Speaker wire

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 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. 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, 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

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 or heavier speaker connection cable has no detectable effect in runs of 50 feet 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 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. 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:

Wire size	2 Ω load	4 Ω load	6 Ω load	8 Ω load
22 AWG	3 ft	6 ft	9 ft	12 ft
20 AWG	5 ft	10 ft	15 ft	20 ft
18 AWG	8 ft	16 ft	24 ft	32 ft
16 AWG	12 ft	24 ft	36 ft	48 ft
14 AWG	20 ft	40 ft	60 ft ^*	80 ft ^*
12 AWG	30 ft	60 ft ^*	90 ft ^*	120 ft ^*
10 AWG	50 ft	100 ft ^*	150 ft ^*	200 ft ^*

^* While in theory heavier wire can have longer runs, recommended household audio lengths should not exceed 50 feet.
The gauge numbers in SWG and AWG 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.

Wire material

Use of copper or copper-clad aluminum is more or less universal for speaker wire. Copper has low resistance compared to most other suitable materials. CCA is cheaper and lighter, at the expense of somewhat higher resistance. Copper and aluminum both oxidize, but oxides of copper are conductive, while those of aluminum are insulating. Also offered is Oxygen-free Copper, sold in several grades. The various grades are marketed as having better conductivity and durability, but they have no significant benefit in audio applications. Commonly available C11000 Electrolytic-Tough-Pitch copper wire is identical to higher-cost C10200 Oxygen-Free copper wire in speaker cable applications. Much more expensive C10100, a highly refined copper with silver impurities removed and oxygen reduced to 0.0005 percent, has only a one percent increase in conductivity rating, insignificant in audio applications.
Silver has a slightly lower resistivity than copper, which allows a thinner wire to have the same resistance. Silver is expensive, so a copper wire with the same resistance costs considerably less. Silver tarnishes to form a thin surface layer of silver sulfide.
Gold has a higher resistivity than either copper or silver, but pure gold does not oxidize, so it can be used for plating wire-end terminations.

Capacitance and inductance

Capacitance

occurs between any two conductors separated by an insulator. In an audio cable, capacitance occurs between the cable's two conductors; the resulting losses are called "dielectric losses" or "dielectric absorption". Capacitance also occurs between the cable's conductors and any nearby conductive objects, including house wiring and damp foundation concrete; this is called "stray capacitance".
Parallel capacitances add together, and so both the dielectric loss and the stray capacitance loss add up to a net capacitance.
Audio signals are alternating current and so are attenuated by such capacitances. Attenuation occurs inversely to frequency: a higher frequency faces less resistance and can more easily leak through a given capacitance. The amount of attenuation can be calculated for any given frequency; the result is called the capacitive reactance, which is an effective resistance measured in ohms:
where:

is the frequency in hertz; and
is the capacitance in farads.

This table shows the capacitive reactance in ohms for various frequencies and capacitances; highlighted rows represent loss greater than 1% at 30 volts RMS:

Capacitance	100 Hz	200 Hz	500 Hz	1,000 Hz	2,000 Hz	5,000 Hz	10,000 Hz	20,000 Hz	50,000 Hz
100 pF	15,915,508	7,957,754	3,183,102	1,591,551	795,775	318,310	159,155	79,578	31,831
200 pF	7,957,754	3,978,877	1,591,551	795,775	397,888	159,155	79,578	39,789	15,916
500 pF	3,183,102	1,591,551	636,620	318,310	159,155	63,662	31,831	15,916	6,366
1,000 pF	1,591,551	795,775	318,310	159,155	79,578	31,831	15,916	7,958	3,183
2,000 pF	795,775	397,888	159,155	79,578	39,789	15,916	7,958	3,979	1,592
5,000 pF	318,310	159,155	63,662	31,831	15,916	6,366	3,183	1,592	637
10,000 pF	159,155	79,578	31,831	15,916	7,958	3,183	1,592	796	318
20,000 pF	79,578	39,789	15,916	7,958	3,979	1,592	796	398	159
50,000 pF	31,831	15,916	6,366	3,183	1,592	637	318	159	64
100,000 pF	15,916	7,958	3,183	1,592	796	318	159	80	32
200,000 pF	7,958	3,979	1,592	796	398	159	80	40	16
500,000 pF	3,183	1,592	637	318	159	64	32	16	6

The voltage on a speaker wire depends on amplifier power; for a 100-watt-per-channel amplifier, the voltage will be about 30 volts RMS. At such voltage, a 1 percent loss will occur at 3,000 ohms or less of capacitive reactance. Therefore, to keep audible losses below 1 percent, the total capacitance in the cabling must be kept below about 2,700 pF.
Ordinary lamp cord has a capacitance of 10–20 pF/ft, plus a few picofarads of stray capacitance, so a 100-foot run will have less than 1 percent capacitive loss in the audible range. Some premium speaker cables have higher capacitance in order to have lower inductance; 100–300 pF is typical, in which case the capacitive loss will exceed 1 percent for runs longer than as little as 10 feet.