Bi-wiring Guide

Bi-wiring your speakers can improve the sound quality in both hi-fi and home cinema systems. This guide explains what bi-wiring is all about, how it can help improve the overall sound quality, and gives advice about how to bi-wire the speakers using additional cables.



The majority of speakers in hi-fi and home cinema systems work by turning an electrical current with a variable strength into sound using different sizes of drivers - the delicate circular units on the front of the speakers. The strength of the electrical signal changes the extent of the vibration and the resulting movement of the drivers is heard by the listener as an airborne sound wave. The quality and clarity of the amplifier signal has an effect on the quality of the sound that the speakers eventually produce. Bi-wiring allows these signals to be used in the most efficient way and can result in small but significant improvements.



The speaker units themselves are made up of a number of components. There are the cable inputs on the back that are usually coloured red and black, where the red (positive) receives the signal from the amplifier and the black (negative) returns the signal back to the amp to complete the electrical circuit. On the front of the cabinet are the speaker 'drivers' which vary in size depending on what sound frequency they reproduce. In a two-way speaker there are two types of driver - the bass driver which handles the low frequency bass, and a smaller 'tweeter' that handles the other sound frequencies, generally those above about 3kHz. A three-way speaker is similar but has three types of driver for low frequency bass, mid-range and high frequency tweeter. Although the number of drivers on most speaker designs will tell you if it is a two-way or three-way unit, this is not always the case as some speakers use multiple drivers for bass, for instance.

Between the cable inputs and the drivers is an electrical circuit called the 'crossover'. This is where the full bandwidth signal from the amp is separated into the component frequencies and passed on to the correct driver. Most speakers will be connected using a single two-core speaker cable, where one core(+) carries the signal to the crossover and the other core(-) returns the signal back to the amplifier. The the downside of this is that there is potential for powerful bass signals to overpower and mask the more delicate low frequencies, particularly on the return stage. This can result in a sound that may not be as clear and focused as it could be. Bi-wiring goes a long way to solving this problem.

A speaker that can be bi-wired can easily be identified by looking at the cable inputs on the back of the cabinet. Where normal speakers have a single pair of inputs, the positive red and the negative black, a bi-wirable speaker has two pairs of inputs, two positive and two negative. These type of speakers can be connected to the amplifier using two separate runs of two-core speaker cable, or a single run of dedicated bi-wire cable containing four individual cores. Either option will work, but a four core bi-wire cable will look neater. The reason for using two cable runs rather than one is that the return signals can be separated from the feed, reducing the amount of masking by low frequencies, and revealing more of the subtle detail often lost with a single cable connection. In essence, what you are doing is dividing the crossover into two separate circuits - one dedicated to the bass driver and the other dedicated to the tweeter. Each part of the crossover therefore has its own amplifier feed and return cable, and the masking effect is reduced. For normal use with a single two core cable, a bi-wirable speaker will have the crossover sections linked together by some form of jumper bar between the two pairs of cable inputs. When these jumpers are in position, the speaker acts just like any normal speaker unit, with a single crossover circuit fed by a single two core cable. To separate the crossover into two circuits, each dedicated to a particular driver, the jumpers must be removed. This is done quite easily from the rear panel without needing to open up the speaker cabinet.

The most common and confusing aspect of bi-wiring is how the extra cable is connected to the amplifier output stage, and the type of connection you use depends a great deal on the type of amplifier you have, the type and quantity of the amp's cable outputs, and the type of cable you are using. Amplifiers need a minimum of two pairs of outputs to drive a single pair of speakers, left channel positive and negative, and right channel positive and negative. Other amplifiers have outputs for four speakers, two left channel + and -, and two right channel + and -, and these are provided generally so that you can connect a second pair of speakers, maybe in another room. Amplifiers with either of the output configurations above can be used to drive bi-wired speakers - it is not dependant on how many outputs the amp has. Take, for example, a single left channel speaker. You connect two cable runs to the speaker inputs, two red (positive) and two black (negative). At the amplifier, you have four wires, two positive and two negative. If the amp only has an output for a single left channel speaker, the two red (+) wires can be bound together and inserted into the single red (+) output, and the same goes for the two black (-) wires. If the amp has outputs for two left channel speakers, the wires can each be connected to a single output, two red(+) and two black(-). This procedure is repeated for the right channel speaker. Which method you use is up to you, but most people find it better to connect each speaker to two outputs if the cable they are using is fairly large, making it difficult to bind the wires together into a single output. Binding post or banana plug outputs on the amp are most suited to attaching two wires into a single output - there is more room. On the other hand, the smaller spring-clip terminals may be too small for even a single run of average size cable, making your choice of cable much more important.

To make the whole thing a bit easier to understand, here are some diagrams that show the various connection options available:  
Single speaker connection diagram
  This diagram shows how a single bi-wirable speaker is connected to an amplifier using a single run of two core speaker cable. The speaker has two pairs of inputs on the back, and in this configuration any pair can be used with the single cable. The speaker crossover operated as a combined circuit, separating and filtering all the frequencies (Hi and Low) and feeding them to the corresponding driver. The jumper bars allow the signal from the single cable input to reach both sections of the crossover.
Single bi-wire speaker connection diagram
This next diagram shows a bi-wire speaker that has actually been bi-wired using a second run of speaker cable. The jumper bars have been removed so that the crossover is split into two separate circuits, each dedicated to the frequency of the driver to which it is associated. This allows each driver to use its own cable to receive and return the amplifier signal, thereby reducing interference and masking between high and low frequencies. At the amplifier, a single pair of outputs is shown with the positive and negative cable pairs bound together, although the same speaker configuration would be used if two pairs of amplifier outputs were used - the cables from the amplifier would not be spliced together.
Normal speaker connections
  This simple diagram shown the most common type of cable connection using a single two core cable to each speaker. Although the speakers can be bi-wired thanks to the extra set of cable inputs, the jumper bars are in place so it acts just like a regular speaker unit.
Bi-wire speaker connection diagram
The next step if you have a pair of bi-wirable speakers is to add a second run of cable, preferably the same type as the first, and connect it to the second set of inputs on the speaker unit. The jumper bars in this diagram have been removed to separate the crossover section into high and low frequencies. Although this diagram shows only one pair of amplifier terminals in use, with the cables bound together, the second set could be used and will produce the same results, as shown in the diagram below:  
Alternative bi-wire speaker connection diagram
Normal and bi-wire speaker cables
  The speaker cable itself should not be added without a little thought. First, you should consider the size of the terminals on the amplifier to ensure that either a single cable or a bound-together bi-wire cable can be fitted. This is much less of a problem if you are using an amplifier with two pairs of outputs for each speaker. Secondly, you should try and make sure that both cable runs to each speaker are the same make. Although not essential, matching the cables will ensure that the sound characteristics of each run is the same and the resulting sound will not be compromised by a second, poorer quality cable. Most cable manufacturers offer a dedicated bi-wire cable containing four cores. These are usually two single cables made within the same insulated casing, and they cost the same as two separate runs. There is no difference in the sound quality of a combined cable over two separate ones, but they allow you to keep things a bit tidier.