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coax vs. twisted pair (1 Viewer)

Michael X

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Well, my post in the Acoustic Research interconnect thread seems to have faded away, so I'm just starting my own to hopefully get an answer.

I'm wondering if theres a consensus on what works better for A/V cable- "digital" coax (all three wires) or the twisted pair (coax video, twisted pair audio)?

Particularly, I'm trying to decide if the cheapo "Digital" RCA (RCA/Thomson Electronics) brand cables available at Target, Home Depot, etc. are better/worse/same as say Standard or Pro grade Acoustic Research cables available at Sears, and Target too. The RCAs are "digital" coax, the ARs are coax video/twisted pair audio.

I'm just needing 3ft/1m cables to connect my Pioneer DVD player to my Pioneer Surround Receiver, so I'm not sure if it will make that big of a deal, but if theres a definite answer one way or the other, I'd like to know.

BTW, I'm just asking one way or the other- NOT trying to start a cable brand/price debate!
 

Wayne A. Pflughaupt

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I'm wondering if theres a consensus on what works better for A/V cable- "digital" coax (all three wires) or the twisted pair (coax video, twisted pair audio)?
It’s not clear what you’re talking about – if the same cable can be used for audio and video, or if they need to be different?

Theoretically, composite video signals work best with a solid center conductor, like with coaxial RG-6 or RG-59. In practice, it’s probably hard to tell coaxial from a regular audio cable, especially if the cable run is short and the television is consumer grade. Actually, those budget A/V cables you see with red, white and yellow RCA connectors, all three are the same internally.

I’m confident most upgraded A/V cables (like the ones you’re talking about) are also the same internally. Nevertheless it’s best to stay away from the cheapie red, white and yellow stuff. Upgraded cables have better connectors, thicker cabling, and will be more reliable, so it’s never a bad idea to get better-built cables.

If your receiver is Dolby Digital, you don’t need so-called A/V cables. All you need is one cable for video and one for the digital connection.

Regards,
Wayne A. Pflughaupt
 

Michael X

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My apologies- I guess the inquiry was a bit unspecific.
I'm aware of the need to upgrade from the cheesy zip cord wire, and I'm actually using a cheaper RCA A/V cord for this connection right now. The specific cables I'm inquiring about are the higher end double shielded gold plated etc etc type.
What I'm asking is does a coaxial (solid copper wire) in cable work better/worse/same as a twisted pair cable for the audio? I'm perplexed because the "twisted pair" design seems to be specific to cables for non-digital out sources, and all digital-out cables seem to be coaxial.
My receiver is not DD (a Pioneer Elite from the days when Dolby Surround was still the latest thing), so thats why I'm not really sure if this will make such a huge difference in my setup anyway, but I wanted to ask. :)
 

Wayne A. Pflughaupt

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Still not sure what you mean by “twisted pair,” Michael. All composite video cables, audio cables and “digital” cables have a single center conductor – at least, that’s all they need. If you’re talking about a cable that has two twisted center conductors, it offers no advantage, except perhaps better EMI rejection over long distances – say over 50 ft.

Again, any of the cables you mentioned in your first post will work fine. Neither one will make a “huge” difference.

Regards,
Wayne A. Pflughaupt
 

Bill_Weinreich

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I'm perplexed because the "twisted pair" design seems to be specific to cables for non-digital out sources, and all digital-out cables seem to be coaxial.
This does hold true in most cases for an important reason. Impedence. The digital signal should have a specific impedence cable (i.e. 75ohm in most AV applications). Because MOST twisted pair wires are not bound together, the will move when flexed causing the impedence to change. Coaxial by design can remain more stable because the center conductor is kept at a specific distance from the outer, kept in place by a foam dialectric. Minimal movement between the leads mean minimal change in impedence.

Hope this is what you were looking for.

Bill
 

Bob McElfresh

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Bill nailed it!

By design, Video cables and Coaxial Digital cables should be 75 ohms impedence. This allows the signals to transfer without reflection problems.

Audio signals are much lower frequency and do not have the 75 ohm requirement. Twisted pair speaker cables for a high-sensitivity system can, in theory, provide a better transfer between the amp and a speaker.

I'm not sure if there is any advantage to twisted pair interconnects.
 

Michael X

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Thanks for all of the replies so far! :)
Is the sole reason for using coax to maintain the 75 ohm impedance for video and digital signals? If so, I guess that would mean theres no point in using such cable for regular audio outputs, or it might even be a disadvantage if twisted pair connects can provide better audio transfer since the top priority isn't maintaining impedance.
I guess if 75 ohm cable were really better for everything, thats all anyone would use.
 

Bob McElfresh

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I guess if 75 ohm cable were really better for everything, thats all anyone would use
Quite a few audio interconnects are made with 75 ohm coax.

You can get coax in 50/75/110/300 ohm variety.

As the frequency of the signals increase, they become sensitive to "impedence matching". Subwoofer and audio frequencies are at the real bottom end of the speed range so they are least-sensitive.

DSS signals (2-3 GigHz) - require 75 ohm coax (RG6)
Video signals (1-35 MHz) - 75 ohm coax
Coaxial Digital signals (DVD) - 75 ohm
CATV signals (100 Khz-1Mhz) - 75 ohm (RG6 or RG59)
Audio Signals (100-20,000 hz) - Any
Subwoofer Signals (20-100 hz) - Any

So many things do standardize on 75 ohm coax.

NOTE: These are all line-level/ un-amplified signals. When you are running watts of power for speaker-level signals, some new issues crop up. This is where twisted-pair speaker wires have some advantages. Dont take what you now know about coaxial interconnects and assume they apply to powered speaker signals - different beasts.

Does this help?
 

Jeff Mills

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Bob,
The advantage to a twisted pair design is noise rejection. There is no audible benefit provided the cable is not subjected to a noisy environment.

In simple terms, 75 ohm coax for all video and digital audio applications, and 50 ohm coax or 50 ohm twisted pair for analog interconnects (this includes the subwoofer).


Jeff
 

Pamela Moore

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May 13, 2002
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One thing that's important to remember here is that twisted pair enhances noise rejection only if the cable is carrying a balanced signal. If one side is grounded (that is, if it's like virtually all equipment using RCA jacks) then common-mode noise rejection doesn't work and you're generally better off using a well-shielded coaxial cable.
 

Michael X

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Once again, thank you all for your helpful responses. :)
The AR cables with 75ohm video and twisted pair for audio were sounding real good until I read Pamelas post. Thats a pretty broad statement, since it implies the twisted pair noise rejection benefit is nullified for virtually all HT audio equipment, and we should all use coax.
Is this true?
I've yet to try twisted pair speaker wire. I imagine anything that reduces interference or offers improved noise rejection is a benefit, though I'd have to hook some up for myself and see if I can tell the difference from good 12-14AWG speaker wire on my system.
 

Mark Austin

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I have used twisted cables for regular audio connections, and for digital/video applications and they have worked very well in all instances.
 

jeff_coil

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Can you use a single twisted pair speaker wire (the type used for in wall) for the sub line level in? The reason I ask is there is one of these coming out of my wall right next to my sub, I currently have a RG-6 running along the wall for the sub signal and it would tidy things up if that existing wire would work.
Any thoughts on this I may just try and see what happens put don't want to damage the SVS amp
 

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