The Kamancheh is a bowed violin-type instrument with a round soundbox, either made from steam-bent strips of wood or hollowed from one piece. The soundbox is covered with skin and produces a very warm tone. The bow strings used to play the kamancheh are attached at one end by a loose leather strip which is held tightly or loosely in the right hand. This enables the tension of the bow to be varied while playing. The origin of the kamancheh, which is more recent than santur and setar, is uncertain. Some scholars have credited the Kurds, an ancient Iranian people, with the instruments, while others claim that bowed instruments originated with nomads from further north, perhaps of the Mongol race. Originally the kamancheh had only three strings, two silk and one brass, but recently a fourth was added and the strings changed to metal under the influence of the violin.