The human ear is designed so that it typically perceives sound waves between 20 Hz and 20 kHz. Anything beyond this limit is called supersonic. However, this “border” is not at all common. Read about why some people hear ultrasound and others don't in the Rambler article.
Some can detect frequencies up to 22–24 kHz, while others cannot distinguish any sound even at frequencies of 15–16 kHz. For adolescents and young adults, high frequencies are often accessible but this ability decreases with age. This does not mean that ultrasound is not accessible to everyone: hearing range is a dynamic characteristic depending on age, genetics, health and living conditions. This is why some people hear a “hiss” from devices operating in the ultrasonic range, while others are not even aware of its existence.
How does sound perception work?
To understand why we hear ultrasound differently, it's important to understand how hearing aids work. Sound waves entering the ear cause the eardrum to vibrate. Vibrations are transmitted to the inner ear through a series of auditory bones—the malleus, incus, and stapes. There is the cochlea, a complex spiral-shaped organ filled with fluid and lined with thousands of hair cells. These cells act as sensors: each cell is “tuned” to a specific frequency range. High-frequency sounds are picked up by cells located at the base of the cochlea, and low-frequency sounds are picked up closer to the top of the cochlea.
The bottom line is that the cells responsible for high frequencies are subjected to the greatest stress and wear out faster than other cells. They feel the shortest and most intense vibrations, which means this particular auditory area is most often the first to be affected. If such cells are damaged or die, it is impossible to restore them – the human body does not know how to regenerate them. Therefore, the ability to hear ultrasound is very fragile and depends on the condition of the most sensitive structures of the inner ear.
Age-related changes
The most important factor influencing perception of ultrasound is age. Most people suffer from presbycusis, a gradual age-related hearing loss. Furthermore, high frequencies will go first. At the age of 20–25, the hearing limit begins to decrease from the usual 20 kHz to 18–19 kHz. At age 40, many people stop hearing sounds above 14–15 kHz, and in older adults, the upper limit may be limited to 10–12 kHz.
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This feature even has practical applications. In some countries, “mosquito alarms” are installed, emitting sounds with a frequency of about 17 kHz. Teenagers and young adults hear and feel uncomfortable, but adults and older adults usually do not react. Such installations are used to prevent night gatherings of young people near shopping centers or train stations. In this way, the natural process of hearing aging is transformed from a biological trait into a social tool.
Genetics and personal characteristics
But age is not the only factor. Genetic characteristics also play an important role. In some people, cochlear cells and nerve endings are more resistant to wear and tear, while in others, they are more susceptible to damage. Variations in genes that control hair cells and ion channels in the inner ear determine individual differences in hearing sensitivity. This explains why some people retain the ability to distinguish ultrasonic frequencies even into adulthood, while others lose this ability much earlier.
There are also differences in the structure of the ear. For some people, the eardrum and auditory bones transmit high-frequency vibrations more effectively, for others less effectively. There are also anatomical differences in cochlear structure that influence cognition. Together, this creates a unique “hearing profile” for each person. That's why two people with the same lifestyle can react differently to the same sound.
Influence of external factors
Hearing is very sensitive to the conditions in which we live. Usually it is affected by exposure to noise. Prolonged exposure to loud noise – such as listening to music at high volume with headphones, operating machinery, construction noise or military service – will damage hair cells, especially those responsible for sensing high frequencies. The organization says the losses may be irreversible NIH.
There are also other factors. Some medications are ototoxic, causing cell damage in the inner ear. For example, these include aminoglycoside antibiotics or drugs used in chemotherapy. Infections accompanied by high fever and intoxication can also reduce hearing sensitivity. Thus, the ability to hear ultrasound is not only a matter of age and genetics but also the result of the entire “biography” of the body.
Cognitive threshold and “training effect”
It has been suggested that hearing can be “trained” so that a person perceives a wider range of sounds. In fact, practice helps the brain to better distinguish nuances and tones within the available range, but cannot restore the lost sensitivity to ultrasound. Musicians, sound engineers and people working in the field of acoustics actually retain the ability to distinguish high frequencies for longer. Their brains interpret audio signals better, and they notice things that are difficult for the average listener to understand.
However, even their biological limits remain unchanged: if the cells that sense ultrasound are destroyed, no amount of training can restore them. In this sense, hearing is similar to vision: you can perceive colors and shades better, but if the retina is damaged the physical range is still limited.
Thus, the ability to hear ultrasound depends on many factors. Young people often perceive sounds with frequencies of 20 kHz or more, and in adults and the elderly, the upper limit gradually decreases. Genetic characteristics and health status determine individual differences: a person at the age of 40 can still distinguish high-pitched sounds, while others at the age of 20 have poorer hearing. Lifestyle plays an important role: noise, medications and illness can accelerate hearing loss.
We've previously written about what “impossible” colors are – and who can see them.
