Chord Construction - Some Special Chords
The Diminished Seventh Chord
The Diminished 7th(dim7) is an interesting chord. It is made up of stacked minor 3rds -
1 b3 b5 bb7
As you can see it contains the rather wonderful term bb7, basically a flattened b7! It is sometimes referred to as a major sixth but technically this is incorrect, although the same note!
There are technically only 3 dim7, once you have played it, for example in E, F and F# you have played all 12 notes. Each dim7 chord after that is a different voicing of a previous chord, otherwise known as an inversion. So, any dim7 chord you play can be viewed as being the dim7 of any note you are playing.
Cdim7 – C Eb Gb Bbb (this is the bb7, ie. a Bb played one semi-tone lower)
So Cdim7 can also be viewed as Ebdim7, Gbdim7 and Bbbdim7, and also the enharmonic equivalents of D#dim7, F#dim7 and Adim7!
Most of the time however, you would play the chord starting from the root note.
There lots of uses of this chord, and these will get covered later, but it is most commonly used as a leading tone chord, for example in the Key of C, the Bdim7.
The m7b5 chord that occurs in the diatonic chords of the major scale (see earlier article) is sometimes referred to as the half-diminished chord. It is made up of the 1, b3, b5, b7. To fully diminish the chord just flatten the b7!
Another interesting chord. As the name suggests, it is constructed as follows.
Min(maj7) 1 b3 5 7
So a minor chord with a Maj7 instead of the normal b7.
It isn’t very common in rock and pop, but was used at times by The Beatles. It is sometimes called the “Hitchcock” chord after being used in the score for Psycho!
Both the Diminished 7th and Min(maj7) chords are derived from The Harmonic Minor Scale, so they fall outside of the diatonic chord sequences we have look at so far. This may give you a clue to what is coming soon!
-Duncan Richardson - MU Columnist
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