Noise cancellation technology is a growing field that capitalizes on the combination of disparate technological advancements. The purpose of the technology is to cancel or at least minimize unwanted sounds. Modern lives seem full of all sorts of noise, some of which are dangerous to the ears. In fact, many people, especially those who live and work in cities, have very little quiet time during the day.
This technology aims to remedy the excess noise that people experience. Of course, there already are low-tech solutions to the problem. Ear-plugs and sound dampeners are available, but they are not very convenient nor very efficient. Noise cancellation tries to "block" the sound at the source instead of trying to prevent the sounds from entering the ear canal.
Sounds travel through the air or through liquids in the form of waves, and each of those waves has a particular shape. Noise canceling technologies first rely on small microphones that detect the sounds in a given environment. A digital signal processor determines what sound wave is required to cancel the unwanted sound wave and then it creates that sound and amplifies it through speakers or headphones. One way to understand this is to imagine a "positive" sound and a "negative" sound created at virtually the same time, and these two sounds cancel themselves out thereby bringing the listener closer to silence.
These technologies are in their early stages, and they cannot completely omit sounds, but improvements are consistently being introduced. The hope is that, one day, these technologies can be used to minimize all sorts of unwanted sounds. A lawn mower, hair dryer, or vacuum cleaner might include such a system, thereby greatly reducing the unpleasantly loud sounds.
Noise canceling headphones are already available. The headphones cancel out unwanted ambient sounds allowing the listener to focus solely on the music. The latest versions of these headphones work surprisingly well, and new applications are certainly on the horizon.