Speaker wire is used to make the electrical connection between loudspeakers and audio amplifiers. Modern speaker wire consists of two or more electrical conductors individually insulated by plastic (such as PVC, PE or Teflon) or, less commonly, rubber. The two wires are electrically identical, but are marked to identify the correct audio signal polarity. Most commonly, speaker wire comes in the form of zip cord. The effect of speaker wire upon the signal it carries has been a much-debated topic in the audiophile and high fidelity worlds. The accuracy of many advertising claims on these points has been disputed by expert engineers who emphasize that simple electrical resistance is by far the most important characteristic of speaker wire.
History Early speaker cable was typically stranded copper wire, insulated with cloth tape, waxed paper or rubber. For portable applications, common lampcord was used, twisted in pairs for mechanical reasons. Cables were often soldered in place at one end. Other terminations were binding posts, terminal strips, and spade lugs for crimp connections. Two-conductor quarter-inch tip-sleeve phone jacks came into use in the 1920s and '30s as convenient terminations. Some early speaker cable designs featured another pair of wires for rectified direct current to supply electrical power for an electromagnet in the loudspeaker. Essentially all speakers manufactured now use permanent magnets, a practice which displaced field electromagnet speakers in the 1940s and 1950s.
Explanation Speaker wire is a passive electrical component described by its electrical impedance, Z. The impedance can be broken up into three properties which determine its performance: the real part of the impedance, or the resistance, and the imaginary component of the impedance: capacitance or inductance. The ideal speaker wire has no resistance, capacitance, or inductance. The shorter and thicker a wire is, the lower is its resistance, as the electrical resistance of a wire is proportional to its length and inversely proportional to its cross-sectional area (except superconductors). The wire's resistance has the greatest effect on its performance. The capacitance and inductance of the wire have less effect because they are insignificant relative to the capacitance and inductance of the loudspeaker. As long as speaker wire resistance is kept to less than 5 percent of the speaker's impedance, the conductor will be adequate for home use. Speaker wires are selected based on price, quality of construction, aesthetic purpose, and convenience. Stranded wire is more flexible than solid wire, and is suitable for movable equipment. For a wire that will be exposed rather than run within walls, under floor coverings, or behind moldings (such as in a home), appearance may be a benefit, but it is irrelevant to electrical characteristics. Better jacketing may be thicker or tougher, less chemically reactive with the conductor, less likely to tangle and easier to pull through a group of other wires, or may incorporate a number of shielding techniques for non-domestic uses.
Resistance Resistance is by far the most important specification of speaker wire. Low-resistance speaker wire allows more of the amplifier's power to energize the loudspeaker's voice coil. The performance of a conductor such as speaker wire is therefore optimised by limiting its length and maximising its cross-sectional area. Depending on the hearing ability of the listener, this resistance begins to have an audible effect when the resistance exceeds 5 percent of the speaker's impedance. A speaker wire's impedance takes into account the wire's resistance, the wire's path, and the dielectric properties of local insulators. The latter two factors also determine the wire's frequency response. The lower the impedance of the speaker, the greater a significance the speaker wire's resistance will have. Where large buildings have long runs of wire to interconnect speakers and amplifiers, a constant-voltage speaker system may be used to reduce losses in the wiring.
Wire gauge Thicker wires reduce resistance. The resistance of copper 16-gauge (1.31 mm2) or heavier speaker connection cable has no detectable effect in runs of 50 feet (15 meters) or less in standard domestic loudspeaker connections for a typical 8 ohm speaker. For aluminum or copper-clad aluminum wire, 14-gauge or heavier cable is needed to support this claim due to higher resistivity. As speaker impedance drops, lower gauge (heavier) wire is needed to prevent degradation to damping factor – a measure of the amplifier's control over the position of the voice coil. Insulation thickness or type also has no audible effect as long as the insulation is of good quality and does not chemically react with the wire itself (poor-quality insulation has occasionally been found to accelerate oxidation of the copper conductor, increasing resistance over time). High-power in-car audio systems using 2-ohm speaker circuits require thicker wire than 4 to 8-ohm home audio applications. Most consumer applications use two conductor wire. A common rule of thumb is that the resistance of the speaker wire should not exceed 5 percent of the rated impedance of the system. The table below shows recommended lengths based on this guideline:
* While in theory heavier wire can have longer runs, recommended household audio lengths should not exceed 50 feet (15 m). The gauge numbers in SWG (standard wire gauge) and AWG (American wire gauge) reduce as the wire gets larger. Sizing in square millimeters is common outside of the US. Suppliers and manufacturers often specify their cable in strand count. A 189 strand count wire has a cross-sectional area of 1.5 mm2 which equates to 126.7 strands per mm2.
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