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B♭ diminished 7th chord on bass (B♭dim7)
Also called or written B♭dim7 or B♭°7
B♭ diminished 7th contains B♭, D♭, F♭, and A♭♭. Its four-note stack sits in the middle of the neck, demanding precise finger independence.
How it is built
Formula 1, ♭3, ♭5, ♭♭7
- Root positionB♭–D♭–F♭–A♭♭B♭dim76-7-5-6
- First inversionD♭–F♭–A♭♭–B♭B♭dim7/D♭9-10-8-9
- Second inversionF♭–A♭♭–B♭–D♭B♭dim7/F♭12-13-11-12
- Third inversionA♭♭–B♭–D♭–F♭B♭dim7/A♭♭3-4-2-3
How do you play a B♭ diminished 7th chord on bass?
B♭ diminished 7th is played at the 5th fret as 6 7 5 6: middle finger on the E string at fret 6, pinky finger on the A string at fret 7, index finger on the D string at fret 5 and ring finger on the G string at fret 6.
Full note and interval breakdown
| String | Fret | Finger | Note |
|---|---|---|---|
| 4 (E) | 6 | 2 | B♭ (1) |
| 3 (A) | 7 | 4 | F♭ (♭5) |
| 2 (D) | 5 | 1 | A♭♭ (6) |
| 1 (G) | 6 | 3 | D♭ (♭3) |
AdvancedThe stretch between the index finger on the 2nd string and the pinky on the 3rd string requires wide finger independence.
B♭dim7/D♭ inversion
B♭ diminished 7th is played at the 8th fret as 9 10 8 9: middle finger on the E string at fret 9, pinky finger on the A string at fret 10, index finger on the D string at fret 8 and ring finger on the G string at fret 9.
Full note and interval breakdown
| String | Fret | Finger | Note |
|---|---|---|---|
| 4 (E) | 9 | 2 | D♭ (♭3) |
| 3 (A) | 10 | 4 | A♭♭ (6) |
| 2 (D) | 8 | 1 | B♭ (1) |
| 1 (G) | 9 | 3 | F♭ (♭5) |
B♭dim7/F♭ inversion
B♭ diminished 7th is played at the 11th fret as 12 13 11 12: middle finger on the E string at fret 12, pinky finger on the A string at fret 13, index finger on the D string at fret 11 and ring finger on the G string at fret 12.
Full note and interval breakdown
| String | Fret | Finger | Note |
|---|---|---|---|
| 4 (E) | 12 | 2 | F♭ (♭5) |
| 3 (A) | 13 | 4 | B♭ (1) |
| 2 (D) | 11 | 1 | D♭ (♭3) |
| 1 (G) | 12 | 3 | A♭♭ (6) |
B♭dim7/A♭♭ inversion
B♭ diminished 7th is played at the 2nd fret as 3 4 2 3: middle finger on the E string at fret 3, pinky finger on the A string at fret 4, index finger on the D string at fret 2 and ring finger on the G string at fret 3.
Full note and interval breakdown
| String | Fret | Finger | Note |
|---|---|---|---|
| 4 (E) | 3 | 2 | A♭♭ (6) |
| 3 (A) | 4 | 4 | D♭ (♭3) |
| 2 (D) | 2 | 1 | F♭ (♭5) |
| 1 (G) | 3 | 3 | B♭ (1) |
Why it sounds like that
B♭ diminished 7th is built from the intervals 1, ♭3, ♭5, and ♭♭7 — a stack of three minor 3rds. The diminished 5th between B♭ and F♭ gives the chord its tense, unstable quality. Compare it with B♭ minor 7th flat 5th, which raises the seventh from A♭♭ to A♭.
What goes wrong with B♭ diminished 7th?
- Letting the index finger flatten and mute the 1st string.
- Pressing too hard with the pinky, causing the 3rd string to buzz.
- Failing to keep the middle finger perpendicular to the fretboard.
When to use it
B♭ diminished 7th often appears as a passing chord in jazz and classical music. It can resolve to B♭ minor 7th flat 5th or C major. B♭ diminished 7th suits dramatic transitions and chromatic bass lines.
Changing to and from B♭ diminished 7th
- Sliding the shape down two frets to the 3rd fret gives A♭ diminished 7th.
- Sliding the shape up two frets to the 7th fret gives C diminished 7th.
Which voicing to use
The 5th fret position keeps B♭ as the lowest note, giving a clear root-position sound. The B♭dim7/C♯ inversion places D♭ in the bass, creating a darker, less stable voicing. Choose the root position for foundational bass lines and inversions for smoother voice leading.
Other B♭ chords
Common questions
How is B♭ diminished 7th written?
B♭ diminished 7th is written as B♭°7 or B♭dim7. The ASCII root is Bb, so you can type Bbdim7. It is also spelled A♯ in enharmonic notation for the same sounding root.
What is the difference between B♭ diminished 7th and B♭ minor 7th flat 5th?
B♭ diminished 7th has a double-flatted seventh (A♭♭), while B♭ minor 7th flat 5th has a minor seventh (A♭). The diminished 7th chord is more dissonant and symmetrical.
Why does B♭ diminished 7th sound so tense?
B♭ diminished 7th contains two diminished 5th intervals: B♭–F♭ and D♭–A♭♭. These tritones create a strong pull toward resolution.