EJ19, a D'Addario hybrid gauge, combines the medium gauge bottom strings for increased resonance and volume with light gauge top strings for more comfortable playability and single note bending. A popular choice for bluegrass pickers but suitable for many genres. Phosphor Bronze was introduced to string making by D'Addario in 1974 and has become synonymous with warm, bright, and well balanced acoustic tone. D'Addario Phosphor Bronze strings are precision wound with corrosion resistant phosphor bronze onto a carefully drawn, hexagonally shaped, high carbon steel core. The result is long lasting, bright sounding tone with excellent intonation.