It appears this display may have closed in 2012, its not clear if the Smithsonian collection can currently be viewed

Website link

“Several instruments made by Antonio Stradivari, universally acknowledged to have been the greatest of all violin makers. The Servais Cello (1701) is considered to be one of the best preserved Stradivarius cellos. Also included is the Herbert R. Axelrod Quartet of Decorated Instruments, also made by Stradivari. Among only 11 rare decorated Stradivarius instruments that survive today, the Axelrod Quartet features the following: Violin, the Ole Bull (1687); Viola, the Axelrod (1695); and Violin, the Greffuhle (1709). While generally on display, these instruments also are used for performances of the Smithsonian Chamber Music Society.”

The Smithsonian has a total of over 6000 instruments.

The Smithsonian provided this clarification on what is currently displayed: “As far as bowed stringed instruments on display, there is a cello in the American Stories exhibition; a violin in The Price of Freedom exhibition; and a Yankee Church Bass in one of the Artifact Walls.  All these may be found in the American History Museum. In a few years, there will be more violins and bowed stringed instruments on display as exhibitions open after museum renovations. ” -Aug 6, 2014.

Updated Aug 6 2014