This summer, the Cape Cod Chamber Music Festival has has given a prominent role to the Jupiter String Quartet. Born 13 years ago, schooled primarily in Boston at NEC, and winner of many prizes, the ensemble is now in residence at the University of Illinois in Champaign-Urbana. It boasts a busy concert schedule that overcomes the potential challenges of sibling and marital interactions, not to mention five young children. As an example of their collaborative instincts, between two of Bartok’s heated movements in the humidity of Wellfleet’s beautiful First Congregational Church, the second violinist, Meg Freivogel, shared a sweat-controlling handkerchief with her cellist husband, Daniel McDonough. He promptly reminded the audience, “After all, we’re married.” Liz Freivogel, the violist who’s Meg’s sister, smiled, while Nelson Lee, their first fiddler, appeared unsurprised.

On Friday, in their third concert in four days at the Festival, they played the “Notturno” movement for piano trio by Schubert, the fourth Bartok string quartet, and a Brahms piano quartet, in which Meg Freivogel played violin. Joined by Brian Zeger, the eminent “collaborative” pianist based at Juilliard who years ago was the second artistic director of the Festival, the program afforded the audience an unusual opportunity to hear the individual voices of the ensemble. The overall impression for this listener was that this was Meg’s night of triumph, her husband’s night to meet extraordinary demands, and that in the years since I heard them in their student days the Quartet has achieved a sum greater than its individual parts.

Schubert’s Notturno in E-Flat Major, Opus 148 (D.897), completed toward the end of his short life in 1827, is an adagio whose genesis is subject to ongoing speculation. The best guess is that it was the original slow movement for the B-flat major piano trio completed the following (and last) year of his life, and it’s remarkable also for the way it presages the slow movement of his sublime string quintet, also completed in 1828. Whatever its roots, it’s a beauty. I’ve heard it several times as an encore, but beginning a program with it was a fine idea. It’s calm and introspective overall, but as is Schubert’s wont, a few agitated measures toward the end lend tension and a degree of anguish. It calls for equal partnership, asking each player to lead and to recede.

Zeger, who must play lots of Schubert as he collaborates with extraordinary singers, displayed the bell-like sound so vital for this composer, and while I missed some space between notes in the runs that help frame the work, his sound at full stick was lovely, without overwhelming the strings. The cellist was elegant, with a warm, expressive sound that was perhaps a bit more intense at times than necessary. Lee, who uses an arm vibrato that yields a narrow, but well-focused sound, played quietly overall, bowing mainly toward the tip. I found the range of his expression a bit limited. Overall, the reading was somewhat metronomic and lacked the nuance that great, longstanding piano trios bring to this work. A nearby listener described the movement as “…a mild piece.” On this evening, she was right. It was lovely and mild, but that was because the ebb, flow and understated excitement that can elevate the movement were missing.

Bartok’s fourth of six string quartets, composed in Budapest in 1928, is in 5 movements, although musicologists tell us it was originally conceived as having four movements. Daniel McDonough told the audience that Bartok had been influenced by music he heard in Africa and brought to this work some thematic material from recordings he made there. He described the “arches” that define the work, with the first and last and second and fourth movements thematically related, while the magnificent slow movement is the fulcrum. He told the audience the Quartet is still working on achieving the “Prestissimo” with which the second movement is marked (the original, landmark Juilliard Quartet recording is indeed faster, but not by much). His intro was helpful; Bartok is still not second nature to many listeners. But he was modest by leaving out indication that the work is brutally demanding.

The Jupiter carried it off brilliantly. The ensemble was spot on, and fine intonation after a few tentative early moments lent clarity and definition. In the first movement, a bit more heft from the lower strings might have helped, but in the rapid-fire second movement, played with mutes, there was mystery and remarkable technical mastery. The slow movement has some wonderful moments, particularly when the players are asked to eschew vibrato. Overall, the cello takes a leading role, and McDonough’s playing was perhaps a bit soft around the gruff edges Bartok constructs. When playing quietly, the Jupiter cellist falls into an “off-on” vibrato, starting sustained notes without vibrato and then adding the soup as the note progresses. That can be effective when used judiciously, but for Bartok it robs the music of the cragginess that’s an important component of his signature. But overall, the movement was played beautifully, particularly by the second violin whose sensitivity and tonal variety enriched the proceedings. The pizzicato movement was terrific, with just the right character for the “Bartok” pizzicato: strings slapping against fingerboards. The final movement was excellent, although the lower voices might have been more prominent. The performance earned agitated applause; this was playing of a high level.

Brahms’s C-Minor Piano Quartet, Op.60, is famed as a cellist’s dream. The slow movement is one of the great cello love songs, and the late Bernard Greenhouse, founding cellist of the Beaux Arts Trio and a Wellfleet citizen for many years, played it often in the same church. His goal was to leave members of the audience weeping at its close, and for many in attendance, that was fully recalled. A tough act to follow!

The work was well played, in particular by Meg Freivogel, who took full advantage of her lead role. She brought warmth, elegance, refinement, and quite a bit of imagination to her reading. As an example, the start of the last movement, a long violin solo with piano accompaniment, was lovely, as she spun a long, lyrical line. For the slow movement, eminent artists choose a wide range of tempi. The Beaux Arts ignored the “Andante” marking and really took their time, perhaps remembering the oft-cited allegations that so far as Brahms himself was concerned, the slower everything was played, the better. Yo Yo Ma, in his celebrity recording with Stern and Ax, plays it quickly. McDonough, performing with passion and intensity, chose to split the difference, proving again that great music can be played beautifully many different ways. In this movement, the piano is relegated to an unusually subsidiary role, but there’s a brief, Schubertian passage toward the end in which the piano reminds the audience of its presence. Zeger did so brilliantly, but at other times, the piano sound was somewhat thick, reflecting perhaps humid air and a tad much pedal. The viola, as was true for much of the evening, was a bit reticent throughout, although in the slow movement lead moments came through nicely.

A side bar about the instruments: Having heard many concerts in this venue, some by players with great old Italian specimens, the quality of their companions clearly makes a difference (as does the player, the humidity, the instrument’s setup, etc). The Jupiter plays on two Italian instruments (first violin and viola), a Dutch violin by the well-recognized Johannes Cuypers, and a cello created in the last century by a talented German maker who worked primarily in the USA. It’s hard to judge on a single hearing, particularly on such a humid night, but their instruments are likely good, rather than great, reflecting the astronomical costs of instruments these days and the apparent lack of a Jupiter “patron” to lend them expensive instruments. The late 18^th-century Cuypers actually sounded terrific (the Dutch are under-appreciated as makers and happily, therefore, less expensive than the Italians). Friday night the others paled by comparison. Such instruments overall put the Jupiter at an unfair disadvantage in the race to win audiences, but they overcome those obstacles with talent, hard work, and considerable intelligence. It was a fine night in Wellfleet.

A final word about the audience and, for me, an attendant mathematical riddle: Given the proposition today that classical music audiences attract primarily those of a certain age who grew up in a different time, I surveyed the almost-full church. Sure enough, other than the Jupiter players, there were exceedingly few listeners below the age of 50, with their years offset by those of several nonagenarians. I’d guess an average age of at least 75. The conundrum: That’s been true in Wellfleet for the last 35 years or so! I invite explanation from those readers mathematically and demographically inclined.

Tom Delbanco is the Koplow-Tullis Professor of General Medicine and Primary Care at Harvard Medical School and Beth Israel Deaconess Hospital. An avid violinist since age nine, he has particular interest in the evolution of stringed instruments from the 16^th century on.