Drop 2 chords

A drop 2 voicing starts from a close-position chord and drops the second note from the top down an octave. That one move turns a stack of thirds into the open, two-handed shapes that pianists and arrangers reach for all the time. Here is the idea with the two chords everyone starts on.

The C major triad

Close position first, in all three inversions:

X:1
M:4/4
L:1/1
K:C
"^root position"[CEG] | "^1st inversion"[EGc] | "^2nd inversion"[Gce] |]

Now take the second note from the top of each chord and move it down an octave:

X:1
M:4/4
L:1/1
K:C
"^root position"[E,CG] | "^1st inversion"[G,Ec] | "^2nd inversion"[CGe] |]

With a triad the result is simply an open voicing. The dropped note lands at or below middle C, so the left hand takes it and the right hand plays the other two. The labels name the close voicing each one came from, not the note that ends up in the bass.

C6

Add the sixth and there are four notes, so four inversions. Close position:

X:1
M:4/4
L:1/1
K:C
"^root position"[CEGA] | "^1st inversion"[EGAc] | "^2nd inversion"[GAce] | "^3rd inversion"[Aceg] |]

And the same four with the second note from the top dropped an octave:

X:1
M:4/4
L:1/1
K:C
"^root position"[G,CEA] | "^1st inversion"[A,EGc] | "^2nd inversion"[CGAe] | "^3rd inversion"[EAcg] |]

These four are the drop 2 shapes proper. Each one puts a fourth or a fifth between the bottom two notes and keeps the top three close together, which is why they sit so well under the hands, and why the top note always reads as the melody. Run them up the keyboard in order and you have the four ways to harmonize a C6 melody note with the chord underneath it.