The Drive Unit, commonly called "alto-falante" or simply driver in Brazil, is the physical device responsible for converting the electrical signal coming from an amplifier into acoustic sound waves that we can hear. Although there are models designed to cover almost the entire audible frequency range, known as full-range, most speakers are optimized to reproduce only a specific part of the sound spectrum. For example, woofers are specialized in bass and tweeters in treble. The most common technology is the moving coil, but there are other variations such as ribbon and electrostatic drivers, each with its own performance characteristics.