Reprinted from the Jan/Feb 2009 issue of Church Production Magazine
Your Wireless Mics after the Post-DTV-transition
How wireless microphones and IEM systems can successfully survive in the post-DTV-transition world
By now, just about every church that presents contemporary music—and many that don’t—have gone through a period of uncertainty regarding the future of their wireless microphone and in-ear monitoring (IEM) systems. The good news is, with the recent FCC ruling on White Spaces, the fate of those systems is now fairly clear, and the prospect of new purchases is not nearly as daunting. The bad news is, the future holds increased competition for open frequencies.
The biggest wireless problem in contemporary worship has been that the number of systems in use has outgrown in-house expertise. As the number of systems increases, the likelihood of everything working without incident, week in and week out, decreases.
While this may sound daunting, the fact is that a few key bits of knowledge and some common sense will go a long way. “It’s not voodoo, and it’s not black magic,” states Karl Winkler, director of business development for Rio Rancho, N.M.-based Lectrosonics. “With proper antenna setup and frequency choice, wireless systems should work flawlessly, every time. But it’s important to know the basics. If you run into interference, you need to know how to change frequencies in a methodical way. Otherwise, you’re just stabbing in the dark.”
Some Basics
Wireless systems are low-power radio stations consisting of a transmitter and a receiver, with each transmitter requiring a separate channel. Each system interacts with the others according to the mathematical relationship of their frequencies, beating against each other in much the same way as musical notes, producing sum and difference products. This can produce intermodulation (“intermod”) that destroys the clean transmission of wireless signals. As more systems are added, avoiding intermod becomes more difficult.
The first step toward ensuring flawless operation is proper physical deployment. Maintaining line-of-sight antenna placement is a critical component in avoiding dropouts. Hiding antennas at floor level is a recipe for disaster, as all the bodies in the congregation effectively block the signal from the receiver. To avoid the visual distraction of having an “antenna farm,” consider investing in an antenna distribution system, allowing multiple systems to share remote antennae. It’s also important to maintain separation of wireless systems from other RF (radio frequency) sources, most notably digital electronics.
Most wireless manufacturers offer educational publications to help teach tech staff the basics of system setup. Niles, Ill.-based Shure’s technical and educational communications manager, Christopher Lyons, notes, “A little knowledge goes a long way. As the wireless environment changes, proper procedures are going to become required practices. Those who do things right, from system deployment through operation, are going to have a much better chance of operating without problems.”
Frequency Coordination
That brings us to frequency selection. Because churches operate in the same environment each Sunday, there is seldom a need to change frequencies. Unfortunately, this has allowed many sound engineers to get by without knowing how to react when things go wrong.
“[Many] people believe that as long as they put a lot of space between frequencies, they’re going to be fine,” say Rick Joyner, manager of Audio-Technica’s Audio Solutions Team in Stow, Ohio. “But no. You actually have to coordinate those frequencies to prevent intermodulation. This is especially true in today’s increasingly crowded wireless environment.”
Unlike cellular phones or Wi-Fi networks, wireless mic frequencies are not seamlessly selected by a network backbone. Instead, they must be assigned individually—and carefully. Each system must be assigned an open frequency, and those frequencies must be mutually compatible. Most systems are designed to make this process relatively painless, with frequencies pre-arranged in mutually compatible groups (also called banks or blocks). As long as the selected group has enough open channels for all the systems in use, there shouldn’t be a problem.
Avoiding TV Channels
The first and most basic rule of wireless usage is avoiding local TV stations, which hold primary licensee privileges. Under FCC rules, wireless microphones and IEM systems may operate within 470-698 MHz (UHF TV channels 14-51)—except for active TV channels. Each TV station uses 6 MHz of bandwidth (enough for several wireless mics), and their massive transmitters will typically overpower any wireless system. Learn which stations are active in your area. The FCC maintains a database of all active stations, and several wireless manufacturers offer online tools that show all stations near a given city.
A new problem area for wireless systems is 698-806 MHz, commonly called the 700 MHz band. The FCC has declared that wireless mics and IEMs must vacate this frequency range permanently, perhaps as soon as February 17, 2009. Because this area was previously safe for wireless mics, many churches have such systems in use. All such systems must be replaced.
Fortunately, most wireless manufacturers saw this coming and stopped selling 700 MHz systems a year or two ago. But some of these systems still exist on the secondary market, such as eBay. It’s important to avoid them.
Mapping Your Systems
Every house of worship should take the time to catalog all their wireless systems. Create a list or spreadsheet showing every system, including brand and model. List each system’s full range of available frequencies, plus the individual channel currently in use. This active channel is displayed directly from the front panel. The system’s full frequency range is typically found on the front or back panel of the rack-mount portion, or in the battery compartment of the bodypack or handheld.
This provides you with the information needed to react to any frequency problems and plan future additions. Make note of any systems operating in the 700 MHz range and earmark them for replacement. Contact the manufacturer to determine whether there is any program available to retune the frequency range or gain partial credit or a rebate on a replacement.
Selecting Frequencies
Today’s wireless systems are generally frequency-agile, with hundreds or even thousands of available frequencies. Even better, many have an onboard scanner that finds and recommends the channel group with the most open, mutually compatible frequencies. Some even offer automated software solutions and online tools to generate a list of suggested frequencies based on those already in use.
When tuning systems, use the group with the most open channels, setting up each system in succession. Leave the transmitters powered on as you follow this procedure. Any bad frequencies should become audibly apparent, making them easy to avoid. However, no system is perfect. Complications arise when different brands of wireless are used together. While there is no technical reason why this can’t work, each brand uses its own frequency scheme, making the outcome less predictable.
Here’s another tip: Keep in-ear and microphone systems in separate frequency ranges. Joe Ciaudelli, Old Lyme, Conn.-based Sennheiser’s team manager for pro products, recommends, “If you’re wearing an IEM receiver pack and using a wireless mic, you want to avoid a phenomenon known as blocking. This could occur when the microphone transmitter is placed or moved close to the IEM receiver. If the two systems are operating within the same TV channel, the mic transmitter can desensitize the IEM receiver, preventing it from distinguishing its own transmitter. This can be avoided by separating your IEM systems from your wireless mics by at least one, preferably more, TV channels. Also, wear the IEM receiver in such a way that physical distance from mic transmitters is maintained.”
Changes in a Wireless World
As of February 17, 2009, all TV broadcasting in the United States will be digital, which is why all local stations have moved to new channels in the UHF band. In addition to the closing of the 700 MHz range for wireless microphone use, the FCC also authorized a new class of unlicensed products, called White Space Devices (WSDs), to share the 470-698 MHz spectrum with wireless mics.
Basically, “white spaces” refers to any frequency that is not being used by licensed, authorized purposes. In this sense, wireless mics, which have shared the spectrum with broadcast TV for decades, are WSDs themselves. These new devices are expected to carry broadband wireless capability—often referred to as “Wi-Fi on steroids.”
Because these new devices aren’t on the market yet, no one can predict their effect on wireless systems with any certainty. However, the FCC order mandates that these devices be able to “detect and avoid” both TV stations and wireless mics, so it is reasonably safe to assume they do not represent a major threat.
So in general, the new rule of thumb is to embrace systems operating between 470-698 MHz, and to avoid the 700 MHz area. It should go without saying that all the wireless manufacturers are now adjusting their product offerings to reflect this new reality.
There’s an old saying in real estate, “Buy the most house you can afford,” and the same is true of wireless systems. Entry-level systems, while more affordable, will be the first to fail under adverse conditions. Shure’s Lyons suggests, “Whatever seems to be the right system to meet your current needs, you might want to take one step above that. It will give more flexibility in terms of tuning range and better selectivity. In the new world of wireless, those are going to be good capabilities to have in your pocket.”
Seeking Higher Ground
Of course, there are other options as well. Some manufacturers offer systems in the 900 MHz and 2.4 GHz (that’s “gigahertz”) ranges. These systems operate“above the fray” of the frequencies involved in the White Spaces debate, and can be viewed as a possible alternative. But it’s important to realize that these higher frequencies contain more than just wireless microphones.
For example, the 902-928 MHz band includes government, military, consumer, industrial, scientific and medical devices, including cordless phones; radar and telemetry systems; ham radio; and wireless Internet services. In the 2.4 GHz range, wireless mics compete with Bluetooth and Wi-Fi devices; cordless phones; microwaves; security and automation systems; and various scientific and medical devices.
Still, many churches have reported success in working with these high-band wireless systems. Put simply, any one device without dedicated spectrum will have to compete with some other wireless products; the only question is to what degree.
Overall, the recent FCC rulings have been good news for wireless microphone users. The government has recognized the rights of wireless microphone users to operate unimpeded in the UHF bands, so systems currently in use (other than 700 MHz products) can continue. Most importantly, churches that have been waiting for the “all clear” to sound before replacing or adding wireless systems can now safely do so.
As Sennheiser’s Ciaudelli puts it, “Wireless microphones will be around next year and for years after that. Will they become a little bit trickier to use? Yes, especially for large multichannel installations. With the advent of white space devices, best practices are going to take a larger role. Those who learn and adhere to them are going to have success.”
Jack Kontney heads Kontney Communications Inc., a marketing and content creation consultancy specializing in pro audio and electronics. He can be contacted at www.kontneycomm.com.