The usual method of extending triads to make 7, 9, 11, and 13 chords is to go above. (And I point out yet once more that's a theoretical and pedagogical convenience, not a historical narrative.) But we can also play with going the opposite direction. Here's an example, where (at a) the top note remains the same (just like the root would do if we were building upward) and the bass moves down by thirds. At (b) I've isolated the fifth movements that get us to Db#11.
This generates a surprisingly large percentage of basic chord types--and also a good sounding progression!
