It’s 11.30pm on a Friday night in the Festival and I’m outside, in the rain, staring at a wall. There is no bar on this side of Summerhall, no official performance space, but chairs and tables have been arranged on a little veranda facing the bare stone facade. An usher hands out sets of wireless headphones and tells us to wait.

And then a tiny epic unfolds. A miniature opera buffa. It lasts for nine minutes and it careens us through a grand drama of life, love, regret, violence, state-of-the-nation political commentary. The visuals are gritty and vivid, a street-art aesthetic laced with tender heart. The music is punchy, searing, propulsive, extravagant, apposite.

Brian Irvine and John McIlduff’s Drive By Shooting is opera, alright: this is no parody. Real voices, real orchestra, real techniques, real emotional impact. The fact it’s a looped graffiti projection with pre-recorded music delivered through headphones – that adds a dislocated, absurdist appeal, as though the dregs of Ligeti’s Le Grand Macabre had been distilled into a cartoon strip only to infiltrate your unsuspecting night out. Even in the midnight drizzle, the unlikeliness is a delight.

This, says Irvine, is comic opera. “Most deadly of genres,” he adds with a grimace. Why deadly? “Because most comic operas are genuinely awful.”

The story is as follows: an octogenarian discovers her husband has been having an affair with the next door neighbour, so she and a friend stage a hit on the cheating man, armed with an ancient shotgun and zimmer frames as getaway vehicles. They shuffle after the culprit with tragicomic slowness, backs stooped and woolly hats drooping. Meanwhile the music builds like a fast and freewheeling thriller, culminating in the immortal operatic line: “Shoot the fecker in the pecker!”

“It’s a proper opera!” Irvine assures me. “Actually it’s pretty old-school. Straightforward narrative. Couple of people communicating with each other through song.” Drive By Shooting is one of five short operas commission by Dublin City Council – operas about the streets of Dublin, performed in the streets of Dublin by people of Dublin.

“I’ve been interested in the idea of what opera is,” Irvine explains. “Who goes to see it. What if we make an opera that is directly targeted at people who never go, who don’t even know what it is? If we come at it from the angle of street art?

"I’m not anti-opera,” he clarifies. “I’m completely pro-opera. It carries an enormous amount of baggage and legacy, but opera can be anything you want it to be.”

One of Irvine’s heroes is the artist Cy Twombly, and there’s a resemblance here in the bold collisions of history and the present, of the public and the private, high and low, formal and flagrantly off-the-wall. Twombly had a brilliant way with big graffiti, often (seemingly) freely-scribbled and virtuosically calligraphic. Irvine’s scores tend to be crazed wonders with huge compassion and mass impact. Praise Aloud the Trees – a collaboration with Seamus Heaney – features two symphony orchestras piled up with improvising choir and two conductors. NEST is a seven-day performance installation involving 3000 collected objects, symphony orchestra, choir, intervention performers and soloists. Even Irvine’s own ensemble is a raucous 12-piece, with turntables, two conductors and free improvising. But the methods are rigorous; the intent is solid.

Like Twombly, the blithe grizzle of Irvine’s public work has a tender, personal impact. “That’s why I wanted people to hear this opera through headphones not speakers,” he says. “Because there’s an intimacy with headphones despite the fact you’re standing on a street corner. And maybe that image clash will jolt people out of their preconceptions.”

Irvine says more people have seen Drive By Shooting than the entire audience for contemporary music in Ireland over the past ten years. “The reach has been stupendous, and I’d hazard a guess that 90 per cent of that audience isn’t opera fans. I thought people would walk away as soon as the opera started, but you know what? That hasn’t happened yet. Not once.”

Drive By Shooting is at Summerhall. Nine performances daily, 15 minutes duration, until August 26