String instruments are musical instruments that produce sound primarily through the vibration of one or more stretched strings. They are also called chordophones in organological classification, although chordophone is a broader technical category that includes many instruments outside the conventional Western string family. A string can vibrate at a frequency determined by factors including its length, tension and linear density.
The vibrating string transfers energy to the instrument's body, soundboard, bridge, resonator or other structure, which helps couple the vibration to the surrounding air and makes the sound more audible. String instruments can be played by bowing, plucking, striking or using other mechanisms. Examples include violin, viola, cello, double bass, harp, guitar, lute, mandolin, piano and many culturally specific instruments. They differ enormously in construction and playing technique, but their common defining feature is that vibrating strings are central to their sound production.
Bowed string instruments produce sustained sound by maintaining friction between a bow and a string. The violin family provides the clearest orchestral example. A bow is drawn across a string, and the interaction causes the string to undergo a repeated stick slip motion that sustains vibration. The performer controls pitch by stopping the string at different points along the fingerboard, while bow speed, pressure and contact position influence loudness and timbre.
Vibrato involves controlled variation of pitch produced by oscillating the stopping finger, creating a characteristic expressive effect. Bowed instruments can also use pizzicato, in which the string is plucked rather than bowed, as well as tremolo, harmonics, sul ponticello and sul tasto. These techniques give string instruments unusually broad control over articulation, sustain, colour and expressive nuance.
Plucked string instruments produce sound by pulling and releasing a string, allowing it to vibrate freely. Guitar, lute, harp, mandolin and ukulele are familiar examples, although their construction and playing techniques differ considerably. In a guitar, the player stops strings against frets or the fingerboard to select pitches and plucks them with fingers or a plectrum.
In a harp, each string generally corresponds to a particular pitch, and pedals or other mechanisms alter the available pitch classes depending on the design. Plucked instruments generally have a distinctive attack followed by decay because the string is not continuously excited after the initial pluck. Players can modify this characteristic through repeated plucking, tremolo techniques, damping, resonance and amplification. The enormous range of plucked string instruments across cultures demonstrates that the basic principle of vibrating strings can support highly different musical systems and performance traditions.
Struck string instruments include the piano, clavichord and various zithers and dulcimers. In a piano, pressing a key activates a mechanism that causes a felt covered hammer to strike one or more strings. The strings then vibrate while the soundboard amplifies their energy. The performer controls dynamics primarily through the speed with which the hammer mechanism strikes the strings rather than directly touching the strings.
A piano therefore belongs physically to the family of chordophones but is usually treated as a keyboard instrument in ensemble contexts. The clavichord uses a different mechanism in which a tangent contacts the string, allowing particularly delicate control. Hammered dulcimers use hammers operated directly by the player to strike strings. These examples show that string instruments need not be bowed or plucked and that classification depends on the mechanism used to excite the strings.
Pitch in a string instrument depends on several physical properties. For an ideal stretched string, increasing tension raises its fundamental frequency, increasing length lowers it, and increasing linear density lowers the frequency. Instrument makers therefore select string materials and dimensions carefully and combine them with suitable tension and scale length. Players on instruments such as violin and guitar change pitch by altering the effective vibrating length, while instruments such as piano and harp provide strings tuned to predetermined pitches.
Harmonics arise when a string vibrates in segments corresponding to multiples of its fundamental frequency. Players can deliberately produce harmonic tones by lightly touching appropriate points on the string. These physical principles explain why string length, tension, thickness and material are fundamental aspects of instrument design and why changes to strings can significantly affect an instrument's response and timbre.
The resonating body of a string instrument is essential because a string by itself moves relatively little air and therefore produces a comparatively weak sound. In many acoustic instruments, vibration is transmitted through a bridge into a soundboard or resonating chamber. The body then couples the string's energy to the air and modifies the spectrum of frequencies that are emphasised.
The shape and materials of a violin body, the soundboard of a piano, the hollow body of a guitar and the resonator of a sitar all influence their distinctive sounds. Some instruments use sympathetic strings that are not directly played but vibrate in response to other frequencies. Others use electronic pickups to convert string vibration into electrical signals for amplification and processing. Consequently, string instrument acoustics involve both the physics of the vibrating string and the complex resonant behaviour of the instrument as a whole.
String instruments occupy major roles in many musical traditions. The violin, viola, cello and double bass form the central bowed string section of the symphony orchestra, while guitars, bass guitars, lutes, sitars, erhu, koto, shamisen and numerous other instruments are important in different cultural and musical contexts. Their functions range from melody and accompaniment to bass lines, drones, rhythmic patterns and complex polyphony. Instrument construction reflects local materials, musical scales, tuning systems and performance practices.
A guitar may use frets and standardised tuning, while a violin uses an unfretted fingerboard that allows continuous pitch adjustment. A sitar uses movable frets and sympathetic strings, while an erhu has two strings and a bow positioned between them. These differences demonstrate that string instruments form a vast technological and cultural category rather than a single musical tradition.
String instruments are valued for their broad expressive and technical capabilities, but they also have limitations. Bowed instruments can sustain notes and produce continuous pitch variation, yet they require substantial physical control to achieve accurate intonation and consistent tone. Fretted instruments simplify pitch selection but restrict continuous pitch movement unless specialised techniques are used. Plucked instruments can produce rapid articulation and complex chordal textures but naturally have decaying notes unless repeated or electronically sustained.
Acoustic volume varies greatly among designs, which has led to amplification in many modern contexts. Strings also wear out, stretch and respond to temperature and humidity, requiring maintenance and tuning. Understanding string instruments therefore requires consideration of acoustics, mechanics, technique, materials, cultural context and musical function rather than simply defining them as instruments containing strings.
