PDA

View Full Version : [Help Needed] What is the difference between a RCA cable, sub cable and a digital coax cable?



djperez81
01-21-2012, 07:55 PM
I know this is probably a noob question but what is the difference in these 3 different cables? They all seem to look the same for the most part. Are they constructed differently? someone please enlighten me on this. Thanks

Dennis Gardner
01-21-2012, 08:13 PM
They are usually similar in design, coaxial (center strands surrounded by insulation and outer shielding). There are some twisted pair designs on the market that are used with RCA terminations, but they all can be used as low level, unbalanced signal cable. Impedance differences are different in some of the designs and those differences are why some will work better with different gear.

nguyendot
01-21-2012, 08:46 PM
RCA cables and sub cables are the same. A sub cable is generally a long rca cable. RCA cables are usually two leads, some are shielded some are not.

A digital coax cable is exactly that - a coax cable with RCA ends on it. It should conform to a 75 ohm standard.

Syndil
01-22-2012, 05:46 AM
Generally speaking (oddball configurations aside, that is) all sub cables are RCA coaxial cables, and all digital coax cables are RCA coaxial cables.

A sub cable is usually marketed as such because it is mono (not a stereo pair) and can usually be found at longer-than-typical lengths since subwoofers are usually placed at a distance from the pre/pro.

A digital coax cable is an RCA coaxial cable rated at 75 Ohms. A sub cable or a regular RCA cable may also be made from 75 Ohm-rated cable, but impedance does not matter for analog audio.

So to recap, any RCA cable can be used for analog audio (including subwoofer use). Does not matter if it is marketed as a sub cable or a digital coax cable.

And any RCA cable can be used as a digital coax cable if it is rated at 75 Ohms. Doesn't matter if it's marketed as a sub cable or something other than digital coax, as long as it is 75 Ohms.

Brasiliaflyer
01-22-2012, 11:45 AM
So decent component video cables can be used as audio interconnect cables? Ever used the Belkin PureAV silver series? They look nice and well made... the video component versions can be had at huge discounts, but the ones marketed for audio are still quite expensive. Seems like one could save some $$ by buying the video cables and using them as interconnects. What y'all think?

nguyendot
01-22-2012, 12:46 PM
No. Video cables are coax cables. Coax cables are NOT good for analog audio as they use the shield as the second conductor most of the time.

Syndil
01-22-2012, 06:59 PM
That of course is debatable, as most analog RCA cables are indeed coaxial. The coax design affects the impedance of the cable, but at analog audio frequencies, impedance is irrelevant.

Of course high-end cable manufacturers will dispute this with their marketing, but most of you know my feelings on that (placebo), and that is not something I am willing to debate. But if you check, for example, Monorprice's cables, you will see that all of their premium-quality RCA cables (analog audio, component/composite video, subwoofer or digital coax) utilize RG59U 75 Ohm coaxial cable in their construction.

mantis
01-22-2012, 08:51 PM
No. Video cables are coax cables. Coax cables are NOT good for analog audio as they use the shield as the second conductor most of the time.
I've seen both designs for many different companies. I'm not sure if not is better then the other by design.


That of course is debatable, as most analog RCA cables are indeed coaxial. The coax design affects the impedance of the cable, but at analog audio frequencies, impedance is irrelevant.

Of course high-end cable manufacturers will dispute this with their marketing, but most of you know my feelings on that (placebo), and that is not something I am willing to debate. But if you check, for example, Monorprice's cables, you will see that all of their premium-quality RCA cables (analog audio, component/composite video, subwoofer or digital coax) utilize RG59U 75 Ohm coaxial cable in their construction.
No one will admit what is better for audio use. A lot of companies use Coax design for video and digital cables only , then use 2 conductor of some kind for audio only cables. I have asked about this very design and never get a straight answer why and which should be used. Materials seem to be the only consistent among wire companies.

Serendipity
01-22-2012, 10:57 PM
No one will admit what is better for audio use. A lot of companies use Coax design for video and digital cables only , then use 2 conductor of some kind for audio only cables. I have asked about this very design and never get a straight answer why and which should be used. Materials seem to be the only consistent among wire companies.

The reason is due to the laws of physics and electromagnetic waves. It would take a lot of writing to explain and some time, but I'll just re-hash the basics from my university Physics text:

Think of a coaxial cable as a transmission line with the center conductor carrying the signal and notice that there is a gap between the shield and the conductor. What the shield is doing is making sure that the electromagnetic field carrying the signal is not propagating outside the cable. This would interfere with other cables nearby and anything that can pick up the EM field. It is important that the electromagnetic field stays only in the space between the inner and outer conductors and that is the reasoning for this design. That is why cable TV, coaxial digital audio cables, and video cables use this design.

Brasiliaflyer
01-22-2012, 11:59 PM
So is this configuration good or bad for analog audio?

tonyb
01-23-2012, 02:22 AM
So decent component video cables can be used as audio interconnect cables? Ever used the Belkin PureAV silver series? They look nice and well made... the video component versions can be had at huge discounts, but the ones marketed for audio are still quite expensive. Seems like one could save some $$ by buying the video cables and using them as interconnects. What y'all think?

No, I wouldn't think. Video componant cables are usually on the cheap side of audio quality, wouldn't even consider the idea since you can buy relatively cheap audio cables to begin with. Old video componant cables are good for one thing, feeding the garbage bin.

Syndil
01-23-2012, 06:13 AM
As you have probably figured out by now, cables are a touchy subject among so-called audiophiles. Some believe they have a huge effect on sound quality and will spend a not-insignificant portion of their audio budget on cables, and others believe they only need be adequate to perform the job they are tasked with. Many here fall into the former camp, I fall into the latter. I believe you will find the Belkin PureAV video cables plenty adequate for carrying audio signals.

Frankly I would be very surprised if Belkin's audio cables were constructed differently from their video cables, other than having differently colored bits of plastic at the ends.

Serendipity
01-23-2012, 11:54 AM
This is exactly what I am trying to find out in this thread:

http://www.polkaudio.com/forums/showthread.php?128503-And-it-begins...

As you can see I have many cables, I am trying out the different combinations discussed above.

Surprisingly, power cords and dedicated circuits made the biggest difference in my rig.