Cleartone EQ's are a revolution in Acoustic guitar strings. They are the world's first materially tuned Acoustic strings. Like a stereo EQ, all four of our wound strings are made from different materials to emphasize a specific frequency range. The low E string is pure Copper for that beautiful warm low-end sound that is always lacking. The A and D strings are the purest Phosphor Bronze for that medium low midrange fullness. And finally, the G string is 80/20 for some mid range brightness. A perfect EQ balance. There is no other string that will create the fullness of Cleartone EQ's.. Additionally, all six strings come with our twice patented Cleartone treatment for Extra Longevity, Increased Volume, and Longer Sustain.