This site is awesome! You can click on any instrument and it provides you with high quality sample sounds, history, and information.
The use of traditional instruments has been decreasing due to the recent pop culture phenomenon for Iran and the underground indie and rap movements. As much as I love the persian pop songs and support them, I hope the use of these instruments doesn’t completely diminish. I had never been extremely fond of classic Iranian songs, but as I’m getting older, I’ve started to realize how much I appreciate it.
Just go out to your yard, drink some tea, and listen to the beautiful melodies of some daf, tar, or santur playing. You won’t regret it.