The đàn bầu (or dan bau, pronounced approximately "dan bou" in English) is a traditional Vietnamese monochordal zither instrument. Although the đàn bầu appears simple in design, and skillful playing of the instrument is so fluid as to seem effortless, looks can be deceiving! While the single string is plucked with one hand (simultaneously shortening and striking the string), the other hand uses the flexible rod to adjust the tension and bend the pitch.
The đàn bầu operates by way of harmonic overtones, meaning that the string is shortened at one of seven nodes: the octave at 1/2 length, perfect fifth at 2/3, perfect fourth at 3/4, just major third at 4/5, just minor third at 5/6, septimal minor third at 6/7, and septimal whole tone at 7/8. Other tones can be achieved by moving the rod to raise or lower pitch, or to add vibrato.
The instrument's name is a compound of đàn (stringed instrument) and bầu (gourd, the material from which the resonator was traditionally constructed). In its early iterations, dating back to at least 1770, the đàn bầu was constructed of a bamboo tube, wooden rod, coconut shell resonator, and a silk string. Modern design has replaced the bamboo with a wooden soundboard and the silk string with metal. The coconut shell is generally now made of wood today, and is more decorative than functional.
Culturally, the đàn bầu is very much Vietnamese, associated with street musicians and beggars. Vietnamese cultural memory is carefully passed down from one generation to the next through the playing of this instrument (as described here). That being said, as Vietnamese people have emigrated around the globe, cultural memory has expanded accordingly to encompass new influences.
Traditionally the đàn bầu is acoustic, but modern instruments with magnetic pickups also exist. While the instrument is central to Vietnamese folk music, many inroads have been made into contemporary Asian pop, rock, and other genres. The haunting and almost ethereal sound of the instrument lends itself well to many musical contexts, and electronic effects are sometimes used to allow for even greater dynamics and tonal texture with this already-versatile instrument.
Some examples of đàn bầu performance: