Bb7(b5,#9)

Construction

Built from these intervals: 1-3-b5-b7-#9.

The b5 creates a second tritone (the interval of six half steps) between 1 and b5, alongside the standard tritone between 3 and b7. The #9 is enharmonically a b3 (same pitch, different name), so the chord contains both a major and minor third at once -- the same major/minor clash found in 7#9. 7(b5,#9) is 7b5 with an added #9. An alteration is a chord tone raised or lowered by a half step from its natural position. Here the two alterations pull in opposite directions: the b5 lowers, the #9 raises, creating both chromatic sliding and tonal ambiguity within one chord.

Harmonic Function

In Roman numeral analysis (uppercase = major, lowercase = minor), this is one of four double-altered dominants -- chords that combine two alterations on a dom7 foundation. The four are 7(b5,b9), 7(b5,#9), 7(#5,b9), and 7(#5,#9). This one pairs a lowered fifth with a raised ninth:

• V7(b5,#9) in minor -- altered dominant where the #9 holds as b7 of i7 (a common tone, meaning a note shared between the two chords) and the b5 resolves chromatically
• V7(b5,#9) in major -- resolves to I, the b5 drops a half step to the root while the 3 rises a half step to the root
• bII7(b5,#9) -- tritone substitution (replacing a V chord with a dominant whose root is a tritone away), chromatic bass descent plus the #9's growl

Character

Aggressive and chromatic. As one of the four double-altered dominants, this chord's two alterations work in contrary directions: the b5 creates sliding instability while the #9 adds its signature major/minor growl. The combination carries both the sophistication of altered jazz harmony and the raw energy of the #9 (the same interval that powers the Hendrix chord). Compare to 7(b5,b9): that chord funnels all its tension inward toward minor, while 7(b5,#9) splits between chromatic pull and tonal ambiguity, making it more versatile in resolution.

Related Sounds

These chords share the dominant core -- each modifies one or two elements:

• 7b5 (1-3-b5-b7) -- parent chord, same double-tritone structure without the #9's ambiguity
• 7#9 (1-3-5-b7-#9) -- natural 5 instead of b5, the #9 growl without chromatic instability from the fifth
• 7(b5,b9) (1-3-b5-b7-b9) -- same b5, but b9 replaces aggression with darkness
• 7(#5,#9) (1-3-#5-b7-#9) -- shares the #9 but pairs it with a raised fifth instead of lowered, a brighter altered color with two common tones to i7
• Pairs with the altered scale (seventh mode of melodic minor), which contains both b5 and #9 along with b9 and #5

Voice Leading

Voice leading tracks how individual notes move from one chord to the next. The b5 resolves by half step down while the #9 has flexible targets, giving this chord multiple strong resolution paths.

• V7(b5,#9) to I: The b5 descends a half step to the root of I. The 3 rises a half step to the root of I, and the b7 descends a half step to the 3rd of I. The #9 can rise a whole step to the root or descend to the 5th of I.
• V7(b5,#9) to i7: The #9 holds as the b7 of i7 (common tone). The b5 drops a half step to the root of i, and the 3 rises a half step to the root. Two voices arrive at the root by half step.
• bII7(b5,#9) to I: The root descends a half step to the root of I. The b5 of bII is the 5th of I (common tone). The 3 of bII descends a half step to the 3rd of I, and the #9 of bII is enharmonically the 3rd of I (common tone).

These movements apply in any key — the intervals are the same regardless of root.

Practice Seeds

Hear the clash. Play the 3 and #9 together in isolation, then add the b5. The major/minor clash is the #9's identity; the b5 adds chromatic weight underneath. This trains your ear for layered dissonance.

Compare ninth alterations. Play 7(b5,b9) then 7(b5,#9) on the same root. Same b5, different ninths. Hear the shift from compressed darkness to aggressive ambiguity -- the ninth choice defines the chord's personality.

Resolution flexibility. Resolve V7(b5,#9) to major, then to i7. In the minor resolution, listen for the #9 holding as the b7 of i7 -- a note that stays still while others move around it. This builds awareness of common-tone voice leading.

Altered scale connection. Play 7(b5,#9), then play the altered scale (seventh mode of melodic minor) from the same root. Both the b5 and #9 belong to this scale -- hearing the scale inside the chord connects vertical harmony to horizontal melody.