Acoustic EJ39 12-String Phosphor Bronze Medium 12-52EJ39, D'Addario's medium gauge 12 string acoustic guitar set provides heavier tension resulting in a bolder, more resonant acoustic tone with higher resistance for heavy strumming or aggressive fingerpicking. 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 Phosphor Bronze strings are precision wound with corrosion resistant phosphor bronze onto