"In the late 1930's, a young John D'Addario, Sr. met world famous luthier John D'Angelico (of course, at that time D'Angelico was not the household name amongst guitarists that it is today) and the two became close friends and business associates. These were the days before amplification, and D'Angelico, always looking for ways of getting more sound out of the guitar, encouraged D'Addario to experiment with new materials and methods. Together, they pioneered the basic set of acoustic guitar string core-to-wrap wire specifications that are now used the world over.
Their developments include the concept of using a smaller core-to-wrap wire ratio, the use of hexagon shaped core wires, the development of 80/20 bronze (technically known as brass), and the idea of giving guitarists the choice of light, medium, and heavy gauges. For decades D'Angelico and other leading luthiers purchased strings from the D'Addario family.
D'Addario's 80/20 bronze strings have the fullest fundamental low end and an extremely bright high end that tends to mellow more quickly than phosphor or 85-15 bronze alloys. 85-15 bronze alloys provide a more even tonal range."