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. The top five levels of the scheme are as follows:
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, as well as 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 latter category includes the xylophone, the marimba, the glockenspiel, and the glass harmonica.
These idiophones are set in vibration by being struck, for example cymbals or xylophones.
Directly struck idiophones (111)
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.
111.242.21 Sets of resting bells whose opening faces upward.
111.242.22 Sets of hanging bells suspended from the apex.
111.242.221 Sets of hanging bells without internal strikers.
111.242.222 Sets of hanging bells with internal strikers.
111.3 Mixed sets of directly struck idiophones
Indirectly struck idiophones (112)
The player himself/herself 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.
Plucked idiophones, or lamellaphones, are idiophones set in vibration by being plucked; examples include the jaw harp or mbira. This group is sub-divided in the following two categories:
In the form of a frame (121)
The lamellae vibrate within a frame or hoop.
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.
121.221 Individual heteroglot guimbardes.
121.222 Sets of heteroglot guimbardes
121.23 Mixed sets of guimbardes
In the form of a comb (122)
The lamellae are tied to a board or cut out from a board like the teeth of a comb.
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.
211.21 Instruments in which the body has the same diameter at the middle and end (cylindrical drums)
211.211 Instruments which have only one usable membrane
211.211.1 Instruments in which the end without a membrane is open
211.211.2 Instruments in which the end without a membrane is closed
211.212 Instruments which have two usable membranes
211.212.1 Single instruments
211.212.2 Sets of instruments
211.213 Mixed sets of cylindrical drums
211.22 Instruments in which the body is barrel-shaped (barrel drums)
211.221 Instruments which have only one usable membrane
211.221.1 Instruments in which the end without a membrane is open
211.221.2 Instruments in which the end without a membrane is closed
211.222 Instruments which have two usable membranes
211.222.1 Single instruments
211.222.2 Sets of instruments
211.223 Mixed sets of barrel drums
211.23 Instruments in which the body is hourglass-shaped
211.231 Instruments which have only one usable membrane
211.231.1 Instruments in which the end without a membrane is open
211.231.2 Instruments in which the end without a membrane is closed
211.232 Instruments which have two usable membranes
211.232.1 Single instruments
211.232.2 Sets of instruments
211.223 Mixed sets of hourglass drums
211.24 Instruments in which the body is conical-shaped (conical drums)
211.241 Instruments which have only one usable membrane
211.241.1 Instruments in which the end without a membrane is open
211.241.2 Instruments in which the end without a membrane is closed
211.242 Instruments which have two usable membranes
211.242.1 Single instruments
211.242.2 Sets of instruments
211.243 Mixed sets of single-conical drums
211.244 Instruments in which the body is double-conical
211.244.1 Instruments which have only one usable membrane
211.244.11 Instruments in which the end without a membrane is open
211.244.12 Instruments in which the end without a membrane is closed
211.244.2 Instruments which have two usable membranes
211.244.21 Single instruments
211.244.22 Sets of instruments
211.245 Mixed sets of double-conical drums
211.246 Mixed sets of conical drums
211.25 Instruments in which the body is goblet-shaped (goblet drums)
211.251 Instruments which have only one usable membrane
211.251.1 Instruments in which the end without a membrane is open
211.251.2 Instruments in which the end without a membrane is closed
211.252 Instruments which have two usable membranes
211.252.1 Single instruments
211.252.2 Sets of instruments
211.253 Mixed sets of goblet drums
211.26 Mixed sets of tubular drums
211.3 Instruments in which the body depth is not greater than the radius of the membrane (frame drums).
211.31 Instruments which do not have a handle
211.311 Instruments which have only one usable membrane
211.312 Instruments which have two usable membranes
211.32 Instruments which have a handle
211.321 Instruments which have only one usable membrane
211.322 Instruments which have two usable membranes
Shaken membranophones (212)
Instruments which are shaken, the membrane being vibrated by objects inside the drum (rattle drums).
Plucked membranophones (22)
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).
Friction membranophones (23)
Instruments in which the membrane vibrates as a result of friction. These are drums which are rubbed, rather than being struck.
Friction drums with stick (231)
Instruments in which the membrane is vibrated from a stick that is rubbed or used to rub the membrane
231.1 Instruments in which the stick is inserted in a hole in the membrane
231.11 Instruments in which the stick can not be moved and is subject to rubbing, causing friction on the membrane
231.12 Instruments in which the stick is semi-movable, and can be used to rub the membrane
231.13 Instruments in which the stick is freely movable, and is used to rub the membrane
231.2 Instruments in which the stick is tied upright to the membrane
Friction drum with cord (232)
Instruments in which a cord, attached to the membrane, is rubbed.
232.1 Instruments in which the drum is held stationary while playing
232.11 Instruments which have only one usable membrane
232.12 Instruments which have two usable membranes
232.2 Instruments in which the drum is twirled by a cord, which rubs in a notch on the stick held by the player
Hand friction drums (233)
Instruments in which the membrane is rubbed by hand
Singing membranes (kazoos) (24)
This group includes kazoos, instruments which do not produce sound of their own, but modify other sounds by way of a vibrating membrane.
Free kazoos (241)
Instruments in which the membrane is vibrated by an unbroken column of wind, without a chamber
Tube or vessel-kazoos (242)
Instruments in which the membrane is placed in a box, tube or other container
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.
The strings are stretched across the mouth of a trough.
315.1 Without resonator.
315.2 With resonator.
Frame zithers (316)
The strings are stretched across an open frame.
316.1 Without resonator.
316.2 With resonator.
Composite chordophones (32)
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.
Instruments in which the vibrating air is not contained within the instrument, for example sirens, or the bullroarer.
Displacement free aerophones (411)
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.
Interruptive free aerophones (412)
The air-stream is interrupted periodically.
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).
The vibrating air is contained within the instrument. This group includes most of the instruments called wind instruments in the west, such as the flute or French 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
421.122.4 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, bock of resin) and an exterior tied-on cover (cane, wood, hide).
(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 theremins or synthesizers, 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. However, the original 1914 version of the system did not acknowledge the existence of his 5th category.
Present-day ethnomusicologists, such as Margaret Kartomi (page 173) 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.
Application of the system
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 (it is basically a bent conical tube through which you blow like a trumpet, but it does not have valves or finger holes). 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.
Suffixes and composite instruments
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.
In the study of musical instruments, organology, there are many different methods of classifying musical instruments. Most methods are specific to a particular cultural group and were developed to serve the requirements of that culture and its musical needs. Such classification schemes often break down when applied outside of their original context. For example, a classification based on instrument use may fail when applied to culture which has a different use, or even multiple uses, for the same instrument.
An aerophone is a musical instrument that produces sound primarily by causing a body of air to vibrate, without the use of strings or membranes, and without the vibration of the instrument itself adding considerably to the sound.
An idiophone is any musical instrument that creates sound primarily by the vibration of the instrument itself, without the use of air flow, strings (chordophones), membranes (membranophones) or electricity (electrophones). It is the first of the four main divisions in the original Hornbostel–Sachs scheme of musical instrument classification. The early classification of Victor-Charles Mahillon called this group of instruments autophones. The most common are struck idiophones, or concussion idiophones, which are made to vibrate by being struck, either directly with a stick or hand or indirectly, by way of a scraping or shaking motion. Various types of bells fall into both categories. A common plucked idiophone is the Jew's harp.
A lamellophone is a member of the family of musical instruments makes its sound by a thin vibrating plate called a lamella or tongue, which is fixed at one end and has the other end free. When the musician depresses the free end of a plate with a finger or fingernail, and then allows the finger to slip off, the released plate vibrates. An instrument may have a single tongue or a series of multiple tongues.
Struck idiophones is one of the categories of idiophones that are found in the Hornbostel-Sachs system of musical instrument classification.
Reed aerophones is one of the categories of musical instruments found in the Hornbostel-Sachs system of musical instrument classification. In order to produce sound with these Aerophones the player's breath is directed against a lamella or pair of lamellae which periodically interrupt the airflow and cause the air to be set in motion.
There are several overlapping schemes for the classification of percussion instruments.