Here you can enjoy them in action:

Rastak a new ensemble for contemporary Persian folk music was formed as an experimental music group in 1997. The group seeks to collect, record and interpret traditional Persian folk music for a global audience, incorporating language, culture and history also merging traditional instruments and forms with contemporary rhythms. The musicians who comprise Rastak have graduated from the best universities in Iran and have done extensive research into Persian folk music.

History
It all began when Siamak and Behzad became friends on a winter’s day in 1994. Three years later, Siamak and Behzad were discussing the idea of forming an ensemble for folk music based on research, collection and interpretation. In 1997 Rastak Music Group was founded in Tehran. …
2002 marks Rastak’s meeting with renowned musicians in folk music from all around Iran such as: Khalifeh Aghe Ghosi from Kurdistan, Noor Mohammad Dorpoor from Khorasan, Shir Mohammad Espandar From Sistan and Balouchestan, Mohsen Heidarieh from Booshehr, Ashigh Imran & Ashigh Hasan from azerbaidjan, Faroogh Kiani from Khorasan, Abolhasan Khoshroo & Mohammadreza Es’haghi from Mazandaran, Dr. Tekkeh & Ghlich Anvar from Turkemen Sahra. Along with these meetings, Rastak began field recording and collecting folk music pieces. These endeavors prepared the material for one of Rastak’s major productions published under the name of ” minimalism in persian folk music “. These recordings demanded a studio, therefor the group made one.
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In 2006, Rastak took new members: Mohammad Mazhari, Yavar Ahmadifar, Akbar Esmaeelipour, Sahar Ebrahim, Sara Naderi, Kaveh Sarvarian and Hale Seyfizade. In addition to the new album, two concerts were conducted which gained considerable popularity.After Majid left and Sara Ahmadi joined the group , Rastak continued hiring educated and versatile musicians in terms of vocal and instrumental skills and capabilities for its international appearances. Eversince this time, Rastak has held worldwide concerts and made numerous recordings.

Sources:

http://irna.ir/fa/Photo/2799616/

http://www.whatsupiran.com/Profile/Rastak/About

Another good read is this beautiful travel blog by a german mexican couple who met Rastak accidently while traveeling through Iran:

http://www.tastingtravels.com/rastak-iranian-music/