A college student just proved you can actually unring a bell
A biomedical engineering student at the University of Wisconsin-Madison, Nguyen is the winner of the GE Unimpossible Innovation Challenge, a contest that prompts students to dispel a popular idiom with the help of physics and chemistry.
Nguyen's design took the top spot thanks to his clever use of destructive interference.
The technique involves cancelling out one sound wave by blasting it with another wave of the opposite sign. When the two waves collide, they add up to zero - silence. In everyday life, destructive interference is what lets your noise-cancelling headphones muffle nearby chatter.
Nguyen placed the bell one one side of an anechoic chamber - essentially a foam-padded room that traps any sound - and placed a microphone at the other end. In between them was a speaker, which Ngyuyen pointed at the bell. Whatever sound the bell produces, the speaker is programmed to emit the acoustic opposite.
When the system works properly, the microphone picks up nothing. The bell gets unrung.
Nguyen says he prepared a long list of idioms for the competition. "Unring a bell" just happened to stand out. "It was the coolest one that I thought I could debunk in terms of the impossibility of it," he says.
Unringing a bell and cancelling out headphone noise aren't the only uses for destructive interference, he explains. "You can use this technology to reduce the noise coming from MRI machines or jet engines." Most of the time the noise won't technically be absent, but it will fall below the threshold for human hearing or at least below the regulatory limits set by specific industries.
Proving the English language wrong just happens to be a fun use of the technology.