"Hey, stop hanging around! You're blocking the doorway!"
That's what shop owners were shouting at teenagers who were loitering outside stores and in malls. The kids were supposedly deterring adult customers - that is, the ones with more spending power.
U.K. inventor Howard Stapleton had just the answer. He patented a "Mosquito device" that emitted a loud, high-pitched sound, a modulated 17-kHz tone that could be played outside the shops. The insect-like buzzing would be audible and annoying to youngsters, driving them away. But the tone would be unheard by more senior customers, thanks to presbycusis, a common age-related hearing loss that mainly affects the ability to hear high frequencies.
Depending on your point of view, Stapleton's idea was either a brilliant solution or an attack on human health.
Of course, teens soon turned the tables. Versions of the Mosquito tone (also called Teen Buzz and Zumbitone) became popular ringtones. They're often slightly lower in pitch (perhaps 14.4 kHz) but have the same effect. Kids can hear the sounds - but many adults, especially when a meter or more away from a soft source, cannot. All the kids in a classroom can hear the phones ringing all the time, while the clueless teacher keeps asking, "What's going on?" General hilarity ensues. The kids have something subversive and cool. They are possibly violating intellectual-property rights. And best of all, the kids can point out that whereas they are young, their teachers and parents are old.
I hear you saying, "But I want to be subversive, too!"
You can be, but only if you can hear the sound that was meant not to be heard. You can audition Mosquito tones for yourself at freemosquitoringtones.org - provided, of course, that your speakers can go high enough. Also, for more discussion, go to the Forums at our own Web site (soundandvisionmag.com) and, under "Polls Section," check out the thread called "Can you hear sound over 20 kHz?"
Think you can hear such sound? Congratulations! You've got great high-end hearing acuity. Those kids can't pull the wool over your ears!
On the downside, now you can't loiter. So, please, move along.
Copyright © 2013 Bonnier Corp. All rights reserved. Reproduction in whole or in part without permission is prohibited.