Last night I went to see Sunn O))) at The Barbican. Notorious as one of the loudest bands in the world, they were, if anything, louder than expected.

The atmosphere is ominous, oppressive, as a pair of shadowy figures – Stephen O’Malley and Greg Greg Anderson – creep silently onstage amid a cloud of smoke.

You can’t see their faces; you can’t see anything except the smoke billowing across the stage and the occasional glimpse of a hooded figure in a floor-length robe and monk’s cowl, wielding an electric guitar.

A relentless hum emerges from the stack of ten-foot high amps stretched from one side to the other. And for five minutes that’s it: just the smoke, and the hum.

Then, without warning, it hits you. I’ve never seen an entire audience jump out of its seats like that.

The opening salvo is like an earthquake, the sound of tectonic plates grinding together at the earth’s core, amplified at maximum volume and fed back for added distortion.

It carries on for an hour and a half.

The opening number alone lasts half an hour: a relentless, purgative metal racket that engulfs your entire body, erases any thoughts you might have had, envelops your entire being.

Seeing Sunn (and I saw them once before, 18 years ago) is as much a physical experience as an aural one. Your body and brain are pummelled by noise; noise without any of the comforts of rhythm or melody. Just noise.

Pure, unadulterated noise.

At the end (if you make it that far) you feel cleansed. You feel as drained physically as a 90-minute yoga session, and as drained mentally – emotionally – as a 90-minute psychotherapy session.

You may well never be the same again.

It’s impossible to replicate the effect without seeing Sunn – the O))) is not pronounced; it’s just a graphic of the sun – for yourself. But you can try… if you put on headphones and turn the volume up to 11.