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NPR has a story about Mosquito, a high frequency outdoor generator being used by some 30 cities to discourage teenagers from staying in parks at night. According to the manufacturer's website, Mosquito generates an 18 kHz signal -- at that frequency, presumably a sine (because where would the harmonics live?) -- with an AGC to keep it 5 dB above ambient. No indication whether their AGC looks at broadband or just 18 kHz... but if it's broadband, then the noise is going to be a lot more obvious up there than +5 dB would suggest. According to NPR, "anyone over age 25 is supposed to be immune because, basically, their ear cells have started to die off." Later in the article: "In 2008, the United Nations Committee on the Rights of the Child implored the United Kingdom 'reconsider ... the Mosquito devices insofar as they may violate the rights of children.' No mention of whether it discriminates against golden-eared audiophiles. ---- About fifteen years ago, NPR had a story about a similar device being used in shopping malls to move the kids along... with an on-air sample. AFAIK NPR back then was distributing its news on a 32kHz s/r channel. They also had a downloadable sample so you could listen on better speakers. I remember checking it out: it was low bit mp3 encoded with a 22 kHz s/r.
Today's NYT has an article about the neuro damage suffered by US diplomats in Cuba and their families, and subsequently reported by some Canadian diplomats. Their reporter -- who doesn't seem to know much about acoustics or hearing -- is basically selling a story of mass hysteria. Evidence includes a history of isolated cases of individuals with psychosomatic ailments, quoting researchers who say "well, we didn't see changes in brain structure", and psychiatrists who say "the brain has powerful effects on the body, and brains can be triggered by non-physical events". And of course it quotes Cuban officials who say "it wasn't us". Conclusion: the damage couldn't be man-made, because in the past few years we haven't found someone to blame, and this psych explanation is convenient. The acoustic science is limited to examples like shopping malls playing high frequency noises to discourage kids. Even simple physical possibilities, like crossed ultrasonic beams intermodulating in the victims' ears, are ignored. And the possibility of natural physical causes isn't mentioned at all. Obviously I'm not convinced. I don't believe this is a conspiracy or government cover-up; more a case of "we don't know, it's not in our department, so it must be one of the other things we already know about." Thoughts?
I was sitting next to a nutritionist on a plane last night. He noticed my ear plugs and said it was good to see a young person taking care of his ears. After telling him I was a sound engineer he began to tell me ways to maintain hearing health. Niacin (B3) is a vasodilator and is especially good for the capillaries in the head, ears and cochlea, and may reduce the risk of tinitus. Ginkgo is also a good supplement to take. Thought I would pass on the info to you soundies, if you didn't know it already. To your health, Ben