How to Bridge a 4-Channel Amp

Once you have a speaker, amplifier, and subwoofer, it is only a matter of time before you try to figure out how to bridge an amp. It is quite tempting because the process ends with the sub receiving a really powerful signal even if in mono.

There are a few advantages to doing this with your audio equipment. And luckily for you, the process itself is not at all complicated.

You just need to connect a few wires and there you have it. And many companies and experts tell you how to go about it with a bridge speakers diagram which only makes it all the more easier.

You must know that not all amplifiers can be bridged. So, you need to make sure that the one you have is built for this feature. If you don’t know how we’ll tell you all about it. But before that, you need to know what it means to bridge an amplifier. So, that’s where we shall begin. Let’s go.

What Is Car Amp Bridging?

A lot of cars with amplifiers come with a setting called bridge mode or bridging. It is a pretty useful feature to have because it allows you to combine two or more channels to increase the output power.

This extra power comes from doubling the load which is typically 2 ohms. It happens when you connect the positive signal of a channel with the negative of another. Every amplifier has a specific maximum wattage when it comes to output but by bridging an amp, you can optimize its power. This is how it works.

The power of any amplifier depends on the voltage it produces and the speaker’s impedance. But before that, you must keep in mind that the amplifier has enough load to support the power supply coming in. Here’s an example to understand this better.

Consider an amplifier that has voltage rails at -21 and +21 volts. Now imagine it is connected to a 4-ohm speaker. To determine the maximum power that the amplifier can produce, you must double the maximum output voltage and divide the result by load impedance.

Amp max power = (Max output voltage)² / load impedance

(measured in watts)

So, in the example given the amplifier’s maximum power will be 100 watts.

Amp max power = (20)² / 4 = 100

A Few Do’s and Don’Ts

There are a few things to keep in mind before you get started with the process of bridging.

  1. It would be best if you determined whether or not you can bridge the amplifier. Go through the instruction manual to make sure that it’s possible. You can also do this by checking the amplifier’s specs online.
  1. You need to check the user manual and make sure that the amp can work at half the resistance load because that’s what happens when you bridge an amp. If it cannot function, it will overheat and cause problems.
  1. You must make sure that the amplifier is not internally bridged because if it is, it cannot and should not be done manually. Make sure you verify that beforehand.
  1. If you have a stereo amplifier, you should know that bridging will make it a mono amp.
  1. Connect the positive wires from the amp to the positive lead of the speaker and the same with the negative terminals.
  1. Secure the wires carefully. You might have to strip less than an inch of the insulation of the wires coming out of the speaker to secure them.
  1. Every individual speaker must meet the minimum impedance requirements. If you want to connect more than one speaker then the total must meet the minimum requirements.
  1. If you want to use dual-voice coil speakers, you must first wire them to meet the requirements.

Setting the Crossovers on a Bridged Amp

If you have the right speaker (which has to do with load impedance), you can do bridging quite easily. What does that mean?

Every amplifier comes with a user manual that tells you about the minimum resistance load of a speaker that can be bridged with the amp. This is impedance and it applies to using the stereo normally or in bridge mode (when it is mono).

Usually, it says stable to 2 ohms which is what the amp can handle. But if this detail is nowhere to be found, you can start the process by assuming that it’s a 4-ohm speaker.

But in some cases, you will have to build a crossover filter. There is the low-pass filter, high-pass filter, and subsonic filter. You may have to build a low-pass crossover which makes sure that the frequency signal that is in the 50-250 Hz range passes over to the speaker or subwoofer while blocking the higher frequencies.

A high-pass crossover makes sure that higher frequencies in the 5-20 kHz range pass to the speaker while blocking the lower frequencies. A subsonic filter blocks the signal in the 10-40 Hz range to improve the sound quality and woofer control.

If you’re interested in buying a 4 channel amp, take a look at the best 4 channel amp article.

How to Bridge a 4 Channel Amp: The Step-By-Step Process

If you want a detailed guide on how to bridge a 4 channel amp, it is a simple process that can be done in five easy steps. Here’s how that goes.

  • Step 1: Make sure your amplifier can be placed in bridge mode using this method. That means looking up the specs as mentioned before. Check the specs to see if the amp can function at half the capacity when connected to the speaker to ensure that it doesn’t overheat.
  • Step 2: Understand the layout of the equipment properly. You need to see eight terminals on your four-channel amplifier. They will be marked as channels 1, 2, 3, and four and each of the channels will have two terminals: positive and negative.
  1. Channel 1 will have A for positive and B for negative.
  2. Channel 2 will have C for positive and D for negative.
  3. Channel 3 will have E for positive and F for negative.
  4. Channel 4 will have G for positive and H for negative.
  • Step 3: Connect your amplifier to the speaker using the wires connected to the speaker. You must join the positive terminal of the speaker to the positive terminal of channel 1 which is A. Now, connect the speaker’s negative terminal to the negative terminal of channel 2 which is D.
  • Step 4: Now connect the wires of the speaker to the amplifier securely. You will have to remove the amplifier terminal’s screw and place the wire between the terminal’s top and bottom. Screw it back on and make sure the wire is secure.
  • Step 5: Following the same method, connect the amp to speaker 2. Connect the wires from the positive terminal of the speaker to the positive terminal of channel 3 which is E and do the same with the wire coming out of the negative terminal by connecting it to the negative terminal of channel 4 which is H.


Q: Can You Bridge a 4 Channel Amp to One Sub?

A: There are some cases when you can make it happen. For instance, it is possible if you are dealing with a dual-voice coil subwoofer. And if you can bridge two channels using one coil each, you can make it happen.

However, this process is not recommended because you will need to tinker with the gain settings to make sure that they are exact. It will also require you to make sure the impedance of your sub, which adds another layer of checks and balances to the process. And, in the end, it might not even be worth it.

Q: Is Bridging an Amp Better?

A: The idea behind bridging an amplifier is to find a way to increase its power so that it can be connected to a speaker for better output. However, bridging does not increase the overall power available for an amplifier.

So, make sure you know the reason behind bridging your amp because that’s what determines whether this is a “better” idea or not. It is also a good time to remind you that the output post-bridging is mono and not stereo.

Q: Does Bridging an Amp Make It Louder?

A: Yes they do. But if the specs are not right the output will be distorted too. You can fix that by getting a bigger amplifier but a 50-watt amplifier will increase the sound level only by three decibels and the power will need to be 10 times what you usually need. So, it’s a bit of a balancing act.

The Bottom Line

In case you didn’t know it already, you can also look up how to bridge a 2 channel amp. The process is almost the same except you won’t need to make as many connections because it only has two channels. If you have an amplifier that allows you to turn it into bridge mode, it can’t be a bad idea to at least try it. But you want to make sure that is an option so that you don’t accidentally overheat it and cause permanent damage.

Last Updated on April 18, 2024 by Brian Beasley

Written by Danny Reid

Hey, I'm Danny, and I know how hard it can be to find the perfect audio gear. Need a new stereo, amp, speakers, or subs? Don't worry – my blog is here to help you cut through the noise! My mission is to give you the best reviews, so you can make the right decision for your audio needs. And if you ever get stuck thinking, "Where does this blue wire go?" don't worry – I've got tons of cool tips to help you out of any jam. So come along with me on this fun, sound-filled adventure, and let's find the perfect audio setup to make your tunes really sing!