Acoustic Instruments

In the modern world, musical instruments are often divided into two broad categories; acoustic instruments, of the kind that usually require nothing more than a player to the produce the sound, and more recent electronic instruments that need electrical power and the participation of modern technology.

Acoustic instruments go back a long way. Indeed, both strings and wind instruments were used in Biblical times and also had a significant role in the ancient Greek and Roman empires. During the Middle Ages small groups of musicians would entertain using the harp, lyre, psaltery, wind instruments and drums. By the 16th century and early 17th century the recorder, lute and viol, as well as a wide range of keyboard instruments had been developed. And by the end of the 18th century most instruments of the orchestra had acquired a form that we would easily recognise today.

Modern electronic instruments are a continuation in this chain of development, either in their method of use or in physical presentation. For example, the keyboard in a modern synthesiser has a similar appearance to that of a piano, as originally conceived nearly three hundred years ago.

Making Sounds

An acoustic instrument is operated entirely by human effort, and in most instances by the energy of the player alone. Although the workings of such devices can be explained by modern science their development was only achieved after years of hit-and-miss experimentation.

Such instruments can produce surprisingly loud sounds by exploiting the resonance of physical structures such as boxes, rods or tubes. This creates a noise that’s tuned around a fundamental frequency, although harmonics, as described below, are also produced. Such harmonics give each kind of instrument its own characteristic tonal quality.

A typical instrument consists of a vibrator, an object that vibrates to create the sound, and a resonator, often a hollow object that amplifies and enhances the sound.

Characteristics of an Instrument

The characteristics of the sound produced by a particular instrument is known as its timbre. This is mainly determined by the instrument’s shape and material, as well as by the way it’s played, usually by striking, blowing, plucking or bowing.

The variation in sound level that occurs whilst playing a single note, known as the instrument’s envelope shape, is a very important timbral characteristic. It can be divided into three time periods: attack (the very beginning of the note), sustain (the main period of sound activity) and decay (the falling-away of sound at the end of the note). In a piano, for example, the attack is very fast and is followed by considerable volume during the sustain period and then a short decay. If the sound of an instrument is edited on a tape recorder or played backwards it can be very difficult to identify.

The second aspect of timbre is the instrument’s frequency spectrum. Most instruments produce numerous harmonics, also known as upper-partials or overtones. These harmonics are at multiples of the fundamental note but are usually quieter than the fundamental. Those harmonics that are at higher multiples of the fundamental are often quieter in proportion to the multiple. One example, the clarinet, is characterised by loud odd harmonics (the fundamental times 3, 5, 7, 9 and so on) whilst a flute has louder even harmonics (the fundamental times 2, 4, 8, 16 and so on).

Thirdly, there are formant regions, the ability of an instrument to amplify particular frequencies in a sound spectrum, usually set by the instrument’s shape. Most instruments have several formant regions, although these are usually fixed by the dimensions. However, the formant regions of the human voice constantly change as the shape of the mouth is adjusted to create vowel sounds. This explains why a recorded voice can sound so peculiar when played back at an incorrect speed.

Instrument Types

Instruments are traditionally divided into families, such as strings, woodwind, brass, percussion and keyboard, although the boundaries between some groups can be rather indistinct. In 1914, Curt Sachs and Eric M von Hornbostel divided instruments into categories known as chordophones, aerophones, idiophones, membranophones and electrophones.

Many of these categories are described in the following sections.


The earliest forms of instruments involve the striking of one object, in some instances the human hand, against another object, so as to create an impulsive sound. This category can be divided into idiophones, membranophones (also known as drums) and metallophones.


An idiophone consists of a resonant wooden or metallic object that’s struck, rattled or stroked to create a sound. This category includes common percussion devices such as the cymbal, triangle and xylophone but not membranophones (see below). A metal device of this kind is known as a metallophone (see below). Idiophones didn’t really become popular in Western music until the 20th century.

Idiophones, excluding metallophones, can be divided into two groups:-

Indefinite Pitch Idiophones

Such instruments produce an untuned sound, consisting mainly of random sound of random frequency (effectively filtered white noise) and usually having a hard attack and short decay. Common instruments in this group include castanets and shakers, as well as the whip or rattle.

Definite Pitch Idiophones

These advanced percussion instruments are pitched or tuned. This is caused by resonance, in which physical dimensions of components in the instrument determine the frequency of cyclic oscillation.

Instruments of this kind, such as a marimba or xylophone, usually contain elements that are tuned to create a scale. For example, the xylophone has wooden bars arranged in a chromatic scale and is struck with wooden hammers. The length of each bar determines the pitch of the corresponding note.

Metallophones (Metal Idiophones)

The acoustic properties of metal (similar to glass, but more durable) ensures a high quality of resonance, giving a pure sound that’s rich in harmonics and having a characteristic tonal quality.

As with other idiophones, the metallophone family can be divided into two groups:-

Indefinite Pitch Metallophones

As with idiophones of indefinite pitch, these instruments produce an untuned sound. This category includes the anvil, cow bells, modern cymbals, tam-tams (Chinese gongs), temple blocks, triangles and sleigh bells. In reality, both temple blocks and triangles have a definite pitch, but aren’t tuned to a standard note and are used purely for percussion.

A pair of cymbals, either struck with a stick or against each other, are usually made of concave brass or bronze disks, which can produce a vast amount of noise. The triangle, which is slightly quieter, consists of a suspended rod, folded into a convenient triangular shape, and struck by another rod.

Definite Pitch Metallophones

This group include church bells, hand bells, celesta, ancient cymbals, glockenspiel, gongs, steel drums, tubular bells, tubular chimes and the vibraphone.

The development of tuned metal instruments has proceeded along several different lines. For example, a tuned rod can be replaced by a tube, which is easier to tune and forms part of a set of tubular bells. Alternatively, the tube can be flared into the familiar shape of a church bell, manufactured using an alloy of copper and tin, with more tin than in bronze. This shape gives a horn effect, increasing the amount of sound that’s projected outwards. A carillon consists of a set of bells in a church tower which is played using a keyboard located within the church itself or lower down the tower.

The glockenspiel is made from a series of bells, metal bars or tubes that are played with hammers. A similar sound is produced by the celesta, a keyboard instrument containing metal bars.

The gong, popular in eastern music, has a turned rim that gives it a resonant note. From the other side of the world, the steel drum, derived from the traditional kettle drum, is actually a fully-tuned instrument. Although constructed of metal, it could be considered to be a membranophone (see below).

Membranophones (Drums)

A membranophone contains a membrane, usually built into some form of drum. Traditionally, this is created by tightly stretching a skin over a hollow cylinder or hemisphere. This is then made to vibrate by striking or shaking. In most instances the membrane is struck directly, although some types of vertical bass drum use a pedal and lever. The drum first appeared in the East, moving into ancient Greece and then into Europe during the medieval period. The horizontal kettledrum, also known as timpani, arrived before 1400 and was used for orchestral work in the 17th century.

Most drums produce more noise components than tonal sounds, although more advanced instruments can be pitched or tuned. As always, this is caused by resonance, in which the physical dimensions determine the frequency of oscillation. The timpani is often used as a tuned instrument, the tuning set by tightening or relaxing the skin of the drum.

Other drums, such as roto toms, can be used as tuned instruments whilst tom toms may or may not be used at a definite pitch. The bass drum, bongos, side drum, tabor, tambourine and tenor drum are invariably used at an indefinite pitch.

Stringed Instruments

The vibration of any string under tension produces resonance, usually at a fundamental frequency determined by the length of the string. However, it can also vibrate in several other modes so as to create harmonics. In a stringed instrument, also known as a chordophone, the string or strings are excited either by plucking, striking, or stroking with a bow. In some instruments such actions are achieved using a mechanical system coupled to a keyboard.

Non-keyboard Chordophones

The strings in most traditional chordophones are excited by hand, as in the harp, violin or guitar. The characteristics of such an instrument are determined by the nature of the strings and associated resonating box or sound box. The strings can be plucked, sometimes with a plectrum, bowed or hammered. Where the strings are hammered the instrument can be considered to be a percussion device, although stringed instruments are rarely used for this purpose.

The Harp and its Derivatives

The oldest kind of chordophone is the harp, which first appeared around 4,000 BC in Africa. It consists of numerous vertical strings held within a frame, usually with a sound box along the bottom of the frame. Unlike many other stringed instruments, the strings aren’t stopped or fingered by the player, meaning that an individually-tuned string is required for every note. A modern harp works in a basic scale of C flat major, although this can be adjusted by a set of pedals.

In the psaltery and zither the strings are positioned above a flat sound box. The latter, which is laid on the knees and plucked, is common in central Europe. It has four or five strings as well as drone strings that can also be plucked, if required. The dulcimer is similar to the zither but its strings are hammered, forming the origins of the piano (see below). The Hungarian dulcimer, which is sometimes used in concerts, is also known as the cimbalom. The Japanese koto, also related to the zither, has 13 strings and is played horizontally with three plectrums.

The harp is large because it has to accommodate so many strings. However, in other instruments the number of strings can be reduced by using fingering, in which the player holds down the strings at specific points to adjust their tuning. Many later instruments were designed in an attempt to compromise between the number of strings and the complexity of fingering.

The Violin Family

The violin and related instruments are derived from the lute, as used 2,000 years ago, but also popular in the 15th and 16th centuries. Instruments of this kind, including the banjo and guitar (see below), usually have frets to assist in fingering. Some variations, such as the sitar, have drone strings that can be plucked or that vibrate in sympathy with the main strings.

The fiddle, originating in the Middle Ages, was first played with an archery bow, but by the 18th century the modern horsehair bow was in use. The viol family, introduced in the Renaissance, were vertical six-stringed and fretted instruments in treble, tenor and bass sizes, whilst the related violone was of double-bass size. Of these, the viol was popular until the end of the 17th century. Unlike others in this family, the viola d'amore was fretless and was played under the chin like a modern violin. The bow was used on 7 strings whilst another 7 strings beneath vibrated in sympathy.

In the 17th century the fretless violin family, consisting of the violin, viola and cello, was developed from the viola family. This entire group, made up of treble violin, alto viola or tenor viola, bass cello, and double-bass, are played with a gut bow, usually have four strings and incorporate a sound box. The violin itself is the highest pitched of the family, covering a range of over three and a half octaves, beginning from G below middle C. Unlike the other instruments in this family, the double-bass is more closely related to the violone.

The sophistication of these instruments is demonstrated by their amazing ability to express human emotion. Modern versions are often fitted with ‘acoustic’ electric pick-ups to make themselves heard above electronic instruments. Players also employ a mute, a pronged damper that can be placed on the bridge of a bowed instrument to reduce its volume or modify the tone.

The Guitar

The banjo and guitar are also derived from the lute, with the guitar having a Spanish origin. Unlike other earlier instruments, they have frets to assist fingering. The guitar usually has six gut strings, covers a range of three octaves and incorporates a sound box that acts as an amplifier: this is tuned to cover the range of the instrument but without unwanted resonances. Alternative fingering can give the same note or chord (a combination of notes) but with subtle variations, whilst the twelve-string guitar, although difficult to play, can create extremely complex sounds. The guitar evolved even further in last century with the arrival of highly-tensioned steel strings and electric pick-ups.

Keyboard Chordophones

Over the last few hundred years, attempts have been made to create stringed instruments that could be played easily. One of the earliest was the clavichord, as used in the 17th and 18th centuries, employing metal tangents to strike the strings. The larger harpsichord was popular between the 16th and 18th centuries. This was sometimes called a cembalo, but was basically a harp, rotated by 90 degrees, and plucked by means of quills or leather points that were controlled by a double keyboard.

The legless virginal was similar to a harpsichord but was oblong, with the keyboard at the longer side of the sounding-board. Unfortunately, the term ‘virginal’ was also applied to other keyboard instruments, perhaps because they were played by young maidens. The spinet is a small wing-shaped variation of the true virginal, although the Italian word spinetto is used for both virginal and spinet.

The Piano

The dulcimer, or cembalo in Italian, was developed from the clavichord. This has its strings positioned over a sounding-board to increase the volume, whilst the strings themselves are struck with hammers instead of being plucked. This was the prototype for the pianoforte or piano of 1709, which used dampers to stop vibrations when a key was released.

The modern piano, built with an iron frame to ensure tuning stability, has 88 keys on its keyboard. In a grand piano the strings are positioned horizontally, with an angled lid that projects the sounds outwards, whilst in an upright piano the strings are set in a vertical position.

All pianos have two pedals, commonly known as piano (soft) and forte (loud), for regulating the tone. The left-hand soft pedal usually works by bringing the hammers closer to the strings prior to their movement, whilst the right-hand sustain pedal, sometimes erroneously known as the loud pedal, allows the player to extend the duration of a sound by lifting away the instrument’s dampers. On some pianos there’s also a centre pedal that allows only chosen notes to be sustained.

Wind Instruments

A wind instrument, or aerophone, creates sound from a vibrating column of air within a tube or cavity, as used in an organ, accordion, woodwind instrument or brass instrument. Some instruments are controlled using a keyboard (see below).

Brass Instruments

The earliest wind instrument is the horn (literally made of animal horn or a shell) that resonates and amplifies the buzzing sound produced by the player’s lips: the player actually forms part of the instrument. More powerful horns exploit the resonance of metal, as in the trumpet, which was originally a long tube with a mouthpiece at one end and a bell-horn at the other. In these ancient forms the note was determined purely by the player, limiting the number of tones that could be played. The bugle is a small trumpet that was used by huntsmen and for military signals.

The technology of the 19th century introduced coiled pipes and valves to many instruments. In the modern version of the trumpet the effective length is adjusted by three valves to give a chromatic scale, whilst the cornet uses valves operated by pistons. In the trombone, known in Early English as the sackbut, the length is made continuously adjustable by using tubes sliding one inside another.

In the saxhorn family of trumpet instruments, including the saxtuba, the bell-mouth either points upwards or the tube encircles the player’s body. The modern tuba, the deepest-toned of the group, has three or four valves, although older valveless types can only play a few tones. The saxophone, although a brass instrument, has a single reed of flat cane and is controlled by keys. As the player blows into the instrument the reed vibrates against the mouthpiece, creating the sound.

Woodwind Instruments

Early woodwind instruments that use a vibrating tongue or reed include the bagpipes, shawm and hautboy. Most of these instruments have double reeds that vibrate to create a nasal sound. The bagpipes are unusual in that a drone, a constant bass note, is played alongside the tune itself.

The hautboy was eventually developed into the oboe, an instrument with a plaintive incisive tone, used in it’s modern form since the 18th century. The bassoon, again double-reeded, is the bass instrument of the oboe family. The cor Anglais, also known as the French horn, has coiled tubes, valves and a wide bell. It sounds similar to the oboe but is lower in pitch.

The clarinet is slightly different, containing a single reed made of flat cane that vibrates against the mouthpiece, and controlled both by fingered tone holes and keys.

A whistle-pipe or penny-whistle is a simple tuned pipe with an orifice near the mouthpiece across which air is forced to pass. The recorder is a development of this, in which the length of the pipe, and hence the pitch, is adjusted by covering tone holes along the pipe by the player’s fingers.

The flute is derived from the recorder, although in this instrument, frequently made of metal, the sound is created by blowing transversely across a hole. The orchestral flute usually has keys and pads instead of tone holes. The piccolo, a smaller brother of the flute, plays one octave higher.

Other Reed Instruments

A wide range of instruments were developed around metal reeds, particularly in the 19th century. The simplest is the mouth-organ or harmonica, which uses a separate reed for each note.

The accordion, which later acquired a piano-like keyboard to become the piano-accordion, is driven by hand-operated bellows, in the same way as the early squeeze-box. A later development, particularly popular in small churches, was the harmonium, a keyboard instrument whose bellows were driven by pedals operated by the performer.

Keyboard Aerophones (Organs)

The first keyboard instrument was the hydraulos, created by Ktesibios of Alexandria in around 250 BC. It used sliders that directly controlled the flow of air into pipes, often requiring the player to close each slider after playing a note. By the 14th century this idea had evolved into the pipe organ, which was really a row of huge whistle-pipes. Air was blown through the pipes (at least one for every note) by bellows, also known as the organ blower, as was the person powering them. In the 16th century a pedal keyboard was added, creating something very similar to a modern organ. Smaller versions were also made, such as the medieval portative organ that could be carried by a player.

The tone of the organ was adjusted by using different stops that determined which set of pipes was used to play a note. The set controlled by a particular stop was known as a register. Such stops could form groups or partial organs, each with a separate keyboard. Up to five of these keyboards were provided: counting upwards they were known as choir, great, swell, solo, and echo, although many organs only had the first three of these or the second pair of keyboards. Most organs also had a pedal keyboard, as developed in Germany at the end of the 15th century.

Early pipe organs only had a few keys but the number eventually increased to the current count of 61 keys, complete with white keys at the front and raised black keys at the rear, as used in a piano.

Keyboard Instruments

This ‘artificial’ category of instruments spans many of the groups described above. Such devices contain sound generators that are excited by a hand or feet-actuated keyboard, connected to each generator via a mechanical or electrical linkage known as an action. In most instances each key actuates a vibrator that creates a sound at the required pitch. In traditional instruments the force on the key itself excites the vibrator, as in a piano, or it can control another source of power, as in a wind-driven organ. And in a modern synthesiser it simply controls electronic circuitry.

Unlike most instruments, where a musician only plays a few notes at once, a keyboard allows several notes to be played simultaneously. It therefore established polyphonic and even-tempered music in the Western world. Unfortunately, keyboard control also prevents the musician from making subtle changes to sound quality, pitch, attack and decay.

By the Middle Ages the simple ‘sliders’ of the hydraulos had been replaced by a balanced keyboard, initially just with ‘white’ keys, restricting the player to a natural or diatonic scale. The raised ‘black’ keys required for the alternative chromatic scale were added at a later date.

At the end of this period, keyboards appeared on stringed instruments related to the zither, leading to the clavichord, harpsichord, and piano, all with distinctive mechanisms for exciting the strings. Around this time pedalboards were also introduced to many instruments. The standard piano-style keyboard has since been used in many other instruments, including numerous electronic devices.

©Ray White 2004.