String instrument

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Numerous stringed instruments of Chinese make on display in a shop.
Musical instruments
Woodwinds
Brass
Percussion
String instruments
Bowed
Plucked
Keyboards
Monochords
Viol, fidel and rebec (from left to right) on display at Amakusa Korejiyokan in Amakusa, Kumamoto, Japan

String instruments, stringed instruments, or chordophones are musical instruments that produce sound from vibrating strings. In most string instruments, the vibrations are transmitted to the body of the instrument, which also vibrates, along with the air inside it. The body of most–but not all string instruments–is hollow. There are exceptions, such as types of electric guitar which have a solid wood body; with the electric guitar, a guitar amplifier is used to make the vibrations of the strings audible.

In the Hornbostel-Sachs scheme of musical instrument classification, used in organology, string instruments are called chordophones. Common instruments in the string family include the violin, guitar, sitar, electric bass, viola, cello, harp, double bass, rebab, banjo, mandolin, ukulele, and bouzouki. String instruments can be sounded using a number of approaches. The classical strings (violin, viola, cello and double bass) are played pizzicato (by plucking) and using a bow. Guitar-family instruments are played with a variety of techniques, including plucking and strumming.

History

Some of the earliest stringed instruments have been identified in archaeological digs of Ancient Mesopotamian sites, like the lyres of Ur which include artifacts over three thousand years old. Lyre instruments with wooden bodies, and strings used for plucking or playing with a bow represent key instruments that point towards later harps and violin type instruments; moreover, Indian instruments from 500 BC have been discovered with anything from 7 to 21 strings.

During the medieval era, the rate by which string instruments developed arguably varied from country to country – Middle Eastern rebecs represented breakthroughs in terms of shape and strings, with a half a pear shape using three strings. Early versions of the violin and fiddle, by comparison, emerged in Europe through instruments such as the gittern, a four stringed precursor to the guitar, and basic lutes. These instruments typically used catgut and other somewhat unpleasant materials for their strings, with higher end versions featuring silk.

String instrument design was refined during the Renaissance and into the Baroque period of musical history – violins and guitars became more stable in terms of their design changes, and were roughly similar to what we now use – the violins of the Renaissance featured intricate woodwork and stringing, while more elaborate bass instruments such as the bandora were produced alongside quill plucked citterns, and Spanish body guitars.

In the 19th century, string instruments were made more widely available through mass production, with woodwind string instruments a key part of orchestras – cellos, violas, and upright basses, for example, were now standard instruments for chamber and smaller orchestras. At the same time, the 19th century guitar became more typically associated with six string models, rather than traditional five string versions. Major changes to string instruments in the 20th century primarily involved innovations in amplification and electronic music – electric violins were available by the 1920s, and were an important part of emerging jazz music trends in the United States. Breakthroughs in electric guitar and basses then saw major breakthroughs in pop and rock music through the middle of the 20th century. The ongoing connection of string instruments to electronic amplification added variety to classical performances, and enabled experimentation in the dynamic range of orchestras, bands, and solo performances.[1]

Types of instruments

Construction

String instruments can be divided in three groups.

Lutes – instruments that support the strings via a neck and a bout ("gourd"), for instance a guitar, a violin, or a saz
Harps – instruments that contain the strings within a frame
Zithers – instruments that have the strings mounted on a body, such as a guqin, a cimbalom, an autoharp, or a piano

It is also possible to divide the instruments in groups focused on how the instrument is played.

Types of playing techniques

An acoustic guitar being strummed.
For a full list, see List of string instruments.

All string instruments produce sound from one or more vibrating strings, transferred to the air by the body of the instrument (or by a pickup in the case of electronically amplified instruments). They are usually categorized by the technique used to make the strings vibrate (or by the primary technique, in the case of instruments where more than one may apply.) The three most common techniques are plucking, bowing, and striking. An important difference between bowing and plucking is that in the former the phenomenon is periodic, so that the overtones are kept in a strictly harmonic relationship to the fundamental.[2]

Plucking

Plucking is a method of playing on instruments such as the veena, banjo, ukulele, guitar, harp, lute, mandolin, oud, and sitar, using either a finger, thumb, or quills (now plastic plectra) to pluck the strings.

Instruments normally played by bowing (see below) may also be plucked, a technique referred to by the Italian term pizzicato.

Bowing

Bowing (Italian: arco) is a method used in some string instruments, including the violin, viola, cello, and the double bass (of the violin family), and the old viol family. The bow consists of a stick with many hairs stretched between its ends. Bowing the instrument's string causes a stick-slip phenomenon to occur, which makes the string vibrate.

The ravanahatha is one of the oldest string instruments. Ancestors of the modern bowed string instruments are the rebab of the Islamic Empires, the Persian kamanche and the Byzantine lira. Other bowed instruments are the rebec, hardingfele, nyckelharpa, kokyū, erhu, igil, sarangi and K'ni. The hurdy-gurdy is bowed by a wheel. Rarely, the guitar has been played with a bow (rather than plucked) for unique effects.

Striking

The third common method of sound production in stringed instruments is to strike the string. The piano and hammered dulcimer use this method of sound production.

Violin family string instrument players are occasionally instructed to strike the string with the stick of the bow, a technique called col legno. This yields a percussive sound along with the pitch of the note. A well-known use of col legno for orchestral strings is Gustav Holst's "Mars" movement from The Planets suite.

Other methods

The aeolian harp employs a very unusual method of sound production: the strings are excited by the movement of the air.

Some instruments that have strings have attached keyboards that the player uses instead of directly manipulating the strings. These include the piano, the clavichord, and the harpsichord.

With these keyboard instruments too, strings are occasionally plucked or bowed by hand. Composers such as Henry Cowell wrote music that requires that the player reach inside the piano and pluck the strings directly, "bow" them with bow hair wrapped around the strings, or play them by rolling the bell of a brass instrument such as a trombone on the array of strings.

Other keyed string instruments, small enough for a strolling musician to play, include the plucked autoharp, the bowed nyckelharpa, and the hurdy-gurdy, which is played by cranking a rosined wheel.

Steel-stringed instruments (such as the guitar, bass, violin, etc.) can be played using a magnetic field. An E-Bow is small hand-held battery-powered device that magnetically excites the strings of an electric string instrument to provide a sustained, singing tone.

Third bridge is a plucking method where the player frets a string and strikes the side opposite the bridge. The technique is mainly used on electric instruments, because these have a pickup that amplifies only the local string vibration. It is possible on acoustic instruments as well, but less effective. For instance, a player might press on the seventh fret on a guitar and pluck it at the head side to make a tone resonate at the opposed side. At electric instruments this technique generates multitone sounds reminiscent of a clock or bell.

Changing the pitch of a vibrating string

Main article: Mersenne's laws

There are three ways to change the pitch of a vibrating string. String instruments are tuned by varying the strings' tension because adjusting length or mass per unit length is impractical. Instruments with a fingerboard are then played by adjusting the length of the vibrating portion of the strings. The following observations all apply to a string that is infinitely flexible strung between two fixed supports. Real strings have finite curvature at the bridge and nut, and the bridge, because of its motion, are not exactly nodes of vibration. Hence the following statements about proportionality are approximations.

Length

String fingering is proportional and not fixed,[3] as on the piano

Pitch can be adjusted by varying the length of the string.[2] A longer string results in a lower pitch, while a shorter string results in a higher pitch. The frequency is inversely proportional to the length:

${\displaystyle f\propto {\frac {1}{l}}}$

A string twice as long produces a tone of half the frequency (one octave lower).

Tension

Pitch can be adjusted by varying the tension of the string. A string with less tension (looser) results in a lower pitch, while a string with greater tension (tighter) results in a higher pitch. The frequency is proportional to the square root of the tension:

${\displaystyle f\propto {\sqrt {T}}}$

Linear density

The pitch of a string can also be varied by changing the linear density (mass per unit length) of the string. The frequency is inversely proportional to the square root of the linear density:

${\displaystyle f\propto {1 \over {\sqrt {\mu }}}}$

Given two strings of equal length and tension, the string with higher mass per unit length produces the lower pitch.

String length or scale length

The length of the string from nut to bridge on bowed or plucked instruments ultimately determines the distance between different notes on the instrument. For example, a double bass with its low range needs a scale length of around 42 inches (110 cm), whilst a violin scale is only about 13 inches (33 cm). On the shorter scale of the violin, the left hand may easily reach a range of slightly more than two octaves without shifting position, while on the bass' longer scale, a single octave or a ninth is reachable in lower positions.

Contact points along the string

The strings of a piano

In bowed instruments, the bow is normally placed perpendicularly to the string, at a point half way between the end of the fingerboard and the bridge. However, different bow placements can be selected to change timbre. Application of the bow close to the bridge (known as sul ponticello) produces an intense, sometimes harsh sound, which acoustically emphasizes the upper harmonics. Bowing above the fingerboard (sul tasto) produces a purer tone with less overtone strength, emphasizing the fundamental, also known as flautando, since it sounds less reedy and more flute-like.

Similar timbral distinctions are also possible with plucked string instruments by selecting an appropriate plucking point, although the difference is perhaps more subtle.

In keyboard instruments, the contact point along the string (whether this be hammer, tangent, or plectrum) is a choice made by the instrument designer. Builders use a combination of experience and acoustic theory to establish the right set of contact points.

In harpsichords, often there are two sets of strings of equal length. These "choirs" usually differ in their plucking points. One choir has a "normal" plucking point, producing a canonical harpsichord sound; the other has a plucking point close to the bridge, producing a reedier "nasal" sound rich in upper harmonics.

Production of multiple notes

A string at a certain tension and length only produces one note, To produce multiple notes, string instruments use one of two methods. One is to add enough strings to cover the required range. The other is to provide a way to stop the strings along their length to shorten the part that vibrates. The piano and harp are examples of the former method, where each note on the instrument has its own string or course of multiple strings. (Many notes on a piano are strung with a "choir" of three strings tuned alike.) A guitar represents the second method—the player's fingers push the string against the fingerboard to force the string over a fret and shorten the vibrating part.

Some zithers combine stoppable (melody) strings with a greater number of "open" harmony or chord strings. On instruments with stoppable strings, such as the violin or guitar, the player can shorten the vibrating length of the string, using their fingers directly (or more rarely through some mechanical device, as in the nyckelharpa and the hurdy-gurdy). Such instruments usually have a fingerboard attached to the neck of the instrument, that provides a hard flat surface the player can stop the strings against. On some string instruments, the fingerboard has frets, raised ridges perpendicular to the strings, that stop the string at precise intervals, in which case the fingerboard is also called a fretboard.

Moving frets during performance is usually impractical. The bridges of a koto, on the other hand, may be moved by the player occasionally in the course of a single piece of music. Many modern Western harps include levers, either directly moved by fingers (on Celtic harps) or controlled by foot pedals (on orchestral harps), to raise the pitch of individual strings by a fixed amount. The Middle Eastern zither, the qanun, is equipped with small levers called mandal that allow each course of multiple strings to be incrementally retuned "on the fly" while the instrument is being played. These levers raise or lower the pitch of the string course by a microtone, less than a half step.

Sympathetic strings

Main article: Sympathetic string

Some instruments are employed with sympathetic strings, additional strings not meant to be plucked. These strings resonate along with the played notes. This system is for instance present on a sarangi.

Sound production

Acoustic instruments

A vibrating string on its own makes only a very quiet sound, so string instruments are usually constructed in such a way that this sound is coupled to a hollow resonating chamber, a soundboard, or both. On the violin, for example the tout strings pass over a bridge resting on a hollow box. The strings vibrations are distributed via the bridge and soundpost to all surfaces of the instrument, and are thus made louder. The correct technical explanation is that they allow a better match to the acoustic impedance of the air.

It is sometimes said that the sounding board or soundbox "amplifies" the sound of the strings. Technically speaking, no amplification occurs, because all of the energy to produce sound comes from the vibrating string. What really happens is that the sounding board of the instrument provides a larger surface area to create sound waves than that of the string. A larger vibrating surface moves more air, hence produces a louder sound.

All lute type instruments traditionally have a bridge, which holds the string at the proper action height from the fret/finger board. On acoustic instruments, the bridge performs an equally important function of transmitting string energy into the "sound box" of the instrument, thereby increasing the sound volume. The specific design, and materials the used in the construction of the bridge of an instrument, have a dramatic impact upon both the sound and responsiveness of the instrument.

Achieving a tonal characteristic that is effective and pleasing to the player's and listener's ear is something of an art, and the makers of string instruments often seek very high quality woods to this end, particularly spruce (chosen for its lightness, strength and flexibility) and maple (a very hard wood). Spruce is used for the sounding boards of instruments from the violin to the piano. Instruments such as the banjo use a drum, covered in natural or synthetic skin as their soundboard.

Acoustic instruments can also be made out of artificial materials, such as carbon fiber and fiberglass (particularly the larger instruments, such as cellos and basses).

In the early 20th century, the Stroh violin used a diaphragm-type resonator and a metal horn to project the string sound, much like early mechanical gramophones. Its use declined beginning about 1920, as electronic amplification came into use.

Electronic amplification

Most string instruments can be fitted with piezoelectric or magnetic pickups to convert the string's vibrations into an electrical signal that is amplified and then converted back into sound by loudspeakers. Some players attach a pickup to their traditional string instrument to "electrify" it. Another option is to use a solid-bodied instrument, which reduces unwanted feedback howls or squeals.

Amplified string instruments can be much louder than their acoustic counterparts, so musicians can play them in relatively loud rock, blues, and jazz ensembles. Amplified instruments can also have their amplified tone modified by using electronic effects such as distortion, reverb, or wah-wah.

Bass-register string instruments such as the double bass and the electric bass are amplified with bass instrument amplifiers that are designed to reproduce low-frequency sounds. To modify the tone of amplified bass instruments, a range of electronic bass effects are available, such as distortion and chorus.

Symphonic strings

The string instruments usually used in the orchestra, and often called the "symphonic strings" are:[4]

When the instrumentation of an orchestral work is said to include "strings," is it very often this combination of string parts that is indicated. Orchestral works rarely omit any of these string parts, but fairly often will include additional string instruments, especially harp and piano. In the Baroque orchestra, harpsichord is almost always used to play the basso continuo part (the written-out bass line and improvised chords), and often a theorbo or lute. In some classical music, such as the string quartet, the double bass is not typically used; the cello plays the bass role in this literature.