The world of sound holds specific frequencies imperceptible to some but audible to others. This phenomenon sparks curiosity, especially when younger individuals can hear sounds that adults cannot. Understanding this unique hearing experience reveals how our ears process sound and how this ability changes over a lifetime.
How Our Hearing Works
Sound travels as waves, with frequency determining the pitch we perceive. These waves enter the outer ear and travel through the ear canal, causing the eardrum to vibrate. The vibrations then move through three tiny bones in the middle ear—the malleus, incus, and stapes—which amplify the sound. The stapes pushes against the oval window, a membrane connecting to the cochlea, a snail-shaped, fluid-filled structure in the inner ear.
Inside the cochlea, thousands of microscopic hair cells line the basilar membrane. These specialized sensory receptors convert mechanical vibrations into electrical signals that the brain interprets as sound. The basilar membrane’s stiffness varies along its length; the base, near the oval window, is stiffer and more sensitive to high-frequency sounds, while the apex responds to lower frequencies. This arrangement means different parts of the cochlea vibrate for different pitches, with high frequencies activating hair cells closer to the entrance. For young people, the typical human hearing range extends from approximately 20 Hertz (Hz) to 20,000 Hz.
The “Mosquito Tone” and Its Uses
A specific high-frequency sound, known as the “Mosquito tone,” is primarily audible to younger individuals. This sound typically falls around 17 kilohertz (kHz) or higher, a frequency most adults cannot perceive. The “Mosquito” device was developed in 2005 by Howard Stapleton in the United Kingdom as a security measure.
The device was designed to deter loitering teenagers by emitting a continuous, high-pitched sound only they could hear, making areas uncomfortable. This application expanded, with the sound adopted as “Mosquito ringtones” for mobile phones. Teenagers used these ringtones to receive calls or messages in classrooms or other settings without adults being aware, as the sound was beyond their hearing range. The use of such devices has raised ethical concerns.
Why Adults Can’t Hear It
The primary reason adults cannot hear these high-frequency sounds is presbycusis, or age-related hearing loss. This condition involves a gradual deterioration of the auditory system, particularly affecting the ability to perceive higher frequencies. The delicate hair cells within the cochlea, especially those at the base responsible for high-frequency detection, can become damaged or degenerate over time.
Unlike other cells in the body, these hair cells in humans do not regenerate once damaged or lost. This progressive loss means that as individuals age, their upper hearing limit steadily decreases. In addition to natural aging, cumulative exposure to loud noises throughout a lifetime can also contribute to this high-frequency hearing loss, further impacting the ear’s sensitivity to these pitches.