Axiom Home Page Forums General Discussion Technical Questions Guide for home theater wire through the wall

---

Fiberglass on your bare skin is very unpleasant.

---

So I take it you've done this procedure, um...in the buff?

I was wearing pants and shorts sleeves when I did the belly shimmy into the deep dark corner of my attic in order to pass a coax cable down from antenna. I itched for hours after that.

I used to be an insulator's assistant (yes, somewhere between starting the industrial revolution and dying on the cross for your sins).. the trick? Shower COLD first, closes up the pores... no itching. It's one thing to lie on bats of insie... another thing to be blowing wool in. That gets EVERYWHERE.

Bren R.

Hi All... I'm planning to do the same in house, my plan is to run it to the first floor wall then to the vents exiting to the 2nd floor, then ran the wires under the carpet on the 2nd floor then drill down to the 1st floor.

Now the things that troubles me are:
1. I'm going to buy from bluejean wires and I'm not sure if those wire is ok to run inside the heating vents?
2. I read that its bad to run speaker wire for more than 5 feet near an AC wire and there are 2 outlets on the wall that I'm running my speaker wires, but if in running the speaker wire outside the wall(under the carpet) will that be ok?

Sorry to hijack the thread.

In reply to:

---

then ran the wires under the carpet

---

Check with one of the sparkies here... I've been told that running any cable under a carpet can void your home insurance (even low voltage). At the very least it's a bad practise.

Bren R.

I would think that your ide of running your cables under the carpet would be a bad idea, I would recommend along the wall, to where you want to drop them though the floor.


Your other concern as far as running cables next to ac wires, such as power wires.. I would not worry about that to much, the idea is sound as to why you should not run the cables next to the power wire.. the power wire is operating at 60hz, a constant 60hz, so the cable has a magnetic field constantly being created and colapsed around it, and this magnetic field could induce a voltage on near by wires, i.e. the speaker wires you are wanting to run…

In the real world, it wont affect your sound quality very much at all, a few options. Keep your speaker wire about 12 inches or more away from the power wire. Look for shielded speaker cable. If you can get shielded cable this will nullify the magnetic field of the power cable.

Hope this helps.


Also, I would recommend a long sleve shirt, and a light weight jacket, and jeans..

I read that its bad to run speaker wire for more than 5 feet near an AC wire

______________________________

Because each AC line has 2 wires carrying the current in the opposite directions the magnetic field from each wire almost cancel each other. The net magnetic field is very small and falls quickly with the distance from the AC line. If you run a speaker wire parallel to an AC line for 30 feet at the separation between them of 3 feet than the induced voltage on you speaker will be about 1 microvolt. Nothing to worry about.

Below is a long a boring derivation of how one can arrive to this number. Read it at your own risk!

For a long AC line a good estimate for induced magnetic field is

B=0.1*I*delta/R^2,

where I is the current in the AC line, delta is the separation between the 2 wires in inches and R is the distance from the line in inches. B is in Gauss, this is a unit for magnetic field measurement.

Let's take an example. I=15A (max for a typical household AC line), delta=3/8", R=36". Then B=0.4 milli Gauss

How large is it? Well, about 1,000 less than the Earth magnetic field. In reality the field will be even less because we assumed the AC line is running flat. If the wires are twisted then field will drop down much quicker with the distance.

How much voltage this field can induce in the speaker wire? Again, the speaker wires run very close to each other, so they form a loop with a small area. Even better if they are twisted.

If, in the worst case scenario the speaker wire run parallel to AC line then the induced voltage can be estimated as

V=B*L*s/3000 where B is our magnetic field in Gauss, L is the distance that the AC line and the speaker wires run parallel to each other (in feet) and s is the separation between the speaker wires (in inches). Frequency 60 Hz is assumed.

Ok, almost over. Take the previously calculated B=0.4 mG , L=30’, s=1/4” then V=1micro volt. Absolutely nothing to worry about.

Wow... thanks for the math behind that...

I suggest a hand's span from AC wires, Gena posts the electrical engineering theory on the exactly inductance.

Bren R.