The Music in the Park Series has always struck me as a terrific deal for concertgoers - the chance to hear top-line chamber musicians performing up close and personal.

This weekend of all-Beethoven string quartets marks the start of the 30th season for the series that takes place in the cozy sanctuary of St. Anthony Park United Church of Christ, where every seat is a good one with the exception of a few pews that have sightlines blocked by a pulpit.

When the Pacifica Quartet concludes its concert late this afternoon, it will have performed six of Beethoven's 16 string quartets, including three that were performed Saturday. Each program includes a quartet from each of the arbitrarily divided three periods of Beethoven's compositional life.

On Saturday, these included the Quartet in B-flat major (Op. 18 No. 6), which barely qualifies as a first-period work and has a radical finale, titled "La Malinconia," which is filled with unconventional modulations and unexpected turns of phrase.

The Pacifica musicians - violinists Simin Ganatra and Sibbi Bernhardsson, violist Masumi Per Rostad and cellist Brandon Vamos - also performed the short, though impassioned, "Serioso" Quartet in F minor (Op. 95) from the composer's middle period and concluded with the extraordinary, emotionally conflicted Quartet in A minor (Op. 132) that ranges from dark pathos through a chorale-like expression of thanksgiving and ultimately an animated finale.

The Pacifica musicians have been performing together for almost 15 years, yet they are still youthful, meaning they have that razor-sharp technique characteristic of young virtuosos, combined with a well-honed, wonderfully integrated ensemble voice. Their playing is like a musical conversation that ebbs and wanes, reacts and responds.

Sometimes the results were exuberant, but the most telling impact Saturday was in the Op. 132 Quartet, when the players were working through - and delicately shaping - the deliberate, meditative slow movement, which Beethoven titled "Holy Song of Thanksgiving to the Divinity by a Convalescent, in the Lydian Mode." In lesser performances, this can sound like abstract meandering, but the Pacifica performers shaped it with tension and poise and made deep sense of it.