Ernie Ball Earthwood Bronze 80/20 strings for steel stringed acoustic guitar. Ernie Ball Earthwood 80/20 Bronze Acoustic Guitar Strings are made from 80% copper, 20% zinc wire wrapped around hex shaped brass plated steel core wire. These acoustic guitar strings provide a crisp, ringing sound with pleasing overtones. Ernie Ball's is the only and obvious choice for guitarists all around the world all over the world.