The Case of the Sunday Morning Squawking

A church located in a residential area of a large city installed a new audio system to project the pastor's voice on Sunday morning. The system has a short-range radio frequency connection between the pulpit microphone and the amplifiers. The sound company installed new speakers and wiring, and the system worked perfectly when tested. But on the first Sunday, the sound system started to squeal, squawk, crackle, and make other untoward noises at random.

Church officials called the sound company, their engineers, the manufacturers -- the whole nine yards. They tested and tested, and the equipment worked fine, except on Sunday mornings.

The church called an independent engineer. He trusted the tests on the system. He figured the source of the noise was external to the sound system.

The system was used primarily on Sunday mornings. Whatever the external source of the interference, it was powerful enough to generate some potent radio frequency disturbance. That eliminated the residential buildings near the church. There was a three-story factory about a block away, but that couldn't be the source of the interference. The factory wasn't open on Sunday mornings.

The next Sunday, the engineer visited the factory, just in case it might be the source of the problem. As expected, it was closed, except for a security guard. "Not us," the security guard told the engineer, so the engineer left. The guard got into the factory's elevator and returned to the third floor to continue his rounds. The engineer went back to the church, and there it was -- the same crackling and squawking.

The engineer started to seek solutions. One possibility was encasing the entire audio system in metal -- building a huge Faraday cage around the pulpit. That certainly wasn't an ideal solution, and the thought of the factory still nagged at the engineer.

Later that Sunday, the engineer and the pastor paid another visit to the factory. They asked the security people if they could avoid using the elevator on a Sunday morning, just as a test. Bingo -- no squawking. As it turned out, whenever the guard took the elevator, the electrical motor sparked at startup.

Since the church didn't often use the audio system at other times, it was a fine fix. Eventually, the factory insulated the elevator motor and ended the problem.

This entry was submitted by Tim Perper and edited by Rob Spiegel.

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