Loudspeaker is a kind of switch device which transforms electrical signals into sound signals, and the performance of speakers has a great influence on the sound quality. Loudspeaker is one of the weakest components in the sound equipment, and it is also one of the most important parts for the sound effect.      
basic feature
1. There are two terminals (two leads). When using a single speaker two pins regardless of positive and negative polarity, the speaker also use two pins have polarity.
2 there is a paper basin, it is usually the color of black, there are white.
3 shapes are round, square and oval, and several other categories.
4 on the back side of the paper is a magnet, external magnetic type speaker with a metal screwdriver to touch the magnet will feel the presence of magnetic; magnetic speakers in this sense, but there is a magnet inside the shell.
5 mounted on the machine panel or in the sound box.
Hope that the above remarks you can understand, you are welcome to call advisory.