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 by John Carlson, Systems Engineer, Sound Vision, Inc.

Have you ever wondered why you can't use your cell phone on an airplane or in the hospital?

Interference is a real problem for many electronic systems, and the RF output from cell phones, wireless networks and Blackberry devices all have the potential to cause problems with delicate instruments.

The same is true for AV systems. Over the last few years, we have heard more and more complaints that these devices are causing a "motor boating" noise in many sound systems. It's a kind of low-toned, vibrating noise that can be very distracting in the middle of a meeting. The problem is that most wired microphones were never designed to handle the type of RF interference generated by these devices. Large-scale use of these frequencies, particularly for silent email and Internet access, caught the manufacturers off guard.

What to do?

There are two or three workable strategies to deal with the issue.

The most obvious and least expensive solution to this kind of microphone interference is simply to ask managers and staff to refrain from checking email or surfing the net during meetings. Since most of the interference comes from transmission, rather than reception of these signals, the problem is not that you have a wireless network installed on your premises, but that people are using it when they're supposed to be paying attention to a presenter. The same is true of staff checking email from a cellular network. It's the transmissions from the phone or PDA that's causing the problem, not the signals from the tower.

If you can't stop employees from accessing the net, or if they have legitimate reasons to be doing so during a meeting, you have two more choices.

First, it may be possible to switch to wireless mics that you already have on your premises. Curiously enough, these kinds of systems are not susceptible to this type of radio interference, since they operate at completely different frequencies.

For most, however, the solution lies in replacing older wired mics with newer versions that have newly designed shielding. It can be an expensive solution, but it's the only way to eliminate the problem.

Phasing out the problem

Cell phone and WiFi interference is no longer an issue for most professional microphones manufactured since 2006. Shure and Audio Technica, for example, both report that they have completely eliminated this kind of mic interference.

You may still run into an issue, however, with lower-cost mics or microphones that have been sitting in a dealerís warehouse. Shure, for one, has not changed any model numbers, but instead phased in the shielding as they sold out their inventories. Other manufacturers have dealt with the issue in different ways.

So if you're concerned about the problem and will be buying new microphones, be sure to ask us to confirm that the mics you buy are, in fact, updated.

After all, just as you don't want to shoot down the jetliner you're riding on, you don't want to shoot down your next training session with that handy Blackberry device.


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