Craig Aguiar-Winter’s recent thread about an installation inspired me to look up this chart:
[Link: belden.com]. It’s included in abbreviated form in Stephen Lampen’s “Audio/Video Cable Installer’s Pocket Guide.” We all should AT LEAST have and peruse this book. Actually reading sections that have more information than we need is a great way to become much more knowledgeable about the copper and plastic we throw around every day.
Let me put together a few of the hundreds of facts in this chart: how long can a wire be while offering only a 1% power loss through the wire? To put this in perspective, 1% is about 0.04 dB loss. The thing to notice here is the amazing distance you get with a 70 volt system, especially when you take this, from the article, into account:
*70 volt line distributed systems, while potentially as high performance as 4 or 8 Ohm applications, follow the same cable loss physics as the higher current (lower impedance) system. For the sake of this calculation a 25 watt 70 volts system (196Ω impendance) was used.
This clearly implies that those of us who think that 70V systems are junk have not sought out good equipment. I liken that to a person working with 8 ohm speakers who has never looked for or heard any 8 ohm speakers better than intercom speakers…. Or Samsung TV rear-facing speakers!
The info for a 1% power loss (-0.04 dB)
20 ga: 4 ohm, 1 ft; 8 ohm, 2 ft; 70 volt, 40 ft
16 ga: 4 ohm, 2 ft; 8 ohm, 4 ft; 70 volt, 102 ft
14 ga: 4 ohm, 3 ft; 8 ohm, 7 ft; 70 volt, 166 ft
For a loss of only 1 dB, which sounds small but is more than 20% of the power, the numbers are
20 ga: 4 ohm, 22 ft; 8 ohm, 44 ft; 70 volt, 1068 ft
16 ga: 4 ohm, 55 ft; 8 ohm, 1104 ft; 70 volt, 2687 ft
14 ga: 4 ohm, 89 ft; 8 ohm, 179 ft; 70 volt, 4380 ft
