Bi-wiring is a means of connecting a loudspeaker to an audio amplifier, primarily used in hi-fi systems. Normally, there is one pair of connectors on a loudspeaker and a single cable (two conductors) runs from the amplifier output to the terminals at the loudspeaker housing. From this point, connections are made to the loudspeaker drivers – most often through audio crossover networks.
In bi-wiring, each loudspeaker has two pairs of connectors and two cables are run from the amplifier output to the speaker cabinet – one for the high frequency or tweeter driver and one for the low frequency driver (through two separate crossover networks). Due to the physics of electrical reactance, the separation creates a natural filter as power amplifier faces a higher electrical impedance on the cable feeding the tweeter at low frequencies and lower impedance at higher frequencies where there are two wires; the converse applies to the woofer signal. Thus, high frequencies will tend to travel in the cable driving the tweeter circuit, and low frequencies preferring the pair connected to the loudspeaker's woofer circuit. The purported advantage of this split is that there is less interaction between high and low frequency signals.
Critics of the bi-wiring science believe that both ways (connecting the two drivers at either the amplifier's end, or internally the speaker cabinet) of making speaker connections are electrically equivalent, and thus cynically refer to the practice as "buy-wiring", implying it is nothing more than a marketing gimmick for expensive speaker wire.
However, there are many audiophiles who fully accept that bi-wiring brings an audible improvement over standard single cabling. For example, John Atkinson, writing in Stereophile, observed "subtle but important" differences, particularly in reduction of treble hardness and improvement in bass control in one review. Bi-wiring should not be confused with the hi-fi practice of bi-amping, or the use of twin amplifiers to power speakers, which may bring improved separation of signal frequencies.