KVEIKURThough it's not necessarily a bad quality, post rock (especially as it trends to the more ambient side of things), can be an awfully passive listening experience, sweeping the listeners up in drifting buildup and inevitable crescendos without ever really confronting them. Challenging this paradigm, Sigur R? s get sonically adventurous with their seventh album, Kveikur, which finds the Icelandic three piece delivering a darker and more aggressive sound