HT wiring (1 Viewer)

[john_anderson]

I am currently re-modeling one of the rooms in my basement and have some home theater wiring questions. I am down to the wall studs and I am getting ready to run wires before sheet rocking. My plan is to have a built-in receiver/processor (and all other components DVD, VHS, CD, etc) in one corner of the room and the TV on a wall about 15 feet away; the cable run itself will be approximately 25-30 feet. My first question is can I run 3 standard RG6 cables (75 ohm coax) from the processor to the TV for component signals? How do other people make longer runs like this? From what I have researched so far the cable lengths are usually less than 10 feet; so can a component signal hold up to these lengths okay? I am also interested in planning for the future so I am wondering what other cables I should run before sealing the walls. I have been reading about DVI cables (length issues?), fiber optic (used for video yet?), and just now on your forum firewire, any other suggestions… I have not purchased any HT equipment yet and at this point I am just trying to be prepared. Also I would like to be able to do progressive with this cabling architecture. Any advice and help would be appreciated in addition any web page references would be great!

John

 

[Bob McElfresh]

can I run 3 standard RG6 cables (75 ohm coax) from the processor to the TV for component signals?

The run-lengths are not a problem. Good quality video cables are tested with 100 ft runs and the results published.

To cover all the bases, I would run:

- Component cables
- SVideo cable
- Composite cable
- Subwoofer cable (you can use ordinary CATV coax for this)

The custom cable sites can make these up for you.

I'm not a big fan of buying generic CATV coax and using it for HD video. The coax are like roads: they all use the same asphalt, but a freeway road is build for different speeds than the ones built in front of your house. Once again- hit the custom cable sites.

You might also consider running 4" flexable conduit and leaving a nylon roap to pull more cable later.

Make sure you run these line-level cables AWAY from your speaker wires and AC power wires in your walls. Dont give into temptation and run these wires and your speaker wires together.

DVI - these seem to have a problem with lengths over about 10 ft. So dont worry about this.

You might also want to run a Telephone outlet to your equipment cabinent. Many CATV and Sat receivers require one of these.

 

[Todd B]

Bob,

What is the problem with running shielded video cables alongside speaker cables?

Todd

 

[john_anderson]

Bob,

Thanks for the information.

You mention "Custom Cable Sites" - could you give some examples.

Thanks,

John

 

[Chu Gai]

the coax and speaker cables can be run next to each other. tape them together if you want.

Regarding DVI length, I've read the limit is about 15 feet. Consider the following link which is chock full of information: http://www.extron.com/technology/arc...tifingcables2&

 

[Bob McElfresh]

What is the problem with running shielded video cables alongside speaker cables?

The 'shield' in your cables is connected to the zero-volt electronics on both ends (TV and DVD player). When lots of power flows through wires in parallel, it induces noise into what SHOULD be always 0.000 volts.

When you read about how superior a shield is, think: "We have a better ANTENNA that hooks into your electronics".

You really want your cables behind your rack bundled into 3 separate sections:

- AC power cords
- Speaker Wires
- Interconnects

This is why I always recommend you put your receiver on the bottom shelf: it allows the speaker wires to flow out without obscuring/coming near most of the other wires.

Did this answer the question?

 

[Wayne A. Pflughaupt]

When you read about how superior a shield is, think: "We have a better ANTENNA that hooks into your electronics".

Ya totally lost me there, Bob!

Regards,
Wayne A. Pflughaupt

 

[Bob McElfresh]

When you read about how superior a shield is, think: "We have a better ANTENNA that hooks into your electronics".

Sorry. There is a major brand of AV cables that 'snow' consumers with techno-babble about how good their shielding is and this justifies the $100-$200 price tag. This bugs me.

Think of it this way: the shield on a cable is like the down-spout on your house. The gutters keep all that water from just pouring down, but you have to have someplace for that water to flow.

In your electronics, the 'shield' needs some place for the electrical interference to flow. Because the shield also acts as the zero-volt reference/signal ground between your electronics, any noise picked up is injected into your electronics and contaminates the ground.

(A signal is really a voltage difference. And your electronics really dont care if the signal is on one wire or the other. A voltage difference is a voltage difference.)

As long as the noise is small amounts, it is ignored. But running interconnects in parallel with speaker wires - different story.

This rough formula for how much noise might be injected into a interconnect is true:

Noise = (Power running in parallel wires) X (number of feet of parallel wire) X (fudge factor)

This is why people are advised to do in-wall wire that crosses AC power lines at a 90 degree angle - to minimize the amount of parallel runs.

So it's NOT a good idea to run speaker wires in the same tube/bundle with speaker wires. And sure, you can get away with it for modest volumes, but try turning up the power and problems you never knew existed start showing up.

(Remember: to get 1 db increase in volume requires TWICE the power. So it's not hard to get 100 or 1000 times the power on a speaker wire with a twist of the knob.)

Any clearer?

 

[Wayne A. Pflughaupt]

Any clearer?

I suppose. Assuming this is true, Bob (and I don’t doubt it is ‘cause I know you’re a saavy guy ) I think a couple of important essentials have been overlooked.

First, the runs we’re talking about in home theater are relatively short.

Second, and perhaps most important, the only time speaker wires will generate high voltage is during demanding (read loud) passages. I think it’s obvious that in those moments, a reduced noise floor caused by interference generated by the same is a non-issue.

Of course, this would only be relevant to audio interference, not video. Nevertheless, in the four years I’ve participated on this and other home theater boards, anytime time I’ve seen anyone complain of noise or interference, either with audio or video, it was almost always traced to ground loops or light dimmers. I’ve never seen anyone complain of interference that was ultimately traced to speaker wiring running alongside signal wiring.

But – you spend a lot more time perusing this board than I do – perhaps you can point us to some examples you’ve seen.

Regards,
Wayne A. Pflughaupt

 

[Bob McElfresh]

In truth, 60hz hum coming in through the CATV coax is a much-more common problem. But it's caused by the same effect - power wires with long runs in parallel with coax.

I dont think you hear much about it because most systems dont have the equipment at the back and the TV at the front where there is a temptation to run speaker & video cables 10-20 feet in parallel. And nearly every "..I'm going to run wires in-wall" type of post gets warned to not run near AC power wires.

There are a FEW cases per year where people experience interference that is solved by separating cables. There was even a recent post about a bundle of line-level cables causing problems until they were separated. Of course I cannot find a good example with a quick search. :frowning:

But speaker wires ARE power wires. And while not fixed-frequency like AC power, they do create magnetic fields. It's really not a good idea to run line-level cables in close proximity to speaker wires because of the induced-signal problem.

 

[Bob McElfresh]

Here is the thread on a SVideo Cable from a Tivo unit in a bundle causing problems.

(I still dont understand it, but I found other posts about the Tivo outputs causing problems.)

 

[Chu Gai]

What would then be everyone's comment on the Residential line of cables that Belden markets? Examples are the 7876A, 7877A, 7878A, 7910A, 7913A, 7914A.

Looks to me like they're running things pretty close in that bundle.