Tech Tip of the Day: Get your wire gauge right

Selection of the appropriate wire gauge is important to system operation. A cable that's too "light" will result in amplifier power being wasted due to the series resistance of the cable. It will also result in the loss of low-frequency performance due to a degraded damping factor.

On the other hand, a cable that is too "heavy" is unnecessarily awkward and costly. In general you want to keep your line losses ("insertion" losses) below 0.5dB (though some engineers would argue this is still too much loss).

The impedance of the load (speaker), the length of cable, the cable gauge, and to less extent the output impedance of the amplifier all play a role in how well the signal gets from the amp to the speaker. Essentially, distance and the impedance of the loudspeaker are the two factors to consider when determining wire gauge.

The following table shows the approximate signal losses in speaker cable for a 100-foot amplifier-to-speaker distance at various impedances:

10 AWG: 4 Ohm = .44 dB, 8 Ohm = .22 dB, 16 Ohm = .11 dB
12 AWG: 4 Ohm = .69 dB, 8 Ohm = .35 dB, 16 Ohm = .18 dB
14 AWG: 4 Ohm = 1.07 dB, 8 Ohm = .55 dB, 16 Ohm = .28 dB
16 AWG: 4 Ohm = 1.65 dB, 8 Ohm = .86 dB, 16 Ohm = .44 dB
18 AWG: 4 Ohm = 2.49 dB, 8 Ohm = 1.33 dB, 16 Ohm = .69 dB

As you can see, an 18-gauge cable with a 4-Ohm speaker at 100 feet results in 2.5 dB of loss. A loss of 3 dB would mean that half the amplifier's power is being dissipated by the wire, not the speaker!

The following information comes from JBL http://www.jblpro.com. It shows some suggested wire gauges for different distances and different impedances.

• 10 feet, 4, 8 & 16 Ohm load = 20 AWG
• 25 feet, 4 Ohm load = 15 - 20 AWG
• 25 feet, 8 & 16 Ohm load = 20 AWG
• 50 feet, 4 Ohm load = 10 - 15 AWG
• 50 feet, 8 Ohm load = 15 AWG
• 50 feet, 16 Ohm load = 15 - 20 AWG
• 100 feet, 4 Ohm load = 10 AWG
• 100 feet, 8 Ohm load = 10 - 15 AWG
• 100 feet, 16 Ohm load = 15 - 18 AWG
• 150 feet, 4 Ohm load = 8 AWG
• 150 feet, 8 Ohm load = 12 AWG
• 150 feet, 16 Ohm load = 15 AWG
• 200 feet, 4 Ohm load = 5 - 8 AWG
• 200 feet, 8 Ohm load = 10 AWG
• 200 feet, 16 Ohm load = 10 - 15 AWG

Some engineers would argue these figures are too conservative, and in "real-world" applications a heavier gauge is needed for the best sound. Whether everyone agrees with these figures or not it should at least be understood that distance and impedance play a major role in how the wire reacts.

Further, in high power applications it may make sense to get much more "stingy" when it comes to power loss. For example, a "small" 0.5 dB loss at 1000 watts is still a loss of more than 100 watts of power! In the end, it's probably best to shoot for higher grade, lower gauged wire in almost any circumstance for best results.