Complex sentence: Coxswains used to communicate to the crew by shouting or through a megaphone that was strapped to their head, however starting in the late 1970s a "cox box" or speaker and microphone system made it so that even the bowman could hear the coxswain's commands.
Split into simpler sentences: Coxswains used to communicate to the crew by shouting or through a megaphone that was strapped to their head. However, since the late 1970s a "cox box" or speaker and microphone system has enabled even the bowman to hear the coxswain's commands.