Electric guitar design and construction vary greatly in the shape of the body and the configuration of the neck, bridge, and pickups. Guitars have a fixed bridge or a spring-loaded hinged bridge that lets players bend notes or chords up or down in pitch or perform vibrato effects. The sound of a guitar can be modified by new playing techniques such as string bending, tapping, hammering on, using audio feedback, or slide guitar playing. There are several types of electric guitar, including the solid-body guitar, various types of hollow-body guitars, the seven-string guitar, which typically adds a low B string below the low E, and the twelve-string electric guitar, which has six pairs of strings.