The voltage pulses produced by an analog or digital component are sent to an amplifier and then to headphones or speakers. A speaker consists of a coil of wire attached to one or more cone-shaped diaphragms. When the voltage pulses are received by the coil, they are converted to magnetic pulses that attract and repel the back of the speaker cone. The motion of the speaker cone creates variations in air pressure that reproduces the sound captured and stored on the sound recording. Low-frequency sounds require that the speaker cone move slowly, and high-frequency sounds require rapid movement. Because no single cone size can move both slowly and quickly enough to cover the full spectrum of perceivable sound, speaker systems often consist multiple cones that are optimized for specific frequency ranges. The typical categories are the woofer (25 Hz-300 Hz), midrange speaker (800 Hz-16 kHz), and the tweeter (6 kHz-30kHz). Computer sound systems often consist of two small midrange speakers and a ``subwoofer'' to reproduce lower frequencies.