Sympathetic resonance or sympathetic vibration is a

harmonic In physics, acoustics, and telecommunications, a harmonic is a sinusoidal wave with a frequency that is a positive integer multiple of the ''fundamental frequency'' of a periodic signal. The fundamental frequency is also called the ''1st har ...

phenomenon wherein a passive string or vibratory body responds to external vibrations to which it has a harmonic likeness. The classic example is demonstrated with two similarly-tuned tuning forks. When one fork is struck and held near the other, vibrations are induced in the unstruck fork, even though there is no physical contact between them. In similar fashion,

string String or strings may refer to: *String (structure), a long flexible structure made from threads twisted together, which is used to tie, bind, or hang other objects Arts, entertainment, and media Films * ''Strings'' (1991 film), a Canadian anim ...

s will respond to the vibrations of a tuning fork when sufficient harmonic relations exist between them. The effect is most noticeable when the two bodies are tuned in unison or an octave apart (corresponding to the first and second

harmonics In physics, acoustics, and telecommunications, a harmonic is a sinusoidal wave with a frequency that is a positive integer multiple of the ''fundamental frequency'' of a periodic signal. The fundamental frequency is also called the ''1st harm ...

, integer multiples of the inducing frequency), as there is the greatest similarity in vibrational frequency. Sympathetic resonance is an example of injection locking occurring between coupled oscillators, in this case coupled through vibrating air. In musical instruments, sympathetic resonance can produce both desirable and undesirable effects. According to ''

The New Grove Dictionary of Music and Musicians ''The New Grove Dictionary of Music and Musicians'' is an encyclopedic dictionary of music and musicians. Along with the German-language '' Die Musik in Geschichte und Gegenwart'', it is one of the largest reference works on the history and t ...

'': This is the online edition of ''

'', Second Edition, with newer revisions.

Sympathetic resonance in music instruments

Sympathetic resonance has been applied to musical instruments from many cultures and time periods, and to

string instrument In musical instrument classification, string instruments, or chordophones, are musical instruments that produce sound from vibrating strings when a performer strums, plucks, strikes or sounds the strings in varying manners. Musicians play some ...

s in particular. In instruments with undamped strings (e.g.

harp The harp is a stringed musical instrument that has individual strings running at an angle to its soundboard; the strings are plucked with the fingers. Harps can be made and played in various ways, standing or sitting, and in orchestras or ...

guitar The guitar is a stringed musical instrument that is usually fretted (with Fretless guitar, some exceptions) and typically has six or Twelve-string guitar, twelve strings. It is usually held flat against the player's body and played by strumming ...

s and kotos), strings will resonate at their fundamental or

overtone An overtone is any resonant frequency above the fundamental frequency of a sound. (An overtone may or may not be a harmonic) In other words, overtones are all pitches higher than the lowest pitch within an individual sound; the fundamental i ...

frequencies when other nearby strings are sounded. 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 (the third harmonic of A and fourth harmonic of E). Sympathetic resonance is a factor in the

timbre In music, timbre (), also known as tone color or tone quality (from psychoacoustics), is the perceived sound of a musical note, sound or tone. Timbre distinguishes sounds according to their source, such as choir voices and musical instrument ...

of a string instrument. Certain instruments are built with

sympathetic string 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 (ex ...

s, auxiliary strings which are not directly played but sympathetically produce sound in response to tones played on the main strings. Sympathetic strings can be found on Indian musical instruments such as the

sitar The sitar ( or ; ) is a plucked stringed instrument, originating from the Indian subcontinent, used in Hindustani classical music. The instrument was invented in the 18th century, and arrived at its present form in 19th-century India. Khusrau K ...

, Western Baroque instruments such as the viola d'amore and folk instruments such as the

hurdy-gurdy The hurdy-gurdy is a string instrument that produces sound by a hand-turned crank, rosined wheel rubbing against the strings. The wheel functions much like a violin (or nyckelharpa) bow, and single notes played on the instrument sound similar ...

and

Hardanger fiddle A hardanger fiddle () is a traditional stringed instrument considered the national instrument of Norway. In modern designs, this type of fiddle is very similar to the violin, though with eight or nine strings (rather than four as on a standard v ...

. Some

pianos A piano is a keyboard instrument that produces sound when its keys are depressed, activating an action mechanism where hammers strike strings. Modern pianos have a row of 88 black and white keys, tuned to a chromatic scale in equal tempe ...

are built with sympathetic strings, a practice known as

aliquot stringing Aliquot stringing is the use of extra, un-struck strings in a piano for the purpose of enriching the tone. Aliquot systems use an additional (hence fourth) string in each note of the top three piano octaves. This string is positioned slightly ab ...

. Sympathetic resonance is sometimes an unwanted effect that must be mitigated when designing an instrument. For example, to dampen resonance in the headstock, some

electric guitar An electric guitar is a guitar that requires external electric Guitar amplifier, sound amplification in order to be heard at typical performance volumes, unlike a standard acoustic guitar. It uses one or more pickup (music technology), pickups ...

s use string trees near their tuning pegs. Similarly, the string length behind the

bridge A bridge is a structure built to Span (engineering), span a physical obstacle (such as a body of water, valley, road, or railway) without blocking the path underneath. It is constructed for the purpose of providing passage over the obstacle, whi ...

must be made as short as possible to dampen resonance.

References

{{Acoustics Acoustics Resonance