A set of headphones have microphones generating left and right feed-forward and feedback signals. A controller governs collection of sensed data and transmission of the sensed data into the underwater environment. Constrictions according to the present invention, which do not uniformly constrict the cross-section of the line, do not produce any ring-shaped eddies that can be heard in the form of whistling noises. Sequentially activating the light sources may include activating each light source individually for a predetermined activation period within an activation cycle.