Infrasound: What lies above — and below

“Everyday Infrasound in an Uncertain World”

Even though you can’t hear it, infrasound fills the air. And because the atmosphere doesn’t absorb it like regular sound, infrasound comes from hundreds, if not thousands, of miles away. If humans could perceive frequencies lower than 20 Hz, then changing ocean currents, wildfires, turbines, receding glaciers, industrial HVACs, superstorms, and other geophysical and anthropogenic sources from across the planet would be part of the quotidian soundscape of our lives, wherever we might be.

I made this recording in the small town of Amherst, Massachusetts. I sped it up by a factor of 60: 24 hours becomes 24 minutes, raising the pitch by almost six octaves and making infrasound audible. Although we might think we hear something familiar when listening to this album, only its very highest sounds could have been detected with an unaided ear.

Since ordinary microphones cannot pick up frequencies this low, I constructed infrasonic “macrophones.” If a microphone amplifies small sounds, a macrophone brings large sounds with long wavelengths into our perceptual range. Each consists of a wind-noise reduction array leading to a microbarometer and a data recorder. I based the design on what the Comprehensive Nuclear Test Ban Treaty Organization uses to detect distant warhead tests. In this case, however, we’re listening to a planet in transition.

This work germinated in Oregon amid an unprecedented season of wildfires. It developed along with my chronic illness, Lyme, a tick-borne disease that has become more common as a result of warming winters. My young son watched over the recording process; our ancestors mined coal. For me, it’s not just a matter of hearing what is novel to the human ear, but of encountering those agencies greater than our own that connect us through the atmosphere.

[via the Washington Post]