Welcome to... "Micro-Lesson 300"
This, "open-string," sound uses chord patterns located all over the neck, yet still fits in open string tones around the chords. These open strings act to enhance the chord ideas with; 7th's, extended, or suspended chord colors.
The melody performed in this Micro Lesson begins from off of the 7th position at the 4th guitar string. It takes a fairly popular 4th string root, "A Power-chord," and applies a broken effect to it's sound using the open 5th string under a suspended 2nd and an extension of a 6th. The effect resonates with a long sustain across into measure two.
In measure three, the open 5th string, "A," continues under a, "D Minor," color. Even though there is no minor 3rd to promote the minor quality off of the, "D," root, we still have the effect due to the previously applied, "F," chord tone in the progression. The open string effect of measure three also includes the third string, "G," tone. While the 5th of the, "D," chord is strong, the bulk of the tones are suspended, (4th's and 2nd's).
The final measure applies use of wide interval three-note chord ideas that influence both, "E Minor," and, "D Minor," sounds. This occurs on the chords by way of, "Root - Octave - 5th," intervals. The lowest note is best played using, "Thumb in the Bass," technique.
Work across the changes slowly, and be careful with your fretting hand technique so as to give each chord good clarity. Enjoy the lesson!
Micro Lesson 300: "A Minor" Open String Melody