you will find more info in links which i posted) and also subwoofer is 4 ohm impedance and my amp will work with 2 or 4 Ohms... Also i have front speakers at 3 ohms which will be fine

  • Mats

    Posted on 9/22/2022

    Hello Buck its me Mats, Thanks for reply. Sorry i forgot write some basic info.. Adding additional info about my amp and sub.. My amp is Audio system germany R.110.4 [link removed] My subwoofer is Audio system germany R12 FLAT EVO G. [Link removed]

    Commenter image

    Buck Pomerantz from Crutchfield

    on 9/22/2022

    Mats, In answer to your original question: That amplifier should be able to send that SVC 4-ohm 400 watts RMS rated sub up to 400 watts RMS from two bridged channels.
  • Mats

    Posted on 9/20/2022

    Hey Buck, I have question... Some people says that is not good connect subwoofer into amp where are connected front speakers... So channell 1 and 2 are connected component speakers.... Chanell 3 and 4 is bridged for subwoofer... Speakers are 100W RMS and 3 ohm and only in front midbass in doors and twitters in dashboard and crossover also. I have subwoofer which have 400W RMS And my amp on : 4 ohm 4x110W RMS 2ohm 4x200W RMS 4ohm bridged 2x400W RMS Also my amp can accept 2 ohm and 4 ohm So question is wil my amp really deliver 400W into my subwoofer which is 400W RMS or it is deliver only half or? So i need exact info how múch power is deliver for sub. If not 400W then i should buy monoblock then i want all 400W because i pay for this and dont want only half for example... I am beginner in this.. I hope that you clarify me about this.. Thank you

    Commenter image

    Buck Pomerantz from Crutchfield

    on 9/21/2022

    Mats, The ultimate answer to your question depends on the sub's impedance and coil configuration, but 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.
  • Brad from Warsaw, IN

    Posted on 9/5/2022

    Hello, I bought a JVC KD-X270BT headunit from you guys for my 2005 Dodge Caravan and surprisingly it really boosted the sound quality and volume with everything else remaining factory. I have since moved it into my 2005 Mack semitruck, which only has 2 factory speakers. Can I bridge 2 channels off this headunit? {left front + and left right - to one speaker and the same for the rears). I need just a bit more volume to get a good sound level... bypassing the factory wiring and running heavier wire from the headunit to the factory speakers is no problem. Or would I be better off just getting 2 more aftermarket speakers and cutting a hole in the dash somewhere to add them?

    Commenter image

    Buck Pomerantz from Crutchfield

    on 9/6/2022

    Brad, I doubt your receiver's output channels can be bridged. The best way to accomplish what you want is to add an aftermarket amplifier to your system. Give us a call and talk to one of our Advisors. We can help you choose the right amp and give you the right advice on how to install it.
  • Rajesh Universal

    Posted on 8/23/2022

    Hi , when bridging a 4 channel 75*4 at 4 ohm amplifier ; will change the output of amplifier into 2 ohm? Or Will output be in the same 4ohm with 200 *2..thank you..

    Commenter image

    Buck Pomerantz from Crutchfield

    on 8/24/2022

    Rajesh, When you bridge two channels together into a 4-ohm load, each individual channel will see a 2-ohm load. That's why the total wattage of 2 bridged channels together results in twice the power of each channel's 2-ohm load power rating.

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