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-   -   microphone cable can also be use as video and audio cable? (https://www.dvinfo.net/forum/all-things-audio/74934-microphone-cable-can-also-use-video-audio-cable.html)

Juan Dela Cruz September 6th, 2006 06:58 AM

microphone cable can also be use as video and audio cable?
 
I saw a very good 1 conductor cable here in my place. combination of foil and braided shield, the cable marking is Quantum High-impedance OFC low-noise microphone cable. the shield wire are not copper. its silver so I guess its aluminum wire, the signal wire is combination of 2 strand of copper together with aluminum wires. My question is can I use it for RCA connector audio video application? I want to make several 2 meter cable with this one. I currently using a DIY spiral-shield cable (swan brand).

Chris Hocking September 6th, 2006 07:39 AM

I've found that most, if not all cables will generally "work". To give you a pretty crazy example, I once visited a house that used metal coat hangers wrapped in gaffer tape to extend a 10A power cable. Illegal, yes! Dangerous, very! But it did work! I've seen people run video down audio multicores and telephone cables. So in answer to your question, yes you can use it. Whether or not it will look/sound OK is a completely different question!

I'm no expert in the matter, but as far as I know, video requires a 75ohm cable to run down. The cable's normally solid bare copper covered with foam polyethylene insulation, and an aluminum foil/polyester tape shield. Belden 7710A/1505F and Canare V3-3CFB are cables that would be suitable for video. I'm pretty sure these cables can also quite happily handle audio signals (as I presume audio uses less bandwidth than video).

So, if your cable is 75ohms (give or take one or two ohms), then you should be fine. However, when you say its microphone cable, I'm thinking that may be a slight problem, as mics are generally well over 150ohms. I would think that trying to run video down a cable with such a high resistance, may result in poor picture quality.

Maybe someone a bit more tech savvy can fill in the gaps (and correct my mistakes!)...

A. J. deLange September 7th, 2006 02:04 PM

That's the essence of it. In a coaxial cable one looks for 1) Characteristic impedance 2) loss per unit length 3) Shield integrity 5) propagation velocity (particularly whether this varies with frequency) 6) physical/chemical properties (will it emit toxic fumes in a fire).

If one uses a cable with mismatched impedance there will be signal reflections (which may appear as ghosts in video). If the loss per unit length is too great the signal will be attenuated to a troublesome degree at the distal end of the cable. If the shielding is poor the cable will either radiate causing interference to other cables/equipment or will pick up signals from the surroundings which will interfere with the signal it is carrying.If the propagation velocity is not uniform with frequency broadband signals will be distorted. All these things are problematical to a greater or lesser degree depending on the application. As a general rule the more broadband the signal and the longer the run the more attention must be paid to these properties. At audio frequencies hum/interference pickup (especially from rf in the environment) is the thing most likely to be a problem. Over a couple of meters you can probably get away with a lot though it wouldn't be considered good practice to use a cable intended for audio for video. If the center conductor is really aluminum you will have a time trying to solder it.

Bogdan Vaglarov September 8th, 2006 10:03 AM

Too much theory and no clear answer!
Well, mic cables transfer very low signal so you'll be fine for audio. I've used Canare cables for my audio system and other applications with great success.
For video go for 75-Ohm single center core cable with insulation from copper strand mesh (aluminum foil, nickel plated still strands are not so friendly when you try to solder RCA chinch).

As a note audio cables should be 50 Ohm but their capacitance is more important characteristic.

Ralph Keyser September 8th, 2006 03:02 PM

Without specifics on the cable, it's hard to tell if it is ideal for the application.

Chris is right though, most wire will more or less work. My favorite was a rancher who got his phone service via a barbed wire fence. It seems the phone company wanted quite a bit of money to plant poles to get the phone wires out to the ranch house, so he used the wires in the existing fence. It worked surprisingly well.

A. J. deLange September 10th, 2006 09:58 AM

Quote:

Originally Posted by Bogdan Vaglarov
As a note audio cables should be 50 Ohm

To put it clearly and without theoretical explanation: That statement is untrue!


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