1911 Encyclopædia Britannica/Theorbo
THEORBO [Fr. théorbe, Ger. Theorba, Ital. theorba, Baritone], the large double-necked bass lute much used during the 16th and 17th centuries as general bass in the orchestra. The body of the theorbo was constructed on the same principles as that of the lute but larger, and the same scheme of decoration was followed. The neck, instead of being bent back at an angle to form the head, was straight, having sufficient pegs set in the sides of the head for from 12 to 16 strings tuned in pairs of unisons; on the fingerboards were marked 8 or more frets for semitones. Above this neck was another without frets, curving forwards and slightly to one side to enable the long bass strings, stretched not over but at the side of the neck, to escape the pegs of the shorter strings. These free strings, known as diapason strings (Ger. Begleitseiten) were plucked à vide like those of the lyre, each giving but one note; the number of these strings varied from 8 to 12.
The theorbo was made in two sizes, the ordinary instrument measuring about 3 ft. 6 in., and the Paduan, also known as archlute, about 5 ft. The chitarrone, or Roman theorbo, was the largest of all, a contrabass lute in fact, and frequently stood over 6 ft. high. It differed slightly from the theorbo; the body was a little smaller than in the Paduan variety, the whole of the extra length being in the second neck. The strings over the fingerboard were of steel or brass, and the diapason strings of spun wire.