RF Coordination: What You Need to Know
The following article is an excerpt from Shure Notes for Houses of Worship, Issue #47 (October 3, 2011).
There was a time when understanding pro audio and having a good pair of ears was enough to handle most church audio challenges. Then, wireless systems came into their own and changed the landscape. Touring acts may have the luxury of a dedicated RF coordinator, but few, if any, churches do. We asked Shure's Monitor Man Michael Johns for his advice on the essentials, and here's what he had to say.
Usually the person responsible for getting the microphones or the in-ear personal monitoring systems on air isn't an RF coordinator. Churches might have a monitor engineer, musical director, or technical director of some sort who is responsible for the audio, but that person might also be a video or lighting person who is responsible for the whole production. More often than not, he or she is a volunteer.
Understanding the basics of RF coordination is a really simple way to become much more comfortable as a user. If you know how the products operate and how they're supposed to work, then it's a lot easier to get them to work right. Teams know how to operate mixing boards, they know how to operate most of the audio equipment that they're using, but wireless systems can mystify even the most experienced audio engineers. They understand the audio side of it, but don't always know a lot about radio frequencies (RF).
Here are four steps that will help most church audio techs get the most from their wireless mic and personal monitor systems:
1) Understand the Basics
Make sure that you learn how wireless systems work.
First of all, the components:
Earphones – compact, high-fidelity sound-isolating stereo in-ear monitors
Bodypack Receivers – sleek, wearable units that receive sound and give you the ability to adjust your volume and move freely on the stage
Transmitters – usually (but not always) a rack-mounted device which sends audio wirelessly to the receiver
Then, the nature of radio waves:
- Most wireless audio equipment accomplishes its task by converting the audio signal into a radio wave, then back to an audio signal.
- Radio waves travel at the speed of light and are able to travel a significant distance from the source. These characteristics make radio the ideal form of transmission for audio applications, from broadcast radio and television to cordless phones.
- Like sound, a radio wave can be described by its frequency and its amplitude. Frequency is measured in hertz (cycles per second). Frequencies in the radio spectrum range from a few hertz to beyond the gigahertz (GHz) range.
- Most professional wireless audio systems operate in the megahertz (MHz) range.
- Since June 2010, the FCC has ruled that only the 470 MHz to 698 MHz spectrum, shared with television broadcast stations, is available for wireless audio users in the U.S.
2) Select the Right Wireless Products and Accessories
Determine your system needs based on your unique situation. It will inform your purchasing decisions.
- Are your performers stationary or mobile? (Do you need a wired or wireless system?)
- Can monitor mixes be shared? (Will you need a personal mixer, and does your system offer multi-channel capabilities?)
- Do you require a stereo mix, or is mono acceptable? (Mono-only systems are less expensive.)
- What's your budget? (The less you require, the less you'll pay.)
More advanced wireless personal monitoring systems offer the ability to combine multiple transmitter antennas (for example, connecting up to four wireless transmitters to one antenna). In these systems, reducing the number of transmitter antennas in close proximity reduces the chance of sound dropouts and is crucial to obtaining the best possible performance. A variety of accessories are available, including different antennas and combiners. Directional antennas can also be used to increase range and reduce the chances of dropouts due to multi-path interference.
3) Properly Select and Coordinate Frequencies
When using Shure PSM® systems, there are three methods for choosing and coordinating frequencies. Which method is best for you will depend on the system features, the number of wireless systems in use, and your access to a computer. No method is foolproof.
Method 1: Use the Frequency Finder on shure.com
If you have internet access, go to the Frequency Finder on the Support page of the Shure website. Enter your city or ZIP code, select the PSM system you are using, and the finder will give you the best options for frequency selection. This is useful if you are using only one wireless model in one frequency band. It cannot accommodate for other wireless microphone or guitar systems in use.
Method 2: Use the Scan function of the PSM receiver (PSM®900 and PSM®1000)
Utilize the scan functions of the receiver to scan for an available frequency or group of frequencies. This gives you a real-time analysis of your operating environment. This method cannot account for all of the potential interactions between your wireless monitor systems in different frequency bands and your wireless microphone or guitar systems.
Method 3: Use a frequency coordination program such as Shure's Wireless Workbench® Software
This is by far the best method, especially when using multiple wireless systems. Software such as Wireless Workbench will give you the most reliable frequency coordination when using multiple wireless systems regardless of the model, frequency range, or even manufacturer. Wireless Workbench is a free download from shure.com.
Advanced: Use software such as Shure's recently updated Wireless Workbench 5.0, which you can download for free. This is recommended when a user has a number of wireless systems to get on air, has the means to scan for RF either as a product feature (for example, PSM 1000 or UHF-R®) or through an RF scanner, and needs to coordinate multiple systems.
4) Lastly, There's No Such Thing As "Set and Forget"
Remember, even if your audio system doesn't move from place to place, the environment changes constantly. It's largely true that television stations remain constant, but if there are other wireless systems in the frequency band — whether it's multiple systems in your own location or interference from the coffeehouse down the street — your wireless frequencies may need to be adjusted. What worked last Sunday (or even last night) may not be failsafe when the service begins. And that's why frequency coordination is so important.
MICHAEL JOHNS is an associate product manager working in the monitoring category in the Shure Global Marketing and Sales (GMS) Division. Michael worked as the main marketing representative on the development team for PSM 900 and PSM 1000 in-ear monitor systems. His duties also include working on and managing the development of Shure's pro headphone line. Michael holds a BA in Sound Engineering from Columbia College Chicago and is also a sound engineer and DJ.
Here are two downloadable publications with more comprehensive information on personal monitor systems. Both are FREE.
A Quick Guide to Personal Monitor Systems (PDF)
Selection and Operation Personal Monitor Systems, Third Edition (PDF)
Also, make sure to check the FAQ section on the Shure site, where you can find questions and answers on the subject just by searching "Personal Monitors."