Wikipedia
Javārī, (also: 'joārī', 'juvārī', 'jvārī' (alternately transcribed 'jawārī', 'jowārī', 'joyārī', 'juwārī', and 'jwārī')) in Indian classical music refers to the overtone-rich "buzzing" sound characteristic of classical Indian string instruments such as the tanpura, sitar, surbahar, rudra veena and Sarasvati veena. Javari can refer to the acoustic phenomenon itself and to the meticulously carved bone, ivory or wooden bridges that support the strings on the sounding board and produce this particular effect. A similar sort of bridge is used on traditional Ethiopian lyres, as well as on the ancient Greek kithara, and the "bray pins" of some early European harps operated on the same principle. A similar sound effect, called in Japanese sawari, is used on some traditional Japanese instruments as well.
Under the strings of tanpuras, which are unfretted (unstopped), and occasionally under those bass drone strings of sitars and surbahars which are seldom fretted, cotton threads are placed on the javari bridge to control the exact position of the node and its height above the curved surface, in order to more precisely refine the sound of javari. These cotton threads are known in Hindi as 'jīvā', meaning "life" and referring to the brighter tone heard from the plucked string once the thread has been slid into the correct position. This process is called "adjusting the javari". After a substantial time of playing, the surface directly under the string will wear out through the erosive impact of the strings. The sound will become thin and sharp and tuning also becomes a problem. Then a skilled, experienced craftsman needs to redress and polish the surface, which is called "doing the javari" ("'Javārī Sāph Karņā' or "Cleaning the Javārī'").
The rich and very much 'alive' resonant sound requires great sensitivity and experience in the tuning process. In the actual tuning, the fundamentals are of lesser interest as attention is drawn to the sustained harmonics that should be clearly audible, particularly the octaves, fifths, major thirds and minor sevenths of the (fundamental) tone of the string. The actual tuning is done on three levels: firstly by means of the large pegs, secondly, by carefully shifting tuning-beads for micro-tuning and thirdly, on a tanpura, by even more careful shifting of the cotton threads that pass between the strings and the bridge, somewhat before the zenith of its curve.