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 to keys that change the vibration length of the string, much as a guitarist uses his or her fingers on the fretboard of a guitar. In the earliest hurdy-gurdies these keys were arranged to provide a Pythagorean temperament, but in later instruments the tunings have varied widely, with equal temperament most common because it allows easier blending with other instruments. However, because the tangents can be adjusted to tune individual notes, it is possible to tune hurdy-gurdies to almost any temperament as needed. Most contemporary hurdy-gurdies have 24 keys that cover a range of two chromatic octaves. To achieve proper