How do noise-canceling headphones actually cancel sound?

When you power up a pair of active noise-canceling headphones, a wave of calm rushes over you. That sensation comes from the headphones creating an ‘‘antiphase’’ sound wave of whatever is going on around you, effectively canceling out the ambient sound swirling around your head. This is how that works.

Think of the quietest place you’ve ever been. Was it the middle of a forest in the dead of winter, where it was too cold for even the heartiest of birds to sing? Or was it on the still heart of a lake, sitting perfectly motionless under a cloudless sky? Do you remember what nothing sounded like?

Nothing is exactly what the engineers at the Orfield Labs in Minneapolis have been replicating over the last two decades. The so-called ‘‘Quiet Room’’ at Orfield Labs is an anechoic chamber, a space custom-built to eliminate any sound from the outside world and create a space that functions at a negative decibel level. (Anechoic refers to the lack of echo produced in the space. Once a sound is created in the chamber, it is trapped by the unique soundproofing, and quickly dies.) Achieving that is no small feat, and requires concrete a foot thick, walls of reinforced steel, and a phalanx of interlocked fiberglass acoustic dampeners shaped like massive triangular prisms. The result is a room that feels disorientating, where the only sounds you can hear are the ones emanating from your own body. The subtle thump of your heart beating, the rasp of your exhale, the low grumble of your stomach and intestines.

The anechoic chamber at Orfield Labs is open to the public, and if you find yourself in Minnesota, you can immerse yourself in the deafening sound of silence for a couple hundred bucks. (It also has some musical pedigree: Before it was an acoustic testing lab, the space was home to Sound 80 Studios, where Bob Dylan recorded his 1975 classic album, Blood on the Tracks.) The results are apparently stunning — and also maddening. Since your brain uses auditory cues to do things like balance. Take away sound and your body has a hell of a time adjusting to the world.

So why build a room where sound goes to die? For one, it helps designers and engineers understand how loud products are in a vacuum. Harley-Davidson uses it to test bikes for their noise levels and learn how to make them quieter, and consumer electronics manufacturers use them to make sure their products aren’t obnoxiously loud sitting in someone’s house.

Anechoic chambers also provide a terrestrial training ground for astronauts who are preparing to float in space, which, as it happens, doesn’t have any sound either. (NASA has its own chamber at its John Glenn Research Center in Cleveland. That one is sadly not open to the public.)

The anechoic chamber at Orfield Labs isn’t even the quietest place in the world, though. That honor goes to a room at Microsoft’s headquarters in Redmond, Washington, where the tech giant spent 18 months designing and building the silent space. The ambient sound at Microsoft’s Building 87 registered an unfathomable -20dB, which puts it in the neighborhood of how loud air molecules are when they collide with each other.

Think about that the next time you find yourself marveling at the quiet around. If it isn’t knocking you off-balance, it isn’t true anechoic quiet.