A monthly concert series in Cleveland is about to mark three years. But you’ve likely never heard of it. That’s because Sofar Sounds’ performances are meant to be kept a secret. For this week’s Shuffle, we look at this subscription-only concert experience. Imagine getting a ticket to a show but all the details --- from the performers to the location --- are a mystery until the last minute. That’s Sofar Sounds , or Sounds From a Room. It’s a subscription to intimate pop-up concerts. "It’s really