Rare Phosphor Bronze. Acoustic Guitar Strings, stainless steel strings handmade. RPM-12 (12-54) Phosphor Bronze Acoustic Guitar Strings. Low tension... the sound is loud and warm. The Rare Phosphor Bronze strings offer a different and stronger "voice." When DR decided to produce a string with new characteristics, the goal was to revolutionize modern thinking about what phosphor bronze can offer to a good acoustic guitar. Handmade arch-tops and dreadnaughts, as well as quality acoustic guitars made from rosewood, maple, and mahogany, seem to benefit from a distinct improvement in tone, depth, and sustain with the Rare Phosphor strings. Players looking for a fuller and louder sound, as well as deeper bass (who enjoy hearing their guitars) will appreciate the qualities of Rare Phosphor. According to our friend from bluegrass, three-time national guitar champion, Steve Kaufman, the Rares last remarkably long. Steve recommends DR to all his students.