Tools / Chords / B♭ diminished major 7th

B♭ diminished major 7th chord on bass (B♭dimMaj7)

Also written B♭dimMaj7, B♭dimM7 or B♭°M7

B♭ diminished major 7th contains B♭, D♭, F♭, and A. The 6th-fret shape places the root on the 4th string and requires a wide stretch.

6th fret6-7-7-6

How it’s built

B♭1Root

D♭♭3Minor 3rd

F♭♭5Diminished 5th

A7Major 7th

Formula 1, ♭3, ♭5, 7

Inversions

The same three notes, with a different one in the bass.

Root positionB♭–D♭–F♭–AB♭dimMaj7Bass B♭

First inversionD♭–F♭–A–B♭B♭dimMaj7/D♭Bass D♭

Second inversionF♭–A–B♭–D♭B♭dimMaj7/F♭Bass F♭

Third inversionA–B♭–D♭–F♭B♭dimMaj7/ABass A

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 mute the 2nd string, which silences the D♭.
Pressing the pinky too lightly, causing the 2nd string to buzz.
Allowing the index finger to drift sharp, making the 4th string note 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 4th fret gives A♭ diminished major 7th.
Sliding the shape up one fret to the 7th fret gives B diminished major 7th.

Which voicing to use

The 6th-fret position places the root B♭ on the 4th string, giving a solid low foundation. The shape is movable, so sliding it up or down changes the chord while keeping the same fingering.

How do you play a B♭ diminished major 7th chord on bass?

6th fret

Intermediate● On the diagram

B♭ diminished major 7th is played at the 6th fret as 6 7 7 6: index finger on the E string at fret 6, ring finger on the A string at fret 7, pinky finger on the D string at fret 7 and middle finger on the G string at fret 6.

Tip — B♭ 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.

String-by-string breakdown

String	Fret	Finger	Note
4 (E)	6	1	B♭ (1)
3 (A)	7	3	F♭ (♭5)
2 (D)	7	4	A (7)
1 (G)	6	2	D♭ (♭3)

Common questions

How is B♭ diminished major 7th written?

B♭ diminished major 7th is written B♭°M7 or B♭dimM7. The root is B♭, with ASCII spelling Bb. It is also spelled A♯ in enharmonic notation for the same sounding root.

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.

Can B♭ diminished major 7th be played in an open position?

No, the supplied voicing is at the 6th fret. The chord contains no open strings, so it can be moved to any fret to change the root.

String

Fret

Finger

Note

4 (E)

B♭ (1)

3 (A)

F♭ (♭5)

2 (D)

A (7)

1 (G)

D♭ (♭3)