TROMBONE, an important member of the brass wind family of musical instruments formerly known as sackbut (q.v.). The trombone is characterized by the slide, consisting of two parallel cylindrical tubes, over which two other cylindrical tubes, communicating at their lower extremities by means of a short semicircular pipe, slips without loss of air. The outer tube, therefore, slides upon the inner, thereby altering the total length of tube and so modifying the pitch. When the slide is closed the instru ment is at its highest pitch. To the upper end of one of the inner tubes is fastened the cup-shaped mouthpiece and to the end of the other tube is fixed the bell-joint, on the proper proportions of which depend the acoustic properties of the instrument.
Sound is produced on the trombone, as on the horn, by means of the lips stretched like a vibrating reed across the cup mouth piece from rim to rim ; the acoustic principles involved are the same for both instruments. By overblowing, i.e., by the varying tension of the lips and pressure of breath, the harmonic series is obtained, which is effective between the second and the tenth harmonics, the fundamental being but rarely of practical use. There are seven positions of the slide on the trombone, each giv ing a theoretical fundamental tone and its upper partials a semi tone lower than the last, and corresponding to the seven shifts on the violin and to the seven positions on valve instruments. These seven positions, which give a complete chromatic compass of two octaves and a sixth, are found by drawing out the slide a little more for each one.
The quality of tone varies greatly in the different instruments and registers. The alto trombone has neither power nor richness of tone, but sounds hard and has a timbre between that of a trumpet and a French horn. The tenor and bass have a full rich quality suitable for heroic, majestic music. The contra-bass trom bone, formerly little in request in the concert hall, is required for some modern orchestral music.
Besides the slide trombone, which is most largely used, there are the valve trombones, and the double-slide trombones. The former in which the slide is replaced by three pistons permit more brilliant execution than the slide instruments, but their tone is inferior. In the double-slide trombone the sliding branches are doubled and their length accordingly halved, thereby making the instrument more compact and lessening the length of the shifts, though demanding greater nicety in the adjustment of the slide.
The evolution of the trombone from the buccina is referred to in the article on the sackbut (q.v.), the name by which the earliest draw or slide trumpets, and subsequently the trombones, were known in England.
Of all wind instruments the trombone has perhaps been least modified in form; changes have occasionally been attempted, but for the most part with only trifling success. The application of ventils or pistons was made for the first time in 1818, in Germany, but instruments of this kind, though extensively used, have never superseded the original sliding type.