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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.

  • 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

    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.

    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

    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

    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.

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