A while back, I surveyed some of my colleagues in the pro audio industry – those with experience with wireless microphone, in-ear monitor (IEM), and intercom systems – for their take on the most common problems they find in our line of work. The lists that came back were remarkably similar and became the basis of an online training class, along with a panel discussion I’ve hosted at the Audio Engineering Society (AES) convention a couple of times.
You may not have encountered (or caused) any of these problems, but rest assured: if you’re involved with using wireless systems at your church, or are helping a worship facility with theirs, then you, too, are likely to come across these issues.
1. Lack Of Frequency Band Planning. These days, most live events involve multiple different types of wireless communication devices, all in one place at one time. Ideally, these would all be in different parts of the radio frequency (RF) spectrum. If not, these devices can interfere with each other even when they may not be on the exact same frequency.
Every receiver has a filter bandwidth, usually ranging from a few hundred kHz up to 20 MHz wide or more. The better systems have narrower, stronger filters thus allowing more channels to be used closer together in one place at one time. In fact, if you’ve ever wondered – “what makes the more expensive wireless systems better?” – this is one answer.
A good general rule of thumb to keep things organized is to operate wireless mic, IEM, and intercom systems in separate frequency bands. A secondary rule is that the “money channels” (think pastor mic, worship leader mic, etc.) should be in the cleanest part of the ultra-high frequency (UHF) spectrum, while intercoms and other less-critical systems can operate in the very high frequency (VHF) band between 174 to 216 MHz, the 1.9 GHz band, etc.
Many people ask about systems in the 2.4 GHz band because it’s a worldwide available, unlicensed band. But therein lies the problem – WiFi routers and a multitude of consumer digital communications devices also operate in this band and may cause unpredictable interference. At the very least, the 2.4 GHz band is generally reliable for a small number of channels.
2. Poor Receiver Antenna Placement. It may seem obvious to avoid enclosing receiver antennas inside a metal rack cabinet, but you’d be surprised how often this is discovered when there are reports of “terrible range and tons of dropouts.”
Even though we can’t see RF energy, we should think of it in similar terms to the way light behaves. A flashlight inside an enclosed cabinet doesn’t provide much light. And, just like light, RF can be blocked by certain materials, namely metal, concrete, stone, wood – and people! As a result and if at all possible, it’s best to mount receiver antennas above head height, usually at about 10 feet above the stage or dais, to avoid objects that can (and usually will) block transmissions from the stage.
3. Improper Transmitter Or IEM Pack Placement (Or Both). Placing bodypack mic transmitters physically close to (and close in frequency, too) bodypack IEM receivers can reduce the range of IEM systems. Because some of these things can’t be helped (physical proximity, in certain cases) it’s wise to separate frequencies by as much as possible. The same goes for IEM transmitter antennas and mic receiver antennas.
Bodypack transmitters are a special case because they’re placed on something (bodies) that tends to absorb RF. The smaller the transmitter, the more “buried” it will tend to be. If at all possible, don’t put transmitters at places where they’ll be covered by body parts or metallic materials, including some costume fabrics.
One trick for improving bodypack performance is to insulate the antenna with plastic tubing material (or anything transparent to RF) that will keep it away from any skin. Damp undergarments are a concern, too. Another way around the problem for some applications of external antennas such as coax dipole designs. Some manufacturers offer these, or you can make your own fairly easily – there’s even a YouTube video showing how to do it!