Torturer's jukebox, The Guardian

The first sound you hear is a bright, solitary trumpet. Then come rumbling tuba, rattling drums, and the familiar refrain of Sousa's Stars and Stripes Forever. A behemothic guitar riff lumbers in, with a flurry of banjo, a skirl of bagpipes, a battery of percussion, and squeals of brass overlaid until they sound like a stampede of panicking elephants. And on it goes, like the devil's own mix tape. This is the sound of Clamor, an installation comprising music related to war, by Puerto Rico-based conceptual artists Jennifer Allora and Guillermo Calzadilla, who direct much of their work at the relationship between global politics and individual identity. The duo once protested against US weapons-testing in the Puerto Rican isle of Vieques: when the US bases finally closed in 2003, the artists attached a trumpet to the exhaust pipe of a moped and drove round the island capturing its triumphant "reveille" in the video Returning a Sound In Clamor, the music related to war - sometimes played live - is broadcast from inside a hulking chamber the artists refer to as "a bunker, a ruin, a cave and a sound booth". Allora and Calzadilla spent a year collating over 100 pieces of music, picking up CDs on their travels and scouring the internet. The resulting 40-minute collage, now at London's Serpentine Gallery, spans centuries and continents. Much of the music in this sonic arsenal was composed with conflict in mind, from the battle hymn of the Hussites, sung during the battle of Domazlice in 1431, to the Horst Wessel song of the Nazis. But the most startling thing about Clamor is the fact that some of the music it includes seems nonsensically out of place - until you learn the context. Among the many dubious achievements of the "war on terror" is the redefinition of what actually constitutes military music. Just ask the prisoners in the Iraqi town of Al Qa'im, incarcerated in packing crates and pounded with songs ranging from Metallica's crushingly heavy Enter Sandman to Barney the Purple Dinosaur's maddeningly perky I Love You. Or alleged 9/11 conspirator Mohamed al-Qahtani, kept awake by Christina Aguilera songs at Guantánamo Bay, according to a report in Time magazine. Or Haj Ali, the hooded man in the notorious Abu Ghraib photographs, who talked of being bludgeoned by a ceaseless, deafening loop of David Gray's Babylon until he thought his head would burst. "Forcibly exposing a prisoner to loud, discordant or relentlessly repeated music is meant to inflict suffering," says Amnesty International UK's Guantánamo campaigner Sara MacNeice. "It amounts to torture or cruel, inhuman and degrading treatment." Despite this, the use of loud music as a method of torture is played for laughs: when news of what had taken place at Al Qa'im emerged, newspapers and TV stations commissioned jokey playlists. On the battlefield, music can serve a dual purpose: to psych up the attacking army, and to intimidate their foes. When tanks rolled into Fallujah in 2004, soldiers blasted the likes of AC/DC's Hells Bells from giant speakers mounted on their gun turrets. Although rock'n'roll was played constantly by US forces in Vietnam, it was more for their own entertainment. The weaponising of pop songs appears to have begun with the US invasion of Panama in 1989. US troops laying siege to Manuel Noriega bombarded him with everything from Led Zeppelin to Twisted Sister. Ben Abel, spokesman for the army's psychological operations command, told the Floridian newspaper that it began as a way of keeping the soldiers energised: "Then Noriega commented that the rock'n'roll was bothering him. Once the guys found that out, they cranked it up." How do the creators of this music feel about it? Interviewed on National Public Radio in the US in November 2004, Metallica frontman James Hetfield responded to reports of Enter Sandman's use by saying: "There's parts of me that want to joke about it. There's a pride also that, you know, it's culturally offensive to them. If they're not used to freedom, I'm glad to be a part of the exposure." Hearing Clamor's elaborate din in an airy gallery in Hyde Park is not the same as enduring a musical assault, but it operates on multiple levels: as unsettling noise; as a collection of culturally specific pieces; and as an illustration of how manipulative music can be. "There are moments when you're hearing little sounds and fragments of melody that trigger certain feelings," says Allora. "You can't help it because this is what you're indoctrinated into. But then it unravels, and precisely the way it is manipulating you seems silly and ridiculous. There are moments when it moves into cacophony and chaos and it renders the whole thing absurd." "All these different tunes are in conflict with each other," adds Calzadilla. "It sounds like the work is at war with itself." Having lived with the music in Clamor for more than a year, however, Allora and Calzadilla would happily never hear it again. "I have an aversion to these songs," says Allora. "It's interesting to look at the ends to which they have been applied. Any pop song could potentially be a weapon".