(Fr. perce; Ger. Bohrung).
The interior of a tubular wind instrument, whatever its material. Although some instruments are loosely described as cylindrical and others as conical or conoidal, the measured bores of wind instruments usually deviate significantly from these simple mathematical forms. The bore of an instrument determines the length and proportions of the contained Air column, and is the principal factor governing the pitches of the notes which may be sounded on it (see Acoustics, §IV). A relatively narrow bore may prevent the sounding of the fundamental frequency, while a wide one may make higher harmonics difficult to sound. The length of the bore in brass instruments may be varied by the use of valves to add or subtract supplementary tubing, while in woodwind the effective length is altered by opening or closing side holes. When the air column is vibrating, irregularities in the bore such as constrictions or the cavities under closed side holes, depending on their position relative to nodes and antinodes, may modify the frequency. Since the sounds of almost all wind instruments are complex, containing harmonic frequencies in varying proportion, the configuration of the bore affects the tone quality of every note. For further information see C. Karp: ‘Woodwind Instrument Bore Measurement’, GSJ, xxxi (1978), 9–28.
PHILIP BATE/MURRAY CAMPBELL