Juilliard Quartet: 70 and far from finished

The Juilliard String Quartet : (from left) Ronald Copes, Joel Krosnick, Roger Tapping, and Joseph Lin.

At 70 years old, the Juilliard String Quartet arrived Sunday afternoon sounding like a work in progress.

Listeners had every right to feel wistful at the group's Philadelphia Chamber Music Society concert at the American Philosophical Society. Musicians are human, and all humans at some point begin to fail. This was Joel Krosnick's last appearance here as the group's cellist (Astrid Schween takes over in September), and a hearty standing ovation recognized his four-plus decades of providing a depth and complexity of sound that is rare in the field.

Despite an ongoing regeneration, there is no old-world/new-world dichotomy in the Juilliard. Joseph Lin became first violinist in 2011, and he is conspicuously a younger and more physical player than the others. He levitates, literally. At the start of Schubert's Quartettsatz in C Minor, D. 703, he lifted himself off the chair with his entrance. But what a sound. With smoothly dispatched inflections, Lin, while more polished than any of his colleagues, showed why he was chosen to link past and future. In tone and the way he hears interpretation, he could have been plucked from any point in the last century.

String quartets - real full-time string quartets - are more than the sum of four free agents, and the idea of a shared philosophy faded in and out. Cohesiveness was especially fleeting in Brahms' String Sextet in G Major, in which the Juilliard was joined by cellist Marcy Rosen and violist Samuel Rhodes. It's hard for an ensemble to arrive at an evolved place while struggling for the basics, and Krosnick often was. Still, you had to be grateful for his pizzicato sound in the third movement - lovely, rich, and resonant.

It's funny to think that the Juilliard formed a few years before Elliott Carter's String Quartet No. 1 took shape in 1950. The Juilliard has made Carter a special focus (in 1991 at the Free Library, they played all the Carter quartets written up to that time), and it shows. Tightly organized and clocking in at an oddly economical 45 minutes, the piece is the most rewarding of challenges.

Dissonance seemed to fall away as the least important factor, given their ardent advocacy at work. Carter here has a great gift for intimating organizing features without stating them obviously - a melodic line that, but for a few displaced notes, might sound conventionally tuneful, or the feeling of a fugue.

One section pairs off the instruments in a series of pas de deux in sound - viola-cello, two violins, then viola-cello again. Krosnick with violist Roger Tapping, then Lin with violinist Ronald Copes, so vividly realized Carter's score that you hated saying goodbye.