First: immersive does not simply mean louder.

Most of us judge concert sound in a fairly primitive way: Was it loud enough? Could I hear the singer? Did the bass hit? Immersive sound asks for a different kind of listening. Instead of treating the entire performance as one block of sound pushed at the audience from the usual left and right positions, L-ISA can treat voices, instruments and effects as individual sound objects and place them across a wider spatial field.

In Düsseldorf, the L-ISA system was configured in 8.2, with 350 loudspeakers across the Merkur Spiel-Arena. Six main hangs spread the sound across the stage, two rear hangs completed the immersive field, and additional hangs covered the tiered seating. But here is the important part: 350 speakers do not automatically mean better sound. The real achievement is when you stop noticing the hardware and the sound simply feels connected to what is happening in front of you.

James McCullagh, the Backstreet Boys’ longtime front-of-house engineer, is the person shaping what tens of thousands of people actually hear in the room. After years of mixing the band’s five voices, he gave us the detail that made the whole idea click:

“That became one of the most useful ways for us to understand immersive sound. It is not a fairground trick in which sounds constantly fly around your head. It is space. Five voices do not have to fight for exactly the same sonic position. An orchestra can stretch across the stage. Details can appear without simply being turned up. Ideally, you notice the music more and the technology less.”

So what should you actually listen for?

Here is the part we wish someone had told us before: you do not need to know anything about sound engineering to hear the difference. At your next big concert, try these four little listening tests:

1. WHERE IS THE VOICE? Look at the singer, then listen. Does the voice feel attached to the stage and the person you are watching, or does it feel as if the entire concert is coming from one giant speaker stack on the side? Good spatial sound should make the visual and sonic picture belong together.

2. CAN YOU CHOOSE ONE VOICE? When several singers harmonise, pick one person and follow them for a few seconds. Can you hear that individual voice without it being obviously louder than the others? Then zoom your ears back out: does the harmony still feel like one whole? This was the Backstreet Boys test, and probably the easiest way to understand what spatial separation can do.

3. WHAT HAPPENS WHEN EVERYONE SCREAMS? The real test is not the quiet verse. It is the chorus everyone knows. Can you still understand the vocal when thousands of people around you are singing too? Loud is easy. Loud and clear is much harder.

4. LISTEN TO THE SPACE BETWEEN THINGS. Is the bass powerful without swallowing the vocal? Can you hear small instrumental details? Does everything turn into one dense wall when the song gets busy, or is there still air around the different parts? That “space” is one of the simplest signs that you are hearing a carefully designed mix rather than just a very loud PA.

Can 45,000 people really have an immersive experience?

This was the question we kept returning to. Spatial audio is easy to imagine in a studio or a small theatre. A stadium is another creature entirely. System designer Carlos Mosquera was refreshingly realistic: there is still such a thing as a better seat. Immersive does not mean physics suddenly disappears.

“There’s always better seats. It doesn’t matter which system. When you have a space that big, it’s impossible to make everyone have the same experience. But not having the same experience doesn’t mean that it’s a bad experience.”
Carlos Mosquera, System Designer / L-ISA

Mosquera also explained why “immersive” does not mean sending every voice dramatically around the stadium. Asked whether a singer’s voice could move with him across the stage, he said it is technically possible, but at this scale he deliberately limited how far it travelled: “I didn’t want to risk too much… step by step.” The point is not to demonstrate the technology. It is to protect the experience in every part of the room.

His comparison was simple: think of a cinema. From the side, you still see the whole film; you simply experience it from another perspective. The aim is to extend the area in which listeners get a convincing spatial image and clear detail, not to pretend every centimetre of a 45,000-person venue is acoustically identical.

There was another layer behind the vocals in Düsseldorf: L-Acoustics Source Intelligence. In plain language, it uses machine-learning-based voice separation to identify the voice in a microphone signal and reduce unwanted material such as PA bleed, stage noise, crowd noise and room reverberation in real time. For a visitor, the relevant result is not the algorithm. It is a voice that can remain natural and intelligible in a brutally noisy environment.

That matters especially at a Backstreet Boys show. Nostalgia is not quiet. Tens of thousands of people know every chorus. The engineering challenge is therefore not to remove the audience, nobody wants that, but to preserve the intimacy of the singers inside all that collective noise.

Could the voice actually follow a Backstreet Boy across the stage? That was one of our questions for Carlos. The answer was yes, technically it can. But the more interesting answer was why you might choose not to. In a stadium this large, pushing a lead voice too far to one side can change the balance for listeners elsewhere. The technology gives the engineer more choices; good sound still depends on knowing when not to use them.

That restraint is perhaps the most interesting lesson from the evening. Better technology does not necessarily mean more effects. The aim is not to make you think about speakers. It is to give voices and instruments enough space that your brain can separate them naturally, and then let you get back to the song.

There was something wonderfully circular about experiencing all of this through the Backstreet Boys. For our generation, their music belongs to a very specific media memory: MTV, music-video premieres, posters, choreography copied in front of mirrors, and pop songs that seemed to be everywhere at once. Germany has a particular place in that history too: it was the first country to embrace the group, and their debut album was released here first in 1996.

Thirty years later, we were standing in Düsseldorf listening to many of those same songs while a completely different generation of live technology tried to make a stadium feel more intimate. The songs did not need reinventing. The way they reached us did.

How do you know when concert sound is actually good? Probably when you stop thinking about the sound system.

Good sound is not simply the loudest show or the one with the most speakers. Try this: can you understand the singer without straining? Can you follow one voice inside a harmony? Does the bass hit without eating the rest of the song? Does the sound feel as if it belongs to the stage? And when the whole room explodes into a chorus, does the music remain clear? If yes, you are probably hearing much more engineering than you realise.

We went to Düsseldorf ready for I Want It That Way, MTV memories and a very millennial reunion. We came back listening differently. Maybe that is the best compliment you can give to L-Acoustics L-ISA immersive technology: 350 loudspeakers, an 8.2 system and an enormous amount of engineering, and, once the song starts, you forget all of it.