Wednesday, 13 November 2013

Speaker Cable Rats Nest Tester

Our new house has speaker cables wired into the walls. There are quite a few pairs coming out in a couple of locations and a manual switch carrying 4 speaker positions. Some of the speakers are dead, none of the cables are labelled = hassle.

I figured that the easiest way to start would be to connect the speaker switch to an amp and see which speakers activated.

When I tried this I got some confusing results. Switch position 1, one of the speakers in the lounge room come on (there are 2). Switch 2 … nothing, Switch 3 … nothing, Switch 4 … nothing. Now for the confusing bit. Switch 1 and 2, I get Lounge and Kitchen. No other combinations give any results.

The next approach is to pass a current down the speaker cable attached to an LED. If there is any illumination in the LED, then the cable is OK. I’d then label the speaker cable and I can then move on. The cables that don’t illuminate are dud.

I built a very simple testing tool that has a power supply at one end (a 9V battery) and an LED at the other end. I connect the speaker cable at one end of the wall to the power supply and probe the remaining speaker cables (including in the roof) until I get a glow.

I must stress that this is a VERY simple tool.


The idea here is that the speaker cable should carry the power from the source to the indicator. It really is that simple.

So far I’ve tested and identified one set of cables, but I still have to crawl around in the roof to locate the others. I don’t know what I’m going to find, but I know that one set of speakers that I pulled apart to investigate (internal speakers mounted out-doors under an awning) had disconnected spade connectors inside. I fixed these and now they work just fine … I just haven’t found the other end of those cables yet.

I expect that I’m going to find speakers in parallel as well as in series. I’ll probably also find cables that have been gnawed by critters.

By the way, the test tool cost be about $10 and the most expensive part of the tool was the pair of project boxes that I bought from Jay Car.

If you run cables through the wall, please label them so that, later when you sell your house, the new occupants don’t curse your name.

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