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Using a 75 ohm RCA video cable for as an analog audio cable.

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#1
I'm not going to ask the usual "Can a video cable be used as a BLAH BLAH BLAH". What I'm curious about are the video cables (usually the higher end ones) that have only a single conductor wire. Can these cables be used as analog audio cables?
 

Krunok

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#3
I'm not going to ask the usual "Can a video cable be used as a BLAH BLAH BLAH". What I'm curious about are the video cables (usually the higher end ones) that have only a single conductor wire. Can these cables be used as analog audio cables?
Yes, you can. 75 Ohm impedance is not a problem with audio frequencies and short lengths.
 
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#5
Most reasonably priced RCA coax analog audio cables have a Radio Frequency Characteristic Impedance of 75 Ohms, almost by accident. It's more convenient and economical to manufacture 75 Ohm cables. The wire, insulator and shield dimensions work out better.
 

LTig

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#6
I'm not going to ask the usual "Can a video cable be used as a BLAH BLAH BLAH". What I'm curious about are the video cables (usually the higher end ones) that have only a single conductor wire. Can these cables be used as analog audio cables?
Yes, this is no problem. Having a single conductor wire is no problem at audio frequencies.

Actually I use 75 Ohm RG-59 as my own standard for RCA cables. The advantage is that you can use those cables for both analog and digital (SPDIF coax) audio connections.
 

DonH56

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#7
Many, if not most, audio interconnects are 75-ohm cables. Since it is ubiquitous for video, and works fine for audio (analog or digital), manufacturers only need buy one type of cable instead of two or three. Saves them, and hopefully you, money.
 
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#8
I always questioned the shielding properties of some coax cables I've seen, when used for analog audio purposes. A thin foil of aluminum and a rather sparse mesh of wires doesn't really help. Add to this the rigidity of the RG-59, RG-60, or even RG316 coax (making it rather inconvenient to use) and you'll find why I usually don't use or recommend using coax cables for audio. Some brand names could certainly be better than the next no name junkstore grade coax, though.

Just look at the heavy shielding of a pro grade audio cable and you'll understand what I am talking about.
 
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#9
I always questioned the shielding properties of some coax cables
Yes for analog audio, you want a coax with a heavy braided shield. Those cables with a thin foil shield are optimized for cable TV frequencies.
When dealing with generic cable number like RG-6 & RG-59, you have to be careful as these cables can be optimized for low frequencies or high frequencies with the same RG number.
 

DonH56

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#10
I always questioned the shielding properties of some coax cables I've seen, when used for analog audio purposes. A thin foil of aluminum and a rather sparse mesh of wires doesn't really help. Add to this the rigidity of the RG-59, RG-60, or even RG316 coax (making it rather inconvenient to use) and you'll find why I usually don't use or recommend using coax cables for audio. Some brand names could certainly be better than the next no name junkstore grade coax, though.

Just look at the heavy shielding of a pro grade audio cable and you'll understand what I am talking about.
The Al foil provides 100% shielding, something harder to achieve with braided copper (or whatever), so that is a good thing. To achieve similar shielding with braids typically requires dual wraps, two layers wrapped at right (90 degree) angles, so make the coax thicker. You can buy RG-59 variations in a wide variety of types having different flexibility, shielding, etc.

For cables that are frequently flexed, the foil can develop splits and tiny openings, so in those cases (which includes interconnects that are fairly frequently moved and pro audio cables used for live sound) braid (and stranded center conductors) works better for longevity (not necessarily for shielding but the good ones are 98% or better). I have a bunch of mic and instrument cables that use thick but flexible outer layers, braided shields, foamed poly or similar flexible inner dielectric, and stranded center conductors. And some less-flexible but better-shielded patch cables for the rack since they are not usually moved and (rarely) stepped upon. At work we have fairly standard RF cables, some with armor to withstand abuse during handling, and some gorgeous very thick yet very flexible lab standard cables that rival some audiophile cables in expense ($10k~$20k for 1 m). Since it is a noisy environment foil shielding foil shielding is common but with a full braid for reliability. I have seen cheaper cables using foil without, or very little, braid but those are not meant for day-to-day lab use.

Flexibility is a function of many things, including the type, number and thickness of the shielding, type and thickness of the center conductor, type of dielectric (insulation inside), and type and thickness of the external sheath (insulation on the outside plus any additional armor). You can buy RF cables in a huge range of flexibilities from small coax that behaves like a thick floppy string, so a range of standard coax from flexible to very stiff (some cables are armored, i.e. include a semi-flexible plastic or metal protective layer, to guard against abrasion and excessive flexure), to semi-rigid that is basically bendable conduit (metal tubes), to hard coax that is like thick pipes.

BTW coax describes the construction: a center conductor with cylindrical insulation layer and outer cylindrical shield layer, with perhaps an outermost insulating layer for protection. The vast majority of audio interconnects are coax in nature, including pro-grade audio cables, exceptions being the twisted-wire and flat cable some manufacturers sell. Speaker cables are usually twin-lead (zip-cord) cables.

FWIWFM - Don
 

solderdude

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#12
In your opinion, the Al foil in a coax cable provides shielding against what?
https://emfacademy.com/aluminum-foil-emf-radiation/

https://slt.co/Products/RFShieldingFoil/RFShieldingFoil.aspx

To work effectively for audio the screen needs to be as low impedance as possible so common mode signals prefer to travel through the shield.
I would not use the cheap stiff antenna cable of old but decent coax works fine for audio, video as well as digital.
In the video and digital case of course they need to be properly matched.
For audio they don't have to match, the wavelengths are too long.
 
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DonH56

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#14
In your opinion, the Al foil in a coax cable provides shielding against what?
RFI/EMI -- radiated signals, like radio frequency interference and electromagnetic interference. Noise.

Not my opinion, see any text on electromagnetics.

This place is hardly worth visiting lately.
 
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#15
Hey. Not a 100 percent sure one this but a 75 ohm cable has as much to do with the connector type as the cable itself. I don't think regular rca solder connectors were designed to be true 75ohm as were the bnc that is used for video. The cable you might want to use may not be 75ohm.
 

LTig

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#16
Hey. Not a 100 percent sure one this but a 75 ohm cable has as much to do with the connector type as the cable itself. I don't think regular rca solder connectors were designed to be true 75ohm as were the bnc that is used for video. The cable you might want to use may not be 75ohm.
You're right, but since almost all available units use RCA for SPDIF complaining doesn't help.

BTW I have seen units using BNC but AFAIK BNC is designed for 50 Ohm so that's not a clever choice.
 
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#17
RFI/EMI -- radiated signals, like radio frequency interference and electromagnetic interference. Noise.
Not my opinion, see any text on electromagnetics.
Great, now use one of those texts on EM theory and calculate how effective is a .1mm aluminum foil against low frequency magnetic fields (like mains hum). Hint: zero, zip, nada. Repeat for the high frequencies these cables were designed for and you'll find it is rather effective, at least that's what Faraday says based on the eddy currents effect.

Don't want to patronize you, but if you decide to keep visiting this place, some reading about the differences between RF shielding and magnetic shielding would be in order.

I'm not saying the heavy pro audio cable shields are uber effective at very low frequencie (as mains hum), but they are certainly effective in shielding KHz range stray magnetic fields. Which the RF coax cables are definitely not.
 

DonH56

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#18
Hey. Not a 100 percent sure one this but a 75 ohm cable has as much to do with the connector type as the cable itself. I don't think regular rca solder connectors were designed to be true 75ohm as were the bnc that is used for video. The cable you might want to use may not be 75ohm.
Yes and no... The connector has a certain impedance, true, but the cable's characteristic impedance is determined by its construction. Without considering loss, the impedance is related to the ratio of inductance and capacitance: Zo = sqrt(L/C). See e.g. https://en.wikipedia.org/wiki/Characteristic_impedance So the cable must be designed and constructed for a specific characteristic impedance, and the connectors are designed to match that impedance over the desired bandwidth. BNC connectors for 75-ohm applications are designed slightly differently than the normal (50-ohm) versions, true. And as you go up in frequency connectors become more critical as cavity resonances in the connector itself start to cause problems.

HTH - Don
 

DonH56

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#20
Don't want to patronize you, but if you decide to keep visiting this place, some reading about the differences between RF shielding and magnetic shielding would be in order.
Thank you, it's good to know experts like you are available to help cure my ineptitude and ignorance of such electrical things.
 
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