Who says they don't understand sound signals? And yes it would be easier to give a wakeless pass if they dropped their speed 20% or even went to neutral ,as you went by, but with all the boats that pass them that would make their trip near 20% longer. As hard as it may be we come down to their speed then bump it up just enough to make the pass, then wait till they come inside our wake before bringing up the throttles and bring them up gradually so we don't leave them a roller coaster ride. Do that and I'd be surprised if you hear any complaints. It's called courtesy.