I rather wondered, after the first time I saw Sunn O))) live, whether I could physically stand going a second time. It wasn’t that I didn’t enjoy it, it was just that the after-effects were like nothing I’d ever experienced after a gig.

That was answered in 2015, when I saw the near-trancendental brilliance of their (bigger, louder) show at the RFH, and I decided that no, I can take it, and I would absolutely go again. So, two years on, I was this time at the Barbican, and there was some trepidation in advance, for two reasons.

One was this widely-shared image the previous week.

Two was that we had front row seats.

For what is one of the loudest live acts in existence.

Yeah.

Still, my upgrade of my earplugs to Etymotics ER-20XS has turned out to be an exceptional choice in recent months, and I was confident they’d cope. But there was the support act first, and I knew nothing about her – would she be loud as well?

Of course she was. Said support was the fascinating Hildur Guðnadóttir, an Icelandic artist who initially seemed dwarfed by the towering monitors behind her. That was, until she started singing, this otherworldly, near-wordless sound that unsettled and awed at the same time. Her Cello playing was hardly orthodox, either, with it played through pedals and looped until it became the kind of rumbling, sonic inferno that the headline band might well be offering. I’d not come across Hildur’s work before, but with her having worked with The Knife, Múm, Pan Sonic and others, I’ll now be hunting it out.

Before Hildur had taken to the stage, and between her set and the headliners, I realised that there was this ominous hum from the monitors and stacks on-stage, making it clear just how loud things were going to be.

So it was a little bit of a surprise to find Sunn O))) start relatively quietly. Attila Csihar came onstage alone (well, with the usual cloud of stage smoke/fog enveloping him from the off), and incanted a lengthy vocal piece – I have no idea what he was saying, mind. The remainder of the band – expanded now to a six-piece, with Hildur Guðnadóttir as part of the band on her treated Cellos, Stephen and Greg on guitars, Tos on Moog and Steve on keys and trombone (more of which later) – then trooped onstage, and unleashed a steady torrent of noise.

Trying to explain what Sunn O))) sound like is astonishingly difficult. Yes, they started out in thrall to drone metal pioneers Earth, but in the two decades or so since they first started dividing metal and non-metal fans alike, they have long since moved into a different realm.

Drones are a core part of their sound – made by drop-tuned guitars, of course, but added to that are the synths and presumably effects pedals that add reverb and a depth of sound that is frankly unmatched by any other band I’ve ever seen or heard. But it’s not only the depth – despite the extreme volume, the clarity of the sound was unbelievable. Even amid the loudest points, individual instruments and elements were still identifiable for the most part.

Their sound, once they get started, is relentless. There are no gaps across the set, less a set of songs than of movements, and the only way I could honestly confirm that they’d moved onto another part was when the colour of the lighting changed, and then the sound would start to shift. I’m fairly certain there were elements of Aghartha early on, and the epic closing piece – probably going on half the 105-minute set – was, I’m pretty sure, an enormously extended take on Candlegoat (much as last time), but in some respects, what actually was played isn’t especially important.

I’m sure this is obvious, but Sunn O))) live, never mind on record, is an acquired taste. The live sound is an immense, physical force, that rolls into you, through you, and is an absolute exhilarating feeling – after it first hits you. That first time for me was almost panic-inducing, but once I relaxed and took it in, the way the sound ebbs and flows (the band’s T-shirts have the wry slogan “ever breathe a frequency?” Yes, yes you can. This show was living proof), it is an astonishing exhibition of exactly what can be done when you turn everything up to eleven. Or twelve.

Things have changed a bit in presentation nowadays, too, as the band have expanded in scope. Five years ago, it was three or four of them, in black robes and cowls – here, it was six of them in black robes and cowls, with endless clouds of smoke inching across the stage, with tentacles of it like sentient beings, shrouding us and the band entirely from view at points, with spectacular lighting that illuminated the smoke to make it appear like the monitor stacks were on fire. That, needless to say, was a little unsettling at points!

Then, later in the set, Atilla vanished from the stage, and re-appeared in what has become something of his signature – a long coat covered in mirror shards, a mask (also mirrored), and an immense crown of thorns made from the same shards…oh, and gloves with lasers from each finger. Needless to say, the effect amid the smoke and gloom is an intimidating, spectacular sight, and as he crouched, pointed at the ceiling and howled his vocals, the intimidating feel only grew.

As the final chord rung out, and normality returned, we were able to applaud the band (the standing ovation lasted a few minutes), and the band themselves, all smiles, happily lapped up the adulation. And too right they should.

Sunn O))) are an unlikely success story. A band that refused to compromise, built on a deceptively simple idea, and made it a “must see”. They are more prolific than you might think, with various collaborations in addition to their album releases (Altar, the one with Japanese band Boris, is easily one of the greatest collaborations I’ve ever heard, and the more recent album with Scott Walker was a surprising success too), and their constant adapting of their sound to take in new influences and new ideas means that there is vastly more to them than just very loud drones by men in hoods.

I’m still never going to convince my wife to come along next time, though.