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 a common bridge, and a relatively small wheel. Due to its size, the organistrum was played by two people, one of whom turned the crank while the other pulled the keys upward. Pulling keys upward is cumbersome, so only slow tunes could be played on the organistrum. The pitches on the organistrum were set according to Pythagorean temperament and the instrument was primarily used in monastic and church settings to accompany choral music. Abbot Odo of Cluny (died 942) is supposed to have written a short description of the construction of the organistrum entitled "Quomodo organistrum construatur" (How the Organistrum