The Dominant Seventh voicings contain the root, the third, and the dominant seventh. Notice that we have changed only one note from the Major seventh; the seventh has been lowered a half-step.
they can be played with a 6th string or 5th string root.
The lowest note in these voicings is the root,and it tells you what chord you are playing. When played on the 3rd fret, these are G7 and C7. If you move to the 10th fret, they become D7 and G7.
Dominant chords are perhaps the most used chord type in jazz. I advise you to learn these voicings well.