Bb7(#5,#9)

Construction

Built from these intervals: 1-3-#5-b7-#9.

This chord raises both the 5th and the 9th on a dom7 foundation. The #5 adds augmented brightness with upward pull. The #9 is enharmonically a b3, giving the chord simultaneous major and minor thirds -- the same clash found in 7#9. An alteration is a chord tone raised or lowered by a half step from its natural position -- here both alterations are raised. 7(#5,#9) is 7#5 with an added #9. The chord contains five of the seven notes in the altered scale (seventh mode of melodic minor, a scale containing all possible dominant alterations: b5, #5, b9, #9).

Harmonic Function

In Roman numeral analysis (uppercase = major, lowercase = minor), dominant chords built on the fifth degree (V) resolve to the tonic (I or i). Four dominant chords carry two alterations at once -- the double-altered dominants: 7(b5,b9), 7(b5,#9), 7(#5,b9), and 7(#5,#9). Each pairs a different 5th with a different 9th. This one raises both:

• V7(#5,#9) in minor -- altered dominant where the #5 (enharmonically b3 of i) and #9 (enharmonically b7 of i7) can both hold as common tones (notes shared between two chords) against i7, creating an exceptionally smooth resolution
• V7(#5,#9) in major -- the #5 resolves up a half step to the 3rd of I, the 3 resolves up a half step to the root
• Altered scale chord -- the strongest chord-scale match for the altered scale among the double-altered dominants; five of seven scale tones are present in the chord

Character

Aggressive and bright. As one of the four double-altered dominants, this chord channels both alterations upward: the #5 reaches with augmented intensity while the #9 growls with its major/minor clash. This is the altered dominant at its most assertive, the sound of bebop harmony at peak density. Compare to 7(#5,b9): that chord splits its energy between upward brightness and downward darkness (contrary motion), while 7(#5,#9) pushes everything in one direction, creating a chord that asserts rather than spreads.

Related Sounds

These chords share the dominant core -- each changes one or two alterations:

• 7#5 (1-3-#5-b7) -- parent chord, augmented dominant without the #9's aggression
• 7#9 (1-3-5-b7-#9) -- natural 5, the #9's growl without augmented brightness
• 7(#5,b9) (1-3-#5-b7-b9) -- same #5, but b9 replaces aggression with darkness and introduces contrary motion
• 7(b5,#9) (1-3-b5-b7-#9) -- shares the #9 but pairs it with b5 for chromatic sliding rather than augmented brightness
• Pairs with the altered scale (seventh mode of melodic minor), containing five of its seven tones

Voice Leading

Voice leading tracks how individual notes move from one chord to the next. Both raised alterations offer half-step resolutions, and the two common tones with i7 make this chord's connection to minor exceptionally smooth.

• V7(#5,#9) to i7: The #5 (enharmonically the b3 of i) holds as a common tone. The #9 holds as the b7 of i7 (common tone), and the 3 rises a half step to the root. Two common tones make this one of the smoothest altered-dominant resolutions.
• V7(#5,#9) to I: The #5 rises a half step to the 3rd of I. The 3 rises a half step to the root, and the #9 rises a whole step to the root or descends before resolving. The #5's half-step resolution to the 3rd of I is the signature voice.
• iiø7 (half-diminished -- minor 7th with a b5) to V7(#5,#9) to i7: The fully altered ii-V-i. The two common tones between V and i7 (#5 as b3, #9 as b7) make the resolution feel inevitable.

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

Practice Seeds

Common-tone discovery. Play V7(#5,#9) resolving to i7 and listen for the two tones that hold still: the #5 becomes the b3, the #9 becomes the b7. Recognizing common tones -- notes shared between chords -- is the key to hearing smooth altered-dominant voice leading.

Altered scale habitat. Play 7(#5,#9), then the altered scale from the root. Five of seven scale tones are in the chord -- this is the strongest chord-scale alignment in the double-altered family. Hear the scale as an extension of the harmony.

Compare the four double-altereds. Play 7(b5,b9), 7(b5,#9), 7(#5,b9), 7(#5,#9) on the same root. Each combines a different pair of alterations. Map the shift from compressed darkness (both lowered) through contrary motion (mixed) to upward aggression (both raised).

Bebop cadence. Play iiø7 to V7(#5,#9) to i7 at a medium tempo in three keys. Feel the chord's assertive energy in context -- the two common tones into i7 make this the smoothest of the four double-altered cadences.