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Why Is Seattle's CenturyLink Field So Loud?

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If you've ever watched a Seattle Seahawks home game on TV, you've surely heard the commentators talk about how loud it is at CenturyLink Field. ("By golly, Jim, it's loud in here," or something to that effect.) It's true—the stadium is remarkably noisy. Last season it was awarded the Guinness World Record for the loudest open-air stadium in the world when it reached 137.6 decibels during a Monday night game against the Saints. Is that loud? Yeah, it's pretty loud.

This noise isn't just for setting world records. Because of the cacophony of shrieks, hoots, and hollers, the Seahawks have the best home field advantage of any team in the NFL. Opposing offenses can't hear play calls, and because of this they rack up false start penalties at an extremely high rate.

But why is CenturyLink so loud?

Is it because Seattle's fans love their team more than you love yours and they're able to yell louder because of this? Are their lungs more powerful because of the crisp Pacific Northwest air, which allows them to push out more impressive screams? In short: not exactly.

While Seattle's fans are enthusiastic, CenturyLink reaches those record-breaking decibel levels because of its design. Paul Allen, the billionaire owner of the team, explicitly wanted a stadium that would be loud, so he approached architect Jon Niemuth with this request. The place, which was built in 2002, is constructed to be loud.

CenturyLink sits on the smallest footprint of any stadium in the NFL. Despite this, it's not small. It holds 67,000 fans, and they are piled steeply to form a tube of swirling sound. As Niemuth told Sports Illustrated, “If you’re trying to create a container, the bigger the cup you can make it the better.”

Sound escapes upwards in open-air stadiums (it's why domes are always so loud), so to counter this, about 70% of CenturyLink's seats are covered by canopies. These canopies are shaped like parabolas, and they point the sound back at the field. Adding to all this are the aluminum bleachers that fill the stands by the north end zone. When stomped on, these create an almighty racket.

Put all these factors together, and you have a recipe for one loud stadium.

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Big Questions
What Causes Sinkholes?
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Mark Ralston/AFP/Getty Images

This week, a sinkhole opened up on the White House lawn—likely the result of excess rainfall on the "legitimate swamp" surrounding the storied building, a geologist told The New York Times. While the event had some suggesting we call for Buffy's help, sinkholes are pretty common. In the past few days alone, cavernous maws in the earth have appeared in Maryland, North Carolina, Tennessee, and of course Florida, home to more sinkholes than any other state.

Sinkholes have gulped down suburban homes, cars, and entire fields in the past. How does the ground just open up like that?

Sinkholes are a simple matter of cause and effect. Urban sinkholes may be directly traced to underground water main breaks or collapsed sewer pipelines, into which city sidewalks crumple in the absence of any structural support. In more rural areas, such catastrophes might be attributed to abandoned mine shafts or salt caverns that can't take the weight anymore. These types of sinkholes are heavily influenced by human action, but most sinkholes are unpredictable, inevitable natural occurrences.

Florida is so prone to sinkholes because it has the misfortune of being built upon a foundation of limestone—solid rock, but the kind that is easily dissolved by acidic rain or groundwater. The karst process, in which the mildly acidic water wears away at fractures in the limestone, leaves empty space where there used to be stone, and even the residue is washed away. Any loose soil, grass, or—for example—luxury condominiums perched atop the hole in the ground aren't left with much support. Just as a house built on a weak foundation is more likely to collapse, the same is true of the ground itself. Gravity eventually takes its toll, aided by natural erosion, and so the hole begins to sink.

About 10 percent of the world's landscape is composed of karst regions. Despite being common, sinkholes' unforeseeable nature serves as proof that the ground beneath our feet may not be as solid as we think.

A version of this story originally ran in 2014.

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Big Questions
How Are Speed Limits Set?
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When driving down a road where speed limits are oppressively low, or high enough to let drivers get away with reckless behavior, it's easy to blame the government for getting it wrong. But you and your fellow drivers play a bigger a role in determining speed limits than you might think.

Before cities can come up with speed limit figures, they first need to look at how fast motorists drive down certain roads when there are no limitations. According to The Sacramento Bee, officials conduct speed surveys on two types of roads: arterial roads (typically four-lane highways) and collector streets (two-lane roads connecting residential areas to arterials). Once the data has been collected, they toss out the fastest 15 percent of drivers. The thinking is that this group is probably going faster than what's safe and isn't representative of the average driver. The sweet spot, according to the state, is the 85th percentile: Drivers in this group are thought to occupy the Goldilocks zone of safety and efficiency.

Officials use whatever speed falls in the 85th percentile to set limits for that street, but they do have some wiggle room. If the average speed is 33 mph, for example, they’d normally round up to 35 or down to 30 to reach the nearest 5-mph increment. Whether they decide to make the number higher or lower depends on other information they know about that area. If there’s a risky turn, they might decide to round down and keep drivers on the slow side.

A road’s crash rate also comes into play: If the number of collisions per million miles traveled for that stretch of road is higher than average, officials might lower the speed limit regardless of the 85th percentile rule. Roads that have a history of accidents might also warrant a special signal or sign to reinforce the new speed limit.

For other types of roads, setting speed limits is more of a cut-and-dry process. Streets that run through school zones, business districts, and residential areas are all assigned standard speed limits that are much lower than what drivers might hit if given free rein.

Have you got a Big Question you'd like us to answer? If so, let us know by emailing us at bigquestions@mentalfloss.com.

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