Mobile phone headphones are divided into two standards: OMTP standard is usually called National standard, CTIA is called international standard. Headphones are classified according to their energy transfer modes, which mainly include moving coil mode, moving iron mode, electrostatic mode and geomagnetic mode. It can be divided into semi-open type and closed type according to its structure and function; earplug type, hanging type, ear-in type and head-wear type according to its wearing form; single earphone and multi-person earphone according to the number of wearers; active earphone and passive earphone according to the sound source; active earphone is often used as well. Called plug-in headphones.!Headphones are the symbol of a person’s portable stereo.