There are many ways to categorize headphones, whether it be by style, power, brand or sound quality. But all headphones fall into one of two basic categories: dynamic or electrostatic. These categories base the headphones on the type of technology used to create their sound. The difference between the two types is in the transducer principle used; that is, how the headphones convert the electrical signal from a media player into sound waves that can be heard.
Dynamic headphones work just like two miniature speakers. The signal is transmitted through a connection to a standard jack. Once the electrical signal reaches the earphones, a magnet forces a voice coil to vibrate rapidly inside a diaphragm — a paper, fibrous or plastic cone-shaped object. The inner works are then lifted up and down much like a piston, often faster than the eye can see. This rapid vibration is what stirs the air and creates vibrations called sound waves which are then picked up by our eardrums.
Dynamic headphones are by far the most common type used by the average music listener, musicians and professional studio mixers alike. The most popular manufacturers in the music industry all make dynamic headphones, including Sony, Bose and Audio-Technica. They can cost $8 or $800 US Dollars (USD) and can be wired or wireless, open-air or closed-back, ear buds or studio-quality.
Electrostatic headphones, on the other hand, require an amplifier to create an electrical field. The field forces air through perforations in sandwiched metal plates, surrounding a thin plastic membrane. As a result of the metal plating, electrostatic phones are often rectangular in shape, as opposed to the common round shape of dynamic headsets.
Most experts agree electrostatic phones can actually produce a higher-quality sound than dynamic headphones. The reason they aren’t more popular is that they are far more expensive, starting at roughly $1,000 USD and reaching to nearly $15,000 USD for the industry's best.
Both of these headphones — sometimes called "cans" or "ears" by those in the Disc Jockey (Dj) and radio industries — are a long way from original designs, dating from the early 1900s for use with radios and telephones. However, while the materials and electrical signal involved are more recent developments, the magnet and coil system of dynamic headphones was used at the turn of the 20th century.