Hornbostel and Sachs based their ideas on a system devised in the late 19th century by Victor-Charles Mahillon, the curator of musical instruments at Brussels Conservatory. Mahillon divided instruments into four broad categories according to the nature of the sound-producing material: an air column; string; membrane; and body of the instrument. From this basis, Hornbostel and Sachs expanded Mahillon's system to make it possible to classify any instrument from any culture.
Formally, the Hornbostel–Sachs is modeled on the Dewey Decimal Classification for libraries. It has five top-level classifications, with several levels below those, adding up to over 300 basic categories in all.
Idiophones primarily produce their sounds by means of the actual body of the instrument vibrating, rather than a string, membrane, or column of air. In essence, this group includes all percussion instruments apart from drums, and some other instruments. In the Hornbostel–Sachs classification, idiophones are first categorized according to the method used to play the instrument. The result is four main categories: struck idiophones (11), plucked idiophones (12), friction idiophones (13) and blown idiophones (14). These groups are subsequently divided through various criteria. In many cases these sub-categories are split in singular specimens and sets of instruments. The class of idiophones includes the xylophone, the marimba, the glockenspiel, and the glass harmonica.
The player executes the movement of striking; whether by mechanical intermediate devices, beaters, keyboards, or by pulling ropes, etc. It is definitive that the player can apply clear, exact, individual strokes, and that the instrument itself is equipped for this kind of percussion.
111.14 Concussion vessels or vessel clappers (spoons).
111.141 Castanets – Natural and hollowed-out vessel clappers.
111.142 Cymbals – Vessel clappers with manufactured rim.
111.2 Percussion idiophones – The instrument is struck either with a non-sonorous object (hand, stick, striker) or against a non-sonorous object (human body, the ground).
111.212 Sets of percussion sticks in a range of different pitches combined into one instrument. – All xylophones, as long as their sounding components are not in two different planes.
The player themself does not go through the movement of striking; percussion results indirectly through some other movement by the player.
112.1 Shaken Idiophones or rattles – The player makes a shaking motion
112.11 Suspension rattles – Perforated idiophones are mounted together, and shaken to strike against each other.
112.111 Strung rattles – Rattling objects are strung in rows on a cord.
112.112 Stick rattles – Rattling objects are strung on a bar or ring.
112.12 Frame rattles – Rattling objects are attached to a carrier against which they strike (flexatone).
112.121 Pendant rattles.
112.122 Sliding rattles.
112.13 Vessel rattles – Rattling objects enclosed in a vessel strike against each other or against the walls of the vessel, or usually against both.
112.2 Scraped Idiophones – The player causes a scraping movement directly or indirectly; a non-sonorous object moves along the notched surface of a sonorous object, to be alternately lifted off the teeth and flicked against them; or an elastic sonorous object moves along the surface of a notched non-sonorous object to cause a series of impacts. This group must not be confused with that of friction idiophones.
112.3 Split idiophones – Instruments in the shape of two springy arms connected at one end and touching at the other: the arms are forced apart by a little stick, to jangle or vibrate on recoil.
Plucked idiophones, or lamellaphones, are idiophones set in vibration by being plucked; examples include the jaw harpormbira. This group is sub-divided in the following two categories:
121.1 Clack idiophones or Cricri – The lamella is carved in the surface of a fruit shell, which serves as resonator.
121.2 Guimbardes and Jaw harps (i. e. "kissed" idiophones) – The lamella is mounted in a rod- or plaque-shaped frame and depends on the player's mouth cavity for resonance.
121.21 Idioglot guimbardes – The lamella is cut through the frame of the instrument (kubing).
121.211 Individual idioglot guimbardes.
121.212 Sets of idioglot guimbardes
121.22 Heteroglot guimbardes – The lamella is attached to the frame (Western Jew's harp, kouxian). Present-day ethnomusicologists, such as Margaret Kartomi (page 173) and Ellingson (PhD dissertation, 1979, p. 544), might support the suggestion that, in keeping with the spirit of the original Hornbostel–Sachs classification scheme, of categorization by what first produces the initial sound in the instrument, that the supposed class 412.13 should count as these instead.
Blown idiophones are idiophones set in vibration by the movement of air, for example the Aeolsklavier, an instrument consisting of several pieces of wood which vibrate when air is blown onto them by a set of bellows. The piano chanteur features plaques.
Instruments with a string attached to the membrane, so that when the string is plucked, the membrane vibrates (plucked drums).
Some commentators believe that instruments in this class ought instead to be regarded as chordophones (see below).
Chordophones primarily produce their sounds by means of the vibration of a string or strings that are stretched between fixed points. This group includes all instruments generally called string instruments in the west, as well as many (but not all) keyboard instruments, such as pianos and harpsichords.
Instruments which are in essence simply a string or strings and a string bearer. These instruments may have a resonator box, but removing it should not render the instrument unplayable, though it may result in quite a different sound being produced. They include the piano therefore, as well as other kinds of zithers such as the koto, and musical bows.
311.22 True stick zithers – NB Round sticks which happen to be hollow by chance do not belong on this account to the tube zithers, but are round-bar zithers; however, instruments in which a tubular cavity is employed as a true resonator, like the modern Mexican harpa, are tube zithers
Acoustic and electro-acoustic instruments which have a resonator as an integral part of the instrument, and solid-body electric chordophones. This includes most western string instruments, including lute-type instruments such as violins and guitars, and harps.
The plane of the strings runs parallel with the resonator's surface.
321.1 Bow lutes – Each string has its own flexible carrier
321.2 Yoke lutes or lyres – The strings are attached to a yoke which lies in the same plane as the sound-table and consists of two arms and a cross-bar
The plane of the strings lies at right angles to the sound-table; a line joining the lower ends of the strings would be perpendicular to the neck. These have notched bridges.
Aerophones primarily produce their sounds by means of vibrating air. The instrument itself does not vibrate, and there are no vibrating strings or membranes.
The air-stream meets a sharp edge, or a sharp edge is moved through the air. In either case, according to more recent views, a periodic displacement of air occurs to the alternate flanks of the edge. Examples are the swordblade or the whip.
412.1 Idiophonic interruptive aerophones or reeds – The air-stream is directed against a lamella, setting it in periodic vibration to interrupt the stream intermittently. In this group also belong reeds with a 'cover,' i.e. a tube in which the air vibrates only in a secondary sense, not producing the sound but simply adding roundness and timbre to the sound made by the reed's vibration; generally recognizable by the absence of fingerholes though present-day ethnomusicologists, such as Margaret Kartomi (page 173) and Ellingson (PhD dissertation, 1979, p. 544), might support the suggestion that, in keeping with the spirit of the original Hornbostel–Sachs classification scheme, of categorization by what first produces the initial sound in the instrument, that such reeds should not really remain as aerophones, exiting for the lamellophones.
412.11 Concussion reeds – Two lamellae make a gap which closes periodically during their vibration.
412.111 Independent pairs of concussion reeds.
412.112 Paired sets of concussion reeds
412.12 Percussion reeds – A single lamella strikes against a frame.
412.121 Independent percussion reeds.
412.122 Sets of percussion reeds. – Earlier organs
412.13 Free-reed instruments feature a reed which vibrates within a closely fitting slot (there may be an attached pipe, but it should only vibrate in sympathy with the reed, and not have an effect on the pitch – instruments of this class can be distinguished from 422.3 by the lack of finger-holes).
412.14 Band reed instruments – The air hits the sharp edge of a band under tension. The acoustics of this instrument have so far not been investigated.[3]
412.141 Individual band reeds.
412.142 Sets of band reeds
412.15 Mixed sets of reeds
412.2 Non-idiophonic interruptive instruments. The interruptive agent is not a reed.
412.21 Rotating aerophones (interruptive agent rotates in its own plane and does not turn on its axis)- Siren disk.
412.211 Independent disks.
412.212 Sets of disks
412.22 Whirling aerophones (interruptive agent turns on its axis) – Bullroarer, whirly tube.
The vibrating air is contained within the instrument. This group includes most of the instruments called wind instruments in the west, such as the fluteorFrench horn, as well as many other kinds of instruments such as conch shells.
421.121.2 Partly stopped side-blown flutes – The lower end of the tube is a natural node of the pipe pierced by a small hole.
421.121.21 Without fingerholes.
421.121.22 With fingerholes
421.121.3 Stopped side-blown flutes.
421.121.31 Without fingerholes.
421.121.311 With fixed stopped lower end – (apparently non-existent).
421.121.312 With adjustable stopped lower end – piston flutes.
421.121.32 With fingerholes.
421.121.321 With fixed stopped lower end
421.121.322 With adjustable stopped lower end
421.122 Sets of side-blown flutes.
421.122.1 Sets of open side-blown flutes.
421.122.2 Sets of partly stopped side-blown flutes.
421.122.3 Sets of stopped side-blown flutes.
421.122.31 With fixed stopped lower end
421.122.32 With adjustable stopped lower end
421.122.33 Mixed
421.122.4 Mixed sets of stopped side-blown flutes.
421.13 Vessel flutes (without distinct beak) The body of the pipe is not tubular but vessel-shaped – Xun.
421.2 Flutes with duct or duct flutes – A narrow duct directs the air-stream against the sharp edge of a lateral orifice.
421.21 Flutes with external duct – The duct is outside the wall of the flute; this group includes flutes with the duct chamfered in the wall under a ring-like sleeve and other similar arrangements.
421.211 (Single) flutes with external duct.
421.211.1 Open flutes with external duct.
421.211.11 Without fingerholes.
421.211.12 With fingerholes.
421.211.2 Partly stopped flutes with external duct.
421.211.21 Without fingerholes.
421.211.22 With fingerholes.
421.211.3 Stopped flutes with external duct.
421.211.31 Without fingerholes.
421.211.32 With fingerholes.
421.212 Sets of flutes with external duct.
421.22 Flutes with internal duct – The duct is inside the tube. This group includes flutes with the duct formed by an internal baffle (natural node, block of resin) and an exterior tied-on cover (cane, wood, hide).
422.3 Reedpipes with free reeds – The reed vibrates through [at] a closely fitted frame. There must be fingerholes, otherwise the instrument belongs to the free reeds 412.13.
(422.4 Reedpipes with band reeds – Though the precise acoustics of 412.14 are as yet unknown, wherefore it is as yet unknown whether the instrument must be fingerholed in order to belong to this class rather than 412.14, nevertheless it should be physically possible to put a band reed in a pipe.)
422.5 Mixed sets of reedpipes
422.6 Non-idiophonic interruptor pipes. The interruptive agent is not a reed.
422.61 Rotating aerophones (interruptive agent rotates in its own plane and does not turn on its axis)- Siren diskpipes.
422.611 (Single) diskpipes
422.611.1 With regular bore
422.611.11 Without fingerholes.
422.611.111 With independent disks.
422.611.112 With sets of disks
422.611.12 With fingerholes
422.611.121 With independent disks.
422.611.122 With sets of disks
422.611.2 With irregular bore
422.611.21 Without fingerholes.
422.611.211 With independent disks.
422.611.212 With sets of disks
422.611.22 With fingerholes
422.611.221 With independent disks.
422.611.222 With sets of disks
422.612 Sets of diskpipes
422.612.1 With regular bore
422.612.11 Without fingerholes.
422.612.111 With independent disks.
422.612.112 With sets of disks
422.612.12 With fingerholes
422.612.121 With independent disks.
422.612.122 With sets of disks
422.612.2 With irregular bore
422.612.21 Without fingerholes.
422.612.211 With independent disks.
422.612.212 With sets of disks
422.612.22 With fingerholes
422.612.221 With independent disks.
422.612.222 With sets of disks
422.612.3 With mixed bores
422.612.31 Without fingerholes.
422.612.311 With independent disks.
422.612.312 With sets of disks
422.612.32 With fingerholes
422.612.321 With independent disks.
422.612.322 With sets of disks
422.62 Whirling aerophones (interruptive agent turns on its axis) – Bullroarerpipes, Matryoshka tubes.
51. Instruments having electric action (e.g. pipe organ with electrically controlled solenoid air valves);
52. Instruments having electrical amplification, such as the Neo-Bechstein piano of 1931, which had 18 microphones built into it;
53. Radioelectric instruments: instruments in which sound is produced by electrical means.
The fifth top-level group, the electrophones category, was added by Sachs in 1940, to describe instruments involving electricity. Sachs broke down his 5th category into 3 subcategories: 51=electrically actuated acoustic instruments; 52=electrically amplified acoustic instruments; 53= instruments which make sound primarily by way of electrically driven oscillators, such as thereminsorsynthesizers, which he called radioelectric instruments. Francis William Galpin provided such a group in his own classification system, which is closer to Mahillon than Sachs–Hornbostel. For example, in Galpin's 1937 book A Textbook of European Musical Instruments, he lists electrophones with three second-level divisions for sound generation ("by oscillation", "electro-magnetic", and "electro-static"), as well as third-level and fourth-level categories based on the control method. Sachs himself proposed subcategories 51, 52, and 53, on pages 447–467 of his 1940 book The History of Musical Instruments.
Present-day ethnomusicologists, such as Margaret Kartomi[4] and Ellingson (PhD dissertation, 1979, p. 544), suggest that, in keeping with the spirit of the original Hornbostel–Sachs classification scheme, of categorization by what first produces the initial sound in the instrument, that only subcategory 53 should remain in the electrophones category. Thus it has been more recently proposed that, for example, the pipe organ (even if it uses electric key action to control solenoid valves) remain in the aerophones category, and that the electric guitar remain in the chordophones category, etc.
Beyond the top three groups are several further levels of classification, so that the xylophone, for example, is in the group labeled 111.212 (periods are usually added after every third digit to make long numbers easier to read). A long classification number does not necessarily indicate the instrument is a complicated one. The valveless bugle, for instance, has the classification number 423.121.22, even though it is generally regarded as a relatively simple instrument. The numbers in the bugle's classification indicate the following:
4 – an aerophone
42 – the vibrating air is enclosed within the instrument
423 – the player's lips cause the air to vibrate directly (as opposed to an instrument with a reed like a clarinet, or an edge-blown instrument, like a flute)
423.1 – the player's lips are the only means of changing the instrument's pitch (that is, there are no valves as on a trumpet)
423.12 – the instrument is tubular, rather than being a conch-type instrument
423.121 – the player blows into the end of the tube, as opposed to the side of the tube
423.121.2 – the tube is bent or folded, as opposed to straight
423.121.22 does not uniquely identify the bugle, but rather identifies the bugle as a certain kind of instrument which has much in common with other instruments in the same class. Another instrument classified as 423.121.22 is the bronze lur, an instrument dating back to the Bronze Age.
After the number described above, a number of suffixes may be appended. An 8 indicates that the instrument has a keyboard attached, while a 9 indicates the instrument is mechanically driven. In addition to these, there are a number of suffixes unique to each of the top-level groups indicating details not considered crucial to the fundamental nature of the instrument. In the membranophone class, for instance, suffixes can indicate whether the skin of a drum is glued, nailed or tied to its body; in the chordophone class, suffixes can indicate whether the strings are plucked with fingers or plectrum, or played with a bow.
There are ways to classify instruments with this system even if they have elements from more than one group. Such instruments may have particularly long classification numbers with colons and hyphens used as well as numbers. Hornbostel and Sachs themselves cite the case of various bagpipes where some of the pipes are single reed (like a clarinet) and others are double reed (like the oboe). A number of similar composite instruments exist.
^Volume 46 (1914) of the Zeitschrift is available online in a variety of formats, as part of the digital collection of the University of Toronto. The article by Hornbostel and Sachs is to be found on pages 553–90.
