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B diminished 7th chord on bass (Bdim7)
Also called or written Bdim7 or B°7
B diminished 7th contains B, D, F, and A♭. The 6th fret position uses all four fingers in a compact cluster.
How it is built
Formula 1, ♭3, ♭5, ♭♭7
- Root positionB–D–F–A♭Bdim77-8-6-7
- First inversionD–F–A♭–BBdim7/D10-11-9-10
- Second inversionF–A♭–B–DBdim7/F1-2-0-1
- Third inversionA♭–B–D–FBdim7/A♭4-5-3-4
How do you play a B diminished 7th chord on bass?
B diminished 7th is played at the 6th fret as 7 8 6 7: middle finger on the E string at fret 7, pinky finger on the A string at fret 8, index finger on the D string at fret 6 and ring finger on the G string at fret 7.
Full note and interval breakdown
| String | Fret | Finger | Note |
|---|---|---|---|
| 4 (E) | 7 | 2 | B (1) |
| 3 (A) | 8 | 4 | F (♭5) |
| 2 (D) | 6 | 1 | A♭ (6) |
| 1 (G) | 7 | 3 | D (♭3) |
AdvancedThe pinky must reach the 8th fret on the A string while the index holds the 6th fret on the D string, requiring a wide stretch.
Bdim7/D inversion
B diminished 7th is played at the 9th fret as 10 11 9 10: middle finger on the E string at fret 10, pinky finger on the A string at fret 11, index finger on the D string at fret 9 and ring finger on the G string at fret 10.
Full note and interval breakdown
| String | Fret | Finger | Note |
|---|---|---|---|
| 4 (E) | 10 | 2 | D (♭3) |
| 3 (A) | 11 | 4 | A♭ (6) |
| 2 (D) | 9 | 1 | B (1) |
| 1 (G) | 10 | 3 | F (♭5) |
Bdim7/F inversion · open position
B diminished 7th is played in open position as 1 2 0 1: index finger on the E string at fret 1, ring finger on the A string at fret 2 and middle finger on the G string at fret 1. The D string rings open.
Full note and interval breakdown
| String | Fret | Finger | Note |
|---|---|---|---|
| 4 (E) | 1 | 1 | F (♭5) |
| 3 (A) | 2 | 3 | B (1) |
| 2 (D) | open | — | D (♭3) |
| 1 (G) | 1 | 2 | A♭ (6) |
Bdim7/F inversion · fret 12
B diminished 7th is played at the 12th fret as 13 14 12 13: middle finger on the E string at fret 13, pinky finger on the A string at fret 14, index finger on the D string at fret 12 and ring finger on the G string at fret 13.
Full note and interval breakdown
| String | Fret | Finger | Note |
|---|---|---|---|
| 4 (E) | 13 | 2 | F (♭5) |
| 3 (A) | 14 | 4 | B (1) |
| 2 (D) | 12 | 1 | D (♭3) |
| 1 (G) | 13 | 3 | A♭ (6) |
Bdim7/A♭ inversion
B diminished 7th is played at the 3rd fret as 4 5 3 4: middle finger on the E string at fret 4, pinky finger on the A string at fret 5, index finger on the D string at fret 3 and ring finger on the G string at fret 4.
Full note and interval breakdown
| String | Fret | Finger | Note |
|---|---|---|---|
| 4 (E) | 4 | 2 | A♭ (6) |
| 3 (A) | 5 | 4 | D (♭3) |
| 2 (D) | 3 | 1 | F (♭5) |
| 1 (G) | 4 | 3 | B (1) |
Why it sounds like that
B diminished 7th is built from the formula 1, ♭3, ♭5, ♭♭7. The diminished 5th between B and F defines its tense character. Compare it to B minor 7th flat 5th, which has a ♭7 instead of ♭♭7.
What goes wrong with B diminished 7th?
- Letting the pinky mute the 3rd string by collapsing.
- Pressing the index finger too hard, causing the 2nd string to buzz.
When to use it
B diminished 7th functions as a leading-tone chord in C major or C minor, resolving to C. Use it in classical bass lines and jazz walking bass. It also connects to B minor 7th flat 5th in ii–V progressions.
Changing to and from B diminished 7th
- Slide the shape down two frets to the 4th fret to reach A diminished 7th.
- Slide the shape up one fret to the 7th fret to reach C diminished 7th.
Which voicing to use
The 6th fret position gives B as the lowest note on the E string, providing a strong root. The Bdim7/F inversion at the 1st fret offers an easier fingering with F in the bass, useful for quick changes.
Other B chords
Common questions
How is B diminished 7th written?
B diminished 7th is written as B°7 or Bdim7.
What is the difference between B diminished 7th and B minor 7th flat 5th?
B diminished 7th has a ♭♭7 (A♭), while B minor 7th flat 5th has a ♭7 (A). The diminished 7th is more dissonant and symmetrical.
Can B diminished 7th be played with open strings?
Yes, the Bdim7/F inversion at the 1st fret uses the open D string. That position is easier for beginners.