Active noise canceling headphones are those that create their own sound waves to counteract undesirable sound waves that may be intruding on a listener. These are different than passive noise canceling headphones, which simply use foam and other materials in an attempt to block out sounds. Though active noise canceling headphones may also use such materials, the emission of the sound waves to actively block other sounds provides yet another method of dealing with unwanted sound.
In most cases,the noise cancellation that takes place with passive headphones has the effect of reducing sounds from the outside by approximately 20 decibels. Most of the time, this may be an acceptable level and provide the user with a good experience. At other times, the sound intrusion may still bother a user, who may then opt for active noise canceling headphones. This is very common with those who travel substantially and must deal with noise from jet engines, subways, trains, or even automobiles.
To understand how active noise canceling headphones actually work, it is necessary to understand the true nature of sound. Sound waves are nothing, but a disruption of air pressure that eventually causes the tympanic membranes in the ear to vibrate. This sets off a series of reactions that the brain eventually interprets as sound. In many cases, there is no need to worry about ambient noises as the brain can easily distinguish desired sounds from those that are not desired. If the sounds are persistent or too loud, however, this could become bothersome.
Without active noise canceling headphones, the best that can be hoped for is to block the sound from entering the ear. When active noise cancellation is employed, sound waves are emitted in the exact opposite pattern of the outside sound waves. Thus, the fluctuations in air pressure cancel each other out. While this may not work for all applications and sounds, it is particularly effective for sound waves at lower frequencies.
The first company to put a set of active noise canceling headphones on the market was Bose®. The company introduced its first set in 1989. Now, the headphones are available both for entertainment, where they are used to listen to CDs, MP3 files and other forms of music, as well as aviation, where they can help pilots communicate with air traffic control personnel and each other. Modern buildings are also beginning to try various active noise cancellation techniques based on the same type of technology used in headphones.