Many configurations have been produced, but the ten-string classical guitar received a particular boost[1] in 1964, when Narciso Yepes performed the Concierto de Aranjuez with the Berlin Philharmonic Orchestra[2] , using a ten-string guitar invented by Yepes in collaboration with José Ramírez III, with a specific tuning designed to supply sympathetic string resonance to all twelve notes of the chromatic scale, in unison with any note played on the treble strings.
[citation needed] These guitars are either custom-made or produced in small quantities due to the very niche market they are intended for.
[7] Stradivarius guitars (of which two, the Hill (1688) and Rawlins (1700) survive complete, plus a neck and several other fragments) all had ten strings in five courses.
This unusual stringing was said to obtain the brightness of the twelve-string guitar, while allowing higher levels of distortion before the sound became muddy.
The four additional strings are tuned by machine heads positioned in the body, past the tailpiece, with a large angled notch allowing access to the tuners.
This radical body shape also countered the common tendency of coursed electric guitars to be head-heavy due to the weight of the extra machine heads.