Sympathetic strings are used to enhance the sound of an instrument. Some instruments have only a few sympathetic strings such as the
Hardanger fiddle (pictured above right). Other instruments which have more include the
sitar with 11-13 sympathetic strings and
sarod with 15 sympathetic strings, and the
sarangi, which has a total of 37 sympathetics. In
Western music, some members of the
viola family appeared in the middle of the 17th century that were fitted with an extra choir of thin wire strings running through a hollow chamber through the
neck of the instrument, the head of which was then elongated to accommodate as many extra tuning pegs as necessary. These were generally called
viola d'amore; another historical example is the
baryton, for which
Haydn wrote many
trios. Other instruments such as the
harp,
lute,
guitar,
harpsichord, and
piano do not have additional strings, but make use of the effect by allowing their playing strings to vibrate sympathetically when they are not being played directly. In
keyboard instruments like the piano, the string dampers can be raised to produce this effect. The
guitar is normally unable to produce effective sympathetic string resonance for tones other than E (resonance from the 6th and 5th strings, tuned to E and A, respectively), B (from the 6th string), D (from the 4th string), and A (from the 5th and 4th strings). The treble strings are negligible in practice, as they are almost constantly being fingered. However, the
ten-string guitar invented in 1963 by
Narciso Yepes, adds four strings tuned to C, A, G, F, which resolves the imbalance of resonance on the guitar. By adding the abovementioned resonances and, of course, their fifths (the fifth being a strong
resonant frequency)—that is to say, G, F, D, C—the guitar's strings now resonate more equally with all 12 notes of the
chromatic scale, bringing the guitar's sound closer to the consistency and sustainability of the
harpsichord and
piano. ==Sympathetic string resonance in music instruments==