teste auditivo

acabei de perceber que, para além de ver mal, também já não oiço muito bem. tudo porque experimentei ouvir(?!) este toque de telemóvel muito utilizado pelos mais jovens durante as aulas. porquê nas aulas? a explicação vem já a seguir.

o toque, de nome 'mosquito' (ou 'teen buzz'), é apenas um ruído emitido na frequência dos 14.4Khz. o ouvido humano, em teoria, consegue ouvir uma gama de frequências entre os 2hz e os 20Khz. com o passar dos anos, essa capacidade começa a 'encolher'. assim, salvo raras excepções, os adultos não conseguem ouvir o toque - e os professores, como é óbvio, também não. com este toque, os alunos, mais do que conseguirem receber mensagens no telemóvel durante as aulas sem serem 'apanhados', gozam com os professores.

o que ainda é mais incrível é a 'origem' deste toque: "The Mosquito is a product made to drive away teenagers from no-loitering zones. Because the ability to hear high frequencies deteriorates with age (a phenomenon known as presbycusis), the Mosquito works by emitting high-frequency tones. According to Welsh inventor, Ig Nobel Prize winner for Peace Howard Stapleton, the tones can only reliably be heard by people younger than 20 and almost never heard by people older than 30. Short exposure has very little effect for someone entering a store where the device is externally installed, but the sound becomes very annoying for those wishing to be around the immediate area for longer than 10 minutes

The Mosquito was originally tested at one location in Newport, South Wales, where it was successful in reducing the number of teenagers loitering outside a grocery store. In spite of this, some adults and seniors were still able to hear the Mosquito. It has not been tested by hearing experts, however the tones are broadcast at 75 decibels, so they fall within the government's auditory-safety limits. The Mosquito was released into the mainstream market in 2006.

Some adolescents, however, have found the once annoying sound can be used as a tool, and turned it into a ringtone to prevent disciplinary actions that would normally be imposed if a cellular phone user was caught using their phones during school hours, by creating a cell phone ringtone that is inaudible to most adults". (via wikipédia)