A loudspeaker, also known as a loudspeaker, is a device used to convert electric energy into sound signal energy radiated to the room or outdoors in sound reproduction. The term signal energy means that electrical energy has a specific form, such as corresponding to any other signal in the voice, music, or audio frequency range (about 20 to 20000 Hz).

The loudspeaker shall maintain the basic characteristics of the signal energy in acoustic form. The definition of a loudspeaker does not include a buzzer, Gong, alarm, and other devices, in which the acoustic signal energy does not correspond to the electrical signal in form. The part of the loudspeaker that converts electrical energy into mechanical energy is usually called a motor or voice coil. The motor vibrates a diaphragm, which in turn vibrates the air in direct contact with it, producing sound waves corresponding to the original voice or music signal mode. The motor is usually composed of coils moving in a strong magnetic field, but the diaphragm can also be operated by electrostatic force or piezoelectric material.

A single speaker cannot completely reproduce the entire frequency range of the recorded sound, so the spectrum is usually divided into multiple parts and reproduced by different types of speakers designed for a specific frequency range. Low-frequency speakers are called bass speakers, and high-frequency speakers are called tweeters. In many sound reproduction systems, a third or mid-range speaker is also used. In a few systems, there are separate "subwoofer" and "tweeter" to reproduce the extreme value of the audio spectrum.

Naturally, the larger the speaker size, the better. Large caliber bass speakers can have better performance in the low-frequency part, which can be selected in the purchase. Speakers made with high-performance speakers mean lower transient distortion and better sound quality. The loudspeaker of the outdoor speaker subwoofer is mostly between 3 and 5 inches. Speakers made with high-performance speakers also mean lower transient distortion and better sound quality.