The Afghan rubab is a short-necked double-chambered plucked lute with three main strings (tuned in 4ths), four frets (giving 12 semitones to the octave), two or three long drone strings, and up to fifteen sympathetic strings. It is the sympathetic strings that give the rubab its special sound. They are tuned to the notes of the rag (melodic mode) being performed, and reinforce the sound of each note as it is played. They produce a wash of sound, with complex interactions of the harmonics of each string. It is like having an echo chamber built into the instrument. The shortest sympathetic string is raised by a protuberance on the bridge so it can be easily struck in isolation and used as a high drone in complex rhythmic patterns that are the hallmark of the virtuoso player. The body of the rubab should be carved from a certain variety of mulberry wood called shah tut, 'king mulberry'. The lower chamber has a skin belly, or velum, while the upper has a wooden lid that serves as the fingerboard. This is often highly decorated with intricate mother-of-pearl inlays, laid out in the form of a tree of life, with leaves, flowers, and songbirds such as nightingales or canaries. Here are the names of the parts of the rubab in Dari (Afghan Persian).
The origins of the Afghan rubab are unclear. It is a member of an ancient family of double-chambered lutes that includes the Indian rubab, the Iranian tar, the Tibetan danyen, the Pamir rubab, the Dulan rewap, the Kashgarrewap, the Nepali tungna, and the Bengali dotara. The most distinctive features of the Afghan rubab are its unique shape and in having sympathetic strings. With minor differences the Afghan type of rubab is also found in adjacent areas of Pakistan and Iran, and in Kashmir. In the nineteenth century it was common amongst the Afghans settled in the Rokhilkand area of North India, especially around the city of Rampur, who traditionally served as mercenaries in the Mughal armies and were much involved in the supply of horses from Central Asia to India for military purposes. In the mid-nineteenth century the Afghan rubab became transformed into the Indian sarod, either in Lucknow or in Calcutta. Credit for this innovation is hotly contested between rival families of sarod players today, as discussed in Adrian McNiel's book Inventing the Sarod.