Watch the Double Stops online guitar lesson by Andrew Ford from Blues Bass Survival Guide
Double stops are playing 2 notes on 2 different strings and creating a chordal effect. These can be very useful in the blues, especially if you are playing in a trio where some chordal support behind the soloist, or in the context of the song would be beneficial. In the examples here technically I am playing triple stops because I play the root also on the open strings but for the purposes of this concept we will refer to them as double stops. In order to outline the chord properly the notes we should target are the 7th degree and the 3rd. They are primarily the notes that give a chord its quality. Of course if it's a diminished or augmented chord then the 5 also comes into play but for the most part we should target the 3rd and 7. In a dominant chord, the chord we use primarily in the blues, it has a major 3rd and and a flat or minor 7. So if we look at the E7 or E dominant 7th chord the two notes we will target are D which is the minor 7th and G# which is the major 3rd. Playing these notes in the higher register gives them more clarity so two options to outline that chord might be using D at the 12th fret of the D string with G# at the 13th fret of the G string. That is the double stop and you can play the open E also to fill out the chord. One other option to outline the E7 is going up higher on the neck and using D at the 19th fret of the G string and G# at the 18th fret of the D string and again using the open E. Now let's outline the A7 chord. The two notes we are targeting to outline the chord are C# which is the major 3rd and G which is the flat 7. We will again use the G and D strings to play the double stops. One way to outline this chord is to use G at the 12 fret of the G string with C# at the 11th fret of the D string along with open A. Another way to outline that same chord is using G at the 17th fret of the D string with C# at the 18th fret of the G string again with the open A. There are many other ways to play double stops even the traditional way of playing the root on the E string, for instance E at the 12th fret of the E string with G# at the 13th fret of the G string and sort of plucking them simultaneously creating a major type chord sound or lowering the G string note a half step and creating a minor type chord. However you use the double stops focus on the notes that give that chord its characteristic sound and play the notes in a register to maintain clarity.