speaker cable: length, thickness, and whether equal runs matter

It does not need to be exotic, but it does need enough copper for the distance and a clean, secure connection at both ends.

Speaker cable attracts two opposite mistakes, and both are expensive in their own way. The first is treating it as a magical component that ought to cost some fixed percentage of the system. The second is assuming any thin length of wire is electrically the same as any other. Neither position survives contact with a tape measure. We take that argument apart properly in do audio cables affect sound quality?; here the question is narrower and entirely practical.

The cable has a simple job, but it is not doing nothing. It carries the amplifier's output current to a passive loudspeaker, and its resistance sits in series with that speaker, so making the run longer or the conductor thinner puts more resistance in the way. Choose ordinary, well-made copper with enough conductor area for the distance, connect it securely at both ends, and the cable gets on with its job without ever becoming the most interesting thing in your system.

length and thickness are one decision

A short hop to an easy loudspeaker does not need the copper that a long route to a lower-impedance design does, and that is because the two are really one decision. Resistance rises with length and falls as the conductor gets thicker, so a cable size only means anything once you know the route it has to take and the load waiting at the end of it. Our guide to speaker impedance explains why that load moves with the music rather than sitting still at 4, 6 or 8 ohms.

Thickness is quoted either in square millimetres or in American Wire Gauge, and AWG runs backwards, so a smaller number is a thicker conductor. Useful reference points: 16 AWG is about 1.3mm², 14 AWG about 2.1mm², and 12 AWG about 3.3mm². Some brands sell rounded metric sizes near those figures, which is why conductor area and published loop resistance tell you far more than the name on the reel.

For most domestic systems, copper between 1.5mm² and 2.5mm² is a sensible place to start. Lean to the thicker end for a longer route, a lower-impedance speaker, or an installation you will not enjoy replacing. Genuinely long runs deserve a calculation rather than a slogan, and the conservative engineering guide is to keep total cable loop resistance comfortably below five per cent of the loudspeaker's nominal impedance. Where the maker publishes loop resistance per metre, multiply it by the one-way run and compare what you get against the speaker's impedance.

equal lengths are tidy, not sacred

Matching the left and right runs is convenient. Both channels end up with the same resistance, the pair is easy to label, and rearranging the room later is simpler. Where the two routes are similar anyway, cutting them equal is entirely sensible.

The trouble starts when equal length turns into a ritual. There is no good reason to hide several unnecessary metres behind one speaker merely because the other sits further from the amplifier. At domestic distances the time the signal takes to travel down the cable is not the issue and never was. Resistance is, and a suitably thick conductor keeps the difference between the two channels small enough to ignore.

A really large imbalance is worth a quick check, particularly with thin cable into a low-impedance speaker. Compare the two loop resistances and go thicker if the sum says so. The right answer is enough copper for both routes, not a tight coil of unused cable sitting behind the near one. And where the amplifier or speaker manual gives a specific instruction, that instruction wins.

measure the route the cable actually takes

A straight line across the floor is almost never the finished route. Measure from each amplifier terminal along the skirting, around the furniture, up the stands and into the matching speaker terminal. Add enough slack to pull the equipment forward and reconnect it comfortably, and no more than that, because a heap of surplus cable behind the rack helps nobody.

Keep the cable away from anywhere furniture can crush it, a door can catch it or a fixing can go through it. Avoid long parallel runs alongside mains wiring where you can, and where the two have to cross, cross them at roughly a right angle. Switch the amplifier off before you connect or change any speaker cable.

Permanent installation brings one more consideration that catches people out. Cable buried in a wall or under a floor may need a particular fire, smoke or building classification, and a flexible cable that is perfectly safe lying loose in a room is not automatically approved for use inside the structure. Check the rating before it disappears behind plaster.

plugs are for a reliable connection, not a badge

Banana plugs come out quickly and keep loose strands under control where 4mm sockets are fitted. Spades clamp neatly beneath a suitable binding post. Clean bare wire, tightly twisted and firmly held, works perfectly well. The best termination is simply the one that fits both products and stays put.

None of them is universal. Some terminals take bare wire only, and some binding posts arrive with safety caps covering the banana opening entirely, so check both the amplifier and the speakers before paying for factory termination. Our banana plugs, spades and bare wire guide goes into the practical differences properly.

A loose or oxidised connection causes far more real trouble than the absence of an elaborate plug. If a channel vanishes, switch the amplifier off and look at both ends: a plug that has worked loose, a conductor that missed the terminal, or one stray strand of copper touching the opposite post. Cut oxidised bare wire back to clean copper before you reconnect it.

polarity and speaker links matter more than folklore

Red positive on the amplifier goes to red positive on the speaker, black negative to black negative, and the same arrangement repeats on both channels. Reverse one speaker and the pair runs out of phase, which usually thins the bass and pulls the solidity out of the centre image while both speakers carry on making sound quite happily.

Many loudspeakers have four terminals joined by metal links. If you are running one ordinary cable per speaker, leave those links firmly in place and connect to the terminals the manual specifies, because taking them out can disconnect part of the crossover. Read our bi-wiring and bi-amping guide before you change the factory arrangement, and our WiiM, Arcam and Wharfedale walkthrough shows the whole job done on one real pair.

One last distinction is worth making, because the words get muddled constantly. A speaker cable is not an RCA or XLR interconnect. Interconnects carry small line-level signals between components; speaker cable carries the amplifier's actual output. Active speakers have their own amplification inside and normally expect a line-level, balanced, digital or network input instead, so establish which kind of speaker you own before ordering anything at all. The active and passive speaker guide sets out what each type asks from the rest of the system.

the two-minute checklist

Measure each real route and add modest working slack. Choose enough copper to keep loop resistance low for that length and that speaker impedance. Equal runs are convenient, but a coil of surplus cable is not an upgrade. Confirm the terminations actually fit, leave the speaker links in place for single wiring, connect red to red and black to black, and check for stray strands before you restore power.

So, how much cable, how thick, and do the runs have to match? Enough for the route it really takes, thick enough that its resistance stops mattering, and no. If you want those figures worked out from the products themselves, build your system plan. Good speaker cable is not mysterious: electrically suitable, mechanically secure, and then happily forgotten. Happy listening.