Audiences here knowledgably devour chamber music these days, but perhaps even the most devout laypersons at the packed concert by the Dover Quartet could only imagine what the performers drew from Tuesday's concert at the American Philosophical Society.

Clearly, this young group has invested great thought and care into cultivating a sound so distinctive as to be easily identified within mere minutes. Brahms' String Quintet in G major Op. 111 had the significant addition of violist Roberto Diaz - an artistic coup since he's one of the best of his generation. The fact that he's also the busy president of the Curtis Institute (where the Dover's members graduated) made his appearance a logistical feat as well, even though there's no spotlight to be had in this quintet.

Between the two viola parts of Op. 111, Diaz took the secondary one, leaving Brahms' world-weary lyricism to the group's Milena Pajaro-van de Stadt, a marvelous player. Diaz gave the music extra inner muscularity that turned up the heat in what was already a pretty heated performance.

The husky tone of violinist Joel Link set the tone for the overall quartet, which doesn't attempt warm, cozy sound but achieves it in moments of tightly knit harmonies. So there was no false ingratiation here, but a level of intensity, even aggression, suggesting that the quintet shows the composer as an aging lion who can still create mighty sounds.

Dover's characteristic sharp-focus quality was particularly welcome in Shostakovich's String Quartet No. 7 Op. 108, a masterpiece of ambiguity without vagueness. In this terse four-movement work, the composer assumes the manner of the Holy Fool, a Russian archetype who seems to talk nonsense but voices truths that can't be said any other way.

The miracle of this piece - quite different from the more famous (and depressive) String Quartet No. 8 - is the way it suggests extremes of triviality and profundity simultaneously, while moving so fast that you can't pin the music down to any one position. Simultaneous incidental solos give different sides of the musical story, creating an intentionally diffuse diversionary tactic that makes you listen all the harder.

The emphatic fugato section sounds like an impulsive tantrum that infects each player in the string quartet one by one, but is in fact as calculated as any such counterpoint must be. The fact that one heard all of this in the Dover performance tells you how good it was. The problem is in giving the individual movements an overall sense of beginning, middle and end. Sometimes that happened, sometimes it didn't.