Review: Mumford and Sons, ‘Babel’: Aidin Vaziri | Mumford and Sons’ first album made them the unlikely leaders of the new folk revival, unleashing a cacophony of banjo and washboards on the pop charts to the tune of double-platinum sales. So it’s little wonder that the members of the London quartet with a weakness for Dust Bowl-era attire appear particularly emboldened on its follow-up. On “Babel,” front man Marcus Mumford howls incessantly as the band ramps up its pummeling acoustic assault. Having spent the past three years on the road has made a clear impression, whether it’s in songs designed for mass sing-alongs (“I Will Wait,” “Whispers in the Dark”) or the ones yearning for some kind of stability (“Lover of the Light,” “Broken Crown”). The band sounds at once triumphant and exhausted, and, by the end, most listeners will be, too.