Some well known players, such as Jim Hall, Les Spann, and Herb Ellis, have used George Van Eps String Dampers. There is not much in print about this devices except that apparently George Van Eps invented it and his company, Vanco, manufactured them for a while. It replaced the truss rod cover and mounted to the headstock of the guitar and was designed to eliminate sympathetic vibrations in open strings of an amplified archtop, thereby achieving a better tonal balance between open and fretted notes, while reducing the electro-acoustic guitar's susceptibility to feedback. Van Eps dampers were available as a guitar accessory throughout the fifties. Gibson actually marketed them for a short period.

The Scotty Moore Website has a great page with information and photos about the history of the string damper.

(My apologies to the uncredited photographer who took this photo of Herb Ellis (with
Ray Brown - likely on stage with the Oscar Peterson Trio) in 1987, using a damper.)

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The original Van Eps Damper manufactured by his company, Vanco

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Gibson manufactured Van Eps' Damper for a while

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Pat Ferrand manufactured these dampers in the 1990s and early 2000s

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View the Van Eps Patent Illustration »