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Freepenguin via Wikimedia Commons // CC BY-SA 3.0

7 Whispering Galleries From Around the World You Can Visit

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Freepenguin via Wikimedia Commons // CC BY-SA 3.0

Curving walls and towering domes can produce great architectural effects. But in some cases, their acoustic qualities are even more impressive.

A whispering gallery takes advantage of the properties of certain curved spaces to offer a unique sound experience. To know if you’ve found one, stand facing a sloping surface while a friend does the same several yards away. When you whisper into the wall, your partner should hear your voice as clearly as if you were standing next to them.

This seemingly magical phenomenon can be explained by whispering gallery waves. When whispers hit the circular or semicircular surface of the gallery, those vibrations cling to the surface and “creep” along the gently curving path. The slight angle of the structure keeps sound waves from dispersing out to either side. When the message reaches its intended listener, it’ll have barely diminished during the journey.

Whispering galleries can be found in some of the most iconic landmarks on Earth. Here are seven enchanting examples.

1. ST. PAUL’S CATHEDRAL // LONDON

 
St. Paul’s in London is home to perhaps the most famous whispering gallery, a circular walkway perched 257 steps above the floor and around the perimeter of the cathedral's famous dome. At nearly 100 feet up, the balcony is not for the faint of heart, but if you’re not ready for a trek yourself, you can send your whispers for a spin. Although architect Sir Christopher Wren didn't design the balcony for its acoustic properties, they've since become well-known: In the late 1870s, the British physicist Lord Rayleigh used it as the setting for groundbreaking research on acoustics. He was the first person to propose the existence of “whispering gallery waves” that travel along a curvilinear path. Today visitors to the cathedral can recreate Lord Rayleigh’s experiment as it was done 140 years ago.

2. THE GOL GUMBAZ MAUSOLEUM // BIJAPUR, INDIA

Santoshsmalagi via Wikimedia Commons // CC BY-SA 3.0

 
Vijayapura, India is home to the 17th century Gol Gumbaz Mausoleum, final resting place of Sultan Mohammed Adil Shah. Its name literally means “circular dome,” and the distinctive topper forms one of India’s most famous whispering galleries. Visitors walking along the balcony that rings the dome’s edge can have the chance to test it out. As is the case at St. Paul’s, sound vibrations hug the walls of the walkway while the dome curling above keeps wayward sound waves contained. A whisper originating at one point can be heard on the opposite side of the 44-foot wide space.

3. GRAND CENTRAL STATION // NEW YORK CITY

 

At most spots in Grand Central Terminal, maintaining a conversation with someone standing 30 feet away during rush hour is an impossible task. There’s one place where that doesn't apply. The herringbone-tiled roof arching outside the Grand Central Oyster Bar creates a whispering gallery in the middle of Manhattan. Rather than transmitting the whispers horizontally, sounds waves shoot up one of the four corners, along the arched surface of the ceiling, and back down the pillar on the opposite side. Travelers passing through Grand Central will know they’ve found the right spot when they see what looks like tourists talking to themselves in the corners.

4. THE BENCH OF WHISPERS // SANTIAGO DE COMPOSTELA, SPAIN

 

Not all whispering galleries are located beneath domes. Sometimes the back of a semi-circular bench will do. After this granite bench was constructed in a park in Spain around 1916, it didn’t take long for couples to catch on to its unique sound effects. Word of the location spread among young singles, and it soon became a popular meeting place for unmarried couples looking for privacy. In a time when the courting process was strictly monitored for indecent behaviors (i.e. touching, or even speaking), the Lovers Bench, or the Bench of Whispers, was the perfect solution. From afar, two people sitting on opposite ends can appear to be minding their own business, when in reality they’re exchanging illicit whispers of affection.

5. THE ECHO WALL IN THE TEMPLE OF HEAVEN // BEIJING

Daniel Case via Wikimedia Commons // CC BY-SA 3.0

 

Erected in the 15th century, the Temple of Heaven long served as a setting for prayer ceremonies asking for good harvests. Today the UNESCO World Heritage Site is a popular Beijing tourist destination. The Imperial Vault of Heaven, located south of the Temple’s main structure, is surrounded by a smooth, round wall—known as the Echo Wall—that’s heard half a millennium's worth of whispers. To get the full experience, visitors should plan to arrive early to avoid being drowned out by crowds of tourists with the same idea.

6. THE WHISPERING ARCH (FLÜSTERBOGEN) // GÖRLITZ, GERMANY

Andreas Praefcke via Wikimedia Commons // CC BY 3.0

 
The whispering gallery in Görlitz, Germany is easy to miss. Instead of an ancient church or mausoleum, it’s located in the entryway of a regular building in the town's Lower Market area. The channeled stone arch above the doorway at house No. 22 carries sound waves from one end to the other. The Flüsterbogen, or “Whispering Arch,” as it's known, is one of many charming attractions in the medieval German town.

7. THE U.S. CAPITOL BUILDING // WASHINGTON D.C.

 
The dome of the U.S. Capitol building is more than a distinctive silhouette against the Washington D.C. skyline. When it was first constructed, the structure helped amplify the voices of members of Congress, long before microphones appeared on the scene. According to one urban legend, John Quincy Adams pretended to be asleep at his desk while listening to echoes of his opponents’ conversations happening in different parts of the room. This so-called “whisper spot," now part of he National Statuary Hall, is now designated by an official plaque on the floor marking the location where the former president sat during his time in Congress. According to the Architect of the Capitol, the whispering gallery effect can still be heard in sections of the hall, but the building’s acoustic properties are less pronounced than they were prior to its renovation at the turn of the 20th century.

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iStock // Ekaterina Minaeva
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Man Buys Two Metric Tons of LEGO Bricks; Sorts Them Via Machine Learning
May 21, 2017
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iStock // Ekaterina Minaeva

Jacques Mattheij made a small, but awesome, mistake. He went on eBay one evening and bid on a bunch of bulk LEGO brick auctions, then went to sleep. Upon waking, he discovered that he was the high bidder on many, and was now the proud owner of two tons of LEGO bricks. (This is about 4400 pounds.) He wrote, "[L]esson 1: if you win almost all bids you are bidding too high."

Mattheij had noticed that bulk, unsorted bricks sell for something like €10/kilogram, whereas sets are roughly €40/kg and rare parts go for up to €100/kg. Much of the value of the bricks is in their sorting. If he could reduce the entropy of these bins of unsorted bricks, he could make a tidy profit. While many people do this work by hand, the problem is enormous—just the kind of challenge for a computer. Mattheij writes:

There are 38000+ shapes and there are 100+ possible shades of color (you can roughly tell how old someone is by asking them what lego colors they remember from their youth).

In the following months, Mattheij built a proof-of-concept sorting system using, of course, LEGO. He broke the problem down into a series of sub-problems (including "feeding LEGO reliably from a hopper is surprisingly hard," one of those facts of nature that will stymie even the best system design). After tinkering with the prototype at length, he expanded the system to a surprisingly complex system of conveyer belts (powered by a home treadmill), various pieces of cabinetry, and "copious quantities of crazy glue."

Here's a video showing the current system running at low speed:

The key part of the system was running the bricks past a camera paired with a computer running a neural net-based image classifier. That allows the computer (when sufficiently trained on brick images) to recognize bricks and thus categorize them by color, shape, or other parameters. Remember that as bricks pass by, they can be in any orientation, can be dirty, can even be stuck to other pieces. So having a flexible software system is key to recognizing—in a fraction of a second—what a given brick is, in order to sort it out. When a match is found, a jet of compressed air pops the piece off the conveyer belt and into a waiting bin.

After much experimentation, Mattheij rewrote the software (several times in fact) to accomplish a variety of basic tasks. At its core, the system takes images from a webcam and feeds them to a neural network to do the classification. Of course, the neural net needs to be "trained" by showing it lots of images, and telling it what those images represent. Mattheij's breakthrough was allowing the machine to effectively train itself, with guidance: Running pieces through allows the system to take its own photos, make a guess, and build on that guess. As long as Mattheij corrects the incorrect guesses, he ends up with a decent (and self-reinforcing) corpus of training data. As the machine continues running, it can rack up more training, allowing it to recognize a broad variety of pieces on the fly.

Here's another video, focusing on how the pieces move on conveyer belts (running at slow speed so puny humans can follow). You can also see the air jets in action:

In an email interview, Mattheij told Mental Floss that the system currently sorts LEGO bricks into more than 50 categories. It can also be run in a color-sorting mode to bin the parts across 12 color groups. (Thus at present you'd likely do a two-pass sort on the bricks: once for shape, then a separate pass for color.) He continues to refine the system, with a focus on making its recognition abilities faster. At some point down the line, he plans to make the software portion open source. You're on your own as far as building conveyer belts, bins, and so forth.

Check out Mattheij's writeup in two parts for more information. It starts with an overview of the story, followed up with a deep dive on the software. He's also tweeting about the project (among other things). And if you look around a bit, you'll find bulk LEGO brick auctions online—it's definitely a thing!

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Name the Author Based on the Character
May 23, 2017
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