How can I figure out the surround sound system left behind by the previous owners?

Question

I have a basement with what appears to be surround-sound infrastructure. At 4 points in the ceiling (let's call them locations C0...C3), there are a pair of speaker wires. At one location near the floor (call it point F), there are two pairs of speaker wires (probably where the audio controller was located). Nearby there is also a coax cable exiting the wall.

I used a multimeter to test the resistance between the wires at point F and points C0...C3 and each time it reads infinite, suggesting that the wires are not actually connected. However, before I moved in, I definitely noticed that the previous owners had speakers in their ceiling.

I don't know anything about home theatre systems, so what are the possible explanations? Is there some kind of variable-resistance component hiding somewhere in the walls (perhaps some kind of junction that only conducts in the presence of a signal? There are 4 pairs of output wires for only 2 pairs of input wires, after all)? Could they have somehow disconnected the wires upon moving out and, if so, how and why?

Answer 1

If you simply used the ohm meter to check between the wire pair at each of the three terminus points then it is very likely that you would read infinite. The reason being is that the other ends of the pair are laying open someplace else.

To check for the wire routing you would need to check for continuity from one wire at say point C0 to one of the wires at point F.

The two pairs of wires at point F may have been connected to speakers located at or near that point. If that is the case then it is likely that all six of your speaker wires terminate at some location that you have not yet located. Some systems that people install put all the equipment out of site in a closet or adjacent room. This is particularly true for cases where the equipment is almost totally controlled through a user interface on the video screen.

You may have wire pairs looking something like this coming from a closet someplace:

You could investigate trying to trace the wire routing. There are tools that you can purchase that inject a signal into a wire from a battery operated transmitter. Then there is a separate receiver unit with a probe that you slide along the wall. The receiver module will produce a sound that chirps and varies in intensity depending upon how close to the driven wire it is located the probe. I own several of these units and have good to mixed results with them. Here is a link to the unit that I have had reasonable success using.

You can find this unit at better hardware stores, big box locations or online. The price showing at the link above is decidedly better than what I paid for the same unit about 10 years ago.

Answer 2

If you actually want to find if the pairs are connected or not:

1. Pick one of the pairs at F.
2. Twist together the ends of said pair of wires.
3. Go around to C0-C3 and test each with the meter set to continuity. When you find a C? that has continuity - they are connected.
4. Repeat for the other pair at F.

You could do also the opposite: Twist together one of C0-C3 and test each pair.

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If there's only two pair in the wall at the receiver location, and there's four speaker spots in the ceiling, and this home was built in the 80s, they may have wired it for "passive matrix surround sound." It's a technique that uses a single stereo output to drive four speakers, with the rear speakers out of phase of the others. It's uncommon now - most systems are truly discrete driven by a surround sound receiver. It can be convincing - Brian Eno recommended it when listening to some of his music. (See here for more info on passive matrix surround: http://kantack.com/surround/surround2.html)