Passive Speaker Cable: Sizing the Run Behind an Amplifier

A passive speaker has no amplifier inside it, so the cable is part of the electrical circuit. Resistance in that circuit wastes power and shifts the response, which is why gauge and length are the only specifications that reliably matter.

What Passive Means in the Cable

The signal on the cable is already amplified. It is a low-voltage, high-current AC waveform, not a line-level signal, and the cable’s job is to deliver it with as little loss as possible.

Passive versus powered speakers

A powered speaker takes line level or digital audio and amplifies internally, so its cable carries almost no current. A passive speaker needs copper sized for current, which is a different cable decision.

Why the circuit resistance matters

Cable resistance adds to the amplifier’s output impedance and to the speaker’s own impedance. With a 4 ohm speaker, a cable that adds 0.4 ohm wastes about ten percent of the power and slightly reduces damping.

Choosing the Gauge

Gauge is the cross-sectional area of each conductor. Lower numbers are thicker, and thicker wire has less resistance per metre.

Construction and Insulation

Two conductors, usually figure-eight or two parallel jackets. Copper is the conductor; copper-clad aluminium costs less and has higher resistance for the same gauge.

OFC and CCA

Oxygen-free copper is the standard choice for audio. Copper-clad aluminium is lighter and cheaper but has about 60 percent more resistance, so treat a CCA cable as one gauge thinner than its label.

In-wall and CL ratings

Cable run inside a wall needs a CL2 or CL3 jacket. Using ordinary figure-eight cable in a wall is a code issue in most jurisdictions, regardless of how it sounds.

Termination and Polarity

The cable ends are as important as the copper. Loose strands, wrong polarity and undersized connectors all produce faults that are easy to hear and hard to find.

Bare wire, banana, spade

Bare wire into a binding post is adequate if the strands are twisted tight and no stray strand bridges the terminals. Banana plugs speed reconnection; spades suit screw terminals that are tightened often.

Keep polarity consistent

Red to positive and black to negative at both ends. A reversed speaker still produces sound but cancels low frequencies when paired with a correctly wired speaker in the same room.

Installation Practice

Run speaker cable away from mains cable where possible, and cross at right angles when they must cross. Keep both channels the same length and the same gauge so the two speakers see the same resistance. Leave a service loop at each end, label both ends, and avoid cable staples that cut into the jacket, because a nick in the insulation is where corrosion starts in a humid room.

Two Passive Setups

Gauge follows current and distance, and both are easy to estimate before the cable is ordered.

Bookshelf speakers on a desk, 3 m runs

16 AWG into spring terminals is adequate and easy to dress. The run is short enough that resistance is not a factor.

In-wall runs to surround speakers, 15 m

14 AWG with a CL3 jacket keeps resistance low and meets the code requirement for in-wall cable. Both channels are cut to the same length.

Frequently Asked Questions

How this guide was built: Built from loudspeaker cable practice: loop resistance versus load impedance, gauge tables, insulation ratings and polarity. Disclosure: No manufacturer names or prices are given. Resistance values are typical for copper; confirm conductor material before sizing a long run.