Minor 7th chords (m7)
To create a "minor seven" you have to add a seventh to a minor chord. In a Cm7 for example this would be a Bb ...and not B which would be a major 7th (maj7) and comes very rarely with a minor chord.
Instead of going up seven steps in the minor scale you can count back a whole step (or two half steps): C → B → Bb
- An m behind the root tone represents "minor" plus a 7 for the 7th, e.g. Em7, Bbm7, etc.
Instead of the m you'll often find a minus sign, e.g. E-7, Bb-7, etc.
Em → Em7
To change an E minor chord (Em) into an E minor seven (Em7) chord we look for a root tone E and lower it by two frets to get the seventh D.
Each fret on the guitars fretboard represents a half step
Drag the slider under the chord shape to the right to change the Em into an Em7 with this method. Also check out the whole thing with displayed intervals and tones and watch carefully how the chord is changing.
A different way to get a seventh is to raise a fifth (5) by three frets (half steps).
In this example we provide an Em chord with even two sevenths with our two methods - sounds good!
If our chord shape contains only one fifth we can raise it nevertheless. It's no problem to omit the fifth in a seventh chord (not for chords with b5 or #5). Root, third and seventh are essential for the character of a seventh chord.
Am → Am7
Same procedure with Am. It's possible to lower the A on G string by two frets. The open G string is the seventh of A.
...and here we additionally raise the fifth by three frets (half steps) again.