Glossary
presbycusis
The gradual loss of hearing that comes with age, affecting the highest frequencies first and most severely. It is the reason a tone can be plainly audible to one person and completely inaudible to another standing beside them, with no device and no deception involved.
The slope is continuous rather than a cliff, and the popular claim that nobody over 25 can hear above 16 kHz is not supported by audiometry. In a 2021 study of 162 adults aged 21 to 70, thresholds at 16 kHz averaged about 25 dB HL in the 21–30 group and 50 to 55 dB HL between 31 and 60. In the 61–70 group fewer than one in five gave any response at 16 kHz, and none had a measurable response at 18 kHz. Just over half of those aged 21 to 30 still responded at 20 kHz.
Documented real-world example: this ordinary biology is the entire operating principle of the Mosquito, an anti-loitering device sold since 2005 that emits roughly 17.4 kHz so that younger people are driven away while older passers-by mostly notice nothing.
Related terms: the Mosquito, microwave auditory effect, phantom sensations