A7b9

A7b9 is A, C#, E, G and Bb, a seven flat nine. The shape this page opens on is written x02323, lowest string first.

Note by note. A is the root, C# is the major third, E is the fifth, G is the flat seventh and Bb is the flat ninth.

Also written A7(b9), A7-9 or A7♭9. The same chord either way; which spelling you meet depends on who wrote the chart.

There are 6 common shapes for A7b9 on the guitar, and 44 derived voicings in 5 families.

One note away. Change a single note of A7b9 and you have A7 (with one note taken away), Aalt (with one note moved), A9 (with one note moved), A7#9 (with one note moved) or A/G (with one note taken away).

The common shapes, written lowest string first: x02323, 5453xx, xx5656, 575656, xx7686, x-12-11-12-11-12.

Under the hand. 1 of the 6 shapes here sits in open position, and the first uses 1 open string with 1 left unplayed. 2 of the 6 need a barre. Together they cover the neck from the 2nd fret to the 12th.

Where it goes. A7b9 is a dominant with its tension raised, so it still points at D — harder than a plain seventh does, because the altered tones sit a semitone from where they are going.

Shell. Root, third and seventh: the guide tones fix the quality, so the fifth is dropped. That is what leaves a string free, so pick a tension to put on top. A7b9 has 5453xx, xx7686, x-12-11-12-11-x, x0x026.

Drop 2. A close-position chord with the second voice from the top lowered an octave. Sits on four adjacent strings. A7b9 has 5453xx, xx7686, x-12-11-12-11-x, x1522x, xx5325, 6-10-7-6-x-x, x-10-8-6-10-x, 9-12-8-12-x-x.

Drop 3. The third voice from the top lowered an octave. The dropped voice becomes the bass, which is why a string is skipped. A7b9 has x1x223, 5x532x, 6x768x, x-10-x-6-10-6, 9-x-8-12-10-x, x-12-x-12-11-9, 15-x-11-14-11-x, x-13-x-14-14-15.

Rootless. The root left to the bass player. Frees a finger for a tension. A7b9 has x1202x, xx2323, x4535x, xx5656, x7868x, xx8989, x-10-11-9-11-x, x-x-11-12-11-12.

Open string. An open string left ringing against a fretted grip. Because it costs no finger, it sounds a note the closed shape has none left for -- a tension on top, or a pedal root underneath. Either a familiar grip with open strings added, or a shape so sparse the open strings carry the chord. These belong to their key rather than to a shape, so D, A, G and E have many and Eb a handful. A7b9 has x02323, 5x5320, 005656, 0x5325.

Tensions. A shell of A7b9, root, third and seventh, leaves a string free, and the tones that belong over it are the #11 (D#), the b13 (F) and the 13 (F#).

What kind of chord this is. A7b9 is an altered chord — a dominant seventh with its fifth or ninth moved. altered dominant chords on every root, and what they are for.

The common shapes and the derived voicings come from different places, and both are explained in where the chords and the theory come from.