By now just about everybody has heard of "The Mosquito," a device developed in Britain a few years ago that is designed to repel loitering teenagers by emitting an annoying, high-frequency sound that only they can hear. The device takes advantage of the natural tendency of people's ears to lose the ability to hear very high-pitched sounds as they age; as such, the noises these devices emit do not bother adults. The device has been deployed at convenience stores, movie theaters and other establishments where teenagers typically congregate in order to drive kids away without affecting paying adult customers.
The device, which has since made its way to the United States and Canada, is controversial. Some people consider its use a cruel form of age descrimination, while others have questioned the health effects of its exposure to young peoples' hearing. Teens, for their part, have begun to use the high-frequency sounds that the device emits to their advantage by downloading them to their cellular phones as ringtones that adults and teachers cannot hear.
Out of curiousity, decided to go to a site that offers these sounds as downloadable ringtones to see just what I, as a 34-year-old who has grown up blasting his ears with headphones attached to Walkmans and iPods, could hear.
As it turns out, I can hear every tone from 8 khz up to 14.9 khz well. I can hear the 15.8 khz tone that nobody over 30 is supposed to be able to hear, if only just barely, and I can even perceive the 16.7 khz tone that nobody over 24 is supposed to be able to hear, although it's not so much as a sound as it is a faint piercing feeling in my head. I have a feeling that, if I could hear it well, I would probably find it to be highly annoying.
I can't perceive any tone higher than that; however, the 17.6 khz tone that Lori and I couldn't hear at all made her 21-year-old sister howl in disgust.
And that, of course, is exactly what these tones are supposed to do.
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