E9 tuning is a common tuning for steel guitar necks of more than six strings. In particular, it is the most common tuning for the far neck on a two-neck table steel guitar or pedal steel guitar, most often combined with C6 tuning for the near neck, and also a popular tuning for single neck instruments of eight or more strings.
The E9 tuning has evolved to support optimal chord and scale patterns across a single fret on the 10-string pedal steel guitar.
Corresponding tunings for a six string lap steel guitar are the E6 tuning E-G#-B-C#-E-G#, or E7 tuning B-D-E-G#-B-E.
A popular E9 tuning for eight string table steel guitar is the western swing tuning E-G#-B-D-F#-G#-B-E, low to high and near to far.
The standard Nashville E9 tuning for ten string pedal steel guitar is B-D-E-F#-G#-B-E-G#-D#-F#.