Guitar Frets are laid out to accomplish an equal tempered division of the octave. Each set of twelve frets represents an octave. The twelfth fret divides the scale length exactly into two halves, and the 24th fret position divides one of those halves in half again. The ratio of the spacing of two consecutive frets is formula_1 (twelfth root of two). In practice, luthiers determine fret positions using the constant 17.817—an approximation to 1/(1-1/formula_1). If the nth fret is a distance x from the bridge, then the distance from the (n+1)th fret to the bridge is x-(x/17.817). Frets are available in
Multi-neck guitar 6-string neck on the bottom and an "octave guitar" for the top neck. This was a 6-string neck tuned an octave higher than the standard guitar, that both extended the range of the instrument, and allowed Maphis to play mandolin-like sounds. Between 1958-1968, Gibson made an instrument of this type which it called the "Double Mandolin" (Gibson EMS 1235). Hybrids with a 6-string guitar neck and a true 8-string mandolin neck were also made (e.g., the 1971 Dawson Electric guitar/mandolin). And Led Zeppelin's John Paul Jones has a triple-neck electroacoustic instrument, custom made for him by luthier Andy Manson, which