Dominant 7th b5 b9
7b5b9
0 - 4 - 6 - 10 - 13Dom7 with diminished 5th and minor 9th
About Dominant 7th b5 b9
A dominant seventh flat five flat nine chord lowers both altered degrees — in C that is C, E, G♭, B♭ and D♭, written C7♭5♭9. Of the four fully altered dominants it is the closest to a diminished chord, and it is the one that sounds least like jazz and most like the nineteenth century.
Notes and formula
The formula is 1 – 3 – ♭5 – ♭7 – ♭9, or 0 – 4 – 6 – 10 – 13 in semitones. Both alterations move downward.
Remove the root and the remaining four notes are close to a diminished seventh: E, G♭, B♭ and D♭ sit at three, four and three semitones apart, one interval away from full symmetry.
Why it sounds older than the others
Lowered alterations belong to the harmonic-minor world that classical harmony was built on, while raised ones belong to the blues. This chord has only lowered alterations, so nothing in it points to the twentieth century.
The result is a dominant that sounds like a Romantic composer's chromatic cadence rather than like bebop, and composers who want that association reach for it deliberately.
How to play it
On guitar the movable form is x–3–4–3–2–x, sounding C–G♭–B♭–D♭. The third is dropped; with two lowered alterations the chord is crowded, and the root and seventh carry it.
On piano the safe voicing keeps D♭ well above C — the two are a semitone apart in pitch class and need at least an octave and a semitone between them in practice.
Where it belongs
Resolving to a minor chord, where both lowered notes are a semitone above notes of the destination and fall into them by step.
It also appears as a substitute for a diminished seventh in a chromatic passage, since the two chords share most of their notes and behave similarly.
Among the four altered dominants
Sharp five with sharp nine is emphatic; sharp five with flat nine is operatic; flat five with sharp nine is ambiguous; and this one, with both degrees lowered, is chromatic and dark.
All four resolve identically. The choice among them is entirely a choice of colour, which is why jazz charts usually delegate it with the single word alt.
Scales that contain it
The half–whole diminished scale contains every note of this chord and is the natural fit, because the chord itself is nearly a diminished seventh with a root added.
The altered scale fits too and treats the chord as one of its own voicings. The two scales differ in the thirteenth, and over this chord that difference is audible.
Frequently asked questions
What notes are in a C7♭5♭9 chord?
C, E, G♭, B♭ and D♭. On guitar, x–3–4–3–2–x.
Why does it sound like a diminished chord?
Because it nearly is one. Remove the root and the remaining four notes are one interval away from a symmetrical diminished seventh.
Which scale should I use?
The half–whole diminished scale is the closest fit. The altered scale also works and gives a more modern, less chromatic flavour.