I was a little confused at your description but now I think I understand. You have an existing wall - 2-inch thick over some sound deadinging material over studs whcih is a little confusing. when you say studs the normal thought is a 2x4 which would provide a 3.5" space not 2". I wonder if you mean firring strips - and if this is against another wall -like firring strips over concrete block with drywall. No matter - you dont mention the typse of audio cable that might be in the wall.
One thought which comes to mind is - if you have access to both ends of the cable you might disconnect it at each end - and protect the far end from a short. Then apply power - 110 volts AC to the near end and trace it with the Zircon. Now that of course can be risky in that the wire may not be rated for that voltage. But most audio cable can take 110 VAC. Most is rated 150 to 300 volts - BUT NOT ALL SO LOOK AT THE JACKET GOOGLE PERHAPS AND DETERMINE. If it was me I would check the rating seal the one end just do it. First - check with a DMM or other ohmmeter to insure there is no short and make darn sure that cable doesn't go anywhere else - to an amp or something. Again you didnt state if its an output power cable (to speaker etal) or an input cable (to line in or microphone or a studio hookup). There are so many questions and variables in what you are doing that this is a tough one to answer but if the wire is in the wall and you can power it up like I said the Zircon would probably find it which is what your basic question was. I also wonder why you are locating them - is it because you wish to break open part of the wall (a new doorway or such) ir just curious or worried about hitting it with a nail when working the wall?
short of renting an xray machine for such work - thats all I can suggest. The wires are likely copper so non-ferrous and magnets won't help. ONe other technique that comes to mind might be to apply a low voltage to the wires with a load ont he far end - so they conduct perhaps an amp or 2 or more if big enough. if it is not coax cable - your zircon might find them too or a compass may even pick up the magnetic field the conductor naturally generates with electricity flowing through it. If its shielded or coax - your screwed I think. one other thing also. If oy can find a vertical plane on the wall where you could slightly open it and probe - like behind a door or such - you take your best shot - cut a narrow slit maybe 1/2" wide up the wall vertically (carbide tipped router or something that doesnt penetrate too deeply and might damage the underlying wires) and route a hole through the drywall or what ever is there. Then probe inside the wall in that groove and find the elevation of the wire. Perhaps in a few other locations too if necessary. Mark the wall with a small drill hole for elecation ( assuming the wire is running horizontally and not vertically. Then patch the wall with tape or if narrow enough wiith spackle. Just some ideas .
Marty
