Ernie Ball Super Slinky Acoustic Phosphor Bronze (2148) Acoustic Guitar Strings have a mellow, ringing sound with excellent clarity. Ernie Ball Super Slinky 2148 Super Slinky acoustic strings are made from 92% copper, 7.7% tin, 0.3% phosphorus wire wrapped around tin plated hex shaped steel core wire. These Super Slinky acoustic guitar strings have a light orange, gold colour and long lasting finish.