Noise Canceling

Nearly 60 years after American folk duo Simon & Garfunkel sang their earworm tune “The Sound of Silence,” three researchers have resurrected the age-old question as to whether the absence of noise is something we can hear and our brains can interpret.

A number of hearing aids are now able to amplify one person's voice while filtering out distracting background voices. Well, it turns out that female tree frogs are able to perform a similar task, in order to hear the mating calls of males.

By moving the microphone usually located within the ear cups of noise-cancelling headphones towards the noise to be cancelled out and employing wireless technology, researchers have now developed better noise-cancelling technology that doesn't require bulky noise-blocking headphones.

Etymotic's HD-15 High-Definition electronic earplugs let users hear normally when things are quiet, but kick in when sudden loud noises occur.

Caltech's "acoustic diodes" only allow sound waves to travel in one direction.