Minneapolis’s Walker Art Center is closed for the year as its building undergoes a major expansion, but rather than fade completely from public view, the museum is mounting a series of interactive exhibitions called “Walker Without Walls.” The latest project has Walker staffers “spending the summer helping as many as 500 locals build and operate their own miniature radio transmitters. It’s called microradio, and organizers hope the combined voices of the new microbroadcasters inspire a ‘Radio ReVolt’ (the project’s title).” The transmitters are all set to the same frequency (97.7FM, an open spot on the Twin Cities dial) and can broadcast for up to 200 feet.