Gauges 12-16-24-34-45-56. Rare Phosphor Bronze Acoustic Guitar Strings are a departure from the standard, good-quality bronze string currently available--not necessarily better, but possessing a new, different, and stronger voice. Hand-carved archtops, dreadnoughts, and good steel string acoustic guitars of rosewood, maple, and mahogany benefit from a distinct improvement in tone, depth, and sustain with a fatter, louder sound and a deeper bottom.