USB speaker systems have different requirements and usage parameters than standard computer speakers. They use special USB audio software rather than the computer's audio drivers.
Most speaker systems connect to a computer system's sound card through a 3.5mm audio jack. The sound card plays sounds using audio drivers; without these drivers, the speakers will not operate. USB speakers, however, connect to a USB port rather than the sound card.
USB speakers do not require the audio drivers used by other speaker systems; rather, they use the system's USB drivers. In effect, USB speakers include a built-in sound card. This makes USB speakers an excellent replacement option for a malfunctioning or inoperative sound card.
Since USB speakers add a second audio device to the system, you may need to switch the computer's playback device in order for the speakers to work. Open the Sound" icon in the Windows Control Panel or the "Sound" section in OS X's System Preferences window to switch the sound to your USB speakers.