Speaker wire

 ( Loudspeakers ) 

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.

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:

$X\_c\; =\; \backslash frac\{1\}\{2\; \backslash pi\; f\; C\}$

where:

• $f$ is the frequency in hertz; and
• $C$ is the capacitance in .

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

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 (up to 20,000 Hz) 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 (200 total feet of conductor) will have less than 1 percent capacitive loss in the audible range (100 ft * 20 pF/ft = 2000 pF, and 2000 pF < 2700 pF). 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 (10 ft * 300 pF/ft = 3000 pF, and 3000 pF > 2700 pF).

$X\_i\; =\; 2\; \backslash pi\; f\; L$

where:

• $f$ is the frequency in hertz; and
• $L$ is the inductance in henries.

Audio signals are alternating current and so are attenuated by inductance. The following table shows the inductive reactance in ohms (lower means lower loss) for typical cable inductances at various audio frequencies; highlighted rows represent loss greater than 1% at 30 volts RMS:

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% loss will occur at 0.3 ohms or more of inductive reactance. Therefore, to keep audible (up to 20,000 Hz) losses below 1%, the total inductance in the cabling must be kept below about 2 μH.

Ordinary lamp cord has an inductance of 0.1–0.2 μH/ft, likewise for shielded cord, 18-2 Shielded Cord data sheet page 1, West Penn Wire. Retrieved 2011-05-24 so a run of up to about 10 feet (20 total feet of conductor) will have less than 1% inductive loss in the audible range (10 ft * 0.2 μH/ft = 2.0 μH, which is at or below the proximate threshold of 2 μH given above). Some premium speaker cables have lower inductance at the cost of higher capacitance; 0.02-0.05μH/ft is typical, which at the worst end means that a run of up to about 40 feet will have less than 1% inductive loss (40 ft * 0.05 μH/ft = 2.0& μH).