Headphones
Headphones are miniature loudspeakers that are placed over the ears and held in place by a band or wire worn over the head. They often feature cushioning to hold in sounds coming in or block outside sounds. Though airplane pilots are among the many professionals to use headphones on the job, most often headphones are thought of as auxiliary stereo equipment, used to listen to music without disturbing others, and in the production of music in the recording studio.
The first stereo headphones were invented in 1958 by John C. Koss, a Milwaukee-based jazz musician and audiophile. Before his time, headphones were used only in industry by telephone operators and the like. Koss's original idea consisted of a total stereo package: a small portable phonograph with attached speakers and his new headphones, designed with an audio engineer. When he took it to a hi-fi show in his hometown that November, the only component that drew interest was the headphones, which became an immediate hit. The idea was so successful that Japanese companies quickly designed copies of Koss's headphones. Though the original Koss headphones were crude--little more than tiny loudspeakers covered in cardboard and held in place by a military headband-- they were the first headphones to provide the listener with a full amplitude of sound.
Headphones work much like a loudspeaker does. The amplifier sends out a signal. This signal propels a light diaphragm in the speaker. The diaphragm vibrates air in the ear canal. This describes headphones at their crudest, though, for headphones have evolved in an effort to recreate the breadth and depth of the original sound. There are several different classes of headphones. Circumaural headphones feature big soft earpads that seal the external ear, and are often bulky and heavy. Supra-aural, also known as velocity, headphones merely rest on the outer ear, with minimal foam cushioning for comfort.
Until the 1980s, headphones continued to improve technologically, but remained rather large. In the early 1980s, with the advent of the walkman, headphones became extremely small and lightweight. In 1990, Koss introduced its first cordless headphones which used an infrared signal to link the amplifier to the headphones. Cordless headphones allow the listener to wander the room, rather than be tethered to a stereo. There is also another kind of cordless headphone, called 900 MHZ headphones and first manufactured by Recoton. They use a tiny radio transmitter in the amplifier, and a receiver in the headphones. The 900 MHZ headphones have one significant advantage over infrared: the listener does not have to be in the same room, within a limited distance of the stereo, to listen. With 900 MHZ headphones, one can amble up to 150 ft (about 45.5 m) from the signal's source. Despite the advantages, these radio headphones were banned in Great Britain in 1997 because they work on an already assigned frequency.
In the future, digital radio technology will probably supplant both of these types of cordless headphones. Other burgeoning headphone technologies that will make headway include 3-D headphones (also known as surround sound headphones) which feature two or three small speakers on each side, creating the effect of space in sound. While headphones have many advantages, there are health risks associated with their use. Listening to the music too loudly can permanently damage hearing, and using headphones while engaged in potentially hazardous situations, such as riding a bike in traffic, can lead to bodily injury, if not death.
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