Virzi Tone Producer, Lloyd Loar

Gibson 1924 Catalog O, features Lloyd Loar's F-5 Mandolin with 'Virzi Tone Amplifier as standard installation'.
Removed from a 1923 Loar Master Model F-5 Mandolin. Note the double U.S. and Foreign Pats stamp. These two stamps are critical to authenticate the originality of the piece.
The underside of the Tone Producer. Once installed on the sounding board, this will face the inside bottom of the instrument.
Gibson 1924 Catalog O.

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.


Note that a real Virzi Tone Producer used by Gibson will have two stamps stating, 'Virzi Tone Producer U.S. and Foreign Pats'. Above from 1924 Gibson Catalog O.
Gibson 1924 Catalog O's description of the Virzi Tone Amplifier.
This Producer is oval, which was intended for a mandolin. A more tear dropped shape piece would have been intended for a guitar.
Note the thinness of the disk. This piece is very light. Feels almost like balsa wood.
This is the top angle of how this piece would be glued to a sounding board. One small foot in front and two feet in the back.
Gibson's 1924 Catalog O revealing the Virzi Tone Amplifier for the first time.