Question #22

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I just used the chord finder on this site to find dim7 chords. I was surprised to find that many of these chords have several different names. Here are a couple of the chord formations and the names I found for them:

xx0101 (Abdim7, Bdim7, Ddim7 and Fdim7)
xx1212 (Adim7, Cdim7, Ebdim7 and Gbdim7)

How can so many names be applied to the same chords? And how do you know which formation to use when a tab calls for...say, a Bdim7?

Answer

Diminished 7th chords are symmetrical. That means that if you look at the basic construction of a diminished 7th chord, you will see that all of the chord tones are the same space away from each other. The interval is called a minor 3rd, and a minor 3rd is equivalent to 3 frets on the guitar.

So a B diminished chord consists of the notes B D F and Ab.

B -- up 3 frets -- D -- up 3 frets -- F -- up 3 frets -- Ab -- up 3 frets -- B

Here are the those notes on the neck of the guitar on the 5th string.

|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|-1st string
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
|---|-B-|---|---|-D-|---|---|-F-|---|---|Ab-|---|---|-B-|---|
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|-6th string
      |           |           |           |           |
     2nd fret    5th fret    8th fret    11th fret   14th fret

Here is one of the basic diminished 7th chord forms.

|---|---|---|---|-1st string
|---|---|-4-|---|
|-1-|---|---|---|
|---|---|-3-|---|
|---|-2-|---|---|
|---|---|---|---|-6th string

Now take a look at the note names if I play that chord shape starting on each of those notes. You still just have the notes B D F and Ab.

<*********> <*********> <*********> <*********> <*********>
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|-1st
|---|---|-D-|---|---|-F-|---|---|Ab-|---|---|-B-|---|---|-D-|
|Ab-|---|---|-B-|---|---|-D-|---|---|-F-|---|---|Ab-|---|---|
|---|---|-F-|---|---|Ab-|---|---|-B-|---|---|-D-|---|---|-F-|
|---|-B-|---|---|-D-|---|---|-F-|---|---|Ab-|---|---|-B-|---|
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|-6th
      |           |           |           |           |
     2nd fret    5th fret    8th fret    11th fret   14th fret


Here are those chords in tablature form.

E:-----------------------
B:--3---6---9---12---15--
G:--1---4---7---10---13--
D:--3---6---9---12---15--
A:--2---5---8---11---14--
E:-----------------------


So a Bdim7, Ddim7, Fdim7, and an Abdim7 all share the same notes. It just depends on which note within the chord form that you are thinking of as the root. And the root is not always the lowest note in a chord form.

Here are the 3 most basic diminished 7th chord forms. If you are looking to play a Bdim7 chord, just make sure that one of the notes within the chord form is a B.


|---|---|---|---|-1st string
|---|---|-4-|---|
|-1-|---|---|---|
|---|---|-3-|---|
|---|-2-|---|---|
|---|---|---|---|-6th string


|---|-4-|---|---|-1st string
|-2-|---|---|---|
|---|-3-|---|---|
|-1-|---|---|---|
|---|---|---|---|
|---|---|---|---|-6th string


You are going to barre you first finger across the 4th, 3rd and 2nd strings for this one.

|---|---|---|---|-1st string
|-1-|---|---|---|
|---|-3-|---|---|
|-1-|---|---|---|
|---|---|---|---|
|---|-2-|---|---|-6th string


And last.....how do you know which Bdim7 to play if you just see a chord name referred to? The answer is that there is no way to tell. You can listen to the song and try and decide from there. If it is a jazz song, which is where you will typically find diminished 7th chords, then any of them is fair game. That is a big part of jazz is the ability to any version of a particular chord.

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