Interference from LED screens. Dirty fuel filters in generators. Tim Kridel explores these and other factors that can wreak havoc with rental and staging AV systems.
With freedom comes responsibility—and often a lot of headaches. Just ask anyone who uses wireless AV systems for events on a daily basis. Cutting the cord provides flexibility, but it also adds reliability challenges.
One challenge is that arenas, exhibition halls and other venues are packed with myriad sources of interference.
“Some of the largest events can easily use in excess of 100 channels of wireless microphones and in-ear monitors,” says Tuomo George-Tolonen, manager of Shure’s pro audio group. “When it comes to potential sources of interference, we most often think of other wireless microphones including your own system. [But] interference can also be caused by other sources such as LED displays. I would argue that understanding what the RF noise floor is like is the most critical aspect of successfully deploying a large wireless system.”
“Design is the key word; great audio does not happen by accident.”
Aesthetics add to the challenge because designers don’t want their sets bristling with antenna farms to maximise coverage and signal strength. Metallica has been wrestling with those challenges on its WorldWired tour, whose stage is about 57 metres wide. Creating an antenna zone for each player wasn’t an option because they roam from one end to the other.
The solution was to tuck the RF Venue CP Beam antennas into a small area upstage of the wing vocal positions. All three guitar rigs share those antennas.
“We had contemplated flying the pair of CP Beams from the upper video or lighting truss, but we didn’t want to add another 100 feet of RF cable or rely on someone else to position the antennas daily,” says Chad Zaemisch, James Hetfield’s guitar tech. “The placement of our antennas had to be negotiated even with the designer as it was an extremely clean looking stage.
“It was unfortunate that we had to place the CP Beams so close to the LED screens. When performing an RF scan, we could clearly see the noise floor increase 10 to 20 dB. With the proliferation of large video screens on nearly every tour these days, it would be nice if someone thought about shielding or somehow controlling the noise emitted by the 60-foot-tall ‘RF absorbers,’ as I called them.”
Metallica’s experience isn’t unusual, which means it’s something to prepare for regardless of whether an event is a concert, convention keynote or playoff game.
“A large LED display can easily increase the noise floor by 20 dBm, and having the antennas too close to the display will unnecessarily increase the noise floor as seen by the wireless receivers,” George-Tolonen says. “The system might work fine most of the time, but something as simple as the speaker cupping the antenna of the handheld microphone is enough to drop the signal below the high noise floor.”
Game plan
The bigger the event, the more media there are to cover it. That spotlight increases not only the pressure to ensure a reliable, high-quality AV experience; it also increases the challenges to doing so.
“For large events, frequency coordination is imperative between not only AV vendors but also the press,” says Michael Wohlitz, Freeman senior vice president for event services.
That’s why the National Football League (NFL) developed Event Frequency Coordination (EFC), a cloud-based platform.
“This system allows broadcasters and event production groups to make self-service requests for the wireless devices they would like to use at the event,” says Michelle McKenna, NFL CIO and senior vice president of IT. “The NFL frequency coordination team then uses the system to assign available bandwidth to these devices and informs the users of the approved frequencies.
“A sports venue, with a high ambient such as crowd cheering; you want the peak to be above that.”
“To prevent unauthorised use of frequencies, we have a device check-in process at the media entrance gates, as well as signage that instructs users of RF devices to register with our frequency coordinators. Throughout our events, our frequency coordinators actively monitor all of the RF usage with spectrum analysers and scanners.”
Frequency coordination can be more challenging for events that travel to multiple countries that have different spectrum allocations and power levels. In those situation, local expertise helps.
“When playing games outside of the US, we rely on the local authority to coordinate and approve the use of all frequencies,” McKenna says. “Ofcom and IFT coordinate all of our frequency usage in the UK and Mexico, respectively. That actually makes things easier for our frequency coordinators for those games.”
Wild cards abound
A spectrum analyser is a valuable tool, whether it’s in the form of a standalone device or a capability built into AV gear such as mic systems.
“Wireless microphone systems such as Digital 6000 come with software that gives you a full overview of what is happening around you spectrum-wise and make suggestions where to best place the frequencies for your wireless mics,” says Tom Vollmers, Sennheiser product manager.
Spectrum analysers also are useful even when there’s frequency coordination because there’s no guarantee that everyone will abide.
“If your event attracts media attention, you can almost be certain that reporters will turn up with wireless equipment which has not been registered with you in advance,” Vollmers says. “So it’s a good idea to continuously scan the spectrum during the event—and catch disturbers early. You will want to keep a spare mic at hand for main speakers at an event to be on the safe side.”
The venue itself also is a factor.
“If the roof or the audience stands are made of metal, the wireless signal can reach the receiver directly or in a delayed manner via reflections,” Vollmers says. “Careful antenna placement helps, as will the receiver software in high-end wireless systems, which is able to differentiate between the direct signal and a reflected signal.”
“I would argue that understanding what the RF noise floor is like is the most critical aspect of successfully deploying a large wireless system.”
If the event is outdoors, weather protection also can affect RF signal paths and reflections, as Metallica found.
“There was a tall metal structure that would be put over the drum riser in the event of rain,” Zaemisch says. “This further degraded reception as it was in the path of both antennas.”
Power up
Wired systems have their share of challenges, too. One example is electricity.
“Power is always a challenge,” Zaemisch says. “Over the years we’ve had to explain to local production that they need to ground the stage or that they need to re-run all of the feeder cable under the stage that is making the guitars hum.”
Those challenges are why big events such as WorldWired sometimes bring power with them.
“This cuts down on the number of ‘construction’ generators that like to bog down due to clogged fuel filters, etc.” Zaemisch says. “We’ve even run into smart generators that just couldn’t handle the sudden power surges caused by the PA amplifiers and the problems this creates with current draw.
“We now use mostly digital gear, which is a blessing these days because of the 100-240VAC input range they tolerate. We often use a Furman power conditioner to level out the fluctuating voltage. I wouldn’t dream of running our racks these days without our uninterruptible power supplies. I rarely worry about the actual voltage these days but rather the fluctuation or sag when the show is up and running full tilt.”
Some of that power is going to devices that create noise, such as fans cooling AV systems. The bigger the production, the more that noise adds up, to the point that it can create problems. The type of event also affects the noise floor and it turn the audio system’s dynamic range requirements.
“Ambient noise floor is one thing that sometimes gets overlooked,” says John Monitto, Meyer Sound director of technical solutions. “A sports venue, with a high ambient such as crowd cheering; you want the peak to be above that.”
Meyer Sound is working with AVIXA on a standard for dynamic range.
“We want to pay more attention to the dynamics of a system and make sure the system can do that with low distortion at an SPL level that will accommodate the ambient [level] of a venue,” Monitto says.
A model system
Modelling software is increasingly common in rental and staging.
“Design is the key word; great audio does not happen by accident,” Wohlitz says. “We spend time modelling the acoustic properties of the room and then use computer modelling to predict the behaviour of audio response in the environment. This allows us to design a sound reinforcement system that maximizes the sound quality and minimises the acoustical deficiencies of a space.
“At Freeman, we have an incredible database of venues around the world, yet each event has its sensibilities and demands. As such, our best practice is to always have a site visit with the client to ensure we are maximizing our event design for their chosen venue.”
A venue’s bottom line suffers if it has a reputation among events and attendees for providing subpar experiences, such as muddy sound. That’s why some now provide models to rental and staging companies.
“Staples Center commissioned an EASE model for the facility, and they require anybody who uses the venue to use that model in order to design their system,” says Bruce Olson, AFMG Services North America managing director. “That’s a very complex space. To build a model would take quite a bit of time. Once you have the model, it doesn’t take that long to deploy loudspeaker systems in there appropriately.”
Using the venue-provided model helps identify and avoid problems that would go unnoticed until a system is already deployed—and possibly too late to change. For example, Staples Center has suites facing the end of the arena where the stage typically goes.
“If you just dead hung arrays in there and aim them like you normally would, you get a 140 ms delayed signal that was 6 dB louder than what they set up,” Olson says. “That’s because the left and right arrays would combine and hit that curved wall [of suites] and come back 140 ms later louder than they went out.”
If an event had been using other types of venues up to that point, it might have used drapes to minimise those kinds of reflection problems. But that isn’t always a viable solution, and the model can provide better alternatives.
“You see [drapes] done a lot in exhibition halls, but you’re not going to do that for three stories of suites—not when those people are coming in to use those for events,” Olson says.
Virtual audiences
Events increasingly are webcast, often to encourage people to attend the next one in person. In some cases, the remote audience is much larger. That trend means rental and staging companies now have to ensure that the streaming audience has a good experience, too.
“The approach is very similar to producing a television event,” Wohlitz says. “Attention and focus certainly considers the experience for the audience in the theatre, but as much, if not more, attention is also focused on delivering a premiere experience for the viewing audience elsewhere.”
If the presenters and the venue audience will interact with one another, then the system needs to be designed so streaming attendees can hear both sides.
“You probably should have a separate broadcast console doing that,” Olson says. “It’s not something you can typically do on an aux. You need to create your own mix, and you need to do that mix from some place other than in the venue so you can hear the relative balances between all of the mics. It’s a lot more complex than people think.”
You can also read full Q&As with Chad Zaemisch, Metallica backline tech and James Hetfield’s guitar tech, and Michael Wohlitz, senior vice president, event services, at global events specialist Freeman.