Disclaimer: MusicTech was invited as a guest to Düsseldorf’s Merkur Spiel-Arena by L-Acoustics.

The Backstreet Boys have me surrounded. No matter which way I turn, an expanse of white singlets, pants, and jackets spread out like some Arctic tundra. “I want it that way…” echoes across the cavernous space.

No, this isn’t an anxiety dream; it’s night six of the Backstreet Boys’ sold-out ten-date residency, Into The Millennium – Homecoming.

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As a human being who was alive during the 90s and early 00s, I have, of course, heard my fair share of the iconic boy band’s numerous hit singles. But unlike the 45,000 uber-fans packing Düsseldorf’s Merkur Spiel-Arena, I didn’t come for the nostalgia — I’m in Germany to hear the future of live sound.

You see, this isn’t just any concert: it’s an immersive audio spectacle on a scale I wouldn’t have previously thought possible. Working with L-Acoustics’ L-ISA—a spatial sound system complemented by a comprehensive software suite for object-based mixing—the stadium has been kitted out with 350 loudspeakers to provide a 360° sound field encompassing the entire space.

As a company, L-Acoustics’ hi-fi pedigree is hard to match: it invented the modern line-array system, helping to make it the industry standard for any large-scale concert; its SoundVision software fundamentally changed the way audio engineers design concert setups; over 50% of the world’s largest music festivals use its hardware; artists such as Adele, Lorde, and Bon Iver have used L-ISA to produce their immersive concert experiences; and L-Acoustics speakers power the new Apple Music Hall in London.

Yet, with all that experience, L-ISA has never been deployed in a venue this large before, and, with almost half a million eager fans attending over the course of the residency, it’s something of a gamble. “It’s the first time we’ve ever done this,” says audio engineer and immersive systems designer, Carlos Mosquera. “Because of the size of the venue, you get more challenges. So, I started with the basics to see if it would work or not.”

Mosquera previously worked at L-Acoustics and was part of the team that designed the software for the L-ISA system. A quick look around is enough to tell me that nothing about his setup for this concert is ‘basic’. There are six hanging line arrays covering the entire breadth of the stage, two more hangs at the rear corners of the stadium’s standing area, and 15 more dotted around the circumference of the venue to reinforce the sound for the higher seating tiers. It took eight months of planning to create the show I’m about to hear.

That time was needed not only to design a bespoke speaker configuration, but also to prepare the musical material. Veteran front-of-house engineer James McCullagh worked with the band and a musical director to recreate and, in some instances, re-record musical parts so that they could be effectively spatialised.

“We knew it could work in theory,” McCullagh tells me. “But we had to roll the dice on making it a reality.” Having toured with Journey, INXS, Katy Perry, and extensively with the Backstreet Boys, McCullagh knows exactly how to craft crowd-pleasing live sound. But moving his mix into 3D space presented a range of new opportunities and challenges.

“In a stereo system you’re using equalisation, compression, panning, and reverb to create separation, and panning, to create separation,” McCullagh explains. “But there’s a compromise because you’re taking a source and putting in compression or EQ to make it fit into a space with a large composition of frequencies. Whereas on this system, you don’t need to degrade or change the tone or sonic characteristic because the sound is being physically placed [in the sound-field].

“The flip side of that comes when you want something to gel and sound like a big ball,” McCullagh continues. “That’s 90s pop, right? It’s all squashed. And so it can be a struggle, because you’ve got inherent separation [between sources] and you’re trying to counter that and make it sound big.”

The answer to this conundrum is still compression and EQ, but in a spatial system those tools become artistic choices instead of mandatory processes. As McCullagh and Mosquera explain this to me, in the background I can hear the crowd getting restless. A few final snatched words and its time the pair returned to the matter at hand: Mosquera sets off with an iPad to walk the upper seating tiers and tweak the sub-mix as needed, and McCullagh takes the driver’s seat in what looks more like a space-ship bridge than a mixing station.

Across a dozen monitor screens, visualisations show the placement of sounds around the stadium. Spectrograms depict incoming frequencies in exquisite detail. Countless volume meters flicker. Stacks of outboard gear, including 147 of L-Acoustics’ amplified controllers, shine a constellation of green dots.

It’s a very impressive setup – but all of those technical details fade into the background when, against all logic and laws of physics, the Backstreet Boys arrive on neon-lit hoverboards. Surfing down from the heavens they land on stage, and the show begins.

There was a time, not that long ago, when attending a stadium gig was a trade-off: you got a massive spectacle but had to accept an echoey blur of audio, especially if you found yourself in the cheap seats. But that was then and this is now. The sound design that accompanies the band’s entrance could be mistaken for an IMAX mix, and as they launch into their opening number Larger Than Life, every word and note is audible over the audience’s enthusiastic screams.

Of course I’m safely ensconced behind the mixing desk, a spot that is usually the best listening position in the house. What does it sound like down on the floor? Taking a stroll across the arena, dodging denim-clad Deutschlanders and their foaming pints of wiesbier, I’m amazed at the consistency of what I’m hearing. From the desk down to the standing area there’s no obvious change in the acoustic image or the volume balance.

The efficacy of the sound system is most obvious in the vocal mix. I’m quickly learning that harmonies are the bedrock of every Backstreet Boys track, and McCullagh’s mix manages to keep each of the five vocal timbres distinct and recognisable, while still landing as a solid harmonic block when necessary.

That vocal clarity is aided by another nifty piece of kit from L-Acoustics – Source Intelligence. Running on a dedicated L-ISA Processor II Core unit, this AI-powered tool ‘cleans’ the vocals of any spill that gets in from the stage mix. The benefit is a focused vocal signal and, crucially for an immersive concert, no feedback.

“The difference is massive,” Mosquera says. “Here, you have sounds coming from so many different places to the microphones. Source Intelligence cleans [the signal] and leaves just the voice. There’s no drums, there’s no guitars, it’s just the voice. We need that; otherwise, I don’t think we could make it work.”

Onstage, the Backstreet Boys are now being pelted with packets of Haribo gummy bears. Far from being annoyed, it seems to signify a touching bond between band and fan. I keep moving.

After getting all the way over to the awkward corner spots next to the stage, and worryingly close to a truly chaotic public bathroom, I’m still hearing a fully balanced mix. That isn’t to say everyone in this stadium will be getting a perfect balance. “There’s always better seats,” Mosquera concedes. “It doesn’t matter which system – when you have a space this big, it’s impossible for everyone to have the same experience. But a different experience doesn’t mean a bad experience, and, using L-ISA, I think at least 70% of the people in the venue get a really good immersive experience.”

A giant disco ball has now descended, and a climactic rendition of Everybody (Backstreet’s Back) closes out the evening’s entertainment. I’m struck by the restraint in McCullagh’s mix. Only in the moments between songs did I get a taste of L-ISA’s capacity to move sound around; effects whizzed and spiralled in a satisfying manner, but most of that fell away when the next song kicked in, leaving the clear, tight harmonies that fans came for.

“You don’t want to draw attention to yourself,” McCullagh explains of his mixing philosophy. “It’s not about me. The fans are here to see the Backstreet Boys, and if somebody is distracted by moving sounds then you’re doing it wrong.”

With another fully immersive stadium residency planned for Toronto, Canada next. The team supporting the Backstreet Boys say this initial outing laid the groundwork to take things even further next time. “Now that I know it works, I can take more risks,” says Mosquera.

Looking around at the departing crowd, it’s hard to say whether the audience consciously noticed how cutting-edge this concert’s sound was – but everyone looks very satisfied. That’s the effect with immersive systems like these: when done right, they’re almost invisible, seamlessly supporting the music without stealing the spotlight. For people like Mosquera, who has worked with spatial audio for years, that paradox helps explain why it’s taken so long for the technology to hit the mainstream.

“Some people don’t want to understand it,” shrugs Mosquera. “Or they don’t care. Usually they care about how big the screen is or how many lights you have. They’re used to going to concerts where it sounds like shit. Stadiums always sound like shit, but that’s what I’m trying to fix; stadiums should sound better.”

Learn more about L-Acoustics spatial systems. 

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