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Able to use Speaker Wire for Digital Coaxial audio?

Last response: in Home Audio
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February 1, 2005 11:20:54 PM

Archived from groups: rec.audio.tech (More info?)

My experience with cables running a digital signal is that they
perform just as good with low grade cable as they do with high grade,
unlike using it for an analog signal. However I'm not sure whether
there would be a difference between using flat or round cable when
used for a digital signal. Obviously the round would be a better
choice, however flat is a much cheaper solution.

I need to run a 50' coaxial digital cable from my computer to my
receiver. I was thinking of just using 50' speaker cable with the
appropriate connectors. I tested it using some left over speaker
cable I had, about 15', and it worked perfectly. Still 15 and 50 is a
big difference, I wonder if the sound would still be as good at that
distance when using it for digital audio?
Anonymous
February 2, 2005 3:46:52 AM

Archived from groups: rec.audio.tech (More info?)

"Mike" <vulcan4d@hotmail.com> wrote in message
news:86fa006a.0502012020.4f002762@posting.google.com...
> My experience with cables running a digital signal is that they
> perform just as good with low grade cable as they do with high grade,
> unlike using it for an analog signal. However I'm not sure whether
> there would be a difference between using flat or round cable when
> used for a digital signal. Obviously the round would be a better
> choice, however flat is a much cheaper solution.
>
> I need to run a 50' coaxial digital cable from my computer to my
> receiver. I was thinking of just using 50' speaker cable with the
> appropriate connectors. I tested it using some left over speaker
> cable I had, about 15', and it worked perfectly. Still 15 and 50 is a
> big difference, I wonder if the sound would still be as good at that
> distance when using it for digital audio?

Using unshielded speaker cable for digital MIGHT work, but
I wouldn't bet on it. And even if it does, it might not be very
reliable.

So go down to Rat Shack and buy a 50-foot length of antenna
coax, and put the appropriate adapters on each end. That stuff
is pretty cheap (likely cheaper than good speaker cable).
Anonymous
February 2, 2005 11:04:11 AM

Archived from groups: rec.audio.tech (More info?)

I've always heard that SPDIF runs best in a coaxial 75ohm cable... I have a
similar setup, using regular installation cabling (cheapest kind but fairly
thick), wich work just as well as a coaxial 75ohm cable (tested it - no
noticeable difference). My problem is though, that any powersurge in my
house will interfere with the audio signal somehow and cause my surround
reciever to loose sync with the signal for about 1-2 seconds... Not sure if
it's the cable or the PCI soundcard (thrust) though...

BTW. if you have a soundblaster card with a jackstick for digital out,
you'll need a mono-jack-to-RCA adapter. Stereo-jack adapters wont work!

VLC-player will output to SPDIF (havent tried though), but I use Mediaplayer
Classic and AC3filter for correct SPDIF output. Other players will just
downsample anything to stereo and use regular output, putting the card
itself in charge of spdif conversion which only gives you stereo...

Regards, Tommy

"Mike" <vulcan4d@hotmail.com> wrote in message
news:86fa006a.0502012020.4f002762@posting.google.com...
> My experience with cables running a digital signal is that they
> perform just as good with low grade cable as they do with high grade,
> unlike using it for an analog signal. However I'm not sure whether
> there would be a difference between using flat or round cable when
> used for a digital signal. Obviously the round would be a better
> choice, however flat is a much cheaper solution.
>
> I need to run a 50' coaxial digital cable from my computer to my
> receiver. I was thinking of just using 50' speaker cable with the
> appropriate connectors. I tested it using some left over speaker
> cable I had, about 15', and it worked perfectly. Still 15 and 50 is a
> big difference, I wonder if the sound would still be as good at that
> distance when using it for digital audio?
Related resources
Anonymous
February 2, 2005 10:08:53 PM

Archived from groups: rec.audio.tech (More info?)

>My experience with cables running a digital signal is that they
>perform just as good with low grade cable as they do with high grade,
>unlike using it for an analog signal. However I'm not sure whether
>there would be a difference between using flat or round cable when
>used for a digital signal. Obviously the round would be a better
>choice, however flat is a much cheaper solution.
>
>I need to run a 50' coaxial digital cable from my computer to my
>receiver. I was thinking of just using 50' speaker cable with the
>appropriate connectors. I tested it using some left over speaker
>cable I had, about 15', and it worked perfectly. Still 15 and 50 is a
>big difference, I wonder if the sound would still be as good at that
>distance when using it for digital audio?

I'd be concerned about this.

The most important characteristic for a digital-audio cable, I
believe, is the cable's characteristic impedance. Coaxial digital-out
is intended to drive a 75-ohm cable (e.g. RG59), and is terminated by
a 75-ohm load at the receiving end. If the cable's characteristic
impedance is significantly different from 75 ohms, the impedance
mismatches will cause a partial reflection of the signal. If you've
got a mismatch at both ends of the cable, you can end up with signal
reflections bouncing back and forth on the cable.

What this can do, is cause significant "glitches" in the rise and fall
of the digital signal as seen by the receiving component - these are
easily visible using an oscilloscope.

Digital receivers usually have fairly tolerant input circuits with a
good deal of hysteresis, but a big enough glitch could overcome the
hysteresis and cause the receiver to mis-detect a bit. The audible
effect of this would probably be popping, a static-like noise,
momentary dropouts as the receiver tries to resynchronize, or (in
really severe cases) a failure of the receiver to detect valid
digital-audio signal at all.

Whether this happens or not will depend on the cable length, the
cable's characteristic impedance, and the details of the driving and
receiving circuits. Since the characteristic impedance of a speaker
cable is usually not characterized, and is likely to be significantly
different than 75 ohms, it would not surprise me if problems occurred.
On the other hand, in some situations, with some equipment and some
speaker cable, a 50-foot length might work just fine. The only way to
know, in your case, is "try it and see".

--
Dave Platt <dplatt@radagast.org> AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
Anonymous
February 2, 2005 10:08:54 PM

Archived from groups: rec.audio.tech (More info?)

"Dave Platt" <dplatt@radagast.org> wrote in message
news:11029a57e43nn0b@corp.supernews.com

> The most important characteristic for a digital-audio cable, I
> believe, is the cable's characteristic impedance. Coaxial digital-out
> is intended to drive a 75-ohm cable (e.g. RG59), and is terminated by
> a 75-ohm load at the receiving end. If the cable's characteristic
> impedance is significantly different from 75 ohms, the impedance
> mismatches will cause a partial reflection of the signal. If you've
> got a mismatch at both ends of the cable, you can end up with signal
> reflections bouncing back and forth on the cable.

True, but surprisingly large mismatches are tolerable at low frequencies and
short lengths, such as are commonly used in SP/DIF

I think that just plain old resistive loss is pretty important, too. Coax
made for cable systems and VHF/UHF work tend to be made up of thin layers of
copper and or silver laid over steel or aluminum. Steel in particular has a
lot more resistance than equal thickness copper.
Anonymous
February 2, 2005 10:16:00 PM

Archived from groups: rec.audio.tech (More info?)

In article <11014rugm930t0d@corp.supernews.com>,
Richard Crowley <rcrowley7@xprt.net> wrote:

>Using unshielded speaker cable for digital MIGHT work, but
>I wouldn't bet on it. And even if it does, it might not be very
>reliable.
>
>So go down to Rat Shack and buy a 50-foot length of antenna
>coax, and put the appropriate adapters on each end. That stuff
>is pretty cheap (likely cheaper than good speaker cable).

Antenna cable has the right characteristic impedance, but it's probably
not the best choice for digital-audio signals. It's usually fairly
stiff, having a solid-copper or copper-plated-steel center conductor.
The stiffness can make it difficult to route in the tight spaces
behind most peoples' AV systems, and can create stresses which pull or
push or rotate the connector. If the cable is terminated in a
screw-on F connector (as is usual in antenna applications) it'll be
held firmly in place, but if it's terminated in a male RCA plug (as is
usual for digital-audio connectors) it may tend to pull out of the
socket.

A better choice is the more flexible 75-ohm cable which is used for
composite-video applications (the pre-made cables come with a
yellow-jacketed RCA plug) This cable uses a stranded center conductor,
and is often as flexible as an audio cable. This cable may be lossier
than an antenna cable at high RF frequencies, but that's irrelevant
for composite video and for digital audio.

--
Dave Platt <dplatt@radagast.org> AE6EO
Hosting the Jade Warrior home page: http://www.radagast.org/jade-warrior
I do _not_ wish to receive unsolicited commercial email, and I will
boycott any company which has the gall to send me such ads!
Anonymous
February 3, 2005 1:08:34 AM

Archived from groups: rec.audio.tech (More info?)

On Wed, 2 Feb 2005 15:43:13 -0500, "Arny Krueger" <arnyk@hotpop.com> wrote:

>True, but surprisingly large mismatches are tolerable at low frequencies and
>short lengths, such as are commonly used in SP/DIF

The initial poster - troll? - mentioned 50', which is an order of magnitude
above anything short.

Anyway, quality 75-ohm coax is cheap and widely available, why bother with
anything else?
Anonymous
February 3, 2005 3:51:04 PM

Archived from groups: rec.audio.tech (More info?)

"François Yves Le Gal" <flegal@aingeal.com> wrote in message
news:44g201ti19c4b374rsve55j5deuc6qne7d@4ax.com
> On Wed, 2 Feb 2005 15:43:13 -0500, "Arny Krueger" <arnyk@hotpop.com>
> wrote:
>
>> True, but surprisingly large mismatches are tolerable at low
>> frequencies and short lengths, such as are commonly used in SP/DIF

> The initial poster - troll? - mentioned 50', which is an order of
> magnitude above anything short.

Agreed.

> Anyway, quality 75-ohm coax is cheap and widely available, why bother
> with anything else?

Agreed.
!