Sound tourism is a real thing, and the Clapping Circle at Purdue University in West Lafayette is one of the hobby’s most popular Midwest stops.
Academy Park sits roughly in the middle of Purdue’s campus, just to the south of Heavilon Hall and to the northwest of the Purdue Memorial Union. Academy Park is a five-acre arboretum of carefully manicured grass, paved pathways and lots of big trees. On paper, Purdue designers wanted to pay homage to the Aristotelian intellectual ideal of the “smart stroll,” as advertised by Socrates, then Plato, and then Aristotle. Somewhere in the park there’s a philosophical musing etched into an obelisk concerning this tradition.
It’s a lovely idea, but in reality Academy Park replaced a mishmash of parking lots and narrow streets ripping through the heart of the campus in 1997. Cracked asphalt and the hot stink of car exhaust are not fodder for eager minds. Trees, benches, and gentle hillsides make up Academy Park, perfect for an outdoor classroom (Plato would approve). The half-dozen paths shooting across the park meet at a center patio, a (roughly) 50-foot circle of paving bricks commonly called the Clapping Circle.
Throughout the day, visitors, students, and even faculty will suddenly stop and clap their hands sharply in the circle, amused at the landmark’s odd acoustics. Odd is right. You’re outdoors, in a wide open park, but CLAP! your hands, and you’ll get an echo in return. This acoustic oddity also makes it possible to lie in the surrounding grass, tuck your hands behind your head, and listen to flashes of chatting as people pass through the circle. It’s delightful and disorienting at the same time.
This feature was not the intention of any architects, civil engineers, or landscape designers. If so, it would mean planning for decades and spending millions of dollars…so people could make odd clapping echoes. The echo likely comes from the placement of the steep stairs leading up to Heavilon Hall to the north of the circle and the surrounding trees.
While clapping in the circle’s center, sound bounces off the concrete stairs. Because of its dissimilarity from the acoustic medium of the sound wave (air), concrete absorbs little of that wave (in other words, concrete is harder than air, so sound bounces off it). On the other hand, trees provide a light, uneven surface for sound waves, easily absorbing them.
