Virzi Tone Producer, Lloyd Loar
Created by the Virzi Brothers and patented in April 11, 1922, Lloyd Loar installed the Virzi Tone Amplifier in his Master Models. The Tone Amplifier, or Producer is a thin, oval disk created from wide grain Spruce. It is attached to the underside of an instrument's sounding board by two or three feet. It is very thin and sensitive to vibration and was supposed to amplify the quality of tone produced.
Although Lloyd Loar did not invent this, he helped Gibson obtain exclusive rights to using it in his Master Models.