Quick answer: Speaker cable has two identical conductors, one marked with a stripe, rib, or text. Treat the marked conductor as positive and connect it to the red terminal at both the amplifier and the speaker. Polarity matters because both speakers must move in the same direction: invert one and the bass cancels in the listening position while the treble still sounds normal. The cable itself is not polarised; the marking exists only to keep the two ends consistent.
Because the conductors are electrically identical, a mistake is invisible until you listen. The symptom is a thin, hollow bass and an image that seems to come from nowhere, and it is often blamed on the room or the amplifier. Checking polarity takes a minute and fixes a fault that no equaliser can.
Why polarity matters
Two drivers moving together
A bass note moves both cones forward and back together. If one speaker is wired in reverse, its cone moves backwards while the other moves forwards, and at wavelengths longer than the distance between them the two pressure waves cancel. The result is a null in the bass at the listening position that no amount of tone control can fill.
How to recognise it
Play a mono recording with strong bass. With correct polarity the bass is centred and solid; with one speaker inverted it becomes diffuse and weak, and moving your head changes the balance. A phase test file, which announces in phase and out of phase, makes the difference obvious in seconds.
Marking conventions
| Cable type | Usual marking | Note |
|---|
| Figure eight | Rib or stripe on one side | Most common domestic type |
| Twin round | Printed text on one core | Text may fade, so label ends |
| Transparent | Copper and silver-coloured strands | Pick one and stay consistent |
| Four core, bi-wire | Two marked, two plain | Keep pairs together at each end |
Wiring at each end
At the amplifier, the marked conductor goes to the red or plus terminal. At the speaker, the same marked conductor goes to the red or plus terminal. If the amplifier is bridged or the terminals are not colour coded, check the manual, because a bridged output may not have a ground reference and mis-wiring can damage the amplifier.
Terminate properly rather than clamping bare strands. A crimped spade or banana plug holds a constant contact area, while bare copper cold-flows and loosens over months, which produces intermittent crackle on one channel that is often misdiagnosed as a failing driver.
Testing without test gear
A 1.5 V battery briefly touched across the terminals makes the cone move: outward for correct polarity when the plus of the battery meets the plus terminal. The movement is small and best seen with the grille off. Alternatively use a phone app that generates a phase test tone, or simply swap one speaker’s connections and listen for which version has more bass.
For a permanent installation, label both ends before the cable disappears. The speaker terminals reference covers binding posts and plates, the OFC speaker wire overview covers conductor construction, and the speaker banana plugs guide covers terminations that stay tight.
Practical scenarios
- New pair of speakers with thin bass: check polarity first, before moving furniture or buying an equaliser.
- In-wall installation: label the marked conductor at both ends, because the cable is out of reach once the wall is closed.
- Bi-wiring with a four-core cable: keep the two positive cores on the red terminals and the two negative on the black, or the bass and treble sections cancel.
- Second zone in another room: the amplifier’s zone terminals may be labelled differently; verify with the battery test rather than assuming.
FAQ
Does it matter which wire is positive?
Not which one, but that both speakers use the same convention. The two conductors are electrically identical, so swapping both is harmless; swapping one inverts that speaker and cancels the bass when both play together.
Can reversed polarity damage anything?
With a normal amplifier, no. The signal is alternating current and the load is symmetrical. Damage happens with mis-wiring across bridged outputs or with a short between the two conductors, not with simple inversion.
Why does one speaker sound quieter?
Check for a loose strand bridging the terminals, a partly inserted banana plug, or a damaged cable. If the level difference is small and only in the bass, polarity is the likely cause; if it affects the whole range, look at the connection.
