Speaker Wire Gauge (AWG) American Wire Gauge for Speaker Cable

What AWG means

American Wire Gauge is a logarithmic stepped gauge used since 1857, with dimensions set by ASTM B 258. A lower number is a thicker wire. Wikipedia's table gives the numbers that matter for speakers. 12 AWG is 2.053 mm in diameter, 3.31 mm² in area and 1.588 mΩ per foot (5.211 mΩ per meter). 14 AWG is 1.628 mm, 2.08 mm² and 2.525 mΩ per foot. 16 AWG is 1.291 mm, 1.31 mm² and 4.016 mΩ per foot. Three gauge steps roughly halve the area: 12 AWG at 3.31 mm² becomes 1.65 mm² at 15 AWG. Stranded wire adds its strand areas, so a stranded cable's effective gauge is the total copper cross-section, not one strand. Tinned copper is a little more resistive: Belden's 16 AWG 9497 (19 x 29 stranded tinned copper) is rated 4.27 ohms per 1000 ft against 4.016 for plain copper.

The 5% rule and the length table

A speaker circuit is a loop, so the wire resistance that counts is the round trip, out to the speaker and back. Diamond Audio's calculator multiplies one-way length by two for that reason. The conventional limit, from former McIntosh engineer Roger Russell, is that wire resistance should not exceed 5% of the speaker's rated impedance. Wikipedia repeats it as the point where the conductor is adequate for home use. Russell's table for two-conductor copper at 8 ohms allows 22 AWG 12 ft, 20 AWG 20 ft, 18 AWG 32 ft, 16 AWG 48 ft, 14 AWG 80 ft, 12 AWG 120 ft and 10 AWG 200 ft. At 4 ohms every length halves: 16 AWG 24 ft, 14 AWG 40 ft, 12 AWG 60 ft. Russell marks lengths beyond 50 ft with asterisks because 50 ft is the maximum recommended for normal line cord or Romex solid copper wire.

Check it with the resistance column. A 48 ft run of 16 AWG to an 8 ohm speaker has 96 ft of conductor x 4.016 mΩ/ft = 0.386 Ω, or 4.8% of 8 Ω. A 24 ft run to a 4 ohm speaker gives 0.193 Ω, 4.8% of 4 Ω. An 80 ft run of 14 AWG to 8 ohms has 160 ft x 2.525 mΩ/ft = 0.404 Ω, 5.05%.

Nominal impedance is a floor, not a constant. Russell's example 4 ohm two-way speaker measures 4.7 Ω at 20 Hz, 4.0 Ω at 300 Hz and 5.9 Ω at 11 kHz, and peaks at 20 Ω at 125 Hz and 28 Ω at 2500 Hz. He advises selecting wire for the lowest impedance in the curve, and adds that under 10% of nominal resistance can still be inaudible with some speakers. See minimum impedance dip.

What extra resistance does to the sound

Russell explains that as series resistance rises, the amplifier looks more like a current source, so the speaker's frequency response starts to follow its impedance curve. In his 4 ohm two-way example, adding 1 ohm in series costs only about 1/2 dB where the impedance is high (125 Hz and 2500 Hz) but about 2 dB where it is lowest (300 Hz and 10 kHz). His recommended wire resistance is 0.2 ohm, far below that test. Damping factor, the load impedance divided by the source impedance, shows the same thing: an amplifier with a damping factor of 500 into 4 ohms has about 0.008 Ω of output impedance, and a 0.2 Ω cable loop cuts the effective figure at the speaker to 4 / 0.208 = 19, while a 1 Ω loop leaves about 4. Wikipedia notes that lower speaker impedance demands heavier wire to avoid degrading damping factor. Russell also points out that a typical 8 ohm woofer coil already holds about 120 ft of 28 gauge copper, so the cable is a small part of the circuit.

Copper, copper-clad aluminum and tinned wire

Russell puts aluminum at about 61% of copper's conductivity, so copper-clad aluminum (CCA) needs a thicker gauge to match. Wikipedia says 16 AWG copper has no detectable effect in runs of 50 feet (15 m) or less to a typical 8 ohm speaker, and that aluminum or CCA needs 14 AWG or heavier to support the same claim. The Home Cinema Guide gives the same rule of thumb: if 16 gauge copper is fine, buy 14 gauge if it is CCA. Belden's 9497 datasheet shows what a real cable lists: 7.1 A per conductor at 25 °C, 0.19 µH per foot of nominal inductance, a 300 V rating and a 0.21 in (5.3 mm) jacket.

Choosing a gauge for a home theater

Denon's AVR-X3800H, for example, is rated 105 W per channel into 8 Ω and 135 W into 6 Ω and accepts speakers from 4 to 16 Ω, so a 6 ohm front speaker limits 16 AWG to 36 ft and 14 AWG to 60 ft. Most surround and height runs are well under that. The Home Cinema Guide notes that for runs of 10 feet or less you are unlikely to hear a difference between gauges, and Russell suggests 50 feet as a practical ceiling. A sensible default is 14 AWG for front and center speakers and any 4 ohm load, and 16 AWG for 8 ohm runs under 36 ft. Use the speaker wire tool to run your own lengths and the receiver match tool to check impedance. In-wall runs also carry a jacket rating; see CL2 and CL3 in-wall ratings. For the electrical background read damping factor, impedance and 4 ohm vs 8 ohm rated power, and for cabling choices the wiring guide.