Headphone manufacturing comes down to two main parts. The first is to produce two miniaturized versions of loudspeakers using a combination of metal compounds and either plastic or paper. The second is to produce a housing for the speakers that fits comfortably on or in the ear, with plastics, rubber and foam all key components depending on the design.
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History of Headphones
Utah resident Nathaniel Baldwin invented headphones in 1910, with his earliest customers including the U.S. Navy. At this time, headphones were the only way to listen to electrical audio signals (rather than the mechanical sound of gramophones) until amplifiers became widely available. Stereo headphones appeared in 1958, while the release of the Sony Walkman in 1979 prompted a switch from headphones that surrounded the ear to smaller ones that merely pressed against the ear. Earbuds, which go inside the ear canal, became popular when they shipped with the iPod.
While a great deal of technology goes into making headphones small and comfortable, in principle they are simply two miniature loudspeakers. This involves three key components: a permanent magnet (which is locked in place), a coiled electromagnet and a cone. The electrical signal from the audio device (such as your MP3 player) passes through the electromagnet and causes its magnetic field to change direction. This means the electromagnet switches rapidly between being attracted to or repelled by the permanent magnet and thus moves about. The electromagnet is attached to the cone, which magnifies the movement and causes air to vibrate in and toward your ear as sound waves.
Originally the metal parts of headphone speakers were made of iron, which made for poor sound quality. Today they are normally ferrite or neodymium, which are both compound materials that include iron and other elements. In the coiled electromagnet, these materials have the big advantage that they can change magnetic field directions with only a minimal loss of energy. The cone in headphones is commonly made of plastic and/or paper rather than metal. This is because flexibility is more important than strength at this size. Some researchers have explored using a new compound material, graphene, to try to get increased strength and flexibility at the same time.
The material that surrounds the speakers in headphones varies depending on the design and budget. For on-ear headphones, the usual design is a rigid plastic casing with a rubber or PVC layer to act as a cushion on the ear. For in-ear headphones, rubber or silicone is common, as it has more flexibility and can thus fit comfortably but snugly into the ear or ear canal. More expensive in-ear models use a form of foam which can adjust to the specific shape of the user's ear canal.