Exhaust sounds True duals vs X-pipe or H-pipe.

isolated duals sound like a steel drum if you have some crazy roller can and Flowmaster. A crossover tube middles all the pulses together and gives a mellower note and possibly less drone. The crossover tube did other things too, Pontiac put a crossover tube on their 63 super duty Tempest drag car for some reason. It was about 3" behind the open headers outlet behind the front wheels. Weird looking setup.