Watch the Cool Grip online guitar lesson by Jimmy Heffernan from Dobro Handbook
Now let's hit that D bar chord at the 7th fret; we'll slide into it and then use the first string open D to drone against.
The open string will yield a cool open ringing sound that makes the dobro really sing out. I have to admit that I do this too much because it's that addictive! Do it without the drone string and you'll hear how flat and lifeless the sound is without the drone.