Bb9b5

Bb9b5 is Bb, D, Fb, Ab and C, a nine flat five. The shape this page opens on is written x10110, lowest string first.

Note by note. Bb is the root, D is the major third, Fb is the flat fifth, Ab is the flat seventh and C is the ninth.

Also written Bb9(b5), Bb9-5 or Bb9♭5. The same chord either way; which spelling you meet depends on who wrote the chart.

There are 7 common shapes for Bb9b5 on the guitar, and 27 derived voicings in 2 families.

One note away. Change a single note of Bb9b5 and you have Bb7b5 (with one note taken away), Bb9 (with one note moved), Bbaug9 (with one note moved) or Bb9#11 (with one note added).

The common shapes, written lowest string first: x10110, 6x0554, 656556, 6767x8, x78798, x-13-12-13-13-0, x-13-12-13-13-12.

Under the hand. 2 of the 7 shapes here sit in open position, and the first uses 2 open strings with 1 left unplayed. 4 of the 7 need a barre. Together they cover the neck from the 1st fret to the 13th.

Where it goes. Bb9b5 is a dominant with its tension raised, so it still points at Eb — 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. Bb9b5 has x1011x, 6565xx, xx8798, x-13-12-13-13-x, x1x130, x1015x, 6x675x, 6569xx.

Rootless. The root left to the bass player. Frees a finger for a tension. Bb9b5 has x3213x, xx0110, x5655x, x-x-10-9-9-10, x-x-12-13-13-12, x-15-14-13-15-x, x3x130, xx2534.

Tensions. A shell of Bb9b5, root, third and seventh, leaves a string free, and the tones that belong over it are the b13 (Gb) and the 13 (G).

What kind of chord this is. Bb9b5 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.