A speaker is a speaker in the box. This speaker requires power to drive to make a loud sound. The function of the power amplifier is to amplify the power of the audio signal input by the sound source. For example, the microphone has a relatively small power in the mouth, and certainly cannot drive passive speakers, right, you need an amplifier to amplify the sound source. Active speakers are built with amplifier circuits in the speakers. Passive speakers have the speakers and amplifier circuits separated into two boxes. If the passive speaker is not connected to the amplifier and the input power is too low, no sound will be heard. Of course, passive speakers can be connected to active speakers. As a younger brother of active speakers, they can also produce sound.