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B diminished major 7th chord on bass (BdimMaj7)
Also called or written BdimMaj7, BdimM7, B°M7, B augmented minor seventh or B minor seventh sharp five
B diminished major 7th contains B, D, F, and A♯. The 7th-fret shape is movable, and an easier inversion at the 1st fret uses an open D string.
How it is built
Formula 1, ♭3, ♭5, 7
How do you play a B diminished major 7th chord on bass?
B diminished major 7th is played at the 7th fret as 7 8 8 7: index finger on the E string at fret 7, ring finger on the A string at fret 8, pinky finger on the D string at fret 8 and middle finger on the G string at fret 7.
Full note and interval breakdown
| String | Fret | Finger | Note |
|---|---|---|---|
| 4 (E) | 7 | 1 | B (1) |
| 3 (A) | 8 | 3 | F (♭5) |
| 2 (D) | 8 | 4 | A♯ (7) |
| 1 (G) | 7 | 2 | D (♭3) |
AdvancedB diminished major 7th requires the ring finger and pinky to fret adjacent strings at the same fret while the index and middle hold the lower fret.
BdimM7/F inversion
B diminished major 7th is played in open position as 1 2 0 3: index finger on the E string at fret 1, middle finger on the A string at fret 2 and ring finger on the G string at fret 3. The D string rings open.
Full note and interval breakdown
| String | Fret | Finger | Note |
|---|---|---|---|
| 4 (E) | 1 | 1 | F (♭5) |
| 3 (A) | 2 | 2 | B (1) |
| 2 (D) | open | — | D (♭3) |
| 1 (G) | 3 | 3 | A♯ (7) |
Why it sounds like that
B diminished major 7th is built from the formula 1, ♭3, ♭5, 7. The diminished 5th between B and F creates a tritone that gives the chord its dark color. The major 7th A♯ is a leading tone that resolves upward to B. Compare with B minor 7th flat 5th, which has A instead of A♯.
What goes wrong with B diminished major 7th?
- Letting the ring finger flatten onto the 2nd string, which deadens the D.
- Pressing the index finger too hard, causing the 4th string to buzz against the fret.
- Allowing the pinky to drift sharp, making the 2nd string note sound out of tune.
When to use it
B diminished major 7th works as a passing chord in B minor, often between B minor and B minor 7th. Its tense sound suits jazz ballads and dramatic film cues. Use it to add chromatic motion on the bass.
Changing to and from B diminished major 7th
- Sliding the shape down two frets to the 5th fret gives A diminished major 7th.
- Sliding the shape up one fret to the 8th fret gives C diminished major 7th.
Which voicing to use
The 7th-fret position places the root B on the 4th string, giving a solid low foundation. The BdimM7/F inversion at the 1st fret puts F in the bass, creating a different color while keeping the same notes.
Other B chords
Common questions
How is B diminished major 7th written?
B diminished major 7th is written B°M7 or BdimM7. The root is B.
What is the difference between B diminished major 7th and B minor 7th flat 5th?
B diminished major 7th has a major 7th (A♯), while B minor 7th flat 5th has a minor 7th (A). The major 7th creates a leading tone that pulls strongly to the octave.
Which inversion of B diminished major 7th is easier for beginners?
The BdimM7/F inversion at the 1st fret is easier because it uses an open D string and lower frets. However, the 7th-fret root position is more common for moving up the neck.