The resonator guitar was invented in the 1920s, with one or more metal cone resonators set into the body. These additions were originally meant to amplify the sound of the acoustic guitar for performance in a band. The distinct timbre of the resonator ensured that the design survived even after electrification, especially in blues and bluegrass genres. A study of the sound radiated from different models of resonator guitars, as well as a similar standard acoustic guitar, compares spectral features to understand the unique sound of the resonator guitar.