Bassoon (Fr. basson; Ger. Fagott; Ital. fagotto), a woodwind instrument with double reed mouthpiece, a member of the oboe (q.v.) family, of which it is the bass. The German and Italian names of the instrument were bestowed from a fancied resemblance to a bundle of sticks, the bassoon being the first instrument of the kind to be doubled back upon itself; its direct ancestor, the bass pommer, 6 ft. in length, was quite straight. The English and French names refer to the pitch of the instrument as the bass of the wood-wind.
The bassoon is composed of five pieces, which, when fitted together, form a wooden tube about 8 ft. long (93 in.) with a conical bore tapering from a diameter of 1&FRAC34; in., at the bell, to 3/16 in. at the reed. The tube is doubled back upon itself, the shorter joint extending to about two-thirds of the length of the longer, whereby the height of the instrument is reduced to about 4 ft. The holes are brought into a convenient position for the fingers by the device of boring them obliquely through the thickness of the wood. The five pieces are: - (1) the bell; (2) the long joint, forming the upper part of the instrument when played, although its notes are the lowest in pitch; (3) the wing overlapping the long joint and having a projecting flap through which are bored three holes; (4) the butt or lower end of the instrument (when played) containing the double bore necessitated by the abrupt bend of the tube upon itself. Both bores are pierced in one block of wood, the prolongation of the double tube being usually stopped by a flat oval pad of cork in the older models, whereas the modern instruments have instead a U-shaped tube; (5) the crook, a narrow curved metal tube about 12 in. long, to which is attached the double reed forming the mouthpiece.
The performer holds the instrument in a diagonal position; the lower part of the tube (the butt joint) played by the right hand resting against his right thigh, and the little bell, turned upwards, pointing over his left shoulder; a strap round the neck affords additional support. The notes are produced by means of seven holes and 16, 17, or 19 keys. The mechanism and fingering are very intricate. Theoretically the whole construction of the bassoon is imperfect and arbitrary, important acoustic principles being disregarded, but these mechanical defects only enhance its value as an artistic musical instrument. The player is obliged to rely very much on his ear in order to obtain a correct intonation, and next to the strings no instrument gives greater scope to the artist.
The bassoon has an eight foot tone, the compass extending from B♭ bass  to A♭ treble , or in modern instruments by means of additional mechanism to C or even F . These extra high notes are from their extreme sweetness called vox humana. The pitch of the bassoon apparently lies two octaves below that of the oboe, since the lowest note of both is B, but in reality the interval is only a twelfth, as may be ascertained by comparing their fundamental scales. On the bassoon the fundamental scale is that of F maj., obtained by opening and closing the holes; the notes downwards from F to B♭ are extra notes obtained by means of interlocking keys on the long joint, worked by the left thumb; they have no counterpart on the oboe and do not belong to the fundamental scale of the bassoon. The fundamental scale of the oboe is that of C, although the compass has been extended a tone to B♭ . Therefore the difference in pitch between the bassoon and the oboe is a twelfth. In the first register of the bassoon, seven semitones are obtained, as stated above, by means of keys in the long joint and bell; the next eight notes (holes and keys) each produce two sounds - the fundamental tone, and, by increased pressure of the breath, its harmonic octave. The remaining notes are obtained by cross fingering and by overblowing the notes of the fundamental scale a twelfth as far as A♭ which forms the normal compass. From A to E♭ the vox humana notes are produced by the help of small harmonic holes opened by means of keys at the top of the wind joint; exceptional players obtain, without additional keys, two or more higher harmonic notes, which, however, are only used by virtuosi. This then forms the intricate scheme of fingering for the bassoon, and in order to appreciate the efforts of such instrument makers as Carl Almenräder in Germany, Triebert and Jancourt in France, Sax in Belgium, Cornelius Ward and Morton in England, to introduce improvements based upon acoustic principles, it is necessary to understand what these general principles are, and why they have been disregarded in the bassoon. In all tubes the note given by the vibrating air column is influenced directly by the length of the tube, but very little, if at all, by the diameter of the bore. The pitch, however, is greatly affected by the diameter of the opening, whether lateral or at the bell, through which the vibrating column of air is again brought into communication with the outer air.
The tube only sounds the normal note in proportion to its length, when the diameter of the lateral opening is equal to the internal diameter of the tube at the opening. As in most of our early wood-wind instruments the holes would in that case have been too large to be stopped by the fingers, and key-mechanism was still primitive, instrument-makers resorted to the expedient of substituting a hole of smaller diameter nearer the mouthpiece for one of greater diameter in the position the hole should theoretically occupy. This important principle was well understood by the Romans, and perhaps even by the ancient Greeks, as is proved by existing specimens of the aulos (q.v.) and by certain passages from the classics.