Sympathetic strings or resonance strings are auxiliary strings found on many Indian musical instruments, as well as some Western Baroque instruments and a variety of folk instruments. They are typically not played directly by the performer (except occasionally as an effect), only indirectly through the tones that are played on the main strings, based on the principle of sympathetic resonance. The resonance is most often heard when the fundamental frequency of the string is in unison or an octave lower or higher than the catalyst (exciter) note, although it can occur for other intervals, such as a fifth, with less effect.
The musician retunes the 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 sympathetic strings (called tarabs in Indian music) will vibrate in response, providing a lingering halo of sound.
Sympathetic strings are used to enhance the sound of an instrument. (wikipedia)
See Also
Figure 10.01 - Tuning Forks in Sympathy
Harmony
Resonance
Sympathetic clock
Sympathetic Harp
sympathetic string
Sympathetic Oscillation
Sympathetic Resonance
Sympathetic Vibration
Sympathy
tuning fork
Unison
1.3 - Brain Strung as a Harp