Thirty-five crashing chords begin one of the greatest orchestral works written in the last 25 years: the Harmonielehre by John Adams. Completed in 1985 after what Adams described as a yearlong "creative lockdown," those Herculean hammer blows of brass, bells, and drums also heralded the advent of a postmodern orchestral music where Mahler, once viewed as not only dead but dowdy, matters as much as the pulsating minimalism of Steve Reich and the tactile surface of pop music. Fizzing cymbals, oracular bells, and hypnotically burbling violins frame melodies that are by turns unabashedly heroic, tender, and savage.

Robert Spano, who masterfully conducted Seattle Opera's Ring cycle last summer, leads the Seattle Symphony in Harmonielehre (Thurs April 29, Sat–Sun May 1–2, Benaroya Hall, various times, $9–$100) along with the Sibelius tone poem Pohjola's Daughter and the reliable "Rach 2," Rachmaninov's Piano Concerto No. 2 with pianist Dejan Lazic.

For more new and newish music, pianist and longtime Piazzolla advocate Amy Rubin (Thurs April 29, Sherman Clay Piano & Organ, 1624 Fourth Ave, 12:15 pm, free) plays her own arrangements of tangos by the famed Argentine composer as well as pieces by Ernesto Nazareth (1863–1934), who filigreed Brazilian folk tunes with the languorous harmonies of Chopin. Another pianist/composer, Rachel Matthews, offers a slew of chamber music (Fri April 30, Chapel Performance Space, 4649 Sunnyside Ave N, 8 pm, $5/$15/$20): a piano quintet, Dreams for viola and piano (with the marvelous and much-missed violist Helen Callus), Ballade for piano, and Partita, a solo violin homage to Bach. Don't judge Matthews's bland titles harshly; while generic monikers sometimes hint at an unhealthy isolation from other contemporary music, some composers rely on staid nouns and adjectives to defer attention to the music.

The following night, Town Hall hosts a 12-hour music marathon called "May Day! May Day!" (Sat May 1, Town Hall, 1119 Eighth Ave, 1 pm–1 am, $5). Nearly everyone who is part of the "new music" scene in Seattle performs a short—20 minutes or less—set, from icons such as William O. Smith (5:48 pm) and Stuart Dempster (8:36 pm) to the ass-kicking Seattle Percussion Collective (5:24 pm), Gamelan Pacifica (7:48 pm), The Esoterics (10:36 pm), and Paul Rucker (11:48 pm). The masterminds of the event, the Seattle Chamber Players, conclude with a 12:36 pm miniconcert. See www.townhallseattle.org/mayday for the complete lineup. I'm not surprised by the overt absence of electronic-based music makers, whose sound checks can either last a minute or an hour. In any case, take those scheduled times with a grain of salt and just show up; your ears will thank you.