A 9th chord is formed by stacking a fifth note on top of the 7th chord.
In root position all chord tones are either on successive lines or in successive spaces on a music staff.

The 9th is exactly one octave above the 2nd of the scale from which the chord is derived.

Audio 5.1

Any 9th chord is simply an extension of the 7th chord.
The chord quality remains the same. The extra note only provides additional colour to the chord.
Therefore :

• stacking an additional note on top of a major 7th chord produces a major 9th chord.
      C   E   G   B + D = Cmaj9
  
  
• stacking an additional note on top of a dominant 7th chord produces a dominant 9th chord.
      C   E   G   Bb + D = C9
  
  
• stacking an additional note on top of a minor 7th chord produces a minor 9th chord.
      C   Eb   G   Bb + D = Cmin9

Audio 5.2

Lines for Nines is a basic blues in G. The entire melody consists of 9th chord tones only.

Use this song to get familiar with the 9th chords of the Blues.

Melody

3-note chord voicings
Keyboard players and guitarists can use 3-note chord vocings incorporating the 9th chord tone.
For example :

Audio 5.3

You can also use the 13th instead of the 5th in the G7 chord. This produces a great sound.

All above chord voicings straddle Middle C on the keyboard. This is the ideal pitch range for right hand chords.
Left hand chords usually need to be somewhat lower so that they do not interfere with the (right hand) melody line, but for this song you can comfortably play them as shown above.

See also BL Comp5 and check out the Blues chord voicings Rulers.

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BL 5.3 - Improvisation with 9th chord tones

1.
Play Lines for Nines until you can play the melody from memory.

2.
Play 9th chord arpeggios ('broken chords') over the basic blues in G.
Use a rhythm pattern (like RP 16) as shown below.

Audio 5.4

3.
Improvise with 9th chord-tones only over the basic blues in G using rhythm patterns : 1-8 or 9-16.

C- instruments use :

G9 chord tones over the G9 chord

C9 chord tones over the C9 chord

D9 chord tones over the D9 chord

Bb- instruments use :

A9 chord tones over the A9 chord

D9 chord tones over the D9 chord

E9 chord tones over the E9 chord

Eb- instruments use :

E9 chord tones over the E9 chord

A9 chord tones over the A9 chord

B9 chord tones over the B9 chord

You can use the Dominant 9th Chord Ruler below to find the notes of the Dominant 7th or 9th chord in any key.

1. Align the root note of the required Dominant chord on the Note Names strip

2. with the 1 on the Dominant 9th Chord strip.

3. Then read the chord tone letter names aligned with chord tone numbers

Here is how it works when finding the notes for the Bb9 chord.