With new Brit cellist Paul Watkins—new meaning joined a year and a half ago—and notionally a somewhat modulated approach (see coverage here), the Emerson String Quartet is no longer the driven, sometimes corporate outfit of the past. Based on their concert at Jordan Hall Thursday night in the Celebrity Series, a program of Purcell and Purcell/Britten, Lowell Liebermann, and late Beethoven, they sound nothing like the old Emerson.

A settling-in stage may still be under way, however, as this concert had some marked patchiness amid the perfections.

Fresh programing for the evening initially took the form of a trio of viol ensemble works by the short-lived Henry Purcell, England’s premier composer of the second half of the 17^th century, as Bostonians know well. Viols were fretted, flatbacked, played upright, but sized according to range, and other modern quartets might do well to explore this old repertory. The Fantasias Nos. 8 and 11 sounded fully suited, and the Emerson playing was luscious except at the start of the evening, where first violin Eugene Drucker took rather a long time to find his pitches. From such pros, that was unusual to hear. The Purcell pieces are, to steal from the fine critic Ted Libbey, angular, chromatic with piquant dissonance, tinged with melancholy and an odd mix of elegance and wistfulness. The third offering was a teenage chaconne, arranged by Britten, which sounded slight while at the same time 100% deft.

The high point of the concert, if one ever may say so with late Beethoven upcoming, was Lowell Liebermann’s powerful, single-movement, abject, tightly through-composed Quartet No. 5 that looked backward, also forward (literally, via inversion and retrograde) with mellow appalledness and appalled mellowness; it might have been Shostakovich’s 16^th .

What a transfixing piece. Polytonal and homophonic, with irregular unisons, and long unbroken lines, it is continuously elegiac: beautiful in sonic conservativism and with more color than most Shostakovich chamber music (plus zero sarcasm). Punctuation within the Pärt- or Gorecki-like dirge grip is provided by spare outbursts of grouchy viola asides and whimpers, plucking, and one or two of those emergency-vehicle glissandos. There is little rhythmic variety or even interest. Liebermann admits in his note to a depressed mindset underlying the Quartet No. 5; withal, he’s a prolific composer (more here), and I certainly look forward to getting to know more. I also can hardly wait to hear this one again, particularly as conveyed by the Emerson Quartet.

By now, after halftime, the evening had become so potent that I was looking forward to Beethoven’s first of the middle three of his late quartets, Opus 132. Any memory of the old Emerson’s unpleasantly tense Mozart and Schubert recordings, simultaneously brutal and slick, had vanished. My keen-eared if classically unseasoned date pointed out that despite the intermission, the weirdly stepped opening of the Beethoven (marked “quite prolonged”) was a fully apposite continuation of the Liebermann’s spooky dolor. She was onto more than she knew going forward: Michael Steinberg explains,

In the cello’s first two notes—G-sharp and A—we meet the musical idea that dominates this quartet as well as the two succeeding ones, Op. 130 and Op. 131…. The cello’s phrase actually consists of two pairs of semitones, and in each of these three quartets Beethoven finds a different way of connecting two such pairs. Here Beethoven begins with two pairs that move in opposite directions, the rising pair (G-sharp/A) being followed by one that falls (F/E). When the cello has gotten no further than its third note, the viola joins in, followed one beat later by the second violin, and for eight measures, pianissimo, all the instruments discourse gravely on this idea.

The spell of those measures was vitiated by now first violinist Philip Seltzer’s opening sourness, but as the strangeness progresses, the Emerson playing gelled, notably from the lightly leading Watkins and violist Lawrence Dutton. The second movement Allegro could have used more profile and bite, and dancing was again either stiff or absent. Yet the “Convalescent’s Holy Song of Thanks to God” was conveyed in all of its still, pained, possibly healed power, the dronelike breathing of illness, up a sixth, down a fifth, in a performance as absorbing and radiant as I have heard live, full of ancient interval style. Steinberg: “Sometimes, in the most solemn moments of his later music, Beethoven leaves our familiar major and minor keys to explore the mystic realms of the old church modes. It was part of the renewal of his language at this time, a renewal that corresponded to a renewal of spirit.”

After the exhalation by all, the Emerson swung into the Alla Marcia and eventually the operatic closing Allegro appassionato with freer playing that was even more technically impressive (some quartets have intonation problems and other letdowns after the evaporation of the Molto adagio ending), unto to the final cadences, landings they stuck for an outstanding close.

Thankfully, no encore.

David Moran has been an occasional Boston-area music critic for 45 years, with special interest in the keyboard.