1. Idiophones
Instruments which make sound primarily by way of the instrument itself vibrating, without the use of membranes or strings.11. Struck idiophones
Idiophones set in motion by a percussion action (includes instruments shaken or scraped as well as directly struck instruments).12. Plucked idiophones
Instruments set into vibration by plucking.13. Friction idiophones
Instruments set into vibration by rubbing.14. Blown idiophones
Instruments set into vibration by blowing or moving air.2. Membranophones
Instruments which make sound primarily by way of a vibrating membrane. Includes all drums.21. Struck drums
22. Plucked drums
Some commentators believe that instruments in this class ought instead to be regarded as chordophones (see below). 23. Friction drums
24. Singing membranes
Instruments in which a membrane modifies some other sound (typically the human voice) in some way (mirlitons).3. Chordophones
31. Simple chordophones
Instruments consisting of a simple string bearer and strings - there may be an additional resonator, but removing it should not destroy the instrument (so the resonator should not be supporting the strings).32. Composite chordophones
Instruments in which the resonator cannot be removed without destruction of the instrument.4. Aerophones
Instruments in which the vibrating air itself is the primary cause of sound. This can include a column of air being set in vibration (as in wind instruments) or an air-flow being interrupted by an edge (as in free-reeds).41. Free aerophones
The vibrating air is not contained within the instrument.412.13. Free-reed instruments
The reed 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).413. Plosive aerophones
The sound is caused by a single compression and release of air.42. Non-free aerophones (wind instruments proper)
The vibrating air is contained within the instrument.421. Edge-blown instruments or flutes
The player makes a ribbon-shaped flow of air with his lips, or his breath is directed against an edge.422. Reed instruments
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.422.1 Double reed instruments
There are two lamellae which beat against one another.422.2 Single reed instruments
There is one lamella which beats against a solid surface.422.3
Similar to the free-reeds with a pipe attached - distinguished from them by the prescence of finger-holes in the pipe.423. Trumpets
The player's vibrating lips set the air in motion.423.1 Natural trumpets
There are no means of changing the pitch apart from the player's lips.423.2 Chromatic trumpets
The pitch can be changed by means of keys (423.21) a slide (423.22) or valves (423.23).5. Electrophones
Instruments in which sound is generated by electrical means.6. Hydrophones
A class of instruments in which sound is generated by water is also under consideration.