How to Bridge A 4 Channel Amp To 1 Sub?

Bridging is a unique feature in many car amplifiers. It is a way of combining two channels into one channel and can produce the maximum power output. With this feature, you can bridge a 4-channel amplifier to speakers and subwoofers.

To bridge an amplifier to a subwoofer, here are the following steps:

  • Check the impedance rating of the amplifier
  • Connect the positive end of the sub to the positive terminal of the amp
  • Connect the negative of the sub to that of the amp
  • The strip of ½ inch of speaker wire
  • Securely clamp down the wire

In this article, we will give a detailed description of how to make the installations. Also, we have included other important details that will come in handy when you are setting up your amplifier.


How to bridge a 4-channel amplifier to a subwoofer?

Step 1- Check the Details Of Your Amplifier

Before you connect your amplifier to your subwoofer, you need to check a few details about it first. For example, you need to make sure that your amplifier is bridgeable.

Some amplifiers cannot be bridged manually. This is because they are already internally bridged. Also, bridging can cut down the resistance load of an amplifier by half. So, if you attempt to bridge it, you may end up damaging your amplifier.

That is why it is important to check on the specifications beforehand. You can find it in the pamphlets, or it may be indicated on the back of the amp or, you can look it up online.

Step 2 – Know the Layout

If you have a four-channel amplifier, then you will notice eight terminals at the back of the amp. Each channel has a set of positive and negative terminals. They are paired together and are marked with (+) and (-) signs accordingly.

Step 3 – Connect the Terminals

Take a Speaker wire long enough to run from the amplifier to the subwoofer. Connect the positive terminal of the first channel of the amp to the positive end of the sub.

Likewise, attach the negative terminal of the amp to the negative end of the sub.

Step 4 – Clamp It Down

After connecting them, remove the insulation off the wire from both ends by half an inch, with the help of a wire stripper. Then, tighten the screw-down clamp of the terminals with a clamp, thus securing the wire properly.

What Does Minimum Impedance Rating Mean for An Amplifier?

The speaker impedance, also known as the ohm rating, is the amount of resistance to the electrical flow at the terminals of the speaker. Most of the vehicular amplifiers are designed to have a resistance of about 2 ohms per channel for stereo (standard) use.

Or a minimum of 4 ohms for bridging. The impedance rating of the amplifier is, in a manner of speaking, a form of warning for you. If you happen to use a load that is lower than the minimum rating, then it can cause the amplifier to get hot and even cause permanent damages to it.

So, when you are purchasing a four-channel amplifier for your car, check its impedance rating.

Amp Wiring Systems

There are primarily three types of systems for a four-channel amplifier.

System 1 – 4 channel amp along with 4 ohms for subwoofer bridging and a minimum impedance rating of 2 ohms for stereo.

System 2 – 4 channel amp along with minimum impedance rating of 2 ohms either in stereo or for bridging.

System 3 – 4 channel amp along with minimum impedance rating of 4 ohms.

  • In the first system, the amp is wired to two speakers parallel to each other to the front channel. Each speaker has a resistance of 2 Ohms. In addition, it has one subwoofer with 4 Ohms that is bridged to the rear channels for extra power. This is by far the best choice when it comes to a 4-channel amplifier.
  • The second system is slightly different from that of the first system. Just like the first one, two speakers, each with 2 Ohms resistance, are wired in a parallel manner to each front channel with one subwoofer bridged to the rear channels. The sub has a resistance of either 2 Ohms or 4 Ohms.
  • The third system has two speakers with parallel wiring to the front channels. Also, it has additional parts for 4 Ohms for each channel. And, finally, a subwoofer with a minimum of 4 Ohms.


Can You Bridge an Amp Without A Built-In Bridge?

There are a couple of ways you can bridge your amplifier:

  • You can build a bridging module, or you can purchase one online.
  • You can incorporate an electronic crossover that has an adjustable phase for each channel. You can use one with a mono feature.


By How Much Does the Power Increase When You Bridge an Amplifier?

When you bridge an amplifier, it increases the power output by a factor of 4. However, this factor depends on a few things, such as the rating on your amplifier, its limitations, and design.

However, it is to be noted that the larger the output, the more power your amplifier drains from your car battery.

Integrating Crossovers

One of the perks of having a luxury car is that they come with the option of using crossovers. With a subwoofer, you can get a good quality bass. That is why you need to separate any high-frequency music and vocals from getting into your sub.

Setting Up the Crossovers on A Bridged Amplifier

Using a crossover allows you to have a high pass, low pass, or full range with the help of sound range control. So, when you are installing it in your car, this is how you proceed:

  1. First, you adjust the crossover switch to a low-pass filter on the amp.
  2. Next, set the low-pass filter dial to the maximum.
  3. Play music containing bass.
  4. Then, slowly start turning down the low-pass filter dial until you hear the upper range of the music. Generally, it is 80 Hz or below. As you keep lowering the dial, you can find out the cut-off frequency of the amplifier.
  5. After knowing the cut-off frequency, turn up the volume dial of the stereo. If it needs more high-volume power, then you can adjust the gain.


With the above information at your fingertips, you can easily bridge a 4-channel amplifier to a subwoofer. And you can also add other devices to your amplifier as well.

Now that you know how it all fits together, it’s time to get the ball rolling! We hope this was helpful to you.