About Bbdim — triad voicings
Bbdim is Bb, Db and Fb — Bbm with the fifth lowered as well.
It sounds compressed and unstable in every direction. Rarely a destination; it is where a line passes through on the way somewhere.
Bbdim notes and formula
| Bb | Db | Fb |
|---|---|---|
| 1 | ♭3 | ♭5 |
Unstable — it does not sit still.
Also written Bb°, Bbo or Bb diminished. The same chord either way; which spelling you meet depends on who wrote the chart.
How to play Bbdim
Three notes on one string set. No seventh, so nothing is claimed about the chord beyond its quality.
Thin on their own, excellent over a bass line or against someone else’s harmony.
Bbdim has 49 of them, on the middle four strings, the top three strings, the low-middle three, the high-middle three, the top four strings, the bottom four strings, the bottom three strings, strings 5-3-2-1 and strings 6-4-3-2, from open position up to the 14th — every inversion the chord has: Bb in the bass, Db in the bass and Fb in the bass. The one to learn first is the Bb shape at the nut, which is the easiest grip here.
6 of them sit on the middle four strings, so you can run the inversions up one set without changing strings — which is the whole reason to learn them as a family rather than as separate grips.
Start with x1232x — down at the nut. None of the shapes for Bbdim uses an open string, so every one of them is movable; the lowest sits at the 1st fret. None of them needs a barre. Together they cover the neck from the 1st fret to the 15th.
| Frets | Where | Bass | Top | Hand |
|---|---|---|---|---|
| x1232x | 1st fret | Bb, root position | Db | all fretted |
| 64x65x | 4th fret | Bb, root position | Fb | all fretted |
| xx89x9 | 8th fret | Bb, root position | Db | all fretted |
| x-13-11-x-11-12 | 11th fret | Bb, root position | Fb | all fretted |
| x-13-14-15-14-x | 13th fret | Bb, root position | Db | all fretted |
Tensions. A shell of Bbdim, root, third and seventh, leaves a string free, and the tones that belong over it are the 11 (Eb) and the b13 (Gb).
How to use Bbdim
In which keys. Every note of Bbdim belongs to Ab minor (the ii°, the supertonic) and B major (the vii°, the leading tone).
What to play over Bbdim
Every note of Bbdim is in Bb blues, Bb locrian, Bb altered, Bb diminished and Bb half-whole diminished.
Chords near Bbdim
Change one note of Bbdim and you have Bbm (the flat fifth becomes a fifth), Bbdim7 (add the sixth), Bbm7b5 (add the flat seventh) or BbmMaj7b5 (add the major seventh).
Bbdim is a diminished chord — root, minor third, flat fifth. Diminished and half-diminished chords on every root.
On Bbdim’s sound and use this page follows Stefan Kostka, Dorothy Payne & Byron Almén, Tonal Harmony (McGraw-Hill, 8th ed., 2018). The shapes and the derived voicings come from different places, and both are explained in where the chords and the theory come from.