Is there any difference between a digital coaxial cable and a single 1 channel RCA cable ?

A digital coax cable should be 75 ohm. So you'd be better with a 'video' cable than a typical audio cable.

+1

What they said. Keep in mind that cables terminated with RCA plugs are not all of coaxial construction but may work as well.

However...

See [Link: electronicdesign.com], then keep reading.

In MANY but not all cases, short signal runs don't need to have cables of the proper impedance to GET BY. I put that in caps because if you GET BY, then the thing works. That doesn't mean that, for instance (in a transmission line), the maximum amount of power available from the source reaches the load.

A result of that is that a cheap audio cable that might work for three feet cannot be used to make that same signal go fifty feet.


Always have the goal of using the exactly proper equipment for the application. Work to learn what will work properly even though it doesn't meet the specs.

The real world answer is...it doesn't matter which RCA terminated cable you use...until it does.

Exactly.

Actually, let's look at the connectors:

I've seen RCAs used inside a 1950s tube TV to carry a 10.7 MHz IF signal from one part of a TV tuner to another. (Look up "turret tuner" or see [Link: modip.ac.uk] to have a clue what we had to go through to receive high frequency signals back then.)

How does this relate to the original question? Well, that RCA cable was perfectly capable of carrying 10.7 MHz ! That is WAY WAY WAY above the audio spectrum. The keys are -- good connectors, excellent soldering (the shield was soldered to the connector's ground all the way around the connector), but most importantly, the entire cable assembly was only about five inches long.

It would work until it wouldn't means that same cable would not have worked if it were, say, three feet long.

Good thread. Ive wondered if using a digi cable (single line with RCA ends) in place of a subwoofer cable on a sub mattered. I have had to do that a few times. Dont know the right answer, but APPEARS to work. Should I never do that?

I'm trying hard to think of an exception to this statement, so let me just put it out and ask anyone if it's not true:

The performance limitations on wire, cable, and connections arise when you try to pass more power and/or higher frequency signals along a wire.

In accord with this, we have these realities:

You can use RG6 to take line level audio to a subwoofer. (See, this stuff is perfectly made to pass 3 GHz or more... audio is child's play for RG6!)

You can't pass high MegaHertz range signals on speaker wire... at least not more than a foot or two

You can't use a single pair of a CAT5 cable to carry 300 watts to a woofer... but You can use 10 gauge to do so

You can take old token ring shielded cable with 110 ohm impedance and use it for line level audio, because line level audio usually has a low source impedance and high load impedance... so transmission line characteristics don't come into play

You can't take a gigaHertz signal as far on a given cable as you can on a cable of the same characteristic impedance of larger conductor and dielectric diameter.


In all of those cases, the wire is made to perform with a signal that's more difficult to transmit than the signal used in the example, except for the skinny wire being asked to pass 300 watts. That's the other side of the coin.

Tell us more Mr. science.

Ernie, the data transmission of S/PDIf over coax is not running at analog audio frequency. Because it is a serial stream and has to carry both channels, and clock, the transmission frequency of S/PDIF is 128 times the sampling rate. So for typical 48 KHz sampling that is common for video soundtracks, the data rate is 6.144 Mhz. That is a heck of a lot above the 24 Khz maximum audio bandwidth we can create with 48 Khz sampling.

In addition, the process of extracting clocks looks at zero crossing point of the waveform. The lower the bandwidth of the cable, the slower that transition and the more possibility for jitter.

So ideally you would want to have a pretty high-bandwidth cable for S/PDIF.

That said, for short lengths it doesn't matter as mentioned. :)

You're totally right. Once I started thinking about it I wanted to stress that a short cable that's designed for analog audio could very well transfer digital audio... but my description went off the rails.

Thanks for making it clear.

so bottom line, using a digi coax cable is fine from wall to subwoofer, 3'. Great!

The only time i ever had an issue with a subwoofer was when i tried to use RG6 for it. RG6 ran about 30' in the wall. Sub would go nuts even when the receiver was off. Electrician pulled the wrong "black wire" to the sub. He used our DirecTV RG6 for the serial digital cable run to the subwoofer.

Luckily we always run Cat5, 14/4 to each subwoofer so i was able to resolve the issue with baluns.

Could you add some detail to "would go nuts"?

Was the thing(s) the subwoofer did different when the receiver was off? In what ways?

I've never seen a digital feed for a subwoofer, nor a digital input on a sub. What components are in that system?