Jim Marshall's famous black box allowed bands to be heard by larger crowds than ever before. Now, though, it's more a symbol of arena concerts than a necessary component of them.

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Ian 'Lemmy' Kilmister of Motorhead plays alongside Marshall stacks at a 2006 concert. AP Images

I'm gonna play some heavy music/
I'm gonna play bad, I'm gonna play loud
- Blue Oyster Cult, "The Marshall Plan"

When Jim Marshall designed his first amplifier in 1962, he used the 12AX7 vacuum tube, a seemingly slight deviation from the 12AY7 tubes of the popular Fender amps—because Marshall couldn't find any in Britain at the time. This accident of geography meant that customers of his music store suddenly had a little more crunch in their guitar sound. In rock and roll—a genre forever entwined with technology—a mere vacuum tube begat a major shift in the music's history.

Marshall, who died last week at 88, also had the fortune of having a 20-year-old Pete Townshend for a customer. Townshend told Marshall he wanted to hear himself over The Who's audience and rhythm section. Thus was born the first 100-watt amp. Add to that two cabinets, each bearing four speakers—together, the components came to be known as the Marshall stack—and Marshall secured himself a permanent spot on any history-of-loudness timeline.

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Loudness is strictly a psychological phenomenon referring to how the brain perceives the strength of a sound. But exactly why loudness appeals to so many of us is still a mystery. In his book, Your Brain on Music, neuroscientist Daniel Levitin suggests that very loud music saturates the auditory system, causing neurons to fire at maximum rates. Studies have shown that louder music causes us to shop more and work out more enthusiastically.

The joys of loudness are hardly confined to rock music, or this century. A 400-pipe organ built in 10th-century England required 70 men to play the instrument, which produced a thunderous tone throughout the city of Winchester. Digs of ancient ruins in Peru have unearthed instruments made from conch shells that could drown out a chainsaw.

But composers had few terms to describe degrees of loudness until the 18th century. "Piano" (soft) and "forte" (loud) and their variations became common features of notation, but they were frustratingly vague and subject to the performer's judgment. Thaddeus Cahill did away with such ambiguities when he invented one of the earliest electronic instruments, the Telharmonium, in the late 19th century. The volume control allowed the performer to choose any one of 24 degrees of loudness. It was a good idea, but the instrument bankrupted him and some family members.

TOWNSHEND'S WISH TO HEAR HIMSELF PLAY over his bandmates and audience was certainly a reasonable one. But his discussing it with Marshall—who could actually do something about it—might be the moment arena rock was born, and the start of a widening divide between audience and performer.

Concerts were held in large venues before there were Marshall stacks. But listen to the recordings of the Beatles at Hollywood Bowl: The screaming crowds are as much a part of the show as the band onstage. Fans were interacting not just with the Beatles, but one another; it became a participatory event. Not that the Beatles were happy about this. They stopped touring partly out of frustration of not being able to hear themselves. The Fab Four never had a Marshall stack; they stuck mostly with Vox amps.

Then the mega-watt amps emerged. At 110-plus decibels, there's not a lot of interaction going on—it's pretty much a one-way conversation. What had once been a barely noticed object on stage now gave rock a new iconography. Bands like Blue Oyster Cult, Judas Priest, and Slayer have used walls of Marshall stacks as backdrops for their performances.

The new technological capabilities sparked a volume war. Led Zeppelin gained a reputation for ear-crushing volume, only to have Black Sabbath promote themselves as "louder than Led Zeppelin." Deep Purple earned a place in the Guinness book of world records in 1972 when a London concert peaked at 117 decibels (according to loudness lore, the volume rendered three concert goers unconscious). Four years later, The Who took the title when the band's loudage reached 126 db (by this time they had switched to Hiwatt amps, due to a misunderstanding with the Marshall family over a bill).

It continues. Kiss declared once declared that "if it's too loud, you're too old," and they've stuck by that. In 2009, the 60-something Gene Simmons and crew clocked in at 136 decibels at an Ottawa concert.

Taking up the mantle of amplifier culture these days is the experimental two-man metal band SunnO))), named for Sunn amps (Norm Sundholm, bassist for the Kingsmen, of "Louie Louie" fame, founded the company). The thick, droning tones of their music explore the textures of severely amplified guitar and bass and the sheer physicality of extreme volume. As others have done—Jimi Hendrix, in particular—SunnO))) treat their amps as if they were instruments.

Kirk Austin, a California-based amp designer, compares the amplifier to a saxophone.

"It has certain limitations and elements that can be exploited in a very musical way," he said. "It doesn't just get louder or softer, it changes its character. In that sense, you're playing it as an instrument, and you're exploiting and exploring those aberrations."

Things have quieted a bit. Townshend now has significant hearing loss, as, one suspects, do many of the original wagers of the volume wars. Even Guinness has stopped tracking who's the loudest.

Low-wattage amps have become more sought after in recent years. Don Mackrill, an amp designer and founder of Ontario-based Mack Amps, notes that PA systems have advanced to the point where guitarists can simply place a microphone to their amps, making behemoth systems—and the lugging they require—unnecessary.

"You could play Wembley Stadium with an 18-watt amp," he said.

Mackrill said he doubts that most people could tell the difference between a Marshall and an Orange amp in a blind listening test. The choice between the two could come down to whether you want the imposing rock god image that a Marshall brings, or the distinct look of the trendy Oranges.

As for those bands with their walls of Marshall stacks, he said, "that's purely image."

"Chances are they're using only one," he said. "And they may not be using any."

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