Ordinarily, you’d see three acts listed on a bill and expect three separate sets with much gear-switching between. Communion — dreamed up by Mumford & Sons’ keyboardist and accordion player Ben Lovett — is intended to profoundly alter the rhythm of a live show, giving it a more youthful and current feel by making it more, well, communal. This — the first-ever U.S. incarnation of the tour — features chicly shabby British folk-rockers Matthew & The Atlas, raucously tuneful hometown entertainers The David Mayfield Parade and Lauren Shera, a California-based singer-songwriter of indie-folk dream sequences. Before the tour began, David Mayfield gave this concise explanation of what it would be like: “It just kind of keeps melding from one act into the next. So it’s a solid two hours of music with lots of collaborating, and this whole little musical community that will go from city to city.” Sounds promising.