WHAT IS it that Prince craves, Cork City relishes, Edge venerates, and ZZ Top slavishly mimics? Nothing that comes in hi-fi manuals or pretty packaging - or even in a kit bag come to think of it - though the object of their collective desires might well dispute the pretty packaging part.

He's a man who's been privy to more beat-up and burnt-out scéals than even the Zoo TV confessional has at its most, well, confessional.

He's confounded otolaryngologists of world renown with the labrynthine passages of his inner ear: cochleas like the Gertrude Stein gallery in New York, all swirling and eddying in a thousand different directions; tympani vibrating with more verve than the entire top shelf of Soho's finest toy shops; and he's going head to head with David Bellamy to see who can tend and nurture the most exotic species of wildlife amid the quilted nesting ground that is his beard. (All nutritive compounds generously sponsored by the World Wildlife Federation.)

He is Joe O'Herlihy. Audio director, sonic engineer or allround sound man. Take your pick or take all three. Like most sophisticated elements in this universe of ours, Joe expands and contracts to suit your available space. Cork's Arcadia and Wembley Arena are irredeemably generation-gapped to all except Joe and - conciliator that he is - he not only tries to throw his arms around them all but he succeeds, with thumbs to spare.

Fifteen years it's been. A decade and a half of hauling and dragging U2's sound to the ends of the earth and back. Squeezing up to 92 inputs into a mixing desk when others'd have settled for 30, or at most 40. Scouring tips for clapped out washing machines that might conceivably double as speaker cabinets when the readies to buy the damn things were less than ready. And stretching the outer limits of noise pollution curfews to encircle the decibel demands of Zoo TV, in all its schizoid incarnations.

Sometimes it doesn't seem like such a long time. But think about it. 1978. Mark Chapman had yet to strike up conversation with John Lennon. Cockney Rebel were drawing their dying gasps and The Undertones were just beginning to get some teenage kicks. And I got a David Soul solo album for my 13th birthday. My, how things have changed . . .

Joe was making a living out of sound engineering when

nobody else in Ireland was. It was he who fashioned a job description and proved that it paid to have this mad Cork bastard on the payroll. Blessed (or burdened) with the ears of a dog, detecting rogue frequencies with more panaché than a Baywatch surfer would eye a promising wave, he propelled the function of the sound systems to their outer Plutonic limits.

Fifteen years spent with U2 is hardly akin to death row, neither could it be a constantly delirious tiptoe down the Mardyke. But O'Herlihy's been, with Paul McGuinness, one of the band's primary constants in an ever-changing constellation encircling the band.

After Boy the thought began to slowly dawn on them that they just might manage to pull off this scam they'd called U2. The bookings were flowing in. The petrol tanks were full and Bono's larynx was tickling for another live expectorant. Round table meetings ensued; a core team was a fundamental requirement; the crew had ebbed and flowed but the boys were insistent that O'Herlihy was a fundamental cog in the grand plan.

Ensconced in the belly of his native Cork, the lure of the bright lights was difficult to resist. After all, he'd toured already with Rory Gallagher, where he learned his trade travelling the length and breadth of Europe and beyond with a rig that catered for bar, barn, concert hall and stadium alike, and had enjoyed life on the road and all its crazy camaraderie.

Likewise with The Undertones, when Derry's finest and fieriest were testing the waters outside of their home town, in search of a door large enough to accommodate their Wittenburgian demands.

A brief period as a bass player had failed to impress his bank manager, so he'd finally made a decision to opt for the divine answerability of self-employment by way of a sound hire company which, at the time seemed to have the makings of a far better mortgage carrier than any gig with a band. But that's a hard station too . . .

Tom Mullally, fellow sound buff (and godson to O'Herlihy's godfather figure in the Cork Mafia) recalls the ropey exploits of Joe's earlier days in the sound hire business.

"I remember an occasion when Joe's kitchen table was sawed in two in the middle of a creative carpentry session when he was into building his own cabinets for the monitors and speakers," he recalls, the operatically-pitched Leeside tones ever rising at the cracked antics of those days of enforced penury. "Of course the washing machine idea was his too - and it made a lot of sense, boy, when you think about it. The bowl of a good front-loading machine was just the right size for his home-made speakers - and a lot cheaper than the fancy wood-cabinets he was expected to have."

O'Herlihy made no secret of his initial scepticism of U2, with visits to their live shows leaving him distinctly underwhelmed. Production Manager (then lone lighting technician) Jake Kennedy recalls having to coax Joe along to have another listen when U2 played the Arcadia - yet once converted to the good cause, he championed their sound with the zeal of the true penitent.

In fact, Kennedy remembers that it was Joe who worked overtime in order to convince Paul McGuinness of the worth of a decent lighting rig. At a time when the balance sheet was still spluttering and gagging at the sight of an extra amp, O'Herlihy was insistent on chasing after and holding onto the best. If the Fab Four needed it, Joe pushed hard, and they got it. It's no small matter, too, when you reflect on just how central to the band's ultimate success was their reputation for doing great live gigs.

For a man who's low to the ground and greater in whisker

than in stature, Joe's got an alarmingly long line of admirers who have no trouble picking him out amid the stacked rigs and towering speakers that are now almost appendages to his torso. (Many seriously believe that it's this very proximity to the ground that gives him the edge over the rest of the posse - Joe feels the vibrations that others scan the monitors to detect.)

Mullally and Kennedy both admit to having fostered him as a father figure at various stages along the way, despite Kennedy's proximity in age (the two pre-date the U2 era and have birth certs that are separated by just a few single digits), and whichever crew member you sidle up to betrays a canny, wry smile when Joe's name crops up.

"Joe is a past master at the art of saying nothing when he has to - in the longest possible space of time," Tom Mullally observes. "He's probably the most diplomatic man I've ever met."

Diplomacy being in demand by the shovel load whenever a corporate body of U2's proportion uplifts and transplants to sundry locations worldwide, it's often that mad bastard from Cork who's called in to smooth frayed tempers and calm jittery nerves. He evidently subscribes to Gonzo's maxim that "when the going gets weird, the weird turn pro".

Steve Iredale cites the voluminous noise pollution constraints that Joe had to contend with amid the cacophony that is, was (and looks like it might well forever be) Zoo TV/Zooropa/

Zoomerang. O'Herlihy simply pulled up a chair, thrashed it out with city officials and soccer club bosses alike and emerged with assorted arrangements that accommodated both the formidable demands of the band and the statute books.

And the net effect is one that inevitably has the big time tourists such as Dylan, Springsteen and Bowie salivating at the mouth in abject envy. Joe's lone peer for many years was Bruce Jackson who used to mix Bruce Springsteen's live shows - and now even he has moved on. His Royal Purpleness has even attempted to poach the O'Herlihy magic from the camp, with figures three times what he's earning already being bandied about like elasticated chickens, but the flashing greenbacks haven't yet managed to seduce the elusive juggler.

The secret of his longevity may be, as though it should come as a surprise from a quartet for whom the medium is the message, in the epistles that sally forth from Bono to Joe even mid-song, with the innocents in the back and front rows blithely ignorant of these cosy little tête à têtes.

"Joe's got his own domain out there and that's it," Steve Iredale (honorary Corkman) insists. "He's got this mental thing going on with Bono the whole time and Bono will talk to Joe during a show sometimes. Joe will hear it and nobody else will. It might be heard as part of a lyric in a song but that's Bono talking to Joe over the headset. Joe just stands there, watches the show and picks up everything. It all comes automatically to him. Even though he's 180 feet away from the stage, it's a short distance to him."

Then again, there are his risque little head to heads with Edge when words like "sound", "timbre" and "resonance" are bandied about with the reverence normally reserved for matters spiritual - or otolaryngological, as his consultants will attest.

All bar none agree that there's Bono, Larry, Edge, Adam and Paul McGuinness - and Joe. Anybody else could up sticks and leave and the show would still go on. But Joe's an integral part of the band. He's surely the only sound engineer whose presence is a precondition to the staging of any show by a major act. His contract has a clause which states that U2 can cancel if Joe's unavailable - a scenario that's highly unlikely given his record of a sole absence in the entire 15 years of their acquaintance, but in the band's view, a necessary out, should he decide to lose himself on the terraces of Cork City away matches in some obscure corner of Turkey (which is where he is ensconced as we write!)

Hell, even Eno was knocked for six when he heard what Joe dragged out of the band at the initial live rehearsals of "Who's Gonna Ride Your Wild Horses?" What had taken months of laborious retreading in the studio Joe had managed to recreate in the arena in one pristine sound check. It has to be those circuitous cochleas firing on all cylinders again . . .

O'Herlihy's constancy with U2 is regarded by all who know him as merely the professional corollary of an enviably well-matched partnership with his wife Marian. A refreshing alternative to the beer-swilling, aggressive American and British role models who are going, (going, gone) at ten-a-penny, he has a family to whom he is incredibly close, a wife who's been there for the difficult decisions,the sawed tables and the inconvenient and downright disruptive separations in the name of the music, and an (almost) congenital inability to make it for the births of his progeny - though he is learning.

Steve Iredale recounts the manic rush to the airport in Hampton, Virginia to get Joe onto a plane to New York and then onto Concorde for a split-second dash to Marian's bedside just in the nick of time for his fourth child, Louise's birth six years ago. After that it was straight back on a plane to Tempe, Arizona for the recording of that key concert for Rattle and Hum.

His propensity for such derring-do did little to impress Marian though, who'd endured many a tight moment (both financially and emotionally) as a result of Joe's resolution to stick with the band. And the propensity to chase after that dream is one that he's passed on - inadvertently or otherwise! - to his eldest son Mark, already at 21 a video technician on the crew, and a promising visual artist in his own right.

Fifteen years of globetrotting has curtailed his family time considerably too. Last Christmas saw the first occasion on which the entire O'Herlihy family set off on holiday together (Disneyland is still recovering). But with the ongoing demands of a band like U2, who appear to have a fundamental difficulty coming to grips with the concept of "holidays", there've been precious few opportunities to indulge the fantasies.

Though fantasies there are plenty - most of them being of a footballing hue. O'Herlihy makes no attempt to disguise his heart-on-sleeve love of the pursuit of a pig's bladder around the perimeter of a pitch. Tom Mullally anxiously points out the fact that Joe is and has been a fan for a long time, long before the advent of the born again soccer fan, circa 1988 when at long last it seemed that under Jack Charlton our lads were beginning to get the hang of this dribbling lark. (The mess they left at the table was a tad embarrassing but Joe could handle the questionable oral dexterity.).

He'd long ago been offered a trial with Coventry City himself, but failed to pursue it whether because of their distinct lack of a decent musician amid the first 11, or the prospect of having to mingle with a crowd of geezers who did everything from showering to tying their velcroed shoes in unison, it's never been quite established. His prowess on the pitch has never been in question, though the years have put a few inches on his well-nurtured waistline but he remains a feared opponent, as the men from Hot Press Munchengladbacdh 1891 will testify, firm in the tackle, good on the ball and with a copious supply of skill and vision.

Still, he's probably the only sound engineer who tests an arena with "Olé, Olé, Olé"! (Though he has been known to switch to Pavarotti when surrounded by a plethora of Italian environmental engineers monitoring the sound levels. Whoever complained that Luciano was a noise pollutant? The man has a refined sense of occasion.).

The entire crew speak enviously of his footballing connections. Denis Irwin, Roy Keane and Brian Carey are good friends who swap sideline tickets for a decent glimpse through the bars of the Zoo whenever possible. Iredale recently took sadistic pleasure in hauling O'Herlihy along to a Manchester Utd./Leeds match, neglecting to forewarn him that he would have to sit in the middle of the Leeds enclave for the duration.

Seventy minutes later O'Herlihy emerged with 10 flattened fingers that'd become intimately acquainted with the upside of the Leeds bench, and a severe and uncharacteristic dose of speechlessness. Long a Man. Utd. fan, the experience of holding his tongue proved a tad disconcerting but was nothing like the ecstacy he enjoyed when witnessing his home town heroes, Cork City, win the League last year.

Tom Mullally remarks that Joe is paralysed with the same awestruck aura when confronted by his soccer heroes as are the countless U2 fans who intrepidly scour every alley and corridor in pursuit of their gods. A soccer groupie without compare, O'Herlihy is on first name terms with the entire Irish and Cork City teams and avidly seeks autographs when the going is good and the spirits are high.

His Irish Jersey is well-recognised on the terraces and the arenas alike where its brilliant green punctuates the designer chic of the stadia with aplomb. It remains to be seen whether his adroitness at following the games will continue now that Telecom have decided to hike the charges for every syllable spoken.

It's a serious question: Can Joe O'Herlihy rise to the cost of channelling the commentaries through his own head-set via the voluminous telecommunication link-ups he'd established in the past? Or has it been put outside of even his grasp? A sobering thought.

His avid support for things and people emanating from Cork extends to an appreciation of things Corkonian to rival the most committed Corleone; having surrounded himself with the cream of Leeside wit and wisdom in the shape of Tim Buckley, Tom Mullally and Sam O'Sullivan, he still returns periodically to old friends and mentors such as Tom O'Driscoll (from the Rory Gallagher camp) and the Cape Cod-based Jimmy O'Hara - formerly of Sir Henry's in Cork - a prankster of note who's wont to leave messages on his answering machine of the sort that nurture his shrink's bills with glee.

With the formidable triumvirate of family, soccer and music

to sustain him, Joe O'Herlihy looks like a man who's listened to his heart a lot more than he's listened to his auditor. Only daydream believers and the foolhardy invested time and effort into U2 in the early days when they had a whole lot less than three chords and the truth. Steve Iredale simply reckons that the key to Joe's longevity and unrivalled success has been the fact that "he's always gotten off on the live music'.

His ticker ticks faster, his eardrums vibrate faster and it's been suggested that his beard even grows faster during the live shows. Who knows? All we know is that the man's a musical wizard and a pied piper who whistles his own tune only to find he's got everyone blissfully pursuing him in the hope that some of that incandescence might rub off on them.

You see him coming, you hear his story and you smile. What better way to get an introduction? Welcome to the next 15, Joe.

• Siobhán Long