Rare Phosphor Bronze. Acoustic Guitar Strings, handmade stainless steel strings. RPL-10 (10-48) Phosphor Bronze Acoustic Guitar Strings. Low tension... the sound is loud and warm. The Rare Phosphor Bronze acoustic strings represent a different approach compared to typical cast bronze strings with good quality. They are not necessarily better, but they have a new, different, and stronger "voice." When DR designed a string with new characteristic properties, the goal was to revolutionize modern thinking about what bronze can offer to a good acoustic guitar. Thick and dreadnought guitars, as well as fine steel-string guitars made from rosewood, maple, and mahogany seem to benefit from a noticeable improvement in tone, depth, and sustain with the Rare Phosphor strings. Players who desire a fuller and louder sound, as well as a deeper bass, will appreciate the tone, sound, and feel of the Rare Phosphor strings.