Axiom Home Page Forums General Discussion Technical Questions Quick quesyion regarding cables

A while back I bought a Behringer Feedback Destroyer, which required the addition of a short run mono RCA interconnect from the receiver to the BFD. I bought an el cheapo Rat Shack one, and not even a good cheap one, but a cheap cheap one (not much shielding, looks pretty cheap in construction), which I thought would be fine for a short run.
Now just recently I purchased a new TV, which after upgrading to component cables, and swapping a few other things, means I now have a pretty decent composite video cable no longer being used at all. It occured to me that this composite video cable is just a gussied up RCA mono interconnect (extra shielding, 75 Ohm something or other...). So, I should be able to use this cable as the connection between my receiver and BFD, correct? There's nothing I'm missing that would make this a poor choice to carry an LFE channel, is there? I figure better to have the $2 cable collecting dust and put the $25 one to use.

It'll work just fine, possibly an imperceptible smidge better, too. Since your run is short, shielding isn't much of an issue, but a better-built cable will, if nothing else, give you peace of mind.

The only small differences in "RCA" cables is a "video" cable uses the shielding path as a signal return and is 75ohm coaxial cable, whereas an audio cable may use separate conductors (and be shielded or unshielded) and doesn't necessarily have to have the drain connected at both ends (in fact in pro audio, usually you drain only at one end - I personally use the source side).

Does that make any sense? Been a long day... still a bit highway-hazy.

Bren R.

I'm sure if we knew what you were talking about, it would make sense.

Boy, that doesn't make sense.

I'll try again tomorrow...

G'night all.

Bren R.

Okay, Craig pretty much had it right when he described what he understood the difference to be between the "composite TV" cable and the "RCA" cable, i.e. that the composite likely would be more heavily shielded and should be close to 75 ohms impedance(also note again that "RCA" is actually the name of the connector on the end, not the cable itself, so even the composite could be termed an "RCA cable"). For the short length involved and at audio frequencies the characteristic impedance of a cable isn't significant and if the shielding is heavier that might not be of audible benefit unless interference is heavy. But, as Peter said, since you have the more expensive cable you might as well use it.

>>The only small differences in "RCA" cables is a "video" cable uses the shielding path as a signal return and is 75ohm coaxial cable, whereas an audio cable may use separate conductors (and be shielded or unshielded) and doesn't necessarily have to have the drain connected at both ends

Are you talking about balanced cables yere ? You pro audio guys do like your fancy-schmancy two-pin connectors

Alrighty... after a good sleep, what I meant was that "video" cables are nearly always coaxial (we all know what that means, right? Centre conductor, dielectric wrapped, and an outer shield (braid/foil or both) on a COmmon AXis) whereas many times "audio" cabling will use line & mic cable (usually two conductors, with "jacket type" insulation and a foil/drain wire or both) - of course, the two conductors are used mostly for TRS/XLR applications - ie: balanced audio.

And again, the shielding/drain doesn't necessarily have to be attached on both ends for audio (and hardly ever is in pro audio - that would tie the chassis grounds of the two pieces of equipment together, and that leads/can lead to hum) but video requires that connection be made at both ends as a signal return, or you get a picture that brings back memories of rabbit ears TV.

Bren R.

Much better! I still don't quite get what drain is, but that's beside the point.

A drain wire is sometimes included in shielded (mostly foil shielded) cable in order to "drain" interference (RFI/EMI) to chassis ground.

That is, the interference gets "trapped" in the shielding (it doesn't actually REPEL it or anything) and it needs a path to ground. The drain wire does this (easier than trying to get a good solid connection with foil)

Bren R.