Sound means other than language, music sound, including the natural environment of sound, the sound of the animals, machine tool acoustics, the action of all kinds of sound, etc. Probably including amplifiers, the neighboring audio equipment (including pressure limit, effect, equalizer, VCD, DVD, etc.), speakers,  Car Speaker , speakers) mixer, microphone, display devices, and so on added up to a set. Among them, the sound is the sound output equipment,  Bluetooth Speaker subwoofer, and so on. A speaker in the three speakers, including high and low, three but not just three.