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.

Interesting. Thanks for the info! Now I'm going to have to dig up that explanation of XLR cables again...

XLR - 3 pin connector, balanced audio.
TRS - Same idea, but on a Tip Ring Sleeve (usually 1/4" phono - ie: big headphone) connector.

Bren R.

OK, the second I didn't know. I'm just having a hard time remembering how XLRs work; ie why there's those 3 conductors. I'll look it up myself.

Blue Jeans Cables has a nice explanation of it. Check out the So... Why Does it Matter? section.

Seems a lot more confusing than it has to be... and BJC seem to be using it to push twisted pair cables (more on that in a moment) they've combined two explanations into one, dare I say erroneously.

BALANCED LINES
One conductor carries the signal (Pin #2 is standard), one carries the signal 180 degrees out of phase (Pin #3)... noise hits both conductors equally (or equally enough) and when Pin #3 is inverted 180 degrees again at the destination and mixed with Pin #2 - the noise is also inverted, and cancels itself out. Easy and ingenious.

Balanced lines do NOT have to be made from twisted pairs.

TWISTED PAIRS
All you MCSEs (I know Microsoft says it's Microsoft Certified System Engineer - we all know it's Minesweeper Consultant and Solitaire Expert!) stand up now. You have nightmares about CAT5 cable - now how do all those twisted pairs carry a cleaner signal than station wire (non-twisted)?

Easy... by twisting the wires, you keep them close to one another, sharing - as close is as physically possible in the real world - the same space. Interference affects both signals in nearly identical ways, instead of how a balanced connection uses an extra wire to cancel noise, TP uses voltage differential between the conductors as the signal. Say your signal is a 100% duty cycle of 10mV (10mV on the hot, 0mV on the neutral), and the noise is a constant +1mV... your conductors would be carrying 11mV (10mV + the 1mV interference) on the hot, 1mV (0+1) on the neutral... leaving you with a difference of 10mV - exactly the signal you want.

Bren R.

Ken - TRS is just another connector at the end... much like coaxial cable can terminate in an RCA, an F-connector or a BNC, balanced audio can end in an XLR or a TRS.

Anyone that has to go XLR to TRS, this is the Rane Corporations' standard:
XLR (OUT)
1 - no connection
2 - RED conductor to TIP
3 - BLACK conductor to RING
Drain wire of course attaches to SLEEVE of TRS

and going the other way all connections are the same except drain wire goes to PIN 1 of XLR and SLEEVE has no connection (ie: Rane says to "drain" to receiving electronics)

Bren R.

OK, cool. That explains why I was able to use both types of ends all the time when I was (extremely) inexpertly doing the sound for my jazz choir in college.

It should also be noted that the term TWISTED PAIRS is one of the more common marketing mumbo jumbo lines in use today. To be honest, it gets embarrassing at times being in the cable racket and reading how some promote twisted designs when a true twisted design isn't even present. Now granted there is a benefit to the design, that's not my problem. It's when people use it in marketing stuff and half of the things they claim in the design aren't present.............and you all would be amazed at how many do it. I shouldn't however be surprised. These are the same people that say an XLR connection is a huge sounding upgrading over a regular RCA connection and that Silver is the greatest thing since slice bread, and rubbing Vaseline on your cables will improve the sound and hooking up a 9 volt battery to your cables and making them active will somehow make them the best cables on earth and so on and so on..........................................

My favourite one that is running around now is just that. Use Silver and hook up a battery to your cable and make them active! Huh????? I want my cables so I can hook my stuff up. I don't need them running around like the energizer bunny!

All kidding aside, I did try this. I took some runs of very high quality Silver and terminated them with the current trendy RCA the Eichman bullet's, shielded them etc. Basically anything you could think of I did. I then made them active. As you would imagine, they sounded exactly the same on the juice, or in rehab without the juice. I even went so far as to test them in various ways and there was squat for measurable difference.......the bunny is pissed at me.

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Now granted there is a benefit to (twisted pairs)

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In network and telephony applications, they have some real benefit, I've seen people have problems with DSL on station wire in older homes. For interconnects, the foundation they work on no longer exists (voltage differential) so the point is moot.

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These are the same people that say an XLR connection is a huge sounding upgrading over a regular RCA connection

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Well, the XLR is balanced. So if you happen to live in a stadium, arena or concert hall and your CD player is backstage and your listening area is 250feet away in the balcony, it will reject more noise.

(Also, XLR and TRS aren't necessarily balanced - it's all in the cable, sometimes you end up with unbalanced sources, and have to put a BALUN into the line, you can have balanced and unbalanced cables with XLR and TRS connectors, unbalanced TS (Tip Sleeve... ie: "mono" 1/4" phono) and TRS can also be wired for an effects loop - sometimes to dual TS connectors - Effect In and Effect Out, even rarely to another TRS)

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Silver is the greatest thing since slice bread

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My rings are made of it...

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rubbing Vaseline on your cables will improve the sound

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I won't touch that one.

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hooking up a 9 volt battery to your cables and making them active will somehow make them the best cables on earth

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AudioQuest, for instance, has a set of cables that run 72 volts through the dielectric, since it is their belief cable break-in has to do with the charging of the dielectric and keeping it in a state of charge negates the break-in period (they also contend you have to break-in non-"active" cables every time they're used - they discharge unless you use their battery operated ones. The battery will last for years (Well, I guess so, the only load on it is the "test LED"... you can push a button and light up an LED to be sure your battery is still functioning) since the battery isn't even part of an electrical circuit, this dives headfirst into the hogwash section.

Bren R.

Not to pick on anybody but the link below is a good example of a guy who is trying to push the buyer beware stuff but then on the same page say's that cable vibration is a problem.

Jeeez, how can you take anything seriously when you put that in writing. Granted there are more then a few who agree with the theory but then again a lot of those people also believe that cables need to break in, speakers need to break in, fancy pucks under your equipment will make everything sound better etc etc etc etc!

It should be noted that I'm not picking on this guy and to a point I agree with a lot of what he say's but to me at least any credibility is lost as a result of one statement.

CABLE VIBRATION

How is it that every time we mention the words "copper", "wire", "cable", "scam" or "the" we start talking about cables again?

Starting to think if I ramble this much at 31, I'd hate to see myself after retirement.

Bren R.

You, retire? Barring any physical malady, of course, will you suddenly be able to sit still when you reach that age?