The Dobro is the instrument that put the twang in country music, but it is much more besides. It was the 1928 creation (and contracted namesake) of the Czech American Dopyera brothers, who placed a steel disc over the sound hole of a guitar and added an aluminum cone underneath it to amplify the sound. Held flat and played from above, Hawaiian style, it allows the player to execute a variety of slides and bends. The Dobro stands at the center of that 1930s confluence of country and blues from which rock 'n' roll emerged. Its sound is as quintessentially American as one can imagine, and Jerry Douglas is its modern master.

Douglas has appeared as a session musician on an enormous variety of recordings, both within the country field and beyond. Chances are, when you hear a Dobro, you're hearing Jerry Douglas. He is one of those musicians so attuned to others' aims that he can seamlessly incorporate his own playing into widely varying projects — the coolly eclectic yet sentimental albums of Alison Krauss and the stone traditionalism of the O Brother, Where Art Thou? sound track, to name two recent examples.

Many musicians who excel in supporting roles lack the commanding quality for solo work, but Douglas has released nine albums, and he keeps getting more and more experimental. His current tour supports his latest, Lookout for Hope. The album, all acoustic with a small accompanying band, goes farther afield from Douglas's bluegrass roots than anything else he's ever done. It's a real tour de force — not because Douglas is terribly virtuosic (though he is in a few places) but because he seems to have reflected on the Dobro as an idea. Think of it as a study of why this mixture of Europe and Hawaii, of wood and metal, should have so insinuated itself into our culture.

The album, then, may spawn a concert that includes one or more lengthy fusion jams, less dramatic than those of Bela Fleck but brainier, with odd dissonances that seem to hang over long stretches of music. Bluegrass is never completely absent from Douglas's music, but the heart of this album resides in a group of compositions, several of them by Douglas himself, that meditatively extend the Dobro's roots genres. There is a lovely Dobro-ized Duane Allman solo, a version of "In the Sweet By and By" whose quiet radiance reminds me of the music of the African American "sacred steel" players, and two terrific country songs in which Douglas gets to show his sensitivity as an accompanist. One of them, "The Suit," is a funeral piece so calm and warm that I'd choose it for my own.

Jerry Douglas visits the Ark on Saturday, June 1.