Note — The whole SHELL-STENSION system can be boiled down to this: play the 3rd and 7th on the D and G strings, and extensions (9ths, 11ths, 13ths) on the B and E strings.
Shell voicings give you the harmonic skeleton of any chord. Extensions are how you put the flesh on the bones — adding colour and sophistication without losing the clear, uncluttered foundation that makes shell voicings so practical.
What you’ll get out of this lesson
A clear map of where extensions lie in relation to the two shell positions, so you can reach for exactly the chord tone you want rather than guessing or memorising shapes in isolation.
The Two Free Strings
With the third and seventh locked onto the D and G strings, you have the B and E strings free for extensions and melody notes. One of those strings covers the range from the ♭7 up to the ♯9; the other covers the 11 through to the 13. The diagrams below map these extensions out clearly. Note: the roots on the 6th and 5th strings are included in the diagrams for reference only — you are not playing them in these voicings.
Learning Through Application
There is no shortcut here: the best way to learn these extension positions is to be creative with them. Play through progressions, try different extensions on the same chord, and notice how each one changes the flavour of the harmony. Trial and error in a musical context will always beat rote memorisation at a desk.
Connecting to the Next Lesson
Look at the common voicings in the next lesson and start applying them whenever and wherever you can. The combination of the shell positions from Step 1 and the extension map from this lesson gives you all the tools you need to construct almost any jazz voicing you encounter.
Taking it further
Once you can place extensions reliably, start making voice-leading choices between chords — for example, keeping an extension note on the B string while the shell below it moves. This kind of inner voice movement is what gives jazz chord playing its characteristic smoothness and sophistication.
Your homework
Take a ii-V-I in one key and experiment with different extensions on each chord, using the diagrams as a reference. Try the 9th on the ii chord, the 13th on the V, and the major 7 on the I. Then experiment freely — trust your ear to tell you what sounds good.