When One Direction performs on their Where We Are tour in August, you'll have to squint your ears to hear the boybands' hits amid a more ancient and fascinating sound: the emptying of adolescent lungs.
Obviously, there will be screaming - high-decibel, high-pitch swells that push hard on the eardrums and then harder, toward the surreal. It's an abstract sound that JC Chasez has had years to ponder as a member of the multi-platinum juggernaut 'N Sync. But putting the power of that communal wail into words still isn't easy.
"Sound is energy," Chasez says. "And the entire room is producing sound, not just the people onstage, so when the entire room is resonating with every human being producing, it's a very exciting feeling."
Surely. But what's behind that feeling? Why do young women assembled at pop concerts express their collective ecstasy with the most alarming sound available to their bodies? Why do they scream?
In some ways, today's young fans are simply imitating the ritualised shrieks of the generations that preceded them, from the Beatlemaniacs to the Beliebers. And while today's tween screams aren't reserved exclusively for young male heartthrobs, concerts by Miley Cyrus and Taylor Swift don't seem to generate quite the same sonic fervor as a performance from One Direction or Ed Sheeran.
Since the splashdown of Elvis Presley in 1956, the American media has often characterised the din of young female fans gathered in the presence of a pop idol as "hysteria" - "a description that denigrates their musical engagement," according to a 2003 article written by Australian researcher Sarah Baker.
"Not only do these screaming, crushing bodies animate these [performance] spaces," Baker writes, "but they also make the pop experience feel intensely real for both the girls involved and the wider public."
So when the lights go down at a 21st century boy band revue, we aren't hearing a helpless, hysteric howl.
We're hearing a complex expression of individualism and collectivity - perhaps with a dash of Darwin thrown in.
Sociologists have different names for different types of crowds. The noisy throngs at a pop concert qualify as an "expressive crowd" - a gathering in which the participants are given implicit permission to abandon decorum and freak out.
"When men cry at a sports event, it's very similar'' to the screaming that takes place at a One Direction concert, says author Rachel Simmons. "It wouldn't be okay for men to do that anywhere else. But the sporting event sanctions that behaviour."
Simmons is the author of The Curse of the Good Girl, a book in which she argues that young women are unfairly asked to squeeze into an impossible mold of politeness and modesty. Simmons says a concert is a unique event that gives girls the rare opportunity to break out of those roles.
"In their day-to-day, non-concert-going lives, girls don't have a lot of permission to scream," she says. "A concert offers an oasis from the daily rules about being good girls. Screaming is about letting go and leaving the confines of being the self-conscious pleaser."
That's one way to explain why so many concerts are filled with screaming girls instead of screaming boys.
"Screaming is a way to control a situation," says Michelle Janning, a professor of sociology at Whitman College in Walla Walla, Wash. "When you're a kid, and a girl, you don't have control. Young people don't have a loud voice in society, so screaming in this kind of space is a way to have a voice. Literally."
Janning also believes that girls have felt an expectation to scream ever since Beatlemania spread across the land in 1964.
"We're constantly being socialised to see crowds of girls screaming at rock stars," Janning says.
"So we're following the crowd, doing what we've seen other people do. But we also want to stand out as individuals."
Both Janning and Simmons agree that concert screaming ultimately provides girls a chance to express their individuality while reinforcing their place in the larger group. And it can also be a place for competition.
"Adolescent girls are really invested in the acceptance of their peers," Simmons says. "But there's a competitive element to fandom and fan-girling - and screaming is an expression of that fandom. So girls are doing it not only to assert their passion for the band, but to compete with each other and to signal to each other that, 'This is what I care about'. It's part competition, but partly a way to connect. During adolescence for girls, that's a very complex and important drive."
Chasez of 'N Sync says he's seen that competitive connection manifest through fascinating displays of vocal teamwork.
The screams that most frequently caught the singers' attention onstage during 'N Sync's heyday often came from "groups of three or four", Chasez says. "They'd be holding hands and jumping up and down, screaming together."
Whether it's an expression of excitement or pleasure or anguish, screaming is ultimately a form of communication - and its fundamental message is almost always the same: "Over here!"
Harold Gouzoules, chairman of the psychology department at Emory University outside Atlanta, recently began studying human screams after years of studying how rhesus monkeys use screams to communicate.
Now Gouzoules is compiling an audio library of human screams and asking his research subjects to try to discern between screams of joy, excitement, surprise, fear, pain, aggression and exasperation. So far, his subjects have been pretty good at it, partially because screaming seems to transcend culture.
"We scream as a species," Gouzoules says. "Evolutionarily, it probably came about as a way to startle a predator. But as [humans] developed socially, you get a greater complexity of interaction, and screams could serve a function within a social group."
During childhood, the effectiveness of our screaming is often reinforced through play. "I can imagine ancestral humans screaming the same way we see kids playing in the back yard today," says Gouzoules.
And that playful way of being noticed is something Gouzoules says can be traced back to public events that predate the rise of the Beatles, Elvis and Frank Sinatra.
"If you got back to Nazi rallies in the '30s, when Hitler was rising to prominence, there are historical accounts that young women were screaming," Gouzoules says. "There's something about that kind of social event - there's excitement being generated by somebody who has power or authority... And those screams are attention-getting. That's how they serve monkeys. That's how they serve us a lot of the time."
But somewhere between childhood and adulthood, those screams cool into shouts, cheers and other forms of hollering we see more commonly in the expressive crowd.
For reunited boybands, though, the scream will always be the barometer of success.
"You have to know how to bring every side of the building to the same decibel level," says Michael Bivins, the 45-year-old vocalist currently on tour with the reunited '80s boyband New Edition. "It's scientific, in a sense. If there isn't screaming, there's disappointment."
In the summer of 2014 - nearly 30 years after the release of the group's signature hit, Cool It Now - New Edition's original fans are now middle-aged, but they're still coming out to see the band in concert. The ritual maintains its shape, even if it sounds a little different.
"Their voices are bigger!" Bivins says. "But it's still the same feeling. They're screaming for the same parts they were screaming for when we were kids."
The Washington Post