The 7b9 Chord

A 7b9 Chord (In other words, a Dominant 7th Chord with a diminished 9th on top), should be built as follows:

1 - 3 - 5 - b7 - b9

This chord fits well into the Minor Scale, used in place of the V chord. This is because the b9 of the chord is equivalent to the 6th Scale Degree of the Minor Scale!

Here's a pleasant voicing of a ii-V-i progression that shows how the dissonant sounding flat 9th can nicely resolve down to the 5th Scale Degree. 

Here it feels like a note held over from the Half-Diminished chord, somewhat reducing the sensation of dissonance.

We haven't spent much time talking about rootless voicings yet, but it bears mentioning here.

A rootless voicing is just what it sounds like, a chord shape that omits the root note. In this case, that leaves us with:

3 - 5- b7 - b9

This is really interesting, because that leaves us with a set of notes that are enharmonically equivalent (sound the same) to a Diminished 7th chord.

That means that we can treat the 7b9 like a portal to the possibilities of Diminished Chords and Arpeggios.

Here we have 2 examples, the first includes a rootless voicing, and the second replaces it with a short run up a Diminished 7th Arpeggio shape!

Pretty cool, right?