Editing Hornbostel–Sachs (section)

===Free aerophones (41)===
Instruments in which the vibrating air is not contained within the instrument, for example, [[acme siren]]s or the [[Bullroarer (music)|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.&nbsp;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 instrument]]s 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).
*** 412.131 Individual free reeds.
*** 412.132 Sets of free reeds – [[Accordion]], [[harmonica]], and [[reed pipe]]s of the [[pipe organ]].
** 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.<ref>"[http://www.mimo-db.eu/HornbostelAndSachs/237 412.14 Ribbon reeds]", ''Mimo-db.eu.''</ref>
*** 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]].
*** 412.221 Independent tubes.
*** 412.222 Sets of tubes
** 412.23 Sets of disks and tubes
* 412.3 Mixed sets of interruptive aerophones

====Plosive aerophones (413)====
The sound is caused by a single compression and release of air. Examples include the [[Botija (instrument)|botija]], the [[gharha]], the [[ghatam]], and the [[udu]].

'''Mixed sets of free aerophones (414)'''