Speaker wire and Video wire in same conduit

[TeeJah]

These are general questions.

What are the issues involved in running #12 (line out) speaker wire and video (monitor) cable in the same conduit? (I don't know exactly which cable is going to be used for the video, but I assume that the same issues may be present regardless of what type it is???)

The furthest length of run that will be run together will be around 125'.

Do they need to have their own outlet boxes?

Thanks in advance.

 

[mtrycrafts]

These are general questions.

What are the issues involved in running #12 (line out) speaker wire and video (monitor) cable in the same conduit? (I don't know exactly which cable is going to be used for the video, but I assume that the same issues may be present regardless of what type it is???)

The furthest length of run that will be run together will be around 125'.

Do they need to have their own outlet boxes?

Thanks in advance.

What kind of application is this with such long runs? That run is longer than what we usually see here. I suppose if you use an RG6 type video cable the speaker wire would be ok.

 

[TLS Guy]

Why so long?

Two questions.

Is this going to be a high performance audio visual system?

Is there a way to get the runs shorter?

The reason I ask this, is that with 125' runs, even if you use car battery cables, the resistance of the speaker wires is going to be too great. You are going to loose half or more of your power in the speaker leads. Not only that, these resistances will upset the bass alignment of the speakers and lead to impaired performance.

If this is going to be a high quality system, then you need professional engineering solutions. Your options are: -

1). Use powered speakers with balanced inputs and an audio visual preamp with balanced outputs.

2). Use an audio visual preamp with balanced outputs, to amps with balanced inputs placed close to the speakers.

If this is going to be a low Fi application, then the solution is to use PA amps with 70 or 100 Volt speaker outputs. You then place a transformer at each speaker, and choose the tap that matches the amp output. If multiple speakers are connected to the same amp then the sum of the transformer taps must equal the amp power. Since this is a high impedance system you can use very thin speaker cables.

There is no problem running the speaker and video cables in the same conduit. In my set up the video and center speaker cables run in the same conduit.

To help you further we need to know more details of what you are trying to do.

 

[Haoleb]

im going to have to disagree with you about 125' long speaker runs. While they are certainly not ideal its not quite as bad as you suggest. Its not uncommon for many of the houses I work in to have runs at least 100' long for multi room audio and no problems whatsoever. Of course in a high end theater you wouldnt want runs like that but sometimes what customer wants isint always the best performance wise. (like in wall speakers and LCR bars) Yuck. The loss of performance of a 70v system and its bandwidth limited transformers surely is worse than what you would discover with longer than ideal speaker runs.

Just to see for myself what kind of effect the wire would have I grabbed a box of 16/2 out of the back of my truck thats got about 218 feet left on it and hooked it up to an 8 ohm JBL ND310 speaker and my 65wpc sansui integrated amplifier. Sounds just fine... all things considered. I Dont think the average person would notice any issues regarding performance with speaker wires this long. There seems to be a bit of high end rolloff but then again these speakers never had clarity as one of their better traits so I cant say for sure.

 

[MDS]

Haoleb, as I am sure you can attest based on your experience with installs, the majority of homes that are 'pre-wired' use 16/2. I know mine does. Now my runs aren't anywhere near 125' (half that at best), 16/2 is fine for the majority of installations.

The rule of thumb from the Roger Russel (McIntosh engineer) site on speaker cables is to keep the loss from the speaker cable to within ~5% of the impedance of the speaker. But honestly, how many people can really tell the minimal difference between 16/2 and 12/2? If I were building the new house from scratch and had 125' runs, I'd opt for 12 gauge, but it won't be the end of the world if you use 14 or 16 ga.

 

[Rickster71]

These are general questions.

What are the issues involved in running #12 (line out) speaker wire and video (monitor) cable in the same conduit? (I don't know exactly which cable is going to be used for the video, but I assume that the same issues may be present regardless of what type it is???)

The furthest length of run that will be run together will be around 125'.

Do they need to have their own outlet boxes?

Thanks in advance.

I would have to agree with Haoleb and MDS.
It's OK to run your low voltage wire in the same conduit. (speaker & video)
Also to answer your question of needing separate boxes. Low voltage can share the same box, it doesn't really need a box, just a low voltage ring, to screw the wall plate to.

As for the 125' wire run. It's really not all that long. It not ideal, but it's not that big a deal.
12-AWG will work fine in most, applications.
It would help to know the load, and the wattage of your amp.
One hates to assume.
Are the long runs for rear surrounds, or a zone-2 application?
If so, they probably won't be played at reference levels, so 12 wire is definitely OK.

 

[TLS Guy]

Measure the resistance of the runs

Measure the resistance of those runs. You need to twist the ends of one end together, and put the ohm meter across the the open ends at the other end of the wire. Please let us know what the resistance is and you will be able to calculate your losses precisely.

I have dug out some 12, 24 and 16 Gauge wire, and it's better than I thought, it is about .002 ohm/ft, which would give you a total resistance of 0.5 ohm. 14 Gauge is about 0.003 ohm per foot, which would give a total resistance of 0.75 ohm. 16 Gauge is about 0.005 ohm/foot, giving you a total resistance of 1.25 ohms. So the 12 gauge run would be 8% of the impedance at 8 ohm, but 16% for 4 ohm speakers. The 14 gauge is 9.4% for 8 ohm speakers and 18.8% for 4 ohm. The 16 gauge is 15.6% for 8 ohm speakers and 31.2% for 4 ohm. I used stranded copper wire by the way.

Anyway measure your wire as results may vary.

 

[Rickster71]

Measure the resistance of those runs. You need to twist the ends of one end together, and put the ohm meter across the the open ends at the other end of the wire. .

Aren't you doubling the length of the wire, by twisting the ends together?
That will double the R.

 

[TLS Guy]

Both runs of the wire are in series with the speaker

No! That is the way it is measured. If the positive speaker wire is R1, the speaker is R2 and the negative speaker wire is R3, then these resistances are all in series. The total resistance is R1 + R2 + R3. So the resistance contributed by the speaker cable is R1 + R3.

Sorry, but that inconvenient fact is the way it is.

 

[fmw]

Aren't you doubling the length of the wire, by twisting the ends together?
That will double the R.

Yes, one length going and another coming.

 

[TeeJah]

i guess to answer one of the questions many of you asked, this A/V system is going to be installed in my church. They are totally renovating the place and part of the "project" is to upgrade their A/V system. At this point, they just wanted to have the conduit and wiring infrastructure for the system installed. They original layout calls for all of the (29 sm + 13 lrg) speaker locations throughout the church and (4) video monitor locations to have their own conduit(s), all of which meet at 1 of the 4 main junction (outlet) boxes nearest to their locations, then homerun back to the A/V closet.

Now they are looking to consolidate where they can (save $$) and cut back on how much conduits are running throughout the church (BTW, most of it will be concealed).

As far as the specifics go for the system, I think that they are still shopping around for the equipment. Again, they just wanted to have the infrastucture installed.

Thanks again for all your responses, it helped out tremendously.

 

[TLS Guy]

That information really helps

That info really helps.

I think for an installation like that you are best using PA amps with high voltage speaker lines and transformers at the speakers. The quality can still be very good. This technology is very mature and goes back to before WWII. It works very well in practice. It makes it duck soup to balance out the speakers.

I was back in England in August where my 84 year old father had just redone the speaker system in his Church. It is a difficult building and never had been right. I made suggestions of products, such as Klipsch PA speakers. The next thing I knew he had purchased two expensive Lowther 6 inch full range drivers. These are highly sensitive. The late Donald Chave of Lowther once filled St. Pauls Cathedral with four Lowther PM 6 drivers horn loaded. It was to reinforce a concert. They filled the place beautifully and it caused quite a stir. Anyhow my father made front loaded horns that looked about right to his eye, and had them mounted on platforms above the altar. He kept the PA amp with the 70 Volt system and transformers. I have to say I was astonished, the rig worked very well. I listened to CDs or organ and choir. I can tell you it was a long way from low Fi. So much so that the next time I'm over, I'm going to upgrade the radio mics and PA amp for him.

 

[Rickster71]

The reason I ask this, is that with 125' runs, even if you use car battery cables, the resistance of the speaker wires is going to be too great.

. So the resistance contributed by the speaker cable is R1 + R3.
Sorry, but that inconvenient fact is the way it is.

Not half as inconvenient as telling poor TeeJah that he would need battery cables for speaker wires, for a 125' run.

 

[mtrycrafts]

Measure the resistance of those runs. You need to twist the ends of one end together, and put the ohm meter across the the open ends at the other end of the wire. Please let us know what the resistance is and you will be able to calculate your losses precisely.

I have dug out some 12, 24 and 16 Gauge wire, and it's better than I thought, it is about .002 ohm/ft, which would give you a total resistance of 0.5 ohm. 14 Gauge is about 0.003 ohm per foot, which would give a total resistance of 0.75 ohm. 16 Gauge is about 0.005 ohm/foot, giving you a total resistance of 1.25 ohms. So the 12 gauge run would be 8% of the impedance at 8 ohm, but 16% for 4 ohm speakers. The 14 gauge is 9.4% for 8 ohm speakers and 18.8% for 4 ohm. The 16 gauge is 15.6% for 8 ohm speakers and 31.2% for 4 ohm. I used stranded copper wire by the way.

Anyway measure your wire as results may vary.

Measure away
Wire reference books call for 16ga as 4 ohms per 1000ft. So that 250ft round trip distance would be 1 ohm. Since the poster implied a new run of wires, he can use larger ga to attain that stated 5% resistance
Let's see. 12ga would be 0.4 ohms for 250ft, at 5% of the desired results, nowhere near your assertions of half power loss from a jumper cable. LOL
10ga would be .25Ohms.
6ga jumper cable would be .1 ohms at 250ft. I doubt his speakers are .1 ohms, you would agree, to get 1/2 power loss in the cables, right?

 

[mtrycrafts]

i guess to answer one of the questions many of you asked, this A/V system is going to be installed in my church. They are totally renovating the place and part of the "project" is to upgrade their A/V system. At this point, they just wanted to have the conduit and wiring infrastructure for the system installed. They original layout calls for all of the (29 sm + 13 lrg) speaker locations throughout the church and (4) video monitor locations to have their own conduit(s), all of which meet at 1 of the 4 main junction (outlet) boxes nearest to their locations, then homerun back to the A/V closet.

Now they are looking to consolidate where they can (save $$) and cut back on how much conduits are running throughout the church (BTW, most of it will be concealed).

As far as the specifics go for the system, I think that they are still shopping around for the equipment. Again, they just wanted to have the infrastucture installed.

Thanks again for all your responses, it helped out tremendously.

Yep, for this application I agree with TLS Guy on the type of system you need, certainly not a home audio amp. With that in mind, your cable needs have changed and less critical but you still need good video cables, RG6 types.

 

[TLS Guy]

Correct

The numbers I gave are what I measured. I'm a old geyser and have cables that are old, and likely have purer copper than current ones, as copper is getting expensive. That is why I said results may vary. If current 12 G cables are 4 ohms per thousand foot, then his resistance will be one ohm. The results of using a I ohm cable will be twice as bad as the results I obtained.

The power loss is not the biggest problem anyway, it is upsetting the frequency response, especially in areas where the speaker's impedance point drops to the low point. Also the increased resistance will upset the bass alignment of speakers to a varying degree. The resistance between woofer and amp has to be taken into account in the total design. This speaker run is well out of the norm for domestic Hi Fi applications. For audiophile results I have to agree with Mac's recommendation to keep cable resistance to 5% of the nominal speaker impedance, or close anyway.

The situation is moot as this installation is for a Church. Home audio engineering practices are not applicable or satisfactory for this type of installation. This needs a high voltage speaker system. What has been PA practice since the dawn of time. If they want to improve on this, then they will be into big bucks, going with fully professional Hi Fidelity audio standards and practices, as I first suggested.

 

[jcPanny]

A/V Cables

i guess to answer one of the questions many of you asked, this A/V system is going to be installed in my church. They are totally renovating the place and part of the "project" is to upgrade their A/V system. At this point, they just wanted to have the conduit and wiring infrastructure for the system installed. They original layout calls for all of the (29 sm + 13 lrg) speaker locations throughout the church and (4) video monitor locations to have their own conduit(s), all of which meet at 1 of the 4 main junction (outlet) boxes nearest to their locations, then homerun back to the A/V closet.

Now they are looking to consolidate where they can (save $$) and cut back on how much conduits are running throughout the church (BTW, most of it will be concealed).

As far as the specifics go for the system, I think that they are still shopping around for the equipment. Again, they just wanted to have the infrastucture installed.

Thanks again for all your responses, it helped out tremendously.

TJ,
Sounds like you have plenty of advice on the speaker wire size so I will try to answer some of your other questions. I don't see any problem running the speaker wire in the same conduit as video wiring. DO NOT, however, run any of your A/V cables with high voltage AC power wiring. It is against code and can cause interference with your A/V signals.

3 runs of RG6 coax will give you a component video signal to each monitor. It has good shielding and shouldn't effect the speaker singals but belden makes shielded speaker wire for extra insurance. Run an extra RG6 coax to locations where you think the monitor might want or need a digital audio feed.