Speaker Cable: Sizing, Types, and Running It First Fix
What speaker cable to buy, what CSA to run, and why AV installers always run it at first fix. OFC vs CCA, 1.5mm² vs 2.5mm², and the routing mistake that ruins ceiling audio.
The plasterer skims your ceiling on a Friday. On Monday you decide you want flush ceiling speakers in the new kitchen. Too late. To get cable up there now means lifting boards from the room above, or chasing channels into fresh plaster and re-skimming. A job that costs nothing if the cable is already there becomes a few hundred pounds and a mess once the ceiling is closed. This is why anyone who has wired a house runs speaker cable at first fix, before the boards go on, even when the AV kit hasn't been chosen yet.
What it is and what it's for
Speaker cable is a two-conductor stranded copper cable that carries an audio signal from an amplifier or AV receiver to a passive speaker. "Passive" means the speaker has no power of its own; it relies on the amplifier to drive it. The cable's only job is to move that amplified signal with as little resistance as possible.
It is not a mains cable. The signal it carries is low-voltage audio, well under 100V even on a loud peak, and it carries no power until the amplifier is switched on. That distinction matters for how you're allowed to run it: speaker cable is extra-low-voltage and isn't a fixed mains circuit, so it doesn't fall under the Part P notification rules that govern your sockets and lighting. You can run it yourself. But it still shares walls and voids with mains cable, so it pays to keep it tidy and separated, which we'll come back to.
The two conductors are usually identical lengths of fine copper strand. One is marked, by a printed line, a coloured strand, or a ridge on the jacket, so you can keep polarity consistent: the marked core goes to the red (+) terminal at both the amplifier and the speaker. Get polarity reversed on one speaker of a pair and the two cones push and pull against each other, which thins out the bass noticeably. It's an easy mistake and an annoying one to chase down after the plaster's on.
Types, sizes, and specifications
Two things define a length of speaker cable: the cross-sectional area of the copper, written as CSA in mm², and what the copper is actually made of.
CSA is the thickness of the conductor. Thicker copper has lower resistance, and lower resistance matters over distance because a long thin run starts to eat the signal before it reaches the speaker. For a domestic extension the sizing rule of thumb is straightforward.
| CSA | Best for | Why |
|---|---|---|
| 1.5mm² | Runs up to 5-6m, standard ceiling speakers | Plenty of copper for short runs at normal listening levels. The default for most ceiling speaker positions. |
| 2.5mm² | Runs of 6-15m, or systems rated 100W+ per channel | Keeps resistance low over longer distances and handles higher power without losing output. |
| 4mm² | Very long runs (15m+) or high-power audiophile systems | Overkill for most homes, but the right call for a media room amp driving big floor-standers across a large space. |
For the great majority of extension ceiling speakers, 1.5mm² is correct. People over-spec this constantly. Unless you're running cable the length of the house or driving serious power, 2.5mm² is the most you'll ever need, and 1.5mm² covers the typical four ceiling speakers in a kitchen-diner without breaking a sweat.
The copper type is where marketing gets loud and the truth gets quiet. There are three grades you'll see.
OFC, oxygen-free copper. The purest, lowest-resistance option. It's what audiophile brands use and what serious installers default to. The audible benefit over ordinary copper at domestic run lengths is small to none, but it's better copper, it doesn't oxidise, and it isn't expensive enough to argue about.
Plain copper. Standard electrolytic copper, not labelled OFC. Perfectly good for home use and what most decent mid-range cable actually is under the marketing. Adequate for any normal extension.
CCA, copper-clad aluminium. An aluminium core with a thin copper coating. It's cheap because aluminium is cheap, but aluminium has higher resistance than copper, so a given CCA cable behaves like a thinner copper one. Worse, aluminium oxidises at the terminals over time, and that oxide layer raises resistance further and can eventually cause a crackly or dropping connection. Avoid CCA for anything you're burying in a wall or ceiling, because the one place you never want a degrading connection is the one you can't get back to.
Jacket colour is purely practical, not a spec. Clear jackets are common for runs hidden behind skirting where nobody sees them. White or grey suits surface-mounted runs against a pale wall. Black is for exposed installations where you want the cable to disappear against a dark background. None of it changes how the cable performs.
One label genuinely matters for in-wall work. Cable run inside walls, ceiling voids, and especially roof spaces should be PVC-jacketed and rated for in-wall use; some is marked "in-wall rated" or carries a Low Smoke (LSZH, low smoke zero halogen) jacket. In a roof void or above a ceiling, smoke behaviour in a fire is a real consideration, and an in-wall or low-smoke cable is the sensible choice there. Skip CCA entirely for buried runs and pick a PVC or low-smoke jacket rated for the job.
How to work with it
Speaker cable is light, flexible, and easy to handle, which is exactly why it's tempting to do it badly. The cable costs little and the work is quick; the discipline is all in the routing.
Run it like a mains cable even though it isn't one. That means dropping it through wall cavities and stapling it neatly along joists, not draping it loosely across a ceiling void. Keep it separated from mains cable where you can, ideally crossing at right angles rather than running parallel and bundled together for long stretches, which keeps any electrical hum out of the audio. A clip every 300mm or so along a joist keeps it off the back of the plasterboard so a future screw doesn't catch it.
Cut it with side cutters or a sharp knife. Strip about 10-15mm of jacket from each conductor with wire strippers, twist the fine strands tight so no whiskers stray, and you're ready to terminate. Don't tin the ends with solder unless the terminal specifically wants it; bare twisted strands clamp better in a spring or screw terminal, and solder can cold-flow over time and loosen the joint.
Leave a service loop at each end. A spare 300-400mm of slack coiled at the speaker position and at the amplifier end means you can re-terminate, move the speaker a few inches, or swap a faceplate later without the cable being a fraction too short. Trimming a long cable down is free; adding length to a short one buried in a wall is not.
Storage is trivial. It doesn't care about damp the way timber or plaster does, but don't leave the stripped ends sitting on a dusty floor for weeks, and tape or cap the ends so plaster and muck don't pack into the strands before you terminate.
How much do you need
Work it out per run, not by the room. Each speaker needs its own continuous length of cable from the amplifier position all the way to that speaker. You do not daisy-chain passive ceiling speakers off one cable.
Measure the straight-line route from your AV location to each speaker position, then add for the up-and-over reality of cable: down a wall, along the joists, across to the speaker. A run that's 6m as the crow flies is often 9-10m once it follows the structure. Then add a service loop at each end and a sensible margin for error.
A worked example. Four ceiling speakers in a kitchen-diner, all run back to an AV hub in a utility cupboard. The two nearest speakers are about 8m of routed cable each, the two furthest about 12m each. That's 8 + 8 + 12 + 12 = 40m of routed length. Add roughly 0.7m of service loop per run (2.8m total) and a 10-15% margin for measuring errors and re-routes, and you'd buy a 50m roll. Rolls come in 25m, 50m, and 100m lengths, so rounding up to the next roll is normal and the spare always gets used.
Order one roll, not four offcuts. Cable from a single roll is consistent, and the leftover is worth having for the speaker you add in two years.
Cost and where to buy
Speaker cable is cheap relative to everything else at first fix, which is the whole argument for running plenty of it. As a guide, decent 1.5mm² OFC runs £1 – £3 per metre, and 2.5mm² around £2 – £4 per metre, depending on copper grade and where you buy. A 50m roll of good mid-range cable is a small line on a first-fix budget.
Brands sit in clear tiers. Amazon Basics and similar own-label rolls are the budget end and are usually CCA, fine for a temporary surface run but not what you want buried. QED is the dependable mid-range, widely stocked and genuinely good copper. Van Damme is professional install cable, the stuff you'll find in studios and serious home cinemas, and is the sweet spot if you want install-grade quality without paying audiophile prices. Chord sits at the high end for people building dedicated listening rooms.
Buy it from an AV specialist or online (Amazon, Richer Sounds, dedicated cable suppliers) rather than a general builders' merchant, which won't stock the better grades. Toolstation and Screwfix carry basic speaker cable, but for anything going in a wall, choose a named install brand and check it's copper, not CCA, and rated for in-wall use.
External resource
Van Damme Cable
Manufacturer of professional install-grade speaker and audio cable widely used in custom home AV. Useful reference for in-wall-rated specifications.
vandammecable.com
Alternatives
For outdoor and buried runs, ordinary speaker cable is the wrong choice and there's a direct substitute. Garden speakers, a patio system, or any cable that goes underground or stays exposed to weather needs UV-resistant direct-burial outdoor speaker cable, which has a tougher jacket that won't perish in sunlight or wick water into the conductors. Use it for anything outside; standard PVC cable will degrade within a couple of seasons exposed to UV.
For the AV signal feeds themselves (the cable from a TV or source to the amplifier) speaker cable doesn't apply at all; those are HDMI, optical, or network runs, which is a separate first-fix consideration. Speaker cable only ever carries the amplified output to passive speakers.
Where you'll need this
- First fix electrics - the stage where speaker cable goes in, alongside power and lighting cable, before the ceiling and walls are boarded
- Electrical layout planning - where you mark ceiling speaker positions and the AV hub location so the cable runs land in the right place
Speaker cable belongs to the same first-fix window across any extension or renovation project, not just a kitchen build. Anywhere walls and ceilings are about to be closed up, that's the moment to run it.
Common mistakes
The mistake that ruins a ceiling audio install is leaving loops of cable coiled in the ceiling void instead of routing every run back to one central point. It feels efficient at the time. It makes adding or repositioning speakers impossible later, because there's no cable path back to the amplifier, only a tangle stranded above a sealed ceiling. Decide your AV location early and route every single speaker run back to it.
Warning
Never bury copper-clad aluminium (CCA) speaker cable in a wall or ceiling. The aluminium oxidises at the terminals over time, resistance climbs, and the connection eventually crackles or drops out. The one cable you can never get back to is exactly the one that must not degrade. Use copper or OFC, PVC-jacketed and rated for in-wall use, for anything buried.
The other common errors are smaller but real. Reversing polarity on one speaker of a stereo pair thins the bass; keep the marked core on the (+) terminal at both ends. Under-running on quantity means a future speaker has no cable path, so run a spare pair to any position you might want later while the walls are open. And skipping the service loop leaves you fighting a cable that's an inch too short at the exact moment the plaster's already on.