Please be gentle with me here lol...

I am wondering exactly when and how an impedance meter might be of benefit to me. Every 70V paging call I have ever been on has been solved with observation and logically breaking things down.

Admittedly, I work on smaller installations of no more than 30 to 40 speakers and I have the advantage of knowing where the legs are and how they are run by either having run them myself or having access to documentation showing how they were run.

So I found myself on a Saturday morning at a large retail store at 5AM to work on a recently installed PA where there was no audio on the sales floor. I know this was a fully working system a few days prior having observed that. The store broadcasts music over the PA so I had the advantage of a constantly playing source while troubleshooting. Having assisted with the installation, I knew how the legs and volume controls were installed.

When I arrived I tested the input to the VC with my test set and had great audio. The output was very faint. This told me there was a short in the cabling somewhere. I went to the point where all the legs on the sales floor were tied together and broke the legs open. Tested and faint audio so I knew the "first" leg had a problem. There were 7 speakers in the leg and spending a short amount of time going from speaker to speaker, I found that the cabling between 2 speakers somehow developed a short to the building up in the truss. I suspect the alarm technician who followed us may have pulled his cabling too vigorously and damaged the PA wiring. So when I can get a lift it is a simple fix. For the call, I just left the offending speaker out of the leg and everything came up perfectly as expected. It was only one speaker not working as it was the "last" speaker in the leg so we left it until a lift can be brought in.

I am always reading that an impedance meter is necessary to troubleshoot 70V but that has not been my experience. Am I lucky? Is it because I usually come into a known installation where I have most of the data needed? Would an impedance meter have sped this up any? Once I found the "offending" area between 2 speakers, a quick continuity test showed a short in the cable and it looks like someone disturbed the wiring in that area.

Here was the process -

Music was being broadcast clearly to the offices, warehouse and the input and output (after pulling the leg off) of the VC for the sales floor so I immediately know it is not the amp or any of the VCs. Not going to waste time on those. I know the taps of all the speakers are within range of the amp because I tapped them. I also know the short would not be between the speaker leads because I took the time to do them correctly. I hate troubleshooting speakers on a 70V and take the time to wire them properly and not expose the copper.

Because the volume was so low on the test set, I was pretty sure there was a short somewhere. This is based on past troubleshooting experience. It is a bit of a PITA to go speaker to speaker to break the leg out and test but it really wasn't that bad.

Where would an impedance meter help me?

Thank you in advance for the explanation.

Last edited by Meyery2k; 03/19/18 01:17 AM.
Michael Meyer