The knobs and other parts on the Stanmore IV and Acton IV speakers are replaceable. | Image: Marshall Marshall announced new versions of its Acton and Stanmore Bluetooth speakers today with upgraded tweeters, bass ports, and internal designs that improve their ability to fill a room with sound. Both the Acton IV and Stanmore IV replace their four-year-old predecessors with a new focus on repairability. Parts including knobs, feet, and the speakers' front grills bearing the iconic Marshall logo