String instrument strings, or play them by rolling the bell of a brass instrument such as a trombone on the array of strings. However, these are relatively rarely used special techniques. Other keyed string instruments, small enough for a strolling musician to play, include the plucked autoharp, the bowed nyckelharpa, and the hurdy-gurdy, which is played by cranking a rosined wheel. Steel-stringed instruments (such as the guitar, bass, violin, etc.) can be played using a magnetic field. An E-Bow is a small hand-held battery-powered device that magnetically excites the strings of an electric string instrument to provide a sustained, singing tone reminiscent
Hurdy-gurdy bridge for additional drone strings on some instruments). The free end of the dog (called the "hammer") rests on the soundboard of the hurdy-gurdy and is more or less free to vibrate. When the wheel is turned regularly and not too fast the pressure on the string (called the "trompette" on French instruments) holds the bridge in place, sounding a drone. When the crank is struck, the hammer lifts up suddenly and vibrates against the soundboard, producing a characteristic rhythmic buzz that is used as an articulation or to provide percussive effect, especially in dance pieces. On French-style instruments, the