Originally Posted by Skytrooper
I always thought you had to use 600 ohm cable for low level audio signals. but reading other posts I see most people use 75 ohm for their subs. Some one commented that was old school thinking.
Audio signal wiring is not
impedance matched. That includes line level audio signals, speaker signals, and phono cables. Neither the sources nor the loads nor the cables are impedance matched. It is a bridging system.
Video and digital audio lines are impedance matched, but given the short cables that are commonly found in home audio systems, there is no need for hyper accurate matching. The wire from your TV antenna or cable trunk in your backyard or on your room is long enough for impedance matching to be a good idea.
Looking at cables, I know about 45 ohm cables, 50 ohm cables, 75 ohm cables, 100 ohm cables, 110 ohm cables, 300 ohm cables and 450 ohm cables. I don't know about any 600 ohm cables.
Impedance is based on conductor spacing and conductor size.
Knowing what 300 and 450 ohm cables look like, 600 ohm lines would be composed of two fairly small wires fairly widely spaced. I'm guessing several inches. Know of any cable like that? Current telephone lines are composed of approximately 24 gauge twisted pair whose impedance I would put at around 100 ohms. These pictures are about 1/4 actual size:
300 Ohm 18g, 0.25 inch separation
450 Ohm 18g, 0.75 inch separation
I googled 600 ohm cable and found just tools and devices, but zero pictures of cable!
The impedance matched 600 ohm systems were dominated by the phone system. The sources and the loads were 600 ohms. However, the telephone lines themselves were generally not 600 ohms, either. Various impedance matching devices, some called loading coils were used to draw the systems together.