Bbdim7 guitar chord
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.
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About Bbdim7 — shell voicings
Bbdim7 is Bb, Db, Fb and G — Bbdim with a diminished seventh stacked on top.
It sounds suspenseful and rootless. Three stacked minor thirds divide the octave evenly, so the same four notes spell four dim7 chords and the shape repeats every three frets.
Bbdim7 notes and formula
| Bb | Db | Fb | G |
|---|---|---|---|
| 1 | ♭3 | ♭5 | ♭♭7 |
Leading-tone or passing chord — it can resolve almost anywhere.
Also written Bb°7, Bbo7 or Bb diminished 7. The same chord either way; which spelling you meet depends on who wrote the chart.
How to play Bbdim7
Root, third and seventh. The third and seventh, the guide tones, are what make the chord major, minor or dominant, so the fifth can go: it says nothing the symbol needs.
Three notes means a spare string, which is the real point. Put a tension on it.
Bbdim7 has 6 of them, on strings 5-3-2-1, strings 6-4-3-2, the middle four strings and the bottom four strings, from open position up to the 12th — all in one inversion, so the bass note never moves. The one to learn first is the Bb shape at the nut.
Start with x12020 — no barre and 2 open strings. 1 of the 8 shapes here sits in open position. 2 of the 8 need a barre. Together they cover the neck from the 1st fret to the 15th.
| Frets | Where | Bass | Top | Hand |
|---|---|---|---|---|
| x12020 | open position | Bb, root position | Fb | 2 open strings |
| xx2323 | 2nd fret | Fb, 2nd inversion | G | all fretted |
| 6x5656 | 5th fret | Bb, root position | Bb | barred |
| 678686 | 6th fret | Bb, root position | Bb | barred |
| xx8989 | 8th fret | Bb, root position | Db | all fretted |
| x-x-11-12-11-12 | 11th fret | Db, 1st inversion | Fb | all fretted |
| x-13-14-12-14-12 | 12th fret | Bb, root position | Fb | all fretted |
| x-x-14-15-14-15 | 14th fret | Fb, 2nd inversion | G | all fretted |
The same notes rebuilt from scratch give 14 drop 2, 10 drop 3 and 6 open string voicings, each on its own page.
Tensions. A shell of Bbdim7, root, third and seventh, leaves a string free, and the tones that belong over it are the 9 (C), the 11 (Eb), the b13 (Gb) and the maj7 (A).
How to use Bbdim7
A diminished seventh divides the octave evenly, so Bbdim7 has no single root and no single destination: it can lead to Eb or to B, and it is the same four notes either way.
What to play over Bbdim7
Every note of Bbdim7 is in Bb diminished and Bb half-whole diminished.
Chords near Bbdim7
Change one note of Bbdim7 and you have Bbdim (drop the sixth), Bbm6 (the flat fifth becomes a fifth), Bbm7b5 (the sixth becomes a flat seventh) or BbmMaj7b5 (the sixth becomes a major seventh).
Bbdim7 is a diminished chord — root, minor third, flat fifth. Diminished and half-diminished chords on every root.
On Bbdim7’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.