TV Reviews : CS&N; in Concert

“Crosby, Stills & Nash: The Acoustic Concert” opens with the sound of cheering and the sight, in a still-photo montage, of the singers as princely young troubadours. At the time of those photos, circa 1969-70, CS&N; seemed the epitome of romance and social relevance in rock.

What follows is a concert, taped last November at the Warfield Theater in San Francisco, in which an audience’s collective sense of nostalgia lets the same threesome, now avuncular middle-age troubadours, limp through a creaky performance while reaping an outpouring of adulation all the same.

The problem with this 12-song concert segment, which will be shown with pledge breaks, at 8 tonight on KCET Channel 28, is that Crosby, Stills & Nash simply doesn’t cut it as a harmony trio--at least not on this night. Admittedly, CS&N;’s complex harmony blend is a tricky, ambitious weave in which the voices must scale sudden, steep cliffs and swirl between moods earthy and ethereal.

The most glaring problem is Stills, who sounds sadly diminished as he tries to negotiate such trademark songs as “Suite: Judy Blue Eyes” and the Buffalo Springfield-era “For What It’s Worth.” Crosby and Nash both sound like reasonable approximations of their better selves, especially on “Taken at All,” an obscure but pretty song culled from CS&N;’s vaults.

(“Crosby, Stills & Nash: The Acoustic Concert” also airs Tuesday at 10 p.m. on KPBS Channel 15 and at 10:30 p.m. on KOCE Channel 50.)