Index Signal & AmplificationSpeaker Cable Loss

Speaker Cable Loss

Resistance, level loss and sensible run lengths by wire gauge.

Loop resistance132mΩ

Level loss−0.14dB

Power lost in cable1.6%

Damping factor cap60.7

Longest sensible run15.2mcable at 5% of load

Loss against length

16 AWG
12 AWG
20 AWG

Conductor cross-sections, to scale

Input

Wire gaugeAWG

1.29 mm diameter, 1.31 mm² of copper. Lower numbers are thicker.

Run length, one waym

About 16.4 ft.

Speaker impedance (Ω)

How it works

Resistance of a run

Current flows out along one conductor and back along the other, so the loop is twice the run length:

R_c = \frac{2\,\ell\,\rho}{A}

\rho_{Cu} = 1.724\times10^{-8}\ \Omega\,\mathrm{m}

The American Wire Gauge defines the diameter geometrically; every three steps roughly halve the area.

d_{mm} = 0.127 \times 92^{(36 - n)/39}

What the resistance costs

The cable and speaker form a divider. The level reaching the speaker and the share of amplifier power heating the wire are

L = 20\log_{10}\!\frac{Z}{Z + R_c}\ \mathrm{dB}

\frac{P_{cable}}{P_{total}} = \frac{R_c}{Z + R_c}

The 5% rule

A long-standing guideline keeps cable resistance under 5% of the speaker's nominal impedance. That holds the loss below about 0.4 dB and, more importantly, keeps the response ripple caused by the speaker's varying impedance small. The dashed line shows where your gauge crosses that limit.

At audio frequencies and domestic lengths, resistance is the property that matters. Inductance and capacitance of ordinary twin cable only become relevant in very long runs.