Some people, particularly younger individuals, can clearly hear high-pitched sounds that others, especially adults, remain completely oblivious to. This difference in auditory perception is not selective listening, but rather a reflection of natural changes in human hearing as we age.
The Science of Age-Related Hearing
The human ear can perceive sounds from about 20 Hz to 20,000 Hz. This range changes throughout life, as individuals experience a natural decline in the ability to hear higher frequencies, known as presbycusis. This decline is due to changes in the inner ear, including the deterioration and loss of tiny sensory hair cells in the cochlea. These hair cells convert sound vibrations into electrical signals for the brain and do not regenerate once damaged or lost.
High frequencies are the first to be affected because they are processed in the initial part of the cochlea, which is more prone to wear. While a person in their twenties might hear up to 17,000 Hz or more, this sensitivity can decline to around 16,000 Hz by their thirties, and further to about 12,000 Hz by their fifties. Sounds from 17,000 Hz to 20,000 Hz are those only teenagers or young adults can perceive, with most people over 18 or 25 losing this ability. This natural auditory shift is a normal part of aging, not a disease, and affects both ears.
Practical Applications of High-Frequency Sound
Differing hearing capabilities across age groups have led to devices utilizing high-frequency sounds. One example is “The Mosquito” device, known as a “teen repellent” or anti-loitering alarm. This machine emits a high-frequency sound, around 17.4 kHz, designed to be audible and irritating to younger individuals, while unnoticed by most adults over 25.
Such devices deter loitering and reduce anti-social behavior in public or private spaces. By creating an annoying, repetitive tone audible to younger people, the device encourages them to disperse without confrontation. Teenagers have also leveraged this age-based hearing difference by using high-frequency sounds as “teen ringer” phone tones, allowing their phones to ring in class undetected by older teachers.
Perception, Limitations, and Safety
While high-frequency sounds are less perceptible to older adults, individual hearing abilities vary. Some older individuals might still detect these sounds, depending on their personal hearing health. For those who can hear them, these high-pitched tones are described as annoying or irritating rather than pleasant.
The effectiveness of high-frequency deterrents can be limited by various factors. The sound can be blocked by obstacles, and its range is not infinite; “The Mosquito” can reach up to 30 meters (approximately 100 feet). While considered safe at exposure levels, prolonged or excessively loud exposure to any sound, including high frequencies, can be harmful. Concerns have been raised about discomfort, headaches, or other effects from continuous exposure, especially for small children and infants who may not be able to leave the area. Careful consideration of placement and exposure duration is important when using high-frequency sound devices.