If you happened to take a cigarette break on the north concourse of Gillette Stadium last night, about a dozen songs into U2’s US-tour kickoff, you might’ve noticed two young men who were not acting like everyone else. For one thing, they were facing away from the stage — a view that afforded them, if anything, a look across Patriot Place, in the direction of the ticketless crowd standing three ardeep in front of the CBS Experience. For another thing, they were wearing studio-monitor headphones and shit-eating grins.

It seemed an awful expensive way to listen to your iPod. Then I saw ‘em offering a few passers-bye a listen to the headphones, and decided to take a closer look. “Listen to this,” one of them said, and placed the headphones on my ears.

They were listening to U2 playing behind us, in real time — and the sound was impeccably crisp, full-bodied, with perfect instrument separation. Bono’s voice had the kind of standing-next-to-you-in-a-crowded-elevator feeling that no stadium speakers (and very few live albums) can reproduce. The sound through the headphones reminded me of a tape a friend once gave me of the Rolling Stones playing in Australia in 1973, taped off the soundboard, in which you can hear Mick Jagger’s breath on the mic in between verses. Commercial recordings clean that sort of thing up, so hearing that faraway voice so close, and unedited, delivers a startling intimacy.

So how’d they do it? Part serendipity, part genius: headphones-guy was plugged into a pager-sized Sennheiser wireless receiver — the type of device that has replaced on-stage monitors for musicians as the way they hear themselves during the concert. He believes his Sennheiser is identical to the model Bono uses . And during soundcheck, he’d simply run through the various channels until he found the one the soundboard was broadcasting on. Bingo.

There was another big difference between what was on the headphones and what the larger audience heard: the subtle but unmistakable sound of a click track. You could even hear a soft voice at the beginning of each song counting the band in, “One, two, three, four.” To longtime U2 fans, it will come as no surprise that the band uses one — lots of artists do, especially when their live show incorporates triggered samples or effects. The presence of the click track led headphones-guy to believe he might be listening to the mix being piped to Larry Mullen’s headset, though there was no way to be sure. Listening to the band the way they hear themselves suggested a plausible explanation for the size of Bono’s ego: maybe he thinks everyone hears him this way. 

Replicating this experiment yourself could get expensive: Sennheiser receivers run about $800 — about the price of three decent U2 tickets. But given the degree of outrage expressed by some upper-deck fans about the quality of audio at last night’s show (for the record: the sound from my seat, in the lower deck, was very good), you could certainly see some cheaper version of this technology — or perhaps a venue-operated version, perhaps a twist on the way Gillette gets a few bucks for binocular rentals — becoming an easy upsell. 

 Review due to be posted later today -