Bbm7b5

Bbm7b5 is Bb, Db, Fb and Ab, a half-diminished seventh. The shape this page opens on is written x1212x, lowest string first.

Note by note. Bb is the root, Db is the minor third, Fb is the flat fifth and Ab is the flat seventh.

Also written Bbø, Bbø7, Bbm7-5, Bbm7(b5) or Bb half diminished. The same chord either way; which spelling you meet depends on who wrote the chart.

There are 8 common shapes for Bbm7b5 on the guitar, and 28 derived voicings in 3 families.

One note away. Change a single note of Bbm7b5 and you have Bbdim (with one note taken away), Bbdim7 (with one note moved), Bbm7 (with one note moved), BbmMaj7b5 (with one note moved) or Bb7b5 (with one note moved).

In which keys. Every note of Bbm7b5 belongs to Ab minor (the ii°) and B major (the vii°).

The common shapes, written lowest string first: x1212x, xx2324, 6xx654, 6x665x, 678696, xx8999, x-13-11-13-11-12, x-13-14-13-14-x.

Under the hand. None of the shapes for Bbm7b5 uses an open string, so every one of them is movable; the lowest sits at the 1st fret. 3 of the 8 need a barre. Together they cover the neck from the 1st fret to the 14th.

Where it goes. Bbm7b5 is the ii of Ab minor, which is where it is nearly always found: half-diminished, then an altered dominant, then the minor tonic.

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. Bbm7b5 has x1x120, 6x665x, x-13-x-13-14-12, x1665x, 6469xx, 6-11-11-9-x-x.

Drop 2. A close-position chord with the second voice from the top lowered an octave. Sits on four adjacent strings. Bbm7b5 has x1212x, xx2324, 4423xx, xx6656, 6766xx, xx8999, x-11-11-9-11-x, 12-13-11-13-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. Bbm7b5 has x1x120, 4x232x, x4x354, 6x665x, x7x696, 9x899x, x-11-x-9-11-9, 12-x-11-13-11-x.

Tensions. A shell of Bbm7b5, root, third and seventh, leaves a string free, and the tones that belong over it are the 11 (Eb) and the b13 (Gb).

What kind of chord this is. Bbm7b5 is a diminished chord — root, minor third, flat fifth. diminished and half-diminished 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.