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Can I use 3 composite video cables for component?


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15 replies to this topic

#1 of 16 OFFLINE   RobertCharlotte

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Posted August 03 2007 - 04:39 AM

I've pretty much eliminated composite video connections from my life, but I have a place where I'm using about a 12' component cable where I really only need about a 3' one. I have several extra composite video cables of the right length, but I thought I'd better ask before hooking them up. I know composite video cables can be used in place of subwoofer cable, but I wasn't sure if the specs would support component.

Will this work?
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#2 of 16 OFFLINE   Phil A

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Posted August 03 2007 - 05:07 AM

Yes - they should be about the same length though (and same type would be best). I guess in theory if there were differences in length you could have some timing issues.

#3 of 16 OFFLINE   Bob McElfresh

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Posted August 04 2007 - 10:24 AM

All video cables need to be made with something called "75 ohm coax". Component cables are just 3 identical length composite cables.

HOWEVER: Composite cables were usually built for 480i video signals (max frequency about 4 Mhz). Progressive video goes up to 13 Mhz and real HD video goes up to 35 Mhz.

So you really do not want to take 3 composite cables and use them for HD video component cables. They will appear to work, but you could have loss of focus, reflection (seen as ghosting), etc.

Does this make sense?

#4 of 16 OFFLINE   Stephen Tu

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Posted August 04 2007 - 10:57 AM

As I've said many times before, no it doesn't make any sense. 3 composite video cables will work perfectly fine for component, SD, HD or otherwise.

Quote:
They will appear to work, but you could have loss of focus, reflection (seen as ghosting), etc.

I guarantee you will not see any of those things.

Bob, you seem to be of the impression that engineers thought in the manner "hmm, we have to have cable that carry 4 MHz signal, OK, let's design a cable that has that much bandwidth and no more". That's *not* what happened here. Instead it's more like, "hey we need to carry a 4 Mhz signal, what do we have around here that we can use? Oh yeah, we have all this 75ohm coax antenna/CATV cable lying around here that has hundreds of Mhz worth of bandwidth, that'll work fine, even though it's overkill." You use stuff that's on hand, cheap, readily available, and more than adequate for your purposes, you don't set out to custom design cable that barely meets your needs.

#5 of 16 OFFLINE   ChristopherDAC

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Posted August 04 2007 - 03:08 PM

To clarify:

Good composite cables are made from RG-59 coax, which is good out to at least 100 MHz with minimal roll-off. The thin little stringy things you get with cheap DVD players are not that, and may not even be 75 ohms, and you shouldn't use them for anything more demanding than digital audio (which is pretty much immune to rolloff and reflections, as long as the run is tolerably short).

#6 of 16 OFFLINE   GregK

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Posted August 04 2007 - 03:38 PM

I used some composite cable of identical length when I first bought my front projector, and immediately noticed ghosting, just like Bob described. When I replaced the cables with different ones, the ghosting disappeared.

#7 of 16 OFFLINE   Bob McElfresh

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Posted August 04 2007 - 06:15 PM



































































NOMINAL ATTENTUATION VALUE
Model Lng.
ft
(m)
10M
Hz
dB
50M
Hz
dB
100M
Hz
dB
150M
Hz
dB
200M
Hz
dB
400M
Hz
dB
700M
Hz
dB
900M
Hz
dB
1.0G
Hz
dB
L-1.5C2VS 100
(100)
2.9
(9.6)
6.5
(21.5)
9.3
(30.4)
11.3
(37.2)
13.1
(42.9)
18.5
(60.7)
24.5
(80.3)
27.8
(91.1)
29.3
(96.0)
L-3C2VS 100
(100)
1.5
(4.9)
3.2
(10.4)
4.7
(15.5)
5.8
(19.0)
6.7
(21.9)
9.4
(31.0)
12.5
(41.0)
14.2
(46.5)
14.9
(49.0)
LV-61S 100
(100)
1.3
(4.2)
2.7
(9.0)
4.1
(13.3)
5.0
(16.3)
5.7
(18.8)
8.1
(26.6)
10.7
(35.1)
12.1
(39.8)
12.8
(42.0)
LV-77S 100
(100)
1.0
(3.4)
2.4
(7.8)
3.3
(10.8)
4.0
(13.2)
4.6
(15.2)
6.6
(21.5)
8.6
(28.4)
9.8
(32.3)
10.4
(34.0)


Quote:
Bob, you seem to be of the impression that engineers thought in the manner "hmm, we have to have cable that carry 4 MHz signal,...

I do know how engineers think. The table above is what engineers use to select a coax for Composite video, and a different coax for Progressive, and yet a different one for HD video.

This is why I urge caution against using 3 composite cables if the application is for HD video. The composite cables might be made with the L-1.5C2VS coax which is fine for Standard Def/480i, but the table clearly shows it is not acceptable for HD or even progressive video.

(My BSEE came from Berkeley and while I dont design analog video equipment for a living, we have members here who design HD video switches or build video cables and they have taught me a lot. Posted Image )

#8 of 16 OFFLINE   RobertCharlotte

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Posted August 04 2007 - 06:30 PM

Will it make any difference to know that the cables I'm planning to use are Acoustic Research "Performance" series (I think that's right, it's the blue ones).
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#9 of 16 OFFLINE   troy evans

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Posted August 04 2007 - 06:43 PM

Quote:
Originally Posted by RobertCharlotte
Will it make any difference to know that the cables I'm planning to use are Acoustic Research "Performance" series (I think that's right, it's the blue ones).
I don't think there's that much difference between good composite vs. good component. If You flip the package over and compare specs You'll be surprised to see that if There from the same company the build will be exactly alike. The only thing different is component is giving You 3 video cables at once in a set and color coding them so You don't accidentally hook the wrong cable to the wrong color jack, That's It! If It's cheaper to buy 3 good composite cables, Do It ,You won't be losing anything IMHO.
" I think it's time we go to plan B". "What's plan B?" "That's the one where we don't do something stupid".

#10 of 16 OFFLINE   Stephen Tu

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Posted August 04 2007 - 08:00 PM

Quote:
The composite cables might be made with the L-1.5C2VS coax which is fine for Standard Def/480i, but the table clearly shows it is not acceptable for HD or even progressive video

Oh come on. The L-1.5C2VS is a *micro coax*, 31 AWG. The composite video cables one finds in the stores are mostly RG59 type, the equivalent of the LV-61S model in your table, 24 AWG. Which is fine for HD. Note they don't make separate "high-def LV-61S" and "std def LV-61S". Cables of similar dimensions & materials will have similar characteristics.

Yeah possibly some throw-ins on a cheapo DVD player might be of the micro type and marginal, but those AR composite video should be just perfectly fine.

#11 of 16 OFFLINE   Phil A

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Posted August 05 2007 - 02:13 AM

Quote:
Originally Posted by Stephen Tu
Oh come on. The L-1.5C2VS is a *micro coax*, 31 AWG. The composite video cables one finds in the stores are mostly RG59 type, the equivalent of the LV-61S model in your table, 24 AWG. Which is fine for HD. Note they don't make separate "high-def LV-61S" and "std def LV-61S". Cables of similar dimensions & materials will have similar characteristics.

Yeah possibly some throw-ins on a cheapo DVD player might be of the micro type and marginal, but those AR composite video should be just perfectly fine.


I concur, I've made Canare RG-6 composite cables in the past and saw no difference on my old 64 inch CRT with an 8 ft. length of either component or separate composite cables. I've done the same now that 64 inch TV is in the secondary basement system and 14 ft. lengths of either and that included watching over a Samsung HD1000 (which I no longer own) which upsampled the video over component to 1080i. I also used my old Proceed PMDT made the same way with BNC connectors on the DVD transport side and RCAs at the display end and I saw no difference when the TV was in the main system with 8 ft. lengths. I'd imagine if you used mini video cables or the cables were of sufficiently difference lengths there could be issues. With a 3 foot length and good cables used as indicated by the original post and subsequent clarifications I don't see a problem. The original poster can also do an A/B with his long component vs. 3 ft. composite cables and report back. Way too many of these discussions unnecessarily rely on the hypothetical vs. real world experience, which I never see the point of especially when there is a situation when one can easily hook up a couple of sets of cables and bring it to a better conclusion. I'd imagine that like anything else the results (preferences) would not go 100% one way or the other 100% of the time, especially with different individuals, equipment, tastes, etc.

#12 of 16 OFFLINE   Clinton McClure

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Posted August 05 2007 - 03:28 AM

Working off this information, I'm using a set of white Monster component cables between my HD-DVD player and HDTV which I bought back around '97. I do not have any model number or product info about them but they appear to be roughly the same diameter as current cables (the jacket anyway) and the connectors and strain reliefs are built well. Can I assume these are of the RG-59 type? The picture quality between the HD-DVD player and HDTV is stunning (1080i) but could there be an improvement with a more modern component set?

#13 of 16 OFFLINE   Phil A

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Posted August 05 2007 - 03:54 AM

Quote:
Originally Posted by Clinton McClure
Working off this information, I'm using a set of white Monster component cables between my HD-DVD player and HDTV which I bought back around '97. I do not have any model number or product info about them but they appear to be roughly the same diameter as current cables (the jacket anyway) and the connectors and strain reliefs are built well. Can I assume these are of the RG-59 type? The picture quality between the HD-DVD player and HDTV is stunning (1080i) but could there be an improvement with a more modern component set?

The difference (among other factors) between RG-59 and RG-6 in general is the thickness of the center conductor. So, in general for the overwhelming majority of cases, RG-6 will have less signal loss. Cables also have different levels of shielding, even the same type (RG-59). Someone can have more, or less, interference from sources (e.g. close to radio transmission towers) that won't necessarily be the same in each situation. At one point when I had my Proceed PMDT transport I had nice store bought cables (before I made my own) that were RG-59 (I later learned it was Belden 89259) and about 11 ft. long (3 separate composite cables. I moved stuff around and had 3 separate runs of Canare RG-6 that were 11 ft. and saw no difference. I later moved stuff around and shortened the RG-6 to 8 ft. and made a Canare component cable and compared to the 2 and saw no differences. This does not mean there will be no differences in every single situation. I've made up numerous runs of Canare RG-6 (3 separate composite cables) and Canare component cable made from RG-6 and I have yet to see a difference in normal 4-14 ft. runs which I've made. If you have access to other cables or can get some with a money-back guarantee there is nothing to be lost (other than your time) to see which you prefer or if there is a difference. Sometimes I've found the flexibility and less individual weight of separate RG-6 just easier to work with and install (with some light DVD players the component cable can really literally pull them along).

#14 of 16 OFFLINE   ChristopherDAC

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Posted August 05 2007 - 01:47 PM

Quote:
Originally Posted by Bob McElfresh
This is why I urge caution against using 3 composite cables if the application is for HD video. The composite cables might be made with the L-1.5C2VS coax which is fine for Standard Def/480i, but the table clearly shows it is not acceptable for HD or even progressive video.

Those rolloff figures are for 100 ft lengths! Even the L-1.5C2VS should be OK at 3 feet.

#15 of 16 OFFLINE   Philip Hamm

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Posted August 06 2007 - 02:06 AM

Quote:
Originally Posted by Phil A
Way too many of these discussions unnecessarily rely on the hypothetical vs. real world experience
Not to mention theoretical differences which while valid, often don't mean much in real world applications.
Philip Hamm
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#16 of 16 OFFLINE   RobertCharlotte

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Posted August 07 2007 - 02:24 AM

Thanks, everybody, for the help!

As to the A/B testing, I don't think my equipment is up to the task of distinguishing much finer differences than "this cable works" and "this cable doesn't work." Posted Image
Blücher!


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