British acoustic guitarist John Renbourn evolved a unique and throughly engaging sound in the mid-'60s with his seminal fold group, Pentangle. Drawing from traditional fold music of the British Isles, that sound assimilated such diverse elements as chamber jazz, renaissance dance music and Midle Eastern ragas. It was then, and is now a music of quiet, subtle grace.

The John Renbourn Group, which appeared at the Cellar Door last night, features former Pentangle vocalist Jacqui McShee and longtime Renbourn collaborator Tony Roberts on flute and pipes. Table player Keshave Sathe and virtuoso dulcimer player John Molinex round out the group, which is essentially a fold chamber quartet augmented by solo and harmony singing, but defined by its languid instrumental interactions.

The emphatically tradtional repertoire lends itself beautifully to the group's eclectic blend -- haunting Middle Eastern airs are cushioned by buoyant dance tunes from the Middle Ages or melancholy ballads from the northern isles. The progressions and improvisations on all these songs are kinetically smooth.

The group's only drawback is that it seems a bit too genteel, particularly McShee's church-like vocals, which manage to evoke beauty despite their lack of dynamics. All in all, it's gentle and soothing music for those who seek cerebral pleasures in the quietude of timeless acoustic music.

The John Renbourn Group returns to the Cellar Door again tonight.