Martin Strings Phosphor Bronze Treated Acoustic Guitar Strings 13-56 MA550TMartin's next generation Lifespan 2. 0 strings are engineered using a new, patented technology only available from Martin. This technology was developed to protect the core wire and the wrap wire to prevent corrosion without compromising tone the single most important attribute of the guitar strings. Authentic Acoustic Lifespan 2. 0 strings look better, sound better, and feel better, providing a smooth playing experience that reduces finger drag. We