If ever our town could pull together enough ambition to stage a string-quartet festival, it would be like striking a vein of artistic gold. Were any presenter visionary enough to host visits from the world's most charismatic pianists, aficionados would rush in.

And if you blended these prospects - along with a singer or two - into a single series, what you would have is the Philadelphia Chamber Music Society, which, clocking an impressive one score and seven years, is anything but speculative. The society's season roster of 64 concerts has one more to go - Friday night - and what's remarkable about this year's iteration isn't its unusually high quality; what's worth noting is that there was nothing unusual in terms of quality, and yet it all happened despite the cloud of uncertainty surrounding the economy. While many other groups in recent years have set off grim pathologies in debt and declining participation, PCMS has been a parable of what's possible when you're doing everything right.

It hasn't done it by flouting mission or diminishing scale. Chamber music has some terrific homes in various series across the country - in Kansas City, Indianapolis, Detroit, San Francisco, Cincinnati, at Stanford University, and elsewhere. But many of these presenters also import jazz, dance, and world music, and among those who still present pure chamber music, PCMS may have no peer in terms of number of concerts.

Is it the largest such series in the United States? The field does not even agree on a universal definition of chamber music, so activities aren't always tracked, making hard data elusive, says Margaret M. Lioi, chief executive officer of Chamber Music America, which represents about 6,000 ensembles, presenters, schools of music, educators, and other advocates.

Still, she says: "I looked at some of our big, important chamber music presenters, and, for example, Detroit has 12 concerts, Martha's Vineyard Chamber Music Society has 12, others have 15 or 20 maybe. I didn't find any that are members that have as many as Philadelphia. There is no doubt they are a prolific presenter."

PCMS' audience - itself a true society - rewards it with loyalty. Paradoxically, the lengths to which listeners will go to hear their Schubert and Janácek was made evident by the sea of empty seats at one recent concert. On May 5, when the Broad Street Run and a crash on I-95 coagulated traffic flow in the area, the soon-to-disband Tokyo String Quartet walked onstage to about 200 empty seats at the Independence Seaport Museum.

But 100 latecomers arrived after the first piece, an additional 50 at intermission, and a few more trickled in during the second half. Steadfast, these string-quartet lovers.

"There were some people who took journeys that exceeded two or three hours, some four, and some who never made it at all," said artistic administrator and manager Miles Cohen. "Some people showed up in the final piece [Bartók] in the second movement - that was wild."

Devotion on this scale is the holy grail among arts groups. What nourishes such fidelity? The low ticket price, to be sure - $18 or $24 (cheaper if you subscribe), considerably more comfortable than the sting you feel from the three-figure prices of some other nights out.

The feeling that you're valued also fans enthusiasm: When you call the PCMS box office, you get a human being who knows his Köchel from his Hoboken numbers and will patiently put your name on the waiting list for tickets.

That's necessary more often lately. Audiences are growing, up more than 20 percent in the past five years - a span, remember, that has coincided with our Great Recession.

But it's really qualities that are harder to articulate that are powering the positive energy around PCMS. My colleague, David Patrick Stearns, and I were able to cover about half the society's 2012-13 concerts, and while that means we missed much, what we heard reinforced the reasons any music lover has for living in this city.

Philadelphia considered itself pretty sophisticated in 1986 when Anthony Cecchia founded PCMS; in retrospect, we hardly knew what we were missing. Today the society - which this season has successfully grown a younger listenership with social media and special programs - has clearly emerged as the city's smartest presenter.

Without a PCMS, we would not have been introduced to stunning young pianist Nareh Arghamanyan, who in October seemed to rewrite Bach, Schumann, and Rachmaninoff on the page. Other pianists this season passed repertoire like Olympic torches, with Jeremy Denk - the intellectual set's It Boy of the moment - taking on more Bach and Schumann in December. Imogen Cooper came in from London in February to establish a link between Denk's Schumann and her own Schubert in the Sixteen Deutsche Tänze, D. 894. By the time Mitsuko Uchida came in last month with Schumann at his most unhinged, the ear was ready for it.

So it went all season long, whether by chance or design, this lively dialogue.

Happily evaporated in nearly all these wisely curated experiences was any sense of time or place. When the lights went down before Cooper's first notes, there were only two people in the room - one who had a date with a knowing audience, and another who would leave two hours later feeling provoked, changed, and extremely fortunate.

Contact Peter Dobrin at 215-854-5611 or pdobrin@phillynews.com. Read his "ArtsWatch" blog at www.inquirer.com/artswatch.