How to Bridge an Amplifier

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Bridging an amplifier combines the available channels into one channel with half the ohm (Ω). It is commonly used in car stereo systems, allowing a powerful mono signal to be sent to a subwoofer.

Method 1
Method 1 of 2:

Two-Channel Amps

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  1. This should be indicated on the documentation pamphlets that came with the amplifier, or the amplifier itself. If the amplifier is used, or lacks documentation, go online and check for the specifications on the manufacturer's website. [1]
    • Bridging an amplifier cuts the resistance load (measured in ohms) in half, which can cause it to overheat. Be sure to check your manual (or the manufacturer’s website) to see if once connected to a speaker, whether or not your amplifier can function at half the ohms it currently uses.
    • Most amplifiers have a small diagram near the channels indicating the terminals you would use to bridge it. If your amplifier does not claim to be able to bridge, don't try to bridge it . It may already be bridged internally, and you could cause damage to your amplifier.
    • Be aware of the fact that if your amplifier is a stereo amplifier (amplifying both left and right), bridging it would cause it to become a mono amplifier (amplifying from one; either the left or right).
  2. On your two-channel amp, you should see 4 terminals: a positive (+) and a negative (-) for channel 1, and a positive (+) and a negative (-) for channel 2. Each terminal will be labeled as follows: [2]
    • Channel 1
      • "A" (positive)
      • "B" (negative)
    • Channel 2
      • "C" (positive)
      • "D" (negative)
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  3. From the wires coming out of the speaker, connect the positive speaker lead to terminal A (the positive for channel 1) and connect the negative speaker lead to terminal D (the negative for channel 2). Connect these wires by unscrewing the screw in that terminal, placing the wire in between the top and bottom portions of the terminal, and then screw the screw down tightly to secure the wire. [3]
    • The wires coming from the speaker are going to be insulated with a plastic coating. You will need to strip off a small portion of the wire insulation (less than 1 inch) using a pair of wire strippers in order to secure it to the terminals. [4]
    • What this connection does is it combines the power from the two separate channels, doubling your power output. [5]
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Method 2
Method 2 of 2:

Four-Channel Amps

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  1. Just like method 1, you must figure out if your four-channel amplifier can be bridged. Taking all the same precautions, be sure to consult the amplifier manual or research your amp model online to be sure it can be bridged. [6]
  2. On your four-channel amp, you should see 8 terminals: channels 1 through 4 each have a positive (+) and negative (-) terminal. Each terminal will be labeled as follows:
    • Channel 1
      • "A" (positive)
      • "B" (negative)
    • Channel 2
      • "C" (positive)
      • "D" (negative)
    • Channel 3
      • "E" (positive)
      • "F" (negative)
    • Channel 4
      • "G" (positive)
      • "H" (negative)
  3. From the wires coming out of the speaker, connect the positive speaker lead to terminal A (the positive for channel 1) and connect the negative speaker lead to terminal D (the negative for channel 2). Again, just like bridging a two-channel amplifier, connect these speaker wires to the amplifier by unscrewing the screw in that whichever terminal you are connecting the wire to, place the wire in between the top and bottom portions of the terminal, and then screw the screw down tightly to secure the wire.
    • Once the wires are secured, the first speaker is connected to the amplifier.
  4. Following the previous method, again take the wires coming from the second speaker, but this time, connect the positive speaker lead to terminal E (the positive for channel 3) and connect the negative speaker lead to terminal H (the negative for channel 4).
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Expert Q&A

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  • Question
    How do I bridge a subwoofer in a car?
    Steven Racz
    Audio, Video, & Automation Expert
    Steven Racz is an Audio, Video, & Automation Expert and Owner at Altitude Audio Video based in Littleton, Colorado. With over 15 years of professional experience, Steven and his team of technicians specialize in installing residential and commercial audio systems, theater design and installation, Josh Ai voice & control systems, and Control4 automation. At Altitude Audio Video, they strive to tailor the perfect system for your needs.
    Steven Racz
    Audio, Video, & Automation Expert
    Expert Answer
    So if you have two subwoofers and a four-channel amp, four channels can be bridged to two channels. Another example is that if you have a two-channel amp with one subwoofer, you could bridge both of the channels for one subwoofer. Typically, the amp will stay on it and be bridgeable, meaning that you'll use one positive and one negative from the two different channels being brought into one.
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  • Question
    How can I play two speakers on one amp using bridged mode?
    Community Answer
    You will need a 4 channel amp to run 2 speakers in bridged mode. Typically the speakers will be hooked to the positive side of one channel and the negative side of another thus bridging the channels, but this is not always the case. Look for the diagram near the speaker connects to see how yours is bridged. Once the speakers are hooked up, there will be a switch marked Stereo, Mono, or Bridged. Set this to Bridged.
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  • Question
    Can I connect one dual-coil speaker to a four-channel amplifier?
    Community Answer
    Surely - this is possible. Simply handle the two voice coils like they were from two separate speakers. (And like the description of "Method 2".) Don`t interchange their connections (+ of one vc to - of another). But beware: you'd better feed the four channels with the same signal (which means: all inputs fed from the same source,mono, not stereo), and surely not 4 different signals ("quadrophonic"), to get best results. Treat the voice coil's terminals as they're marked, + as +, - as -.
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      Tips

      • Before trying to connect anything, you can quickly and easily consult an electronics or car audio store.
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      • Try to stay one level above the amplifiers lowest rated resistance. For example, if your amplifier says that it can handle 2 Ohms, wire it so it produces 4 Ohms. If you go lower than its displayed lowest rated resistance, your amp could shut off.
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      Warnings

      • Be extra careful when bridging a four-channel amp! This can put too much strain on your alternator or speaker.
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      References

      1. ↑ https://www.jazzloftproject.org/bridge-a-4-channel-amp/
      2. ↑ https://www.jazzloftproject.org/bridge-a-4-channel-amp/
      3. ↑ https://www.jazzloftproject.org/bridge-a-4-channel-amp/
      4. ↑ https://www.youtube.com/watch?v=8p88aCFgJMY
      5. ↑ https://www.youtube.com/watch?v=KuaWvMjvZkM
      6. ↑ https://www.jazzloftproject.org/bridge-a-4-channel-amp/

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      • Anonymous

        Dec 29, 2016

        "Didn't know I needed a 4 channel amp to bridge 2 woofers."
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