In theory, at least, the new acoustic movement represents a pretty adventurous idea. By combining the instrumentation of bluegrass with the harmonic invention of jazz and the dynamics of chamber music, the musicians hoped to carve out a new niche in American music.

It was a nice idea, but somehow things haven't worked out as planned. True, some performers have managed to deliver the sort of stylistic fusion the new acoustic music promised, but so far, those are the exceptions. Far more common is music that is soft, pretty, vaguely tuneful and largely unobtrusive -- in short, upscale easy listening, the white wine equivalent of cocktail jazz.

Consider the Darol Anger/Barbara Higbie Quintet's "Live at Montreux" (Windham Hill WH-1036). Although this group, which will be playing the Birchmere on Tuesday, includes some of the ablest instrumentalists on the Windham Hill roster, the players apply their abilities not to stimulate one another, but to take a tuneful trip down the path of least resistance. The ensemble passages are uncluttered to the point of reticence, as if the quintet's members were deathly afraid of treading on one another's toes, and the improvisation clings so closely to the compositional structures that a glib sterility sets into the performances.

Mind you, there are some attractive moments, such as the deft layering of voices in Higbie's "Egrets," or the way the shimmering textures of mandolin, steel drums and piano animate mandolinist Mike Marshall's "Egypt." But for all its carefully cultivated textures and dramatically shifting dynamics, the music never goes anywhere.

Part of that may result from the group's aversion to overtly rhythmic playing, for there's never enough heat generated to get any of the solos sizzling. Mostly, though, it seems a matter of not wanting to generate that sort of excitement, if only because it's easier (and more profitable) to play prettily.

After all, these musicians certainly are capable of more energetic work. Marshall's own album, "Gator Strut" (Rounder 0208), variously features four of the Anger/Higbie quintet's members, yet avoids most of that group's weaknesses. The difference is largely a matter of stylistic focus; like the work of David Grisman, Marshall's occasional employer, the music on "Gator Strut" emphasizes freewheeling virtuosity and a bouncy, western swing beat. As a result, Marshall and company are kept on their toes throughout.

True, the record is guilty at times of overreach. Marshall's rendition of Thelonious Monk's " 'Round Midnight" grasps the essential melancholy of the melody but is unsure of what to do with it; and the mandolin transcription of an excerpt from the Ravel String Quartet is a pointless bit of flash. But there are more hits here than misses, from the witty interplay of "Dance of the Planktons" to the apt fusion of "Scotch & Swing."

Marshall, Anger and Higbie represent only one aspect of the new acoustic movement, the post-bluegrass virtuosi. More prevalent by far is the new generation of solo pianists, to which Steven Schoenberg belongs. Epitomized by the pastoral meanderings of George Winston, this school can more or less be traced back to Keith Jarrett's spate of solo concert recordings.

The magic words among this group are "spontaneously improvised compositions," a sort of musical free fall in which the pianist either pulls the whole of his or her musical experience into one graceful flight, or flails haplessly at a random series of chords. On his "Three Days in May" (Quabbin QBR 1002), Schoenberg demonstrates that he has a fairly wide range of tricks at his disposal, ranging from sturdy, classically based technique to an admirable ability at voicing chord progressions. But all too often, his efforts don't go any further than a display of musical agility; instead of developing an idea melodically, he prefers to dress it up with busy arpeggios and clever inversions. The end result is ultimately too glib to be worth the exertion Schoenberg expends.

Still, Schoenberg, who'll be spontaneously composing at Blues Alley on Monday, has our best interests at heart. Why else would he have dedicated his album "to the thoughts, feelings and beliefs which we can share to bring about peace throughout the world"? Nor is such altruism unusual among these musicians. Andreas Vollenweider, the Swiss harpist and composer who will be at Baltimore's Meyerhoff Concert Hall on April 15, intends his albums for those seeking inner as well as outer peace. In fact, his "White Winds" (CBS FM 39963) offers an allegory of just such a quest.

Exactly how this allegory is to be read is another matter altogether, one on which Vollenweider declines to elaborate. Then again, given the vaporous quality of the music here, that may be all for the best. Vollenweider is a remarkably capable player, but his writing has degenerated into sparsely populated soundscapes in which the melody appears but fleetingly and texture is exploited for its own sake. Unlike many of his colleagues, Vollenweider understands the importance of rhythm and maintains enough of a pulse for his listeners to tap their feet idly as the music wafts by, but for the most part, "White Winds" is an exercise in vapidity.