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Sounds can be classified into two groups: those that fall within our hearing range and those that lie beyond it.
The human ear is capable of detecting sounds within the frequency range of 20 hertz (Hz) to 20 kilohertz (kHz). Sounds below this threshold are considered infrasonic, while those above are ultrasonic. Unfortunately, our ears are unable to perceive either of these types of sounds.
In addition to the sounds outside our hearing range, there is also a subset of sounds between 20 Hz and 20 kHz that we cannot detect. These sounds should be audible under normal circumstances, but various factors prevent us from hearing them.
This article highlights 10 loud sounds that remain undetectable to us.
10. The Sound of Dog Whistles
Standing next to someone using a dog whistle, all you would hear is a faint hissing noise, even though these whistles can actually produce quite loud sounds.
Dog whistles operate at frequencies above our hearing range. The typical human ear detects sounds only up to 20 kHz, and for those with sensitive hearing, it may extend to 23 kHz (with 1 kHz being equal to 1000 Hz). However, dogs can hear up to 45 kHz. Depending on the design, dog whistles emit frequencies between 23 kHz and 45 kHz.
That said, it’s not advisable to use dog whistles for amusement. Just as you’d be startled by someone blowing a loud whistle near you for an extended period, dogs too can become distressed by continuous dog whistle sounds. Additionally, blowing a dog whistle too loudly near your dog could attract other dogs, which you probably don’t want to happen.
9. The Sound of the Sun
Picture a world filled with police sirens, all blaring at once. Now amplify that noise by 10,000 times. That’s the intensity of the sun's sound.
However, since the sun is 92 million miles away, by the time the sound reaches us, it would be much quieter. The sound we would hear would be a dull roar at about 100 decibels, comparable to the noise level of a rock concert. Still, that's quite loud.
Researchers believe that such constant noise would have hindered the development of speech. Even if we did manage to communicate, we would need to shout just to talk to someone nearby. Fortunately, this deafening noise would only occur during the day, meaning we'd have some peace and quiet at night.
Fortunately for our ears, we don’t hear the sun. Why? Because sound requires air to travel, and space is void of air.
8. The Range from 12 kHz to 20 kHz
Everyone over the age of 18 experiences a condition known as presbycusis, which is the medical term for 'age-related hearing loss.'
While humans can generally hear sounds between 20 Hz and 20 kHz, most of us lose the ability to hear frequencies above 17.4 kHz as soon as we turn 18. By the time we reach 40, we struggle to hear anything above 15 kHz, and by age 50, we can't hear frequencies above 12 kHz.
Some businesses have taken advantage of this by using devices that emit irritating sounds between 17.4 and 20 kHz to prevent teens from loitering near their stores. However, teens have responded by using ringtones in these frequencies, enabling them to get calls in class without their teachers noticing.
7. Bat Echolocation
Despite what we’ve been told, bats can indeed see. However, they don’t always depend on their sight to navigate—they rely on sound instead.
More than half of all bat species emit ultrasonic sounds ranging from 20 kHz to 200 kHz through their mouths or nostrils. They then listen for the echoes that bounce off nearby objects, helping them detect obstacles and locate food.
The volume of these sounds can vary but generally falls between 50 and 120 decibels, which is louder than a smoke detector going off right next to you.
6. Rocket Launches
Rockets are extremely loud, but did you know they could be even louder?
Rockets produce sounds that are beyond our hearing range. Unlike bats, which emit sounds above the limits of human hearing, rockets generate infrasonic sounds, which are below the threshold of what we can perceive.
Though we can't hear infrasonic sounds, special equipment allows us to detect and record them. By speeding up the playback, we can get a sense of what they might sound like. This technique was used by researchers when they recorded sound from the November 2009 Space Shuttle Atlantis launch. The recording was sped up 250 times to make it audible.
5. Sperm Whale Sounds
Sperm whales produce a range of sounds, including infrasonic, ultrasonic, and those within the human hearing range.
What all three types of sounds have in common is their incredible loudness. These sounds are so intense that scientists believe sperm whales may use them to stun their primary prey, giant squids, rendering them unconscious before they are eaten.
Although research is still ongoing, experiments have shown that sperm whales do not use ultrasonic sounds to stun their prey. However, it's still unclear whether they rely on infrasonic or audible sounds for this purpose.
It's also worth noting that whales might use sound to harm their prey in ways other than stunning them. For example, they could use sound to rupture blood vessels or to confuse and disorient their prey, making it harder for them to detect the whale’s approach.
4. Volcanic Eruptions
Volcanoes produce a tremendous amount of noise when they erupt. But did you know that a large portion of that noise remains inaudible to us?
This is because some of the sounds fall into the infrasonic range, which is below the frequencies our ears can detect. Interestingly, infrasound—especially at high volumes—can be more hazardous than ultrasound, as it travels much further. In fact, infrasound-detecting stations often pick up the sounds of distant volcanoes and use these signals to analyze the nature of eruptions.
But it's not just during eruptions that volcanoes produce infrasonic sounds. They emit these low-frequency sounds continuously, and researchers have been tracking them to monitor changes in lava levels and help predict future eruptions.
3. Burglar Alarms
Photo credit: Wikimedia Commons
Have you ever been curious about how motion-sensing lights, alarms, and security systems function? They rely on ultrasound.
Most ultrasonic security systems use sound waves within the range of 30 kHz to 50 kHz, which are beyond the hearing threshold. Additionally, ultrasonic waves can’t pass through solid objects like infrasonic waves can, making them ideal for detecting humans, animals, or other objects in a given space.
There are two main types of ultrasonic security systems. One type listens for ultrasonic sounds in the environment, while the other emits ultrasonic sounds and waits for the return signals. When the system detects any variation in the ultrasonic waves within its range, it instantly recognizes the presence of a new object or creature, triggering an alert.
2. Sound Weapons
Although we cannot hear infrasonic or ultrasonic sounds, we can certainly feel them, especially when they're loud. Just like any sound within our hearing range that becomes uncomfortable over time, these inaudible sounds can also create discomfort and may even cause significant internal harm.
Sound (or sonic) weapons operate by targeting a person or group with either infrasonic or ultrasonic sounds. Various countries have used infrasonic sound weapons, which tend to have milder effects compared to ultrasonic ones, against protesters, who often remain unaware they are being targeted, even after the effects set in.
People exposed to infrasonic sound weapons typically experience sudden discomfort, followed by symptoms like vomiting or diarrhea. Ultrasonic weapons have similar effects but can also cause headaches, form bubbles inside tissues, and raise the temperature of cells, leading to tissue damage.
1. Elephant Rumbles
In the 1980s, scientists discovered that elephants use infrasound to communicate with one another over distances as long as 10 kilometers (6.2 miles). While it's not surprising that infrasound can travel vast distances, it was also revealed that elephants utilize it to communicate with elephants nearby.
Female elephants, who lead their herds, use this infrasound to guide the other members of the group. Mothers rely on it to stay connected with their calves, and male elephants use it to send warnings to other males during the mating season.
Elephants typically produce infrasonic sounds between 1 Hz and 20 Hz, which are inaudible to us. However, they also make audible rumbles within our hearing range. The reason behind this behavior remains a mystery.
