An open string left ringing against a fretted grip. Because it costs no finger, it sounds a note the closed shape has none left for -- a tension on top, or a pedal root underneath. Either a familiar grip with open strings added, or a shape so sparse the open strings carry the chord. These belong to their key rather than to a shape, so D, A, G and E have many and Eb a handful.
Bbmaj7b5 is Bb, D, Fb and A — Bbmaj7 with the fifth lowered a semitone.
It sounds hollow and hard to place. Far more often met spelled the other way round, as a ♯11 over a chord that kept its fifth.

| Bb | D | Fb | A |
|---|---|---|---|
| 1 | 3 | ♭5 | 7 |
Coloured tonic — rare, and unstable for a major chord.
Also written BbM7b5, BbΔ7b5 or Bbmaj7(b5). The same chord either way; which spelling you meet depends on who wrote the chart.
An open string left ringing against a fretted grip. It costs no finger, so it can sound a note the closed shape has none left for: a tension on top, or a pedal root underneath.
These belong to their key rather than to a shape: they cannot be moved up the neck. D, A, G and E have many; E♭ has a handful.
Bbmaj7b5 has 6 of them, on strings 5-4-3-2-1, strings 6-5-4-3-2-1, strings 6-5-4-3-2, the top four strings, the middle four strings and the bottom four strings, from the 2nd fret up to the 5th — every inversion the chord has: D in the bass, Fb in the bass and A in the bass. The one to learn first is the A shape at the 2nd fret, which is the easiest grip here.
Start with x1223x — no barre and down at the nut. None of the shapes for Bbmaj7b5 uses an open string, so every one of them is movable; the lowest sits at the 1st fret. 3 of the 7 need a barre. Together they cover the neck from the 1st fret to the 15th.
| Frets | Where | Bass | Top | Hand |
|---|---|---|---|---|
| x1223x | 1st fret | Bb, root position | D | all fretted |
| 657755 | 5th fret | Bb, root position | A | barred |
| 6777x0 | 6th fret | Bb, root position | Fb | barred |
| 6777x6 | 6th fret | Bb, root position | Bb | barred |
| x-x-8-9-10-10 | 8th fret | Bb, root position | D | all fretted |
| x-13-12-14-15-12 | 12th fret | Bb, root position | Fb | all fretted |
| x-13-14-14-15-x | 13th fret | Bb, root position | D | all fretted |
The same notes rebuilt from scratch give 7 shell, 14 drop 2 and 9 drop 3 voicings, each on its own page.
Tensions. A shell of Bbmaj7b5, root, third and seventh, leaves a string free, and the tones that belong over it are the 9 (C) and the 13 (G).
How you get to it. The turn that lands on Bbmaj7b5 is Cm7 to F7 — the ii and the V of Bb — and F7 shares its third and seventh with Cm7, so the hand barely moves between them.
In which keys. Every note of Bbmaj7b5 belongs to D minor (the ♭VI) and F major (the IV, the subdominant).
Every note of Bbmaj7b5 is in Bb lydian.
Change one note of Bbmaj7b5 and you have Bbmaj7 (the flat fifth becomes a fifth), Bbmaj7#5 (the flat fifth becomes a sharp fifth), BbmMaj7b5 (the major third becomes a minor third) or Bb7b5 (the major seventh becomes a flat seventh).
Bbmaj7b5 is a major chord — root, major third, fifth. Major chords on every root.
On Bbmaj7b5’s sound and use this page follows Robert Rawlins & Nor Eddine Bahha, Jazzology (Hal Leonard, 2005). The shapes and the derived voicings come from different places, and both are explained in where the chords and the theory come from.
Shows each chord the way this style would voice it, and marks which of its alternatives belong to the idiom.