An earphone 1 (also known as a hearing aid ; 2 one is generally used in each ear, so it is common to use the plural name: headphones , earphones or also helmets 3 ) are transducers that receive an electrical signal originating from a electronic source (such as a radio , synthesizer or audio player ) that by design allows speakers to be placed near the ears to generate audible sound waves .
The headphones are normally detachable and interchangeable, that is, they can be easily plugged in or unplugged from the equipment that requires them. The same headphones can be used by various audio systems.
In the telecommunications context , headphones refer to a type of device that consists of a combination of headphones and microphone for two-way communication . For example, a mobile phone .
Headphones began to be used from telephony and radio . Weak electrical signals from early electrical instruments (not yet electronic) required custom amplification for the telephony arena.
A company called Beyerdynamic was officially credited with the invention in the late 1930s, and as the first company to sell headphones to the general public: Model DT48 in 1937.
Its use became widespread after the emergence of personal audio systems: portable radios and portable cassette players ; Later the phenomenon was increased with the use of the CD player , the digital audio player , the personal computer and smartphones .
With the advancement of electronics, the AM / FM radio receiver has been incorporated and other capabilities have been acquired, such as wireless communication (via infrared , Bluetooth , or Wi-Fi ) to receive signals.