Multiple amplifiers running in series to double the maximum power (quadruple the power at a specific voltage gain). Bridging two amplifiers is typically done by feeding one amplifier an inverted signal, connecting the negatives of each amplifier together, and connecting the load between the positives.

In a multi-channel amplifier, the connection of two channels to drive a single load. The input signal is split, and then the phase of one of the signals is inverted. The non-inverted signal is sent to the left amplifier and the inverted signal is sent to the right amplifier (L+R-). The load is connected between the two outputs so it receives twice the voltage at a given input level. The resultant power is much greater than the two 4-ohm channels combined.

bridged is a user-space alternative to the in-kernel bridge code in Linux. It uses AVL trees to speed lookups. It is just a proof of concept project, not yet fully debugged, and with no spanning tree. It has been released for those interested in working with raw sockets, or basic bridging.