Traditionally, speakers only had a single pair of terminals and required a single two-core cable for each speaker. Increasingly, however, speakers became available with two pairs of posts, allowing for bi-wiring. The posts are normally connected with a copper connector or shorting post which needs to be removed for bi-wiring to take place. Bi-wiring is intended to make the most of your system's performance by allowing for a greater frequency response.
In a standard stereo wiring system the amplifier has two sets of connections at the rear for the left and right speakers. Each set of connections consists of a positive and a negative connection, typically coloured red and black respectively. In traditional wiring systems, a length of dual-core wire is fastened to each pair of connections on the amplifier and runs to the left or right speaker. Inside each loudspeaker there are usually at least two drivers, a woofer and a tweeter. An electronic circuit inside the loudspeaker sends the higher frequencies to tweeter and the lower frequencies to the woofer.
In bi-wiring the electrically conductive copper links between the connectors on the speaker are removed. Instead of a single dual-strand wire being run from the amplifier to each speaker, two wires are used. One end of each strand is connected to the posts on the amplifier as before; at this end, the wires share a connection. The other end of each strand is connected to a separate post on the back of the speaker. The same signal is now being fed into two distinct sets of connectors.
Inside the speaker, each set of positive and negative connectors goes to either the woofer or the tweeter. Typically, the top pair goes to the tweeter and the lower pair to the woofer. Now, instead of splitting a single signal, each speaker is receiving its own signal from the amplifier. This allows distortion to be minimized as unwanted electrical and mechanical resonances are cancelled out. Done correctly, bi-wiring is described as producing a more detailed sound with a crisper bass.
A traditional stereo system uses to speakers and a single amplifier. In true bi-amping, three amplifiers are used: a standard pre-amplifier and a separate stereo amplifier for each speaker. The full range audio signal for both left and right speakers travels from the player to the pre-amplifier. It is then split into left and right channels, as before; only instead of traveling straight to the speakers, each channel is sent to one or other of the stereo amplifiers.
The signal is then split again, this time into high and low frequencies, by the crossover circuit inside each stereo amplifier. Separate wires carry the high and low frequencies to the appropriate set of connectors on the speaker.
This means that when the signal arrives at the speaker, the high and low frequencies have been amplified separately before they are directed to the tweeter and the woofer respectively. Distortion is greatly reduced; unlike passive bi-wiring, there is no loss of power as the signal is boosted by the stereo amps.