Loudspeaker is also called "horn". It is a very common electro-acoustic transducer, which can be seen in the electronic and electrical equipment.

Loudspeaker is the weakest device in audio equipment, and it is the most important component for audio effect. There is a wide variety of speakers and prices vary widely. Audio Power produces sound by electromagnetic, piezoelectric, or electrostatic effects that cause the bowl or diaphragm to vibrate and resonate with the surrounding air. According to the energy exchange mechanism and structure of moving coil type (electric), capacitance type (electrostatic), piezoelectric type (crystal or ceramic), electromagnetic type (pressure spring type), electric ion type and pneumatic loudspeaker, electrodynamic loudspeaker has good electro-acoustic performance, firm structure, low cost advantages, widely used; According to the sound radiation material paper basin type, number cylinder type, diaphragm type; According to the paper basin shape divided into round, oval, double paper basin and rubber folding ring; According to the working frequency points bass, alto, treble, some are also divided into answering machine special, TV special, common and high fidelity loudspeaker; According to the voice coil impedance into low impedance and high impedance; According to the effect, it can be divided into direct radiation and environmental sound.

Loudhailer is divided for built-in loudhailer and outside buy loudhailer, and outside buy loudhailer to indicate commonly namely sound box. Built-in speaker means that the MP4 player has a built-in speaker, so that users can listen to the sound of the MP4 player not only through the headphone jack but also through the built-in speaker. The MP4 player with built-in speaker eliminates the need for external speakers and avoids the inconvenience of wearing headphones for a long time.