Finding audio cable behind drywall - AVS Forum
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post #1 of 15 Old 09-16-2009, 06:12 PM - Thread Starter
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When our home was built it was wired for a surround sound system. There is a cover plate housing a bunch of audio cables 4 with cut ends and 3 continuous looped cables going up toward the ceiling. Unfortunately I have no idea where in the wall or ceiling the other ends of the cables are and therefore where I should make the holes for my speakers. Neither the builder nor the electrician have any clue other than that I should call a professional to locate them.

I tried a "Tone and Probe" type unit from HD but according to their support like these units require that you have access to both ends of the cabling. Since I only have access to one end of the cables this will not work.

Any ideas how I could do this myself?

Thanks in advance for any pointers.
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post #2 of 15 Old 09-16-2009, 07:07 PM
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Something like this should do it. Might be able to rent one for a day somewhere. Might be cheaper to hire a pro...

When I need to find a cable, I just look at the pictures taken of the house before the drywall went up...
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post #3 of 15 Old 09-16-2009, 09:53 PM
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Fluke is like the Ferrari of testing equipment. I bet you can find one much, much cheaper.

But that Fluke tester does look pretty awesome.

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post #4 of 15 Old 09-17-2009, 07:37 AM
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Quote:
Originally Posted by a57oval View Post

I tried a "Tone and Probe" type unit from HD but according to their support like these units require that you have access to both ends of the cabling. Since I only have access to one end of the cables this will not work.

Access to both ends? Well, what would you need the thing for, if you know where the cable begins and ends???

That sounds really peculiar. If the one you bought is something like this, then you only need access to one end. Just strip back the insulation of the two conductors, attach the tone generator, and you're good to go. You'll have to cut those loops in order to trace them. Keep in mind, these things will NOT work with shielded cable, only unshielded stuff like speaker cable, phone cable, etc.

Regards,
Wayne A. Pflughaupt

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post #5 of 15 Old 09-17-2009, 08:59 AM
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How does the tone generator work, if the wires aren't shorted?

I have that same exact unit, Wayne.

Believe nothing, no matter where you read it, or who said it, no matter if I have said it, unless it agrees with your own reason and your own common sense. -Buddha

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post #6 of 15 Old 09-17-2009, 09:49 AM
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Good to hear, that’s a first-class unit. I have one myself.

Actually if the wires are shorted it won’t work at all. It generates a high-level signal on the wires, and the probe picks it up and audibly plays the tone over its built-speaker. You can check it out without connecting it to anything. Just turn on the tone generator and press the button on the probe. You’ll see the sound get louder the closer you move the probe to the black and red wires w/ the clips.

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post #7 of 15 Old 09-17-2009, 10:07 AM
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I should probably research this online, but this is more sociable.

How does it generate a signal on the wire without a complete circuit? I understand basic electronics, and this doesn't jive with my experience.

This is something I've wondered for a long time.

Believe nothing, no matter where you read it, or who said it, no matter if I have said it, unless it agrees with your own reason and your own common sense. -Buddha

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post #8 of 15 Old 09-17-2009, 11:27 AM
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Good question. I really have no idea; I just know it works.

Regards,
Wayne A. Pflughaupt

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post #9 of 15 Old 09-17-2009, 11:31 AM
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That is what we just used to trace the cables now I only needed it to figure out which went where and had both ends.

Just a stupid thought (since I really know nothing of this) isn't the circuit complete because that receiver unit picks up the signal . Now you got a transmitter, cable and receiver
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post #10 of 15 Old 09-17-2009, 11:52 AM
 
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Quote:
Originally Posted by Wayne A. Pflughaupt View Post


Access to both ends? Well, what would you need the thing for, if you know where the cable begins and ends???

That sounds really peculiar. If the one you bought is something like this, then you only need access to one end. Just strip back the insulation of the two conductors, attach the tone generator, and you're good to go. You'll have to cut those loops in order to trace them. Keep in mind, these things will NOT work with shielded cable, only unshielded stuff like speaker cable, phone cable, etc.

Regards,
Wayne A. Pflughaupt


Right. That's the standard tool used for finding wire. If you connect one lead to ground it gets way way louder as well, if the wire is buried deep.

It works by magic.
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post #11 of 15 Old 09-17-2009, 12:14 PM
 
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Quote:


Just a stupid thought (since I really know nothing of this) isn't the circuit complete because that receiver unit picks up the signal

No.

It probably injects a high frequency modulated signal, capacitive coupling to ground completes the circuit.
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post #12 of 15 Old 09-17-2009, 01:11 PM
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The generator uses a very wide bandwidth, low power AM RF signal with the tone. The receiver is basically a very insensitive radio receiver. The probe on the end of the receiver is a heavily carbon-impregnated piece of plastic connected as an antenna.

These are DC and AC isolated contacts so they can be used on powered lines that carry everything short of live AC line voltage. They CAN be used on AC lines that are dead though.

There are similar devices where the transmitter plugs into a live outlet and the receiver is then taken to the load center and passed along the breakers until a tone appears. This is great for locating unknown breakers tied to a particular outlet or fixture.

The toner system does not need access to the traced wire conductors. These are easily used to locate a wire in the middle of the bundle. The stronger the tone, the closer you are to the wire.
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post #13 of 15 Old 09-17-2009, 08:09 PM
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Quote:
Originally Posted by ChrisWiggles View Post

It works by magic.

I really like that answer!

Believe nothing, no matter where you read it, or who said it, no matter if I have said it, unless it agrees with your own reason and your own common sense. -Buddha

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post #14 of 15 Old 09-18-2009, 06:28 AM
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I did some digging.

The Triplett 'Fox & Hound 3' instruction manual
http://www.jewellinstruments.com/pdf...dfs/84-863.pdf
goes into some detail of how it works to find a pair (or more) of wires where you don't have access to both ends of the wire.

From what I gather, the toner signal travels down 1 wire, and induces the current in the other wire, completing the circuit. The probe can then detect the signal through drywall. The manual calls this 'floating' or 'line-to-line' tracing.

The manual also describes the use of the toner using 1 probe attached to 1 wire, and another probe to ground - manual says this is the better way (called 'line to ground' method).

Believe nothing, no matter where you read it, or who said it, no matter if I have said it, unless it agrees with your own reason and your own common sense. -Buddha

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post #15 of 15 Old 09-19-2009, 08:22 AM
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Quote:
Originally Posted by Gizmologist View Post

These are DC and AC isolated contacts so they can be used on powered lines that carry everything short of live AC line voltage.

I don't know about the other brands, but I've used the one linked above from Tempo (formerly Progressive Electronics) on live AC. It was an accident of course (don't ask ). I figured the thing was toast, but amazingly the only damage was that the power LED burned out.

As they say, "don't try this at home!"

Regards,
Wayne A. Pflughaupt
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