A resonator mandolin or "resophonic mandolin" is a mandolin whose sound is produced by one or more metal cones (resonators) instead of the customary wooden soundboard (mandolin top/face). These instruments are sometimes referred to as "Dobro mandolins," after pioneering instruments designed and produced by the Dopyera Brothers, which evolved into a brand name. The trademark "Dobro" is currently the property of the Gibson Guitar Corporation. When Gibson acquired the trademark in 1993, they announced that they would defend their right to its exclusive use.