Felix Mendelssohn didn't leave the world a lot to discover this 200th birthday year, at least in terms of hard notes.

Fastidious in his composing habits, refined in the extreme, he created a series of masterworks or close to it whose single-dimension emotionalism assures that new meaning probably won't be uncovered - particularly when the music is confined to a concert's first half and not expected to leave audiences sated.

Yet in an unusual role reversal, the Emerson String Quartet ended its Kimmel Center concert Monday with Mendelssohn's String Quartet Op. 80, written when some scholars say the composer was in creative decline.

In a performance that bested the Emerson's 2005 recording of the piece, such received wisdom was defied so handily as to leave a burning question about what was different. Often, 21st century Americans seem cramped by Mendelssohn's tidy, Biedermeier world. This quartet, however, was written following the death of the composer's sister, Fanny. Thus, even the most typical Mendelssohnisms can be credibly charged with greater-than-usual meaning.

Projecting that can often be a matter of surface inflection, though on Monday the Emersons created a sound better blended than usual - unusually warm under the surface but pulsating with something hotter underneath. On first violin, Philip Setzer gave a tonal glimmer to all that he played in ways that drew the ear deeper into the music. The group's classical-era, straight-ahead tempos maintained a sense of composure that became all the more moving because the performance so clearly projected an underlying dire emotionalism. In nearly all respects - strategy, emotional presence, and quality of playing - the performance was among the Emerson Quartet's best.

The rest of the program in this Philadelphia Chamber Music Society concert was curiously pale. Schubert's String Quartet D. 87, written when the composer was a mere 16, was interrupted by a wayward string on Eugene Drucker's violin, and it's not much of a piece anyway, especially in the Emerson's unvarnished approach.

Beethoven's String Quartet Op. 74 ("Harp"), easily the most immediately appealing work in the composer's quartet output, had plenty of touches that reflected the Emerson's multi-decade relationship with the music. A younger quartet might treat the music's structural points as a needed compass for charting a stable course through the piece; the Emersons take a long view that emphasizes cohesive integration. That's all quite welcome, though the piece didn't catch fire until the last two movements, with violist Lawrence Dutton and cellist David Finckel touching Beethovenian fire in their incidental solos.