- Philip Bate
- , revised by Murray Campbell
The body of air inside a tubular wind instrument. When a note is sounded the air column is in a state of longitudinal vibration, i.e. subject to a cyclic succession of local compressions and rarefactions (see Acoustics §IV 2.). The frequency of these disturbances determines the pitch of the sound heard; it is governed mainly by the form and dimensions of the air column (see Bore), but also to an extent by the way in which the disturbances are engendered. Frequency is affected by such factors as the temperature and moisture content of the air, frictional effects at the surface of the confining tube or vessel and the transfer of viscous energy among its particles. When the column is in vibration the periodic disturbances do not terminate abruptly at the ends of the confining tube but extend a short distance into the surrounding air. Thus it is necessary to apply a correction factor when determining its effective or ...