POLK POLK 4-CHANNEL CLASS-D POWER AMPLIFIERThis is How You Build a Really Cool Amplifier
The PA D4000.4 amplifier is capable of bridging two full-range channels into a single full range channel with higher output power. For instance, one front and one rear channel will increase the output power from 125W per channel to 400W per channel (for a 4 ohm load). The most common hookups for the PA D4000.4 would be four full-range channels, two full-range channels and a bridged sub, or two bridged subwoofers.