Quietus readers are a smart bunch, right? You know a huckster when you see one. So if I invite you to click the video above and witness pioneering television evangelist Oral Roberts in action, I trust you won't immediately make out a fat cheque to the Oral Roberts Ministries. Roberts built a career applying healing hands to the faithful in exchange for their prayers and later, their dollars. He prayed with presidents, built a hospital on the orders of a 900ft Jesus, founded a university in Tulsa that's still churning out graduates as esteemed as one Michelle Bachman, and was, at one point, America's richest, most finely-attired man of the cloth.

A subject ripe for sneering, you might think. Yet Evangelist, a four-day audio-visual installation held as part of Sheffield's annual Sensoria Festival, doesn't give in to easy swipes, instead presenting a nuanced portrait of a strangely compelling man. A collaboration between vocalist Jon Foulger and cellist Lins Wilson, Evangelist asks visitors to clip on a tiny MP3 player and wander through a series of rooms representing different stages of the preacher's life. Foulger's wiry, gossamer thin voice wraps around Wilson's pretty, often unsettling, playing, and the result is an installation that shakes your certainty.

We start small,  in the wheat fields of the South, charting the near-death teenage bout of tuberculosis that supposedly led Roberts to a life in the service of the Lord. There's self-doubt – 'Do I dare to imitate? Will you speak well of me?' – on opener 'Epistle', and the most vulnerable sounding vocal you could imagine on the fragile 'Oklahoma', as the artists use the first few rooms to question what might have driven Roberts to start his healing tours.

'Cash!', you might reply. And Foulger and Wilson explore that too. Indeed, it's when Roberts goes from small-town shaman to big-money maestro that the music takes a turn for the sinister. In room five – 'Television' – Roberts is shown preaching in sweaty, Nixonian close-up. A caption flashes up asking us to touch the screen and be well. Foulger gives a low purr: 'Would you rather be wasted? Would you rather be saved? Would you rather be bathed in light?'. A swirl of TV static builds in your ears, and the two flickering sets let us bask in glorious monochrome.

Two completely contrasting instrumental pieces by Wilson take us from the glory years – Roberts sending out thousands of mail order cloths he'd handled for the faithful – over to the dark side. The discordant, ominous '900ft Jesus' puts us in the waiting room of the City of Faith Medical Research Centre that would help push Roberts into debt, while room eight, 'The Ears of Presidents' is the most troubling of the bunch. It mixes hokey footage of American family life with shots of the Kennedy assassination, the attempt on Reagan's life and a pair of White House aides goofing around ahead of a State of the Union.

Meanwhile, Foulger is piped into our ears, singing this time from the perspective of Roberts' son, who, battling drug addiction, put a bullet in his heart while sitting in the back of his car, one of several personal tragedies that would befall Roberts in his lifetime. There's nothing snarky or knowing about this room: the lyrics speak of a troubled mind – "I look in the mirror and see no reflection". It's just horribly sad, even more so when it comes to a halt suddenly, unresolved.

In the final room, Roberts speaks with God at the end of his 91-year life, and the preacher asks the boss: 'Have you come to take me home?'. It's a sympathetic interpretation, suggesting that Roberts really did believe in all this stuff, and it's bolstered by the sparseness of the room: placed neatly in the corner are two pairs of shoes, one for Roberts and one for his beloved wife Evelyn. Even if you leave Evangelist firmly convinced that Roberts was a Midwestern witch doctor, the installation also makes the case for him as a human being, with all the conviction and hypocrisy that involves. Now, go on – touch the screen.

There are plans to take 'Evangelist' on tour. In the meantime, you can download/stream the album here