Big Bear BIG BEAR (Monitor)

Thanks to Converge, the Blood Brothers, and Dillinger Escape Plan, heavy metal sounds much more unruly than it did last century: the primacy of momentous riffs has given way to cracked-mirror refractions, shards and splatters delivered at hardcore's hyperspeed tempi. The old thrash metal evoked the militaristic trudge of lumbering heavy machinery; in the new language, riffs that begin in dense, rhythmic gurgles often end in dissonant, raking screeches, like the sudden sickening gasp of twisting steel in a car wreck. The songs are usually so fast that to listeners, like rubberneckers in the passing lane, they register as only a blur.

The Allston quintet Big Bear have absorbed this lexicon and its many permutations, but on their debut album, they do something new with it: they slow it down. And that makes a huge difference. Big Bear is something like the South of Heaven of spazz metal: its songs aren’t slow, just slower. The riffs unspool, tangle, and quiver as if someone were tying suspension-bridge cables into geo-abstractionist knots, but they stay riveted in place just long enough for onlookers to appreciate their sculptural integrity. On the opening track (the disc has no track listing; all its songs are officially untitled), guitarists John McWilliams and Joel Roston claw out a punishing chord — but then the chord gets loose, squirming away in different directions like a fistful of slippery eels. You picture them chasing after the notes and strangling them, just as singer Jordyn Bonds rushes in and screams, in a high-pitched rasp, "What is choice, then, a ruse?" In another band’s hands, this would all fly by before the song’s stark edges snapped into sharp focus, but on Big Bear, it’s picture-perfect.

(Big Bear play a CD-release party this Saturday, April 30, upstairs at the Middle East, 472 Massachusetts Avenue in Central Square; call 617-864-EAST.)