How to Bridge an Amplifier

Bridging refers to combining two (four) channels of an amplifier into one (two) channel(s) with twice the voltage. A two channel amp can be bridged to one channel, and a four channel amp into two channels. Bridging the channels increases the power output. An amplifier is usually bridged to combine two channels to power one subwoofer, or to combine four channels into powering two subwoofers.  To clarify, you cannot bridge a monoblock amplifier! The definition of bridging is combining two or more channels, and a monoblock amplifier has only one channel. You will need opposing channels in order to bridge the amplifier. In technical terms, you using a low source impedance to drive a large load impedance, which results in maximum voltage transfer.

Bridgeable amplifiers are designed with an inverted channel for bridging purposes. The inverted channel produces voltage that is generated at the opposite polarity of the regular, un-bridged channel. Bridging an amplifier produces almost four times the amount of power as it would in an un-bridged status.

Before you attempt to bridge an amplifier, there are certain conditions you must keep in mind. Only bridge an amplifier that can handle the increased power load. Do not bridge an amp that will be unstable at the bridged load, or if the speakers cannot handle the increased power. Always check your product’s paperwork and diagrams before you bridge your amplifier. Using your amplifier’s paperwork is the easiest way to figure out how to bridge your amplifier.

Unless otherwise stated, all multi-channel amplifiers have a minimum bridged stability that is higher than the minimum stated impedance from one of its channels. For example, a 2 channel amplifier that is 1 ohm stable per channel would have a minimum impedance of 2 ohms when bridged. In reality, most amps are only stable at a 4 ohm load in mono/bridged configuration.

Amp Bridging To bridge your amplifier, locate the amp terminals. For a 2-channel amplifier, you will see four terminals. A positive and a negative terminal for channel one, and likewise for channel two. If you are bridging this 2-channel amp to one subwoofer, you will connect one piece of speaker wire from the positive terminal of channel 1 to the speaker’s positive terminal. Next connect a separate cut of speaker wire to the negative terminal of channel 2 to the speaker’s negative terminal.

That's the gist of amplifier bridging. If you are totally inexperienced, ask a knowledeable friend to help guide you.

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Written by Gary Brikowski