How To Bridge a 4 Channel Car Amp To 1 Sub

How To Bridge A 4-Channel Amp To 2 Subwoofer

How To Bridge A 4-Channel Amp To 2 Subwoofer

If you have a four-channel amplifier designed for mids and highs in door speakers, you can still connect it to a single subwoofer with the help of a low pass filter. Bridging is another term commonly used in car audio. It involves connecting two channels together to combine their power outputs.

To wire a four-channel amplifier to a single subwoofer, follow these steps:

  1. Turn off the power to your amplifier to avoid any accidental shorts or sparks. This precautionary step prevents blowing a fuse.
  2. Using a screwdriver, unscrew the minus terminal from the left channel and the plus terminal from the right channel. Ensure the screws are not fully removed but loosened enough to insert the wires.
  3. Strip approximately two centimeters of insulation from the speaker wires if they are not already prepared. Connect the negative speaker wire to the terminal labeled “-” on the left channel and the positive speaker wire to the terminal labeled “+” on the right channel.

If you have a four-channel amplifier and want to connect it to just one subwoofer, don’t worry. This article explains how to wire a four-channel amp to one subwoofer. However, if you have two subwoofers, you can refer to our guide on how to bridge a four-channel amplifier to two subwoofers. Keep in mind that four-channel amplifiers are primarily designed for mids and highs in door speakers for both the front and rear of the car. While it is possible to connect a four-channel amp to one subwoofer, you will need a low pass filter on your amplifier since subwoofers use frequencies passed by the low pass filter.

Bridging the amplifier involves connecting two channels together to combine their power outputs. For example, if you have a four-channel amp with two front channels rated at 150 RMS each, bridging them will result in a total output of 300 watts RMS per channel when connected together. This wiring configuration is similar to how you would connect two amplifier channels to one speaker. If your subwoofer is rated at 300 watts, bridging the two channels will provide sufficient power to drive it. However, a subwoofer rated at 150 watts would not receive enough power from the bridged channels.

How To Bridge A 4 Channel Amp To 1 Sub

Bridging an amplifier, regardless of the number of channels it has, may initially seem complex and challenging. However, once you understand the correct process, it becomes straightforward, and anyone can do it themselves. The bridging process is essentially the same for each channel, so once you learn how to bridge a two-channel amp, you can apply the same principles to bridge a four-channel amp. By bridging a four-channel amp, you can effectively double its power output, allowing you to deliver more power to your speakers. With a basic understanding of car audio wiring, you can confidently bridge a four-channel amp.

How To Bridge A 4 Channel Amp To One Sub

What You Need

Before you begin the process, you need to have some materials to work with. Here’s a list of what you need:

  • Four-channel amp: check if your four-channel amp has a bridging option.
  • Screwdriver: this will help with hooking up the screws attached to the amp as you have seen in the procedures above.
  • Wire stripper: this will be used to separate the edge of the wire before putting it into the amplifier channel.
  • Speaker wires: the speaker wires will be needed for connecting to the terminals of the amplifier.
  • Manual: before you well understand the connection process, you will need to go through the manual to understand whether the amp can be bridged or not.
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The most common way to have your amp bridged is to connect it to a pair of 4-ohm subwoofers. Follow the procedure below to bridge the amp:

Step 1: Locate The Speaker Wire Terminals

Locate the terminals of the speaker wires on the amp. You should be able to see four-speaker wire terminals or channels. The terminals consist of both positive and negative terminals. Locate The Speaker Wire Terminals on an amplifier Each of the terminals has a screw-down clamping system that helps to hold the speaker wire in place. Bridge A 4 Channel Amp To 1 Sub

Step 2: Connect The Positive Terminal Of Channel One To The Subwoofer

Use a wire stripper to strip about ½ inch of insulation from the ends of the wire. Run speaker wire from the positive terminal of channel one to the positive terminal of the first subwoofer. Run the speaker wires from the positive terminal of the first channel to the positive terminal of the first subwoofer. Ensure the speaker wire is securely clamped down using a screwdriver in the amp’s terminal.

Step 3: Connect The Negative Terminal Of Channel Two To The Subwoofer

Again, use a wire stripper to strip about ½ inch of insulation from the ends of the wire. Run the speaker wire from channel two’s negative terminal to the first subwoofer’s negative terminal. Clamp down the speaker wire and ensure the connection is secure by tightening the terminal screw-down clamp.

Step 4: Repeat Steps One And Two For Channels Three And Four

Now repeat step two and step three for channels three and four. Run a speaker wire from the positive terminal of channel three to the positive terminal of subwoofer two. Finally, run the speaker wire from channel four’s negative terminal to subwoofer two’s negative terminal. Here is a guide on how to connect your amplifier to your subwoofer if you don’t know how.

How To Wire A 4 Channel Amp To 4 Speakers And A Sub

Although a four-channel amp provides greater flexibility for your audio connections, they are mainly used with four-speaker or two speakers and a subwoofer, not both. However, you can still wire a 4-channel amp to four speakers and a sub. Fortunately, you can do this with three methods.

Method 1: Using A Four Channel Amp Rated 2 Ohms Stereo, 4 Ohms Bridged

This is the most common setup. Each front amplifier channel is wired with two speakers in parallel for 2 ohms per channel. The subwoofer is then connected to the two rear channels. Remember to check the amp’s bridged wiring instructions as not all amps use the same bridged wiring.

Method 2: Using A Fourfour Channel Amp Rated For 2 Ohms Stereo, 2 Ohms Bridged

In this method, each front amp channel is wired with two speakers in parallel for 2 ohms per channel. The subwoofer can be either 2 or 4 ohms.

Method 3: Using A 4-Channel Amp Rated For 4 Ohms Minimum Speaker Load

Each of the front amp channels is connected in parallel to 2 speakers for 4 ohms per channel. You will need resistors to keep the total speaker load at 4 ohms per channel.

4 Channel Amp Wiring Sub And 2 Speakers

You can wire two speakers and a subwoofer to a four-channel amplifier. You will, however, need to bridge two of the channels to power the sub while the two speakers are connected to the other two channels.

How To Bridge A 4-Channel Amp To 2 Speakers And 1 Sub

This is an easy connection. Wire the two speakers to the front channels of the amp. Then, wire the subwoofer to the rear channels by bridging the channels to the sub. The channels can, however, be used interchangeably with the speakers going to the rear channels and the sub to the front ones.

Can You Use A 4 Channel Amp For 1 Sub

Like we already said, you can easily bridge two outputs to the sub and leave the other two channels for front speakers.

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How To Bridge A 4 Channel Amp To 2 Subs

Bridging a four-channel amp to two subwoofers is an easy process. Just like we have discussed above, you can bridge your four-channel amplifier to two subs easily by following the process we have outlined below.

Step 1: Strip The Wire

Remove about ½ inch of insulation of the wire with the wire stripper.

Step 2: Fix The Positive Wire

Put the red wire into terminal one, to the positive option of the first channel.

Step 3: Fix The Negative Wire

Put the black wire into terminal four, to the negative option of the second channel to complete the connection of the first speaker.

Step 4: Connect Speaker Two

Repeat steps 1 and 2 to connect speaker two through terminal five and terminal eight of the third and fourth channels. Tighten the screws and check the connection. Ensure the connection is secure and there are no loose wires. To learn more, check out our complete guide on how to bridge a 4 channel amplifier to 2 subwoofers.

What Happens if You Bridge a Non-Bridgable Amp?

You can’t bridge a non-bridgable amp. You’ll need to make sure the amps you purchase and install are compatible with your stereo system, as well as each other. If they aren’t bridgable, you won’t be able to do anything but replace them both. You can also look into buying an aftermarket receiver that offers additional channels of amplification for subwoofers (or “satellite speakers”).

When Should I Bridge My Amp?

When you bridge the channels, this increases the power output. To power a subwoofer, most amplifiers are bridged to combine two channels into one subwoofer or four channels into two subwoofers. Therefore, this is usually the best time you should consider bridging your amp.

Does Bridging an Amp Change the OHM Load?

When you bridge an amplifier, you are essentially using it as a mono amp. That means the impedance on each channel is cut in half because there’s only one load being driven instead of two. You won’t change your OHM load when bridging – that stays the same at four ohms per channel (two channels x two ohms = eight total). What changes with this setup is maximum power output by splitting up the wattage between both channels and putting them together to drive one speaker or subwoofer.

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.

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


To connect a four-channel amp in bridged mode, you can follow the following steps:

  1. Start by running a dual RCA cable from the front left and right RCA outputs on your receiver.
  2. At the amp end of the cable, attach a Y-adapter to each RCA connector. This will split the signal into four RCA connectors, which you can then plug into the four RCA inputs on the amp.
  3. For the speaker connections, you will need to connect the amp’s front right negative output terminal to the negative terminal of the left speaker (or the crossover box connected to it). Similarly, connect the amp’s front left positive terminal to the positive terminal of the left speaker (or crossover box).
  4. Repeat the same connection scheme for the rear channels of the amp, connecting them to the right speaker (or crossover box).

In this setup, the roles of the channel pairs in the four-channel amp have been changed. Instead of powering front and rear speakers, they are now powering a left and a right speaker.


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