When people talk about "challenging" music, they're usually talking about music that's tough to listen to. By this definition, virtually any metal album above a certain threshold of technicality or with sufficiently shitty sound quality is challenging just because it's hard to tell what the hell is going on.

But music can also be challenging because it's tough to think about. Take Yakuza, for example. After eleven years and five albums, this band continues to defy description. They're unquestionably a metal band, with a well-deserved 'progressive' tag, but the easy categorization stops there.

Yakuza's roots can be traced to turn-of-the-century noisy metalcore (think Converge, Burnt By the Sun, and that crowd). As the years have gone by, their sound has opened up considerably. Frontman Bruce Lamont's brutalist saxophone work--that's right, brutal saxophone--has pushed further into the spotlight, and the band's songwriting has grown increasingly doomy, tripped-out, and expansive.

Of Seismic Consequence, like Transmutations before it, pushes Yakuza further into the unknown. Every one of this band's left-of-center features has been ratcheted up a notch--more long songs, more dynamic shifts, more clean vocals, and more effects-addled sax.

Yakuza can still crank out rippers at will. The album's proper opener "Thinning the Herd," "The Elephant Walkers," and "The Great War" all display Yakuza's capacity for compact, vicious songwriting. Even on these terse efforts, Lamont's clean voice gets more face time than it ever has before, but they're still comparatively conventional riffsplosions.

Considerably more seems to be at stake on Of Seismic Consequence's lengthier cuts. The first, the 8-minute "Be That As It May," might well be the best in Yakuza's catalog. It passes in turns from vocal-centric contemplation to furious guitar workout and ecstatic sax solo to a painfully anthemic climax. Though the whole band clicks, the song is really a testament to Lamont's skills. His singing will never bring the house down on its own, but he displays a real ability to craft emotive melodies and lyrics, and he manages to integrate his sax work into Yakuza's metallic craft without even a touch of gimmickry.

"Farewell to the Flesh," which immediately follows "Be That As It May," can't help but disappoint. After such a varied, emotionally charged song, eleven minutes of lugubrious trudging kills the album's momentum, and one can't help but wonder if Yakuza's desire to experiment has them playing against their strengths.

Like most restlessly creative bands, Yakuza can be a mixed bag. That said, Of Seismic Consequence contains far more killer than filler, and it's loaded with great moments--the feverish tribal jamming of "Testing the Water," the pounding chorus of "Stones and Bones," the vocal ranting that dominates "The Knuckle Walkers" and "The Great War." But its title will nonetheless turn out less accurate than Yakuza hopes. The very ambition that makes their music so noteworthy has also neatly deprived them of anything like a niche audience to appeal to, and in all likelihood, this band will continue to toil away in unjust obscurity. After all, playing such challenging music has its merits, but it also has its price.