Cable and power
Speaker Cable Gauge Chart
Quick answer
A 100 foot run to an 8 ohm loudspeaker needs 12 AWG cable, because that is the first gauge whose round-trip resistance stays under 5 percent of the load. 14 AWG covers 79 feet, 10 AWG covers 200 feet, and 16 AWG runs out at 50 feet.
Speaker cable is the cheapest part of a sound system and the part churches most often get wrong, usually by running a hundred feet of lamp cord to a loudspeaker at the back of a balcony and then wondering why the box sounds soft and woolly. The cable is in series with the loudspeaker, so its resistance steals power and, worse, it wrecks the damping factor that lets an amplifier control a woofer.
The accepted design rule is one line: keep the round-trip resistance of the cable under 5 percent of the loudspeaker’s nominal impedance. That costs about 0.42 dB of the amplifier’s power, which nobody can hear, and it keeps the damping factor usable. Everything on this page is that rule applied to the gauges you can actually buy. Work your own run with the speaker cable gauge calculator.
On this page
What is the maximum speaker cable run for each gauge?
Find your loudspeaker’s nominal impedance across the top and your gauge down the side. The figure is the longest one-way run that keeps round-trip resistance at or under 5 percent of the load. Halving the impedance halves the allowed length, which is why a 4 ohm load punishes thin cable twice as hard.
At 8 ohms the 5 percent limit allows 79 feet on 14 AWG, 126 feet on 12 AWG and 200 feet on 10 AWG, and every one of those lengths halves if the loudspeaker is 4 ohms.
| Gauge | Ohms per 1,000 ft, one conductor | Max run at 4 ohms | Max run at 8 ohms | Max run at 16 ohms |
|---|---|---|---|---|
| 18 AWG | 6.385 | 15.7 ft | 31.3 ft | 62.7 ft |
| 16 AWG | 4.016 | 24.9 ft | 49.8 ft | 99.6 ft |
| 14 AWG | 2.525 | 39.6 ft | 79.2 ft | 158.4 ft |
| 12 AWG | 1.588 | 63.0 ft | 125.9 ft | 251.9 ft |
| 10 AWG | 0.999 | 100.1 ft | 200.2 ft | 400.4 ft |
| 8 AWG | 0.6282 | 159.2 ft | 318.4 ft | 636.8 ft |
Resistance figures are annealed copper at 68 F, one conductor. Round-trip resistance is twice the one-way figure because the current returns down the second conductor. Copper-clad aluminium cable sold at the same gauge number has roughly 1.6 times the resistance, so treat a copper-clad 12 AWG run as if it were 14 AWG.
Which gauge should I buy for my run length?
The same rule read the other way round, which is the direction a church actually shops in. Measure the cable path, not the straight line: a loudspeaker 40 feet away across the room is usually a 70 foot run once the cable has gone up a wall, along a ceiling and back down.
An 8 ohm loudspeaker needs 14 AWG out to 79 feet, 12 AWG out to 126 feet and 10 AWG out to 200 feet, and beyond about 318 feet no common gauge satisfies the rule.
| One-way run | Gauge for 4 ohms | Gauge for 8 ohms | Gauge for 16 ohms | Comment |
|---|---|---|---|---|
| Up to 15 ft | 18 AWG | 18 AWG | 18 AWG | Patch length behind a rack. Anything works. |
| 25 ft | 16 AWG | 18 AWG | 18 AWG | A typical stage monitor run. |
| 35 ft | 14 AWG | 16 AWG | 18 AWG | Platform to a mid-room fill. |
| 50 ft | 12 AWG | 14 AWG | 16 AWG | The common portable PA distance. 16 AWG just fails at 8 ohms. |
| 75 ft | 12 AWG | 14 AWG | 16 AWG | Rack to a flown main in a small sanctuary. |
| 100 ft | 10 AWG | 12 AWG | 14 AWG | Rack to a balcony delay. |
| 125 ft | 10 AWG | 12 AWG | 14 AWG | Long side-wall run in a 500 seat room. |
| 150 ft | 8 AWG | 10 AWG | 12 AWG | Consider moving the amplifier instead. |
| 200 ft | 8 AWG | 10 AWG | 12 AWG | At this distance a 70 volt line is usually cheaper. |
| 250 ft | Not practical | 8 AWG | 10 AWG | Copper cost now exceeds a local amplifier. |
| 300 ft | Not practical | 8 AWG | 10 AWG | Use 70 volt distribution or a remote amplifier rack. |
| 400 ft | Not practical | Not practical | 10 AWG | Low impedance has stopped making sense. |
Gauges are the thinnest that satisfies the 5 percent rule, which is the same test the site’s cable calculator applies. Buying one gauge heavier than the table says is cheap insurance and gives you room to move the loudspeaker later. Buying two gauges lighter is the mistake this chart exists to prevent.
What does the cable actually cost you in resistance?
The raw numbers, so you can check any run rather than trusting a rule. Round-trip resistance is the gauge figure divided by 1,000, multiplied by the length, multiplied by two. The percentage column is that resistance against an 8 ohm load, and the 5 percent line is where the recommendation changes.
A 100 foot run of 16 AWG presents 0.80 ohms round trip, which is 10 percent of an 8 ohm load, double the accepted limit, while the same run in 12 AWG presents 0.32 ohms and 4 percent.
| One-way run | 16 AWG | 14 AWG | 12 AWG | 10 AWG |
|---|---|---|---|---|
| 25 ft | 0.201 ohm, 2.5% | 0.126 ohm, 1.6% | 0.079 ohm, 1.0% | 0.050 ohm, 0.6% |
| 50 ft | 0.402 ohm, 5.0% | 0.253 ohm, 3.2% | 0.159 ohm, 2.0% | 0.100 ohm, 1.2% |
| 75 ft | 0.602 ohm, 7.5% | 0.379 ohm, 4.7% | 0.238 ohm, 3.0% | 0.150 ohm, 1.9% |
| 100 ft | 0.803 ohm, 10.0% | 0.505 ohm, 6.3% | 0.318 ohm, 4.0% | 0.200 ohm, 2.5% |
| 150 ft | 1.205 ohm, 15.1% | 0.758 ohm, 9.5% | 0.476 ohm, 6.0% | 0.300 ohm, 3.7% |
| 200 ft | 1.606 ohm, 20.1% | 1.010 ohm, 12.6% | 0.635 ohm, 7.9% | 0.400 ohm, 5.0% |
| 250 ft | 2.008 ohm, 25.1% | 1.263 ohm, 15.8% | 0.794 ohm, 9.9% | 0.500 ohm, 6.2% |
| 300 ft | 2.410 ohm, 30.1% | 1.515 ohm, 18.9% | 0.953 ohm, 11.9% | 0.599 ohm, 7.5% |
Percentages are against an 8 ohm nominal load. Double them for a 4 ohm load and halve them for 16 ohms. At the 5 percent limit the cable dissipates about 0.42 dB worth of the amplifier’s power. The site’s calculator also reports the level drop as a voltage ratio, which reads about 0.42 dB at the same point: the two figures are the same condition expressed as power and as pressure, and the difference is explained in the decibel reference chart.
Why 5 percent, and why damping factor is the real reason
Losing 5 percent of the power is not the point. A fifth of a decibel is inaudible and nobody would run heavy cable to recover it. The reason the rule exists is damping factor, the ratio of the load impedance to everything in series with the woofer, which includes the amplifier’s output impedance and every ohm of cable.
A modern amplifier has an output impedance in the milliohms, giving a damping factor in the hundreds on paper. Put 0.8 ohms of 16 AWG between it and an 8 ohm box and the damping factor collapses to about 10, because the cable now dominates. What that sounds like is a bass note that starts on time and then keeps going: the amplifier can no longer brake the cone against its own momentum. It is heard as woolly, indistinct low end, and it is routinely blamed on the loudspeaker.
Keeping the cable under 5 percent of the load keeps the worst-case damping factor at 20 or better, which is the point past which further improvement stops being audible. That is the whole argument. It is also why the rule scales with impedance rather than with distance: the cable does not care how far it goes, it cares how big it is compared with the speaker.
Where this chart does not apply
It does not apply to 70 volt lines. A constant voltage system runs at high voltage and low current on purpose, so cable resistance is a trivial fraction of a load that is measured in thousands of ohms. A 70 volt run of 16 AWG can be many hundreds of feet. Those runs are sized by insertion loss and by the total tap load instead, which is the 70 volt tap chart.
It does not apply to powered loudspeakers. A QSC K12.2 or a JBL EON712 has its amplifier inside the cabinet, so what runs to it is a balanced line level signal on a microphone cable plus a mains cord. Neither is affected by this table, and the mains cord is covered by the circuit load chart.
Nominal impedance is not the real impedance. An "8 ohm" loudspeaker dips below 8 ohms somewhere in its range, often to 5 or 6 ohms near the woofer resonance, and that dip is exactly where the damping matters most. The 5 percent rule already carries enough margin to absorb this, which is another reason not to shave it.
Two loudspeakers on one run change the arithmetic. Two 8 ohm boxes in parallel present 4 ohms, so the allowed length halves. Churches daisy-chain monitors and then blame the amplifier.
Exotic cable does nothing here. Oxygen-free copper, braided geometries and directional markings do not change resistance, and resistance is the only property in this table. Buy the right gauge from a reputable maker in the right jacket rating for the space it runs through, and spend the difference on treating the room.
Sources
- Copper conductor resistance per 1,000 feet at 68 F, as implemented in this site’s cable gauge calculator
- The 5 percent of nominal impedance cable sizing convention used in loudspeaker manufacturer application guides
- NFPA 70 National Electrical Code Article 640, audio signal processing, amplification and reproduction equipment, for jacket ratings in plenum and riser spaces
Frequently asked questions
What gauge speaker wire do I need for a 100 foot run?
For an 8 ohm loudspeaker, 12 AWG. That is the first gauge whose round-trip resistance over 100 feet, about 0.32 ohms, stays under 5 percent of an 8 ohm load. If the loudspeaker is 4 ohms, or if two boxes share the run, step up to 10 AWG. 14 AWG at that distance is 6.3 percent and 16 AWG is 10 percent, which is double the accepted limit.
Can I use 16 AWG for my church speakers?
Only for short runs. At 8 ohms, 16 AWG reaches about 50 feet before it breaks the 5 percent rule, and at 4 ohms only 25 feet. It is fine for a monitor beside the platform and wrong for anything flown or run to a balcony. The failure is not silence, it is a soft and indistinct low end that gets blamed on the loudspeaker.
Does speaker cable quality actually matter?
Gauge and copper content matter, and nothing else in this table does. Resistance is set by cross-sectional area and by the metal, so a heavier gauge of ordinary stranded copper beats a thinner exotic cable every time. Watch for copper-clad aluminium sold at a copper gauge number: it has roughly 1.6 times the resistance, so treat copper-clad 12 AWG as 14 AWG.
At what distance should I switch to a 70 volt system?
Around 150 to 200 feet, or as soon as you have more than about six loudspeakers to feed. Past that point the copper for a low impedance run costs more than the transformers, and a constant voltage line lets you tap each speaker at the wattage that zone needs. Distributed systems suit background music and speech, not a worship band.
Why does my bass sound muddy through long speaker cable?
Damping factor. The cable resistance sits in series with the woofer, so an amplifier that would otherwise control the cone can no longer brake it. About 0.8 ohms of cable on an 8 ohm box drops the damping factor to roughly 10, which is audible as low end that starts on time and then keeps going. Heavier cable fixes it; more equalisation does not.
Should I run one cable to two loudspeakers?
You can, but halve the allowed length. Two 8 ohm boxes in parallel present 4 ohms, so a 100 foot run that was fine for one now needs 10 AWG rather than 12. Check the amplifier tolerates the combined load as well: many two channel amplifiers are rated to 4 ohms per channel and some install amplifiers only to 8.
Researched, not professional advice. This page is compiled from published manufacturer specifications, operator manuals, FCC rules, published standards and owner-review consensus, not hands-on testing. Sound system design, rigging loudspeakers overhead, and any electrical work are jobs for a qualified professional: have flown loudspeakers and their attachment points signed off by a structural engineer or a certified rigger, and have all wiring done by a licensed electrician to your local code. Wireless microphone rules change, so confirm the current FCC position before buying. As an Amazon Associate we earn from qualifying purchases.