STRING SET FOR ACOUSTIC GUITAR Strings acoustic guitar EJ17 Series EJ Phosphor Bronze Medium (013 - 017 - 026 - 035 - 045 - 056). D'Addario Phosphor Bronze strings for acoustic guitar are recognized all over the world for their magnificent and lasting tone. The Phosphor Bronze was introduced for the manufacture of strings by D'Addario in 1974 and has become synonymous with warmth, brilliance and good balanced acoustic tone. They are D'Addario's most popular acoustic guitar strings.