They’ve happened to the best of us. After paging through stacks of manuals, phoning and perhaps yelling at manufacturer technical support lines, and checking and re-checking dozens of options on menu screens, we discover the cause of our wireless microphone malfunction is something so breathtaking simply, so glaringly obvious, that we can’t believe we didn’t think of it in the first place.
The following five mistakes are blunders shared by inexperienced and experienced audio pros alike. Do not be ashamed.
1. Dead Battery
The lifeblood of the wireless microphone transmitter, the battery, is a fickle creature.
The useable life of a battery is influenced by a number of factors, which makes it hard to pin down just how many hours you’ll get out of a microphone. The type of battery in use, the brand, the temperature, and - the oft-ignored curveball - the transmitter power (20 mW vs 50 mW, etc), can all dramatically change how long your handheld perseveres.
Some people play the russian roulette game of guessing how much juice they’ve got left on a case by case basis. Others invest in a battery tester or multimeter. The most paranoid users (and the wisest) don’t let a mic go up on stage without fresh batteries. This results in a lot of half-used batteries that go in the battery recycling bin, but it is a heck of a lot better than a mic going dead. You can purchase batteries by the case from your favorite audiovisual retailer. If you do any kind of mission critical work, we encourage you to do the same.
2. Wrong Frequency
Always make sure your receiver is set to the same frequency as your transmitter. Some microphone systems will sync automatically. Others need just the touch of a “sync” button somewhere on the handheld or receiver. Older and less expensive models, though, will sometimes need to be manually programmed to the exact same channel.
3. No Line of Sight
Always make sure there is a clear, unobstructed path from the receiver antenna to the handheld transmitter. That means no walls, cables, rack cases, or burning wreckage in between the two antennas. Sure, you can get a clean signal without line of sight. But for a variety of reasons, wireless audio radios work best when they are picking up a direct signal with line-of-sight, not a reflected one. Without line of sight, you raise the probability of dropouts significantly.
Can’t move your receiver because it’s in a rack or FOH booth that obstructs the signal path? Invest in a few feet of RG8X, a remote antenna, and a distributor to move the antenna out from behind the rack or closet and into a location where it can pick up direct signals arriving from the stage or performance area.
4. Damaged Coax
Coaxial cable is fragile. Small kinks, bends, dents, holes, and water damage can severely undermine the ability of the cable to reliably carry a signal, even if there is no obvious damage revealed by a visual inspection. We discuss cable damage in greater detail here, and here.
Wrapping cable properly, checking it with an ohmmeter before each performance, and routinely “retiring” cable older than a certain age are all great ways of eliminating cable as a source of problems. We have also seen many engineers switch from unpredictable coaxial cable to fiber optic technology for runs over 100 feet.
5. Wrong Coax
This one actually isn’t so obvious, but it is easy to make. Wireless audio systems are standarized around 50 ohms of impedance. You want any device or cable you hook up to any component in that system to be 50 ohms, too, in order to be impedence matched.
Many pros know they need coaxial cable to connect radio equipment and antennas to their receivers and distributors, but don’t know what specific kind of coaxial to get. They will go to their local RadioShack or Best Buy and ask “for some coaxial cable.” Consumer coaxial cable for television devices is not the correct type for wireless audio, even though it has the same connector. The cable you find at Best Buy is 75 ohm, “RG-59” type. Wireless audio users should only purchase low loss, 50 ohm, RG-8X. There are other types of 50 ohm cable, too, but types that are less expensive than RG8-X will cause excessive signal loss, and types more expensive than RG8-X (like LMR-400), while occasionally useful, are often bulky and devastatingly expensive.