AV Police Squad

Never Assume Anything

In addition to Third Party Commissioning services, we also provide Third Party Field Engineering services. While commissioning, we measure and document issues with the systems. While field engineering, we actually have to fix them. They are complementary services and help keep our fingers “dirty.” (If you have a testing-only (“after the fact”) team, and an engineering-only (“before the fact”) team, I highly recommend switching them up a bit to round out both sides. The engineers will benefit from seeing their designs IRL, and the testing folks will benefit from having to create something virtually, hopefully beginning with their commissioning process in mind…but I digress.)

So, while out on a recent field engineering project, an important lesson that is sometimes forgotten was reinforced. That lesson is to never assume anything. ANYTHING!

It was the typical time that we, as AV service providers, uncover large problems: Friday, 6PM. There was no audio getting into the room. The control system appeared to be sending the appropriate commands. The mixer looked good from the GUI, and we heard audio coming out of it with a portable audio tester. The amplifier worked when we replaced the mixer feed with a generator source. Clearly the issue was with the cabling between the mixer and amplifier. It took about an hour of troubleshooting to get to this diagnosis.

Troubleshooting the cable is where things took an interesting turn. The first thing we thought of was to simply replace the cable, but it was roughly a 30′ run and neatly dressed in the rack. We had some small hunks of cable, but nothing long enough to really do it right. Also, since it was installed by someone else, we didn’t have the same strain relief and cable labels they used, so it would have looked funny. So, we decided to take a closer look at the offending cable. We couldn’t believe what we found.

The installer never stripped the conductors on the audio cables. The outer jacket was trimmed. The strain relief and cable insulation (“spaghetti”) looked great. The cable labels were readable and the rack dressing was neat and serviceable. But, none of the conductors were stripped at the phoenix connectors to make a good electrical connection.


I consider myself a reasonable man. Maybe they assumed that the phoenix connectors were of the insulation displacement variety. Maybe some efficiency guru decided that the seconds saved by not stripping conductors at phoenix connectors would be the key to record profits. And, if I’m being honest, most of the terminations passed audio, so it sort of worked. But that doesn’t make it right.

Phoenix connectors are not meant to be tightened down so hard that they cut through the insulation and make an electrical connection. Further, they typically loosen slightly with time…and then what happens? All your audio connections mysteriously stop working in random intervals. Any potential time savings is nowhere near the risks.

Even though it was a good looking rack, the cable dress was acceptable and the labels were great, the most important aspect of the audio system (the electrical connections) was completely flawed. For the sake of the client, they all had to be re-done. Also, just because a rack looks good doesn’t mean you can ease up on your inspection of it. This reminded me of my mother’s experience teaching math at a predominantly liberal arts college. She was teaching a class literally called Math for Artists, and her description of her students was, “Their problem sets were beautiful works of art with impeccable handwriting, some even bordering on calligraphy…but they were all wrong.”

Never. Assume. Anything.

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