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For Remote Trucks, It’s About Noise Control

LOS ANGELES, CA—Designing an audio control room for a remote broadcast production vehicle is a very different proposition from constructing a studio within a building.

LOS ANGELES, CA—Designing an audio control room for a remote broadcast production vehicle is a very different proposition from constructing a studio within a building. The same general criteria need to be considered, including noise control, acoustics, space and equipment location, but the limitations presented by a mobile unit pose unique challenges.

In truck audio control rooms, size really does matter. “There’s only so much space,” observes George Hoover, CTO, NEP Broadcasting, a major teleproduction services provider. “You’re competing not only for the video portion of the technology but then all of the production people that physically need to get into this mobile unit.”

One of the factors affecting acoustics— in any room—is volume, notes Russ Berger, president of the Russ Berger Design Group (RBDG). In a remote vehicle, he says, “Unfortunately, the volume is already dictated; you’re relegated to whatever is left in the back of the truck.”

He continues, “The primary factors that limit audio performance in production trucks, or just about any room, are inadequate volume and noise. You can’t reference if you don’t have a decent background noise floor to work with. It affects your imaging; you can’t hear back into a mix; you can’t tell if you have issues with noise on individual mic or channels.”

Some of that noise can come from the air conditioning. There are methods to significantly reduce that noise, including positioning the AC unit as far away as possible and isolating the compressors and air handlers.

NEP’s Denali Summit is designed for entertainment events, such as the 2011 Grammy Awards telecast, for which Tom Holmes was once again the production mixer.But there is an even bigger potential source of noise. On his wish list of considerations for the ideal room design, says Kevin Cleary, senior technical audio producer for ESPN, “Number one is getting all of the large, fanned, noisemaking, core-type devices— whether they be router cores or ADAM frames—and moving them into a machine room, or into someplace else where listening is not as critical. You wouldn’t put a skylight in the video control room, so why would you put a large, noisy thing in the audio control room?”

Of course, the problem may be linked to space issues. In a sports truck, where the mixer is typically working alone in his room, Hoover points out, “He needs patching, distribution, processing and the console, and oftentimes there’s no room to keep all those noisy things out of the way.”

NEP, which supplies trucks built for sports and for entertainment events, has been toying with a design for its next-gen twin (A and B unit) vehicles that would house just the console in the control room with the noisy gear located in an adjacent machine room, reveals Hoover. “Because what we’re seeing on most of these really big shows is that the mixer is not patching, and he’s not doing transmission; there’s an audio assist handling that.”

But, cautions Cleary, “The intercommunication between the mixer and that person at the backbench is key, so we’d have to take that into account. Those two individuals communicate quite a lot during the course of an event. But the less ambient noise that we can have in the room to start with, the better off we are.”

External noise, too, is a challenge. Even with an optimally treated vehicle, notes Cleary, there are always those events where “they manage to park a very large generator next to it or the marching band is warming up outside.”

Unfortunately, soundproofing materials add to the weight of the vehicle, which is governed by Federal regulations. “When you talk about sound isolation, you’re talking about mass,” Berger explains. “As good as the exotic materials are for noise control, they will only do so much. The goal is to get even, broadband noise control. So we go as far as we can based on the weight limits.”

“TV trucks are not ideal in terms of air conditioning and the amount of weight you can put in there for acoustical treatment,” acknowledges Hoover. “We typically use heavy, lead-backed lining in the audio rooms on all the walls. But you can’t put an acoustical door in; you can’t sustain the weight and dimensionality. In some areas, you just have to grin and bear it.”

A further challenge to good acoustics is posed by the need to focus on the video image, and also to have essential gear within easy reach. “Large monitors truly change the acoustics in the room. Positioning them where they’re out of the way and minimizing the impact on the quality of the monitoring is a real sonic challenge,” says Berger, who also notes the detrimental impact on good quality acoustics created by the typical equipment over-bridge found in trucks. Lately, he has observed truck builders installing consoles with built-in processing or control of outboard devices, obviating the need for an over-bridge within arm’s reach.

In a new truck RBDG is designing for MTV in Nashville, Berger continues, “We made the requirement that the monitor bridge be accommodated in another place. We’ve got to keep all the equipment below the median line, below the ears.”

Speaker placement is critical, agrees Hoover. “The challenge is that the engineer needs video monitors. With all due respect to mixers, it’s amazing how many don’t understand some basic paradigms. The monitor speakers need to be in the same horizontal and vertical planes. You can’t take the center speaker and raise it six inches above your head and move it a foot and a half forward, so you can put the program monitor down low, then expect to have a mix that accurately reflects anything that’s going on in the world.”

Ultimately, notes Berger, “It comes down to the constraints of what it takes to deliver audio to a human being. They have two ears, and they want to be sitting symmetrically on the central axis of a room. They want to be at least 10 feet away from the back wall, which you can’t achieve, so you have to find a way to make the back wall disappear acoustically, so it has minimal impact on the mix. In a room this size, the locally reacting surfaces control what’s heard at the mix position.”

Normally, designers have some variables to work with, namely the volume of the space and the ratios of height, length and width; the shape of the space; and finishes, he enumerates. But in a truck with volume and shape dictated by available space, Berger continues, “You have to rely on other methods to deal with what normally you would handle through room shape and size. That’s typically how you control flutter echoes and redirect energy into treatments at other places in the room. So finishes are all we are left with to control such issues.”

That said, even in a less than perfect acoustic environment, comments Cleary, it is sometimes possible to make ad hoc modifications: “Room acoustics can be adjusted; we’ve even done that on trucks that were already built.” For example, he shares, “We’ve put in different treatments to make the room sound better, whether it be curtains or flat panels.”

Berger came up with an innovative solution on the new MTV truck, adapting RBDG’s “leaky wall” technology, developed over many years, to increase the air volume beyond the walls of the audio room. “We’re venting low-frequency energy into adjacent spaces, acoustically crossing over in the range that we want,” he explains.

A storage bay for stands, cases and other gear located beneath the audio room was ideally placed to provide lowend extension, Berger continues. “Once the truck is in place and all the equipment is deployed, that belly pan is empty. We ensured that the belly pan was sealed and could become a part of the volume of the space above. Having that extra volume is a benefit, and allows for low-end relief in there. We’re making improvements at frequencies below the lower range of the male voice.”

Overall, providing suitable acoustics in a truck audio room is a difficult challenge and must ultimately involve compromises, observes Hoover. “As a person who started his career audio mixing in really nice acoustical spaces, I cringe at what we have to do. It’s not fair, and I marvel at how good things sound, all factors considered.”

Yet the mixers are able to adapt to any circumstances, he comments. “Truck mixers have a tendency over time to tune their ears to what it sounds like in a truck versus what it sounds like at home, and know how to compensate. You listen to an Ed Greene mix, and he’s doing things in the truck that might seem really weird, but ultimately it’s what’s being delivered at home that matters. That just comes with experience.”

Berger concurs: “A good engineer can get accustomed to almost any room and coax a mix out of it. But it’s no substitute for providing them with a reference where they can actually hear what they’re doing, instead of constantly having to guess.”

NEP Broadcasting

Russ Berger Design Group