Sympathetic string

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Hardingfele, showing sympathetic strings underneath playing strings

Sympathetic strings or resonant strings are auxiliary strings found on many Indian musical instruments, as well as some Western Renaissance-era instruments. They are typically not played directly by the performer (except occasionally as an effect) but instead resonate along with the main strings played on an instrument. The effect is most often heard when the fundamental frequency of the string is in unison or an octave lower or higher than the catalyst note, although it can occur for other intervals such as a fifth with less effect.

The musician retunes the resonant (often referred to as "sympathetic") strings for each mode or raga, so that when the corresponding note (or one an octave below it) is played on the main strings of the instrument, the resonant strings vibrate sympathetically, providing a sound analogous to our modern echo chamber, and aiding in the instrument's projection.

Sympathetic strings are used to enhance the sound of an instrument. Some have resonant strings added which exist solely to provide the effect and are not played at all. Common examples of this would be the sitar and the harp, and less common would be specially-fitted guitars. Other instruments such as the piano do not have additional strings, but make use of the effect by allowing their regular strings to vibrate sympathetically when they are not being played directly, particularly when the damper pedal is used.

[edit] Sympathetic string resonance in music instruments

Main article: String resonance (music)

Strings or parts of strings may resonate at their fundamental or harmonic frequencies when other strings are sounded. In general, non-played strings responding in sympathy to other strings being played. Two tones of the same pitch will give maximum sympathetic resonance as all harmonics of both strings will overlap. Other harmonic combinations will cause sympathetic resonance at the fifth, fourth and major third. For example, an A string at 440 Hz will cause an E string at 330 Hz to resonate, because they share an overtone of 1320 Hz (third overtone of A and fourth overtone of E).