The dhrupad tradition in North Indian classical music came to fruition in the 16th century. The product of a three-thousand-year evolution, its origins were in the chanting of the Vedas. Though the art of dhrupad was primarily a vocal tradition,  an instrumental verson was developed  on the stringed instrument called  "rudra veena" or "been".
In the Twenty-First Century
Later, the gradual development of a more highly ornamented and rhythmic style called "khyal" gave rise to new instruments with different characteristics. One of these was the sitar. Though well suited for the exciting rhythmics and plucked string techniques of instrumental khyal, sitars of the time were restricted in their ability to render the meend, and certain other subtleties characteristic of dhrupad. 
By the 19th century, the dhrupad style had been eclipsed in popularity by khyal. As a consequence, been players, and their instruments, dwindled in number. Fearing the loss of the great dhrupad tradition entirely, certain musicians turned their attention toward a revival of dhrupad. Part of this revival involved the creation of new instruments. One important one was the surbahar. 
Surbahar combined the tone and volume of the sitar with the sustain and lower range of the rudra veena. The new instrument could also be fitted with sympathetic resonating strings, which were becoming very popular on sitars. Theresulting hybrid instrument gradually gained in popularity and contributed to the revival of interest in instrumental dhrupad. By the late 19th and early 20th century the surbahar was commonly used by sitar players to perform an introductory section in dhrupad style, which was followed by a khyal on sitar with tabla accompaniment.
The large size of  the surbahar made it difficult and tiring to play for the average musician. Meanwhile, in the twentieth century, instrument makers began to redesign the sitar to increase its sustain, add a lower range, and increase the number of sympathetic strings, creating a hybrid between traditional sitar and surbahar. Due to these advances, and the difficulties of playing, the surbahar waned in popularity. 
By the mid-to-late 20th century the surbahar had become a rarity. But now, at the dawn of the 21st century, there appears to be another revival of interest in dhrupad, worldwide. A few dedicated players are determined to carry on the tradition of surbahar, as a  modern equivalent for the nearly extinct rudra veena.
Copyright 2002, David Pontbriand Arts
The Surbahar
Due to its extended string length, the been could produce a relatively long sustain for a stringed instrument. This allowed the development oftechniques that could in many ways effectively emulate dhrupad vocal expression, especially in the use of  a graceful gliding technique called meendIn addition, the rudra veena had a four-octave range, extending to a very low pitch,  that was particularly well suited to the majestic and meditative qualities of dhrupad.
SURBAHAR
David Pontbriand
American Sitarist
Surbaharist
Photo: R. Scott Sherman