What Is Infrasound, and Why Should You Care?

Have you ever felt a strange sense of unease in an area, but you couldn’t put your finger on what was causing it? Or maybe you went to the cinema for a truly immersive horror movie and found yourself unable to shake that anxious feeling. There’s a good chance you were experiencing infrasound.

What Is Infrasound?

Infrasound (aka subsonic sound) is the term used to describe sounds that are so low that we can’t hear them. Humans can hear within a range of around 20Hz to 20,000Hz (audible spectrum), and infrasound refers to sound waves below the 20Hz threshold.

Although we can’t hear infrasound at all, we can still feel or “sense” it, in a way. Our bodies can feel it as physical vibrations in some parts of the body. After all, these inaudible low-frequency vibrations can travel long distances and have a lot of energy, sufficient to pass through some materials, so it would be odd if they didn’t have any effect on us. More on that shortly.

Interestingly, infrasound isn’t some exotic, uncharted frequency. It’s naturally occurring, just like any other sound. Natural phenomena like earthquakes and volcanic eruptions and human activities like explosions, drilling, and industrial machinery all produce infrasound. Moreover, we use infrasound sensors to detect earthquakes.

An example of infrasound in action that you might have heard of is some species of whales, like the blue whale, using infrasonic waves to communicate. Unlike us, they can both hear and “speak” in infrasound. Cool!

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What Does The Hz-KHz Range For Speakers And Headphones Mean?

If you’ve looked at high-end headphones or speakers, you’ve probably noticed numbers on the spec sheet that read something like “20Hz-20KHz.

The Effects of Infrasound on Humans

We know that audible low-frequency (bass) sound waves can already have a profound effect on us, both physically and emotionally. Listening to powerful bass in music is an enjoyable experience for many of us. However, while more research is still needed, it’s believed that prolonged listening sessions to powerful bass can cause discomfort and trigger cardiovascular issues, at least in some people (just ask my mom).

Infrasound has a similar, potentially more potent effect. One source notes that infrasound can evoke feelings of nausea, aversion to an area, sleep disturbances, and even pain. In another report, a case was described in which a fan created a standing wave at a frequency of 19Hz, allegedly causing dizziness, anxiety, and other similar symptoms, which disappeared upon shutting the fan down. Some even believe that the presence of infrasound in some areas is what makes us believe that they’re “haunted.”

In one experiment, 17.5Hz sounds were played to audiences at a concert, with 22% of participants reporting unease, fear, and revulsion. A different study found no observable behavioral changes caused by infrasound, though participants reported greater feelings of weakness. Ultimately, more research is still needed to get concrete answers about the effects of infrasound and its health implications.

What’s the Point of Infrasound?

If infrasound causes nothing but negative feelings like anxiety and fear, why would we want to use it? For one, we still don’t fully understand it, and it’s entirely possible that specific frequencies within infrasound could have more positive effects, like repairing muscle damage—kind of like how cats purr to heal.

The second reason why we might want to use infrasound is entertainment. Apparently, sound engineers use infrasound in horror movies in combination with other sounds to evoke feelings of distress, fear, and helplessness. If you’re a fan of the genre, I can see the appeal!

How Low Can You Go?

Most headphones and speakers on the market today focus on the 20–20kHz audible range. However, some models can go lower. Some large, powerful subwoofers can go below 20Hz. For example, the Klipsch RP-1600SW‘s frequency range starts at 14.5Hz. Imagine placing that against your couch! In the headphones segment, the Sony MDR-M1 can go as low as 5Hz.

There’s even a special type of subwoofer designed just to reproduce infrasonic sounds called a rotary subwoofer. It’s essentially a modified fan attached to a voice coil, which responds to an audio signal and adjusts the pitch of the blades. Although these specialized subwoofers are fun to experiment with, they’re also very noisy and not practical at all.

While infrasound is certainly fascinating, more research is needed to fully understand its potential and applications. If you’re a fan of horror and want to experiment with infrasound at home, you could use headphones or speakers capable of producing frequencies below 20 Hz. Personally, I would prioritize sound quality, durability, and comfort when choosing audio equipment, but if you find a pair that meets these criteria and can reproduce infrasound, I’d say go for it!