The long-string instrument is an instrument in which the string is of such a length that the fundamental transverse wave is below what a person can hear as a tone (±20 Hz). If the tension and the length result in sounds with such a frequency, the tone becomes a beating frequency that ranges from a short reverb (approx 5–10 meters) to longer echo sounds (longer than 10 meters). Besides the beating frequency, the string also gives higher pitched natural overtones. Since the length is that long, this has an effect on the attack tone. The attack tone shoots through the string in a longitudinal wave and generates the typical science-fiction laser-gun sound as heard in Star Wars. The sound is also similar to that occurring in upper electricity cables for trains (which are ready made long-string instruments in a way).
One early example of a long-string instrument was invented by the American composer Ellen Fullman. It is tuned in just intonation and played by walking along the length of its approximately 100 90-foot-long strings and rubbing them with rosined hands and producing longitudinal vibrations. A C-clamp is used on each string for putting tension on the strings, much like a guitarcapo, and a resonator is placed on the end the musician faces. This long-string instrument's range is centered on the octave of middle C and extends above and below this by an octave. The strings of the bass octave extend the instrument's full 90 feet.
The experimental luthier and recording artist Yuri Landman built a portable electric long-string instrument. A three-minute solo that he recorded in a garden on this instrument can be heard on YouTube, uploaded in 2011.
Sound lab and research centre Sonoscopia in Porto, Portugal has a permanent electric amplified long-string instrument mounted to the wall in the hall of their building.