Thomastik Spectrum Bronze strings set for acoustic guitars 10-50. The ultimate bronze round wound acoustic string! The Spectrum Bronze strings are specially designed for the demands of professional recording, yet is also unsurpassed in live performance situations. A unique bronze formula, combined with Thomastik-Infeld's mastery of mechanical filtering with their silk inlay technology, gives a full warm tone, with a sparkling clarity that lets you cut through a dense sound mix. Playing feel is very balanced, and they are surprisingly long lasting.