LeStrange Viols preformed at the National Gallery of Art on Sunday. (Brian Hall)

The National Gallery of Art offered a genteel soundtrack to its extensive collection of old Flemish masters Sunday. Le­Strange Viols, formed two years ago, presented a program of ­early-17th-century works with connections to Amsterdam, Antwerp and the Duarte family of arts patrons.

Viols, cousins to the modern string family, produce dainty sounds that blend together with the utmost euphony when played well. One thinks of a children’s choir (though the bass viols go very low) in its dulcet innocence. These instruments and their repertoire represent a time and aesthetic that is appreciated mostly by specialists today; the audience at the close of the concert was considerably smaller than when it began. But this glimpse into the past was expertly presented.

The program was all original viol music, other than arrangements of keyboard works by John Bull and Jan Sweelinck. The latter’s “Fantasia Chromatica” was certainly the most interesting piece of the afternoon, even if the musicians sometimes struggled to articulate the fastest passages. The work was pungent and yearning, with a particularly spooky section in quiet, overlapping descending scales. Earlier, Sweelinck’s “Pavana Philippi” brought out a range of expression that was missing in the rest of the concert.

On Sunday, LeStrange comprised five players on three sizes of instruments, and one player would often sit out a particular number. Each musician seemed adept and engaged, and tuning was carefully and efficiently done as often as needed; the purity of the final chords gave real pleasure. The design of the instruments and bows (which are held underhanded, like a spoon), precludes much in the way of dynamic contrast. And rapid notes on the larger instruments are often lost in the mix, thin and gentle though it was. But this was clearly a labor of love for the musicians, and one felt approving smiles from the nearby Flincks, van ­Dycks and Cuyps.