Mandolin-banjo became more popular. In the heyday of mandolin orchestras and banjo bands (late 19th–early 20th century), all sorts of instruments were produced. The mandolin-banjo is one of the hybrids that resulted. It enabled mandolinists to produce a banjo sound without having to learn that instrument's fingerings. The instrument adds the banjo's volume to the mandolin. The banjolin is different from the banjo-mandolin in the number of strings that it has. Banjolins today are supposed to have four strings instead of 8 strings (in courses or pairs). However, that distinction is not universal; the "banjolin" name was patented in 1885 by
Mandolin suit them to Cai luong opera music. In the mid-1930s, they made concave frets, scooping out extra wood between the frets, making the space between them deep and to allow the musicians to bend the notes, and stringing them with four single strings. Musicians Hai Nén and Hai Nhành were associated with the instruments, possibly being the first to use them. The "sunken-fret mandolin" (mandolin phím lõm) did not meet the musical needs as well as the sunken-fret guitar, because the mandolin's rigidity made it painful to get the same effects from the strings. Also the mandolin's narrow fretboard made