A device includes a housing. The housing can define a duct having a central axis. A first loading surface can extend into the duct toward the central axis, while a second loading surface can extend into the duct toward the central axis. A first driver and a second driver can be situated within the duct along the central axis. The first driver can abut the second driver. A first spring biases the first driver away from the first loading surface, thereby causing the first driver to apply a first loading force to the second driver. A second spring applies a second loading force to the second driver, along a common direction with the first loading force, to bias the second driver away from the second loading surface, with the first spring and second spring operating in parallel on the second driver.