AKA: Bb diminished seventh, Bb°, Bbdim, Bbdim7, Bbdim7th, Bbdim/6, Bbdim(add6)
Bbdim7 Accordion Chord Chart
Green bass pattern: Bbdim7(omit5) = Bbm6(omit5)
Blue counter bass pattern: Bbdim7
dim 7th Chords
A diminished 7th chords is a chord that consists of a root, a minor 3rd, a diminished 5th, and a diminished 7th. They can be formed by stacking minor 3rd intervals on top of each other. A minor 3rd interval is the distance between two notes that are three half steps apart, such as C and Eb. When you stack two minor 3rd intervals you get a diminished chord (triad), if you add another minor 3rd, you get a diminished 7th chord. It’s a chord that has regular intervals between each note.
Minor 3rd is a consonant interval but when you combine two minor 3rd intervals, you create an interval of 6 half steps from the root. This interval is known as a tritone and is a dissonant interval.
For example, if you start with the note C and stack two minor 3rd intervals on top of it (C-Eb-Gb), you will have formed a C diminished chord; adding another minor 3rd you get C-Eb-Gb-Bbb, which is C diminished 7th chord. This chord is typically represented by the abbreviation “dim7” or “o7”.
This chord has a very dissonant, unstable sound and is often used to create tension in music. It can be resolved by moving to a chord with a more stable sound, such as a major or minor chord.
Equivalent chords:
A diminished seventh chord is equivalent to all four diminished seventh chords built on each of its notes. In other words, a diminished seventh chord can have any of its four notes as its root.
In this case:
B♭dim7 = D♭dim7 = Edim7 = Gdim7
(Please note that chord inversions do not work on the Stradella bass system like they do on other instruments or on the accordion keyboard itself. So although these equivalent chords have the exact same notes, they are not interchangeable and should not be intended as inversions of the same chord, at least for what concerns the left hand.)
dim 7th Chord Buttons
The diminished chord buttons on the accordion actually play diminished 7th chords without the 5th, this means that they play just the root, the minor 3rd, and the diminished 7th (which is a 6th). For this reason, diminished 7th chords on the Stradella bass system, can be seen also as minor 6th chords with no 5th.
Notes:
B♭, D♭, F♭, A♭♭
(B♭, D♭, E, G)
B♭dim button plays:
B♭, D♭, A♭♭ (no F♭)
Intervals:
R, m3°, dim5°, dim7°
Dim buttons play:
R, m3°, dim7° (no dim5°)
Left hand:
Green bass pattern:
Bbdim7(omit5), same as Bbm6(omit5)
B♭ + B♭dim
(A# + A#dim)
Blue counter bass pattern: Bbdim7
B♭ + F♭dim
(A# + Edim)
Fingering:
4 + 2