Education, Latest News, Vaageesha Das

What is infrasound?

When I’m speaking, my family members are able to hear the sound waves my mouth emits. They are able to then turn these sounds into ideas and thoughts and emit sound waves so that I can hear them. The cycle continues in a seemingly simple yet beautiful manner.

Sounds come from waves traveling through a medium (e.g. air and water). The frequency of waves determines its pitch. If the wavelength (distance between the top of one wave to the next wave) is really short, the frequency will be high because a higher number of waves can pass a certain point in one second.

Since the frequency is high, the pitch will also be high. Similarly, if the wavelength is longer, the frequency will be low, and a smaller number of waves will pass a certain point in one second. Since the frequency is low, the pitch will also be low. Frequency is measured in wavelengths per second, which is also called Hertz.

Our ears are made up of the outer ear, middle ear and inner ear.

The outer ear is made up of the ear canal and the eardrum. Behind the eardrum and making up the middle ear are three tiny bones called the hammer, the anvil, and the stirrup.

The inner ear is made up of the cochlea which is shaped like a snail. It is lined with tiny hairs. Sound waves enter our ears, travel through our ear canals, and strike the eardrum, causing it to vibrate. This vibration makes the bones move. Fluid in the cochlea transfers the motion to the tiny hair cells. The movement of the hair cells is converted to electrical impulses. These electrical impulses are sent off to the brain.

Humans can typically hear sounds that are 20 Hz to 20kHz. Sound waves that have a higher frequency are called ultrasounds and those with lower frequencies are called infrasound.

Animals such as elephants can hear infrasound. They use it to communicate between groups that are separated by a long distance. Both groups start traveling parallel to each other and switch directions at the same time. Other animals with the ability to hear infrasonic waves would run away for shelter or safer places before an earthquake occurred. During ancient times, cattle running away in distress was an indication to humans that an earthquake was imminent.

Mountain lions’ growls are very low in frequency. Our eardrums cannot pick up their growls, but our brains can. That’s where the sense of dread when humans are being stalked by mountain lions comes from. Infrasound can make humans feel anxious, sad, uneasy and scared. It can also disrupt our sleeping patterns and even give us panic attacks. Infrasound produces a scared response in humans but on the bright side, the fear lets us know that something is wrong. If we aren’t scared of the mountain lion, how will we protect ourselves?

All objects have a natural frequency at which they vibrate. Objects nearby that are sensitive to the same frequency will absorb the sound waves coming from the first object and start to vibrate in return. Sound waves with a frequency of about 19 Hz have the same frequency as our eyes. This can cause us to see optical illusions whenever we are around objects emitting a frequency of about 19 Hz, resulting in us seeing “ghosts.” So, the next time you see a ghost, it’s probably just an effect due to infrasound.

Infrasound can also be used to monitor earthquakes, chart rock and petroleum formations occurring below the earth’s surface, and study mechanics of the heart. It can come from natural sources and even man-made sources, such as wind turbines. Infrasound is in a lot of places and limiting it can help us feel less scared and anxious.

VAAGEESHA DAS is a senior at Morgantown High School. 

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