Bi-Wiring Introduction
Introduction
Bi-wiring involves using two pairs of speaker cables between your loudspeakers and an amplifier, where usually only one cable to each speaker would be used. If you are using loudspeakers that are capable of being bi-wired, it may be worth considering installing the extra cables to make the most of your system's audio performance.
Normally Wired Loudspeakers
The simplest connection between an amplifier and a loudspeaker is with a single length of two-core speaker cable. Each 'core' is a conductor for an electrical signal and is separated from the other using plastic or rubber insulation. On the rear panel of the loudspeaker will be a pair of terminals that the cable is attached to, one usually coloured red or marked as positive (+), and the other usually black and marked negative (-). The output stage on the rear panel of the amplifier will have a similar arrangement of terminals for each speaker connection. The cable is connected between the amp and the loudspeaker so that red/+ connects to red/+ and black/- connects to black/-. The audio leaves the amplifier as an electrical signal through the red/+ conductor. When it reaches the loudspeaker, it passes through an electric circuit called the 'crossover'. This circuit filters the full signal and directs particular frequencies to the correct loudspeaker driver. In a two-way speaker, high frequencies go to the tweeter and low frequencies go to the woofer. The electrical signal then returns back to the amplifier's output stage along the black/- conductor, and the circuit is complete.
Normally Wired Loudspeakers
The main problem with normally-wired loudspeakers is that a single cable carries the entire electrical signal from the amplifier to the speaker and back again to the amp, passing through the crossover along the way. In this situation, the low frequency bass tends to overpower and swamp the delicate treble signals, particularly on the return trip back to the amplifier. The diagram below shows a pair of loudspeakers connected to the amplifier's output stage using single runs of dual-core speaker cable
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The solution to this frequency disruption is to separate the signal more efficiently at the crossover by using two separate runs of speaker cable to each loudspeaker.
Bi-wiring
A bi-wirable speaker has two pairs on cable inputs on its rear panel, two red/+ and two black/-, rather than a single pair as found on regular loudspeakers. Two separate lengths of speaker cable are used to connect the amplifier output to the loudspeaker input, with the additional cable connected to the second pair of cable inputs on the speaker. The internal crossover circuit in a biwirable speaker is basically two separate circuits that will initially be linked (red to red and black to black) by some form of metal link. By removing this link, each crossover section receives a full signal of its own from the amplifier.
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This diagram shows how a biwirable speaker is connected to the amplifier using two pairs of speaker cable. At the amp, both red and both black conductors are terminated into the same binding post. The metal links bars that join the similar coloured speaker terminals have been removed.
The Benefits
When the metal link bars are removed from a biwirable loudspeaker, the crossover becomes two separate circuits, with each circuit directly connected to one of the drivers on the front of the loudspeaker. Therefore, in a two-way speaker, one crossover is linked to the woofer and the other is linked to the tweeter. Each crossover features a filter that blocks all frequency bands except for the ones needed by the drive unit to which it is attached.
Using two runs of speaker cable allows each crossover to be connected directly to the amplifier's output stage. The full-frequency signal arrives at both crossovers through the red/+ conductor and each is filtered so that the driver receives only the signal it needs. The signals are then passed back to the amp along the corresponding black/- conductors, but because the high and low frequencies have already been separated, each has no affect on the other - the delicate treble is not overpowered by the bass.
The advantage gained by bi-wiring is that a cleaner, less distorted signal arrives at the speaker driver and at the amplifier when the circuit is completed. A cleaner signal will contain more of the subtle detail that would otherwise be lost if the full bandwidth was travelling along one conductor. As a result, some systems can produce an improved sound with better stereo soundstaging thanks to the fine detail within the signal being retained.
More Options
One of the main questions that I get asked is "Do I use the second set of speaker outputs on my amplifier to bi-wire my speakers?". The answer is both yes and no. Most amplifiers, particularly stereo hi-fi amps, have outputs for two pairs of main loudspeakers, usually named A and B. While the A outputs are commonly used to connect the main pair of speakers, the B outputs are normally used to attach a second pair of speakers, maybe a pair in a different room to your hi-fi. It is not necessary to use the B outputs when you bi-wire your speakers, although you can use them if you want - just ensure that both A and B speakers are selected on the amplifier.
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Some people prefer to terminate both bi-wire cables into just the A output stage. This works just as well as using A and B together, and is tidier looking if the amplifier has large binding post terminals. The smaller spring-clip terminals often won't allow the connection of thick bi-wire cables, so using the A and B terminals may be the only way.
