D'Addario Acoustic Guitar StringsD'Addario EJ15 Extra-Light Phosphor Bronze Acoustic Guitar StringsD'Addario Phosphor Bronze Acoustic Guitar strings are acclaimed worldwide for their superb, long-lasting tone. Phosphor Bronze was introduced to string making by D'Addario in 1974 and has become synonymous with warm, bright, and well balanced acoustic tone. D'Addario's most popular acoustic guitar strings.