Originally Posted by mchalebk
By definition, coaxial cable is a single conductor wire surrounded by an outer conductor, which just so happens to function as a shield (coaxial meaning that the two conductors share the same axis).
That is correct.
With the RCA plugs used for analog audio, the center contact is connected to a wire that runs down the center and the outer contact connects to the outer conductor (shield).
That is not at all correct. There are many MANY RCA plugs from various manufacturers that are not at all designed to work with coaxial cables, because many audio cables are NOT coax. They're twisted pair.
For instance, Canare, one of the premier professional termination companies, has these very common solder-on RCA connectors that are totally unusable on coaxial cable:http://www.canare.com/index.cfm?obje...5DA43EE99C3A24
It is true that not all shielded cable is coax. However, if there are only two contacts on a connector (such as an RCA plug) and one is connected to a shield and the other is connected to a wire that runs inside the shield, it is a coaxial cable.
Except in the thousands of times that it isn't at all. In the Canare connector as linked above, one conductor is soldered to the center pin contact, the other conductor is soldered to the outer contact on the RCA plug, which is the neutral/ground. That isn't a coaxial cable. You can't use that connector with a coaxial cable. And yet, hundreds of professional technicians use these connectors all day every day. How? BECAUSE THEY'RE USING TWISTED PAIR, and not coax!
Actually, I do have some idea what I’m talking about. I’m an electrical engineer and part-time musician (for many years). I have a great deal of experience with and knowledge of analog audio signals. I have never seen a 2-contact audio cable (other than speaker cable) that is not coaxial.
Unbelievable. As an audio tech, I spend a lot of time MAKING these cables, that apparently you've never run into. Using connectors that are industry standard, that apaprently you've never even heard of.
Twisted pairs work great for balanced signals, such as professional microphone cables. However, these use 3-contact XLR connectors. I believe we were talking about RCA plugs which, the last time I looked, were 2-conductor. Only an incredibly bad manufacturer would use unshielded lines for unbalanced audio signals.
Twisted pair cabling can be shielded, and commonly is.
But your claims that all RCA cables are coax is demonstrably ridiculous. Totally, 100% ridiculous.
Great. What's the relevance of this?
Here’s an excerpt that is germane to the topic at hand:
That describes a coaxial cable. Which as I already said above, was about the only thing you're correct about. And Kurt at BlueJeans also includes the qualifier "generally," because as he well knows, many cables used for audio signals aren't coaxial at all. They're TP.
Let’s address a few of the other statements you made:
“However audio cables are often not only not 75ohm”. Why would you say this in response to my quote when I didn’t mention 75 ohms at all?
Because you ommitted the second part of that sentence, which continues: "they're often not coax at all.
" The point I am making is that there is no reason for audio cables to be a coaxial cable at a specific impedance because impedance is not a concern. And as a result, many audio cables are simply twisted pair which can be smaller and easier to deal with than multiple coaxial cables which can be more costly and more difficult to deal with. But apparently, you aren't even aware that audio cables can be made from non-coax cable.
“What on earth are solder-on RCA ends for? Certainly not for coax” Well, how would you solder coax to an RCA connector? This statement is ludicrous and doesn’t mean anything.
That's the whole POINT. RCA plugs exist and are commonly used on cabling THAT IS NOT COAXIAL CABLE. Solder-on RCA connectors like the Canare connector linked above is such an example.
Or see this one: http://www.partsexpress.com/pe/showd...umber=091-1065
Or ALL of these: http://www.enjoythemusic.com/magazin...cashootout.htm
Or this ProAV Magazine article on how to solder an RCA connector onto a two-conductor (non-coaxial) wire: http://www.proavmagazine.com/industr...ticleID=597313
But you claim that ALL RCA cables are coax. This is flat, completely 100% wrong.
“Here's a whole BUNCH of Belden audio cabling that isn't coaxial at all, and very commonly used professionally”. Yes, for balanced audio lines, not unbalanced.
No, also they're commonly used for regular, unbalanced audio. Using the solder-on RCA plugs as just linked to. How do I know this? Because anybody who is at ALL familiar with audio knows this. Because I do this every day. Because I've torn apart consumer cabling because the connector came de-soldered and fixed them. Because some cabling manufacturers actually ADVERTISE the fact that they use twisted pair cable in their interconnects. And if you unscrew the connector body, gee look what's inside, TWISTED PAIR!
“You might be wondering how, for instance, balanced XLR connections are made in the professional domain with a single cable when a coaxial cable has only two conductors(pin and shield). Well gee, maybe that's because it's not coaxial audio cabling at all...”. Here was how I started my post: “Actually, any cable that is designed for audio and video with RCA plugs is almost certainly coaxial.” Did you happen to notice I qualified my statement by saying “with RCA plugs”? How many RCA plugs are used in professional applications or with XLR connectors? Pretty astute comment.
And how many times do I have to point out that you are completely wrong.
“Your assertions here are ridiculous. I'm sitting inside a warehouse right now that's full of a variety of kinds of audio cabling, and a lot of it isn't coax at all.” Once again, you’re talking about balanced lines. How the heck did we ever get on that topic?
NO I AM NOT. I am talking about unbalanced, two-conductor RCA connectors that are terminated to wire that is NOT coaxial cable.
I would appreciate it in the future, before you start spouting off, that you at least read my entire post and then not throw out a bunch of "facts" that have nothing to do with it. I was clearly talking about unbalanced audio lines when I mentioned RCA plugs, yet most of your post was about balanced audio lines which have absolutely nothing to do with this discussion.
I used XLR as ONE specific example of the fact that audio cables very commonly are NOT coaxial cabling.
You are dead-set of the opinion that a cable with an RCA connector at the end is a coaxial cable.
You are COMPLETLY wrong about this.
How do I know this? Because making audio cables is part of what I do for a living. And I make and take apart and fix audio cabling and interconnects, SOME of which are coax, and SOME of which are NOT.
That's why if you go into an electronics supply house, they have RCA connectors that are solder-on, which are used for twisted pair, and they have RCA connectors that are crimp-on (of various sizes and types) for coaxial cables (of various sizes and types).
Your claim that RCA cables are ONLY coaxial is completely wrong.